The goal of the present work is to improve the prediction of propeller performance at model-scale using a local correlation transition model. Results are presented for two marine propellers for which paint-tests have been conducted and experimental open-water data is available. The numerical results using the k-\omega SST turbulence model and the \gamma-Re_\theta transition model are compared with the experiments. In order to distinguish between numerical and modelling errors in the comparison with experimental results, a verification study using a range of geometrically similar grids with different grid densities is made. The influence of the turbulence inlet quantities on the numerical results is discussed and boundary-layer characteristics are presented. Finally, the numerical predictions are compared with the experimental results. An improvement in the flow pattern is achieved with the transition model. However, the model strongly depends on the turbulence inlet quantities for the prediction of the transition location. Both propellers show an increase in thrust of 2% to 4% and similar torque when using the transition model.
Prediction of the Open-Water Performance of Ducted Propellers With a Panel Me...João Baltazar
This document discusses the prediction of open-water performance for ducted propellers using a panel method. Panel methods provide a computationally efficient tool for analysis and design of marine propulsors. Application to ducted propellers involves additional modeling issues such as the complex interaction between propeller blades and duct surfaces. The document reviews previous work developing the panel method for ducted propellers, including models for the gap flow, wake alignment, duct boundary layers, and new Kutta conditions. It presents comparisons of panel method predictions to experimental and RANS results. The motivation is to improve performance predictions near bollard pull conditions through refinements to the numerical methods.
A Comparison of Panel Method and RANS Calculations for a Ducted Propeller Sys...João Baltazar
In this paper, a comparison between results of a panel method and a RANS solver is made for a ducted propeller system in open-water. The panel method calculations were made at IST with the panel code PROPAN. Different wake models are used in the inviscid computations: rigid wake model with prescribed wake geometry and a vortex pitch wake alignment model without and with a duct boundary layer correction. For the flow in the gap region a closed gap width and a gap flow model with transpiration velocity are considered. The RANS calculations were carried out at MARIN with the RANS code ReFRESCO. A comparison of the blade and duct pressure distributions, wake geometry and thrust and torque coefficients is presented. In general, good agreement of the pressure distributions, wake geometries and force coefficients between the two codes is achieved. A reasonable agreement between the inviscid blade wake position and the blade wake viscous vorticity field is obtained when using the wake alignment model. It is seen that the correlation improves when introducing the duct boundary layer correction. The force coefficients are also compared with experimental data available from open-water tests. A reasonable to good agreement is seen for the thrust and torque coefficients over the entire openwater range.
This document summarizes ANSYS' results from the AIAA 2nd High Lift Prediction Workshop. Key findings include excellent prediction of trends and force/moment values using hybrid and polyhedral meshes in ANSYS Fluent and CFX. Polyhedral meshes improved accuracy and speed for Fluent. The SST k-omega turbulence model showed reasonably good results for low Reynolds number cases, though some discrepancies were likely due to missing fairings in the simulation geometry. Further tests will incorporate fairings and additional turbulence models.
This document summarizes research on enhancing gene expression programming (GEP) for Reynolds-averaged Navier-Stokes equations turbulence modeling with unsupervised clustering. It presents a GEP-enhanced multi-model framework that uses feature selection, dimensionality reduction, and clustering to assign different turbulence models to distinct regions of a flow, improving simulation accuracy. Results show the approach produces more accurate mean velocities and Reynolds stresses for a body-of-revolution testcase compared to baseline and GEP-driven models. Ongoing work includes optimizing the framework configuration and extending it to 3D domains.
Prediction of the Propeller Performance at Different Reynolds Number Regimes ...João Baltazar
In this study, a Reynolds averaged Navier-Stokes solver is used for prediction of the propeller performance in open-water conditions at different Reynolds numbers ranging from 10^4 to 10^7. The k-\omega SST turbulence model and the \gamma-Re_\theta transition model are utilised and results compared for a conventional marine propeller. First, the selection of the turbulence inlet quantities for different flow regimes is discussed. Then, an analysis of the iterative and discretisation errors is made. This work is followed by an investigation of the predicted propeller flow and wake field at variable Reynolds numbers. Finally, the propeller scale-effects and the influence of the turbulence and transition models on the performance prediction are discussed. The variation of the flow regime showed an increase in thrust and decrease in torque for increasing Reynolds number. From the comparison between the turbulence model and the transition model, different flow solutions are obtained for the Reynolds numbers between 10^5 and 10^6.
Modelling of Laminar-to-Turbulent Flow Transition on a Marine Propeller Using...João Baltazar
Several numerical studies are presented in this paper, which includes an estimation of the numerical errors in the simulations, an evaluation of the influence of inlet turbulence quantities on the transition location, identification of the flow regime, and an analysis of the predicted propeller blade boundary-layer flow. Finally, a comparison between the RANS simulations and experimental data is made, which will help to improve the propeller flow modelling at model-scale. This comparison will help in the definition of more realistic inlet turbulence quantities that may be used for numerical predictions at model-scale without the need of any type of calibration based on experimental information.
A Numerical Study on the Iterative Techniques to Solve Partial Cavitation on ...João Baltazar
This study addresses some aspects of the numerical solution with the Boundary Element Method of the three-dimensional potential flow on marine propellers with partial cavitation. An alternative iteratively coupled procedure is proposed to solve the linear system of equations resulting from the formulation of the cavitating flow problem. The alternative procedure is aimed to avoid solving anew the large system of equations at each iteration step for the determination of the cavity extension. The numerical studies are carried out for the MARIN S-Propeller. A large reduction in computational time is achieved with the alternative procedure for the cavitating potential flow solution.
Prediction of the Open-Water Performance of Ducted Propellers With a Panel Me...João Baltazar
This document discusses the prediction of open-water performance for ducted propellers using a panel method. Panel methods provide a computationally efficient tool for analysis and design of marine propulsors. Application to ducted propellers involves additional modeling issues such as the complex interaction between propeller blades and duct surfaces. The document reviews previous work developing the panel method for ducted propellers, including models for the gap flow, wake alignment, duct boundary layers, and new Kutta conditions. It presents comparisons of panel method predictions to experimental and RANS results. The motivation is to improve performance predictions near bollard pull conditions through refinements to the numerical methods.
A Comparison of Panel Method and RANS Calculations for a Ducted Propeller Sys...João Baltazar
In this paper, a comparison between results of a panel method and a RANS solver is made for a ducted propeller system in open-water. The panel method calculations were made at IST with the panel code PROPAN. Different wake models are used in the inviscid computations: rigid wake model with prescribed wake geometry and a vortex pitch wake alignment model without and with a duct boundary layer correction. For the flow in the gap region a closed gap width and a gap flow model with transpiration velocity are considered. The RANS calculations were carried out at MARIN with the RANS code ReFRESCO. A comparison of the blade and duct pressure distributions, wake geometry and thrust and torque coefficients is presented. In general, good agreement of the pressure distributions, wake geometries and force coefficients between the two codes is achieved. A reasonable agreement between the inviscid blade wake position and the blade wake viscous vorticity field is obtained when using the wake alignment model. It is seen that the correlation improves when introducing the duct boundary layer correction. The force coefficients are also compared with experimental data available from open-water tests. A reasonable to good agreement is seen for the thrust and torque coefficients over the entire openwater range.
This document summarizes ANSYS' results from the AIAA 2nd High Lift Prediction Workshop. Key findings include excellent prediction of trends and force/moment values using hybrid and polyhedral meshes in ANSYS Fluent and CFX. Polyhedral meshes improved accuracy and speed for Fluent. The SST k-omega turbulence model showed reasonably good results for low Reynolds number cases, though some discrepancies were likely due to missing fairings in the simulation geometry. Further tests will incorporate fairings and additional turbulence models.
This document summarizes research on enhancing gene expression programming (GEP) for Reynolds-averaged Navier-Stokes equations turbulence modeling with unsupervised clustering. It presents a GEP-enhanced multi-model framework that uses feature selection, dimensionality reduction, and clustering to assign different turbulence models to distinct regions of a flow, improving simulation accuracy. Results show the approach produces more accurate mean velocities and Reynolds stresses for a body-of-revolution testcase compared to baseline and GEP-driven models. Ongoing work includes optimizing the framework configuration and extending it to 3D domains.
Prediction of the Propeller Performance at Different Reynolds Number Regimes ...João Baltazar
In this study, a Reynolds averaged Navier-Stokes solver is used for prediction of the propeller performance in open-water conditions at different Reynolds numbers ranging from 10^4 to 10^7. The k-\omega SST turbulence model and the \gamma-Re_\theta transition model are utilised and results compared for a conventional marine propeller. First, the selection of the turbulence inlet quantities for different flow regimes is discussed. Then, an analysis of the iterative and discretisation errors is made. This work is followed by an investigation of the predicted propeller flow and wake field at variable Reynolds numbers. Finally, the propeller scale-effects and the influence of the turbulence and transition models on the performance prediction are discussed. The variation of the flow regime showed an increase in thrust and decrease in torque for increasing Reynolds number. From the comparison between the turbulence model and the transition model, different flow solutions are obtained for the Reynolds numbers between 10^5 and 10^6.
Modelling of Laminar-to-Turbulent Flow Transition on a Marine Propeller Using...João Baltazar
Several numerical studies are presented in this paper, which includes an estimation of the numerical errors in the simulations, an evaluation of the influence of inlet turbulence quantities on the transition location, identification of the flow regime, and an analysis of the predicted propeller blade boundary-layer flow. Finally, a comparison between the RANS simulations and experimental data is made, which will help to improve the propeller flow modelling at model-scale. This comparison will help in the definition of more realistic inlet turbulence quantities that may be used for numerical predictions at model-scale without the need of any type of calibration based on experimental information.
A Numerical Study on the Iterative Techniques to Solve Partial Cavitation on ...João Baltazar
This study addresses some aspects of the numerical solution with the Boundary Element Method of the three-dimensional potential flow on marine propellers with partial cavitation. An alternative iteratively coupled procedure is proposed to solve the linear system of equations resulting from the formulation of the cavitating flow problem. The alternative procedure is aimed to avoid solving anew the large system of equations at each iteration step for the determination of the cavity extension. The numerical studies are carried out for the MARIN S-Propeller. A large reduction in computational time is achieved with the alternative procedure for the cavitating potential flow solution.
The primary objective of this project is to extend the conveniences of
deconvolution to non-linear problems of fluid flow in porous media. Unlike
conventional approaches, which are based on an approximate linearization of the
problem, here the solution of the non-linear problem is linearized by a perturbation
approach, which permits term-by-term application of deconvolution. Because the
proposed perturbation solution is more conveniently evaluated in the Laplacetransform
domain and the standard deconvolution algorithms are in the time-domain,
an efficient deconvolution procedure in the Laplace domain is a prerequisite.
For this research objective, a new algorithm is introduced which uses inverse
mirroring at the points of discontinuity and adaptive cubic splines to approximate rate
or pressure versus time data. This algorithm accurately transforms sampled data into
Laplace space and eliminates the Numerical inversion instabilities at discontinuities
or boundary points commonly encountered with the piece-wise linear approximations
of the data.
Applying the algorithm to the field data obtained from published works, we can
unveil the early-time behavior of a reservoir system masked by wellbore-storage
effects. The wellbore-storage coefficient can be variable in the general case. The new
method thus provides a powerful tool to improve pressure-transient-test
interpretation.
Practical use of the algorithm presented in this research has applications in a
variety of Pressure Transient Analysis (PTA) and Rate Transient Analysis (RTA)
problems. A renewed interest in this procedure is inspired from the need to evaluate
production performances of wells in unconventional reservoirs. With this approach,
ESTIMATE OF THE HEAD PRODUCED BY ELECTRICAL SUBMERSIBLE PUMPS ON GASEOUS PETR...ijaia
This paper reports successful development of an exact and an efficient radial basis function network (RBFN) model to estimate the head of gaseous petroleum fluids (GPFs) in electrical submersible pumps (ESPs). Head of GPFs in ESPs is now often estimated using empirical models. Overfitting and its consequent lack of model generality data is a potentially serious issue. In addition, available data series is fairly small, including the results of 110 experiments. All these limits were considered in RBFN design process, and highly accurate RBFNs were developed and cross validated.
This document presents a new approach for dense non-rigid structure from motion (NRSfM) using monocular video. Previous NRSfM methods provided sparse 3D reconstructions, while this new approach enables dense 3D reconstruction for every frame. It formulates NRSfM as a variational energy minimization problem that estimates projection matrices and 3D shapes by minimizing reprojection error with spatial smoothness and low-rank priors. The energy is optimized iteratively to estimate rotations and refine shapes. Results on real sequences demonstrate improved accuracy over previous sparse NRSfM methods.
This document summarizes a study that compares the performance of three different single expansion ramp nozzles (AP1, BP1, and CP1) at various nozzle pressure ratios (NPRs). The nozzles have different initial ramp angles. Computational fluid dynamics is used to analyze the flow and pressure variations inside the nozzles. Meshing is performed on the nozzle geometries at different NPR conditions. Parameters like centerline Mach number, wall shear stress, thrust, and efficiency are compared for the three nozzle designs at various operating pressures to determine the most efficient configuration. The effect of initial ramp angle on nozzle performance is also investigated.
Statistical issues in global fits: Lessons from PDF determinationsJuan Rojo
The document discusses statistical issues that arise in global fits to determine parton distribution functions (PDFs) from experimental data. It notes that PDF fits must combine data from different collision types and experiments, which can have inconsistent measurements. Traditional PDF fitting methods make restrictive assumptions that introduce bias, while the NNPDF approach uses neural networks and Monte Carlo replicas to avoid biases and faithfully represent uncertainties, including in regions with limited data. Inconsistent data poses challenges and requires delicate handling in global fits to obtain statistically sound PDF results.
This document is a thesis submitted by Aad Vijn to the Delft University of Technology in partial fulfillment of the requirements for a Master of Science degree in Applied Mathematics. The thesis investigates inverse modeling techniques to predict the magnetic signature of naval ships based on onboard measurements of the magnetic field and an accurate description of the ship's steel geometry. The thesis first derives the relevant forward and inverse problems and discusses the ill-posed nature of the inverse problem. It then presents methods for discretizing and solving the inverse problem, including regularization techniques. The performance of the resulting prediction model is analyzed using both simulated and real measurement data obtained from a measurement campaign on a mock-up model. While initial results are promising, the thesis identifies several
This document outlines José Cupertino Ruiz Vargas's PhD thesis on searching for diboson resonances in CMS data. It begins with an introduction to the standard model of particle physics and motivations for physics beyond the standard model, including the Randall-Sundrum model with extra dimensions. It then describes the CMS detector and object identification techniques. The analysis strategy is to select events with two opposite-sign leptons and two jets, and estimate backgrounds using Monte Carlo simulations and data-driven techniques. Unblinded results show agreement between data and background predictions in control regions.
Anomalous Synchronization Stability of Power-grid NetworkHeetae Kim
The document summarizes research on the synchronization stability of power grid networks. It presents analysis of a toy model that shows an anomalous peak in stability during a transition as the transmission capacity increases. Real data is also presented on the Chilean power grid network, which includes information on different power sources. The research aims to better understand stability at both the community and individual node levels between theoretical analysis and real-world applications.
This document discusses polyhedral computation techniques for characterizing regions of entropic vectors and computing achievable rate regions of coded networks. It begins with background on polyhedra, including representations and conversions between representations. It then discusses two algorithms - lexicographic reverse search and the double description method - for performing representation conversions. The document outlines applying polyhedral projection techniques like the convex hull method to these network coding problems.
Variation aware design of custom integrated circuits a hands on field guideSpringer
This document discusses different process-voltage-temperature (PVT) design flows and compares their speed and accuracy. It introduces a "Fast PVT" flow that can quickly extract the most relevant worst-case PVT corners through a global optimization algorithm. This flow allows for fast and accurate iterative design and verification, completing on average 5 times faster than simulating all PVT corners while still reliably finding the true worst-case corners. The document provides details on the Fast PVT algorithm and shows results from its use in industrial circuit design projects.
Numerical Studies for Verification and Validation of Open-Water Propeller RAN...João Baltazar
In this paper, viscous flow calculations using a RANS method are presented for two marine propellers in open-water conditions at model-scale. A verification study from a range of geometrically similar grids with different grid densities is made. The results show that the numerical uncertainties for the propeller forces are in the order of 0.4%-2.2%. The influence of the domain size and boundary conditions on the prediction of the propeller forces is analysed. The numerical predictions are compared with the experimental results. These differences (comparison error) are larger than the numerical uncertainty, suggesting that the comparison error is dominated by the modelling error.
Succinct Summarisation of Large Networks via Small Synthetic Representative G...Jérôme KUNEGIS
Talk by Jérôme Kunegis at BeNet'17 in Gent.
In this talk, Jérôme Kunegis presented ongoing work, see the abstract below.
Abstract: We describe a method for visually summarising the structure of large network datasets that works by drawing smaller graphs generated to have similar structural properties to the input graphs. Visualising complex networks is crucial to understand and make sense of networked data and the relationships it represents. Due to the large size of many networks, visualisation is extremely difficult; the simple method of \emph{drawing} large networks like those of Facebook or Twitter leads to graphics that convey little or no information. While modern graph layout algorithms can scale computationally to large networks, their output tends to a common \emph{hairball} look, which makes it difficult to even distinguish different graphs from each other. Graph sampling and graph coarsening techniques partially address these limitations but they are only able to preserve a subset of the properties of the original graphs. In this paper we take the
problem of visualising large graphs from a novel perspective: we leave the original graph's nodes and edges behind, and instead summarise its properties such as the clustering coefficient and bipartivity by generating a completely new graph whose structural properties match that of the original graph. To verify the utility of this approach as compared to other graph visualisation algorithms, we perform an experimental evaluation in which we repeatedly asked experimental subjects (professionals in graph mining and related areas) to determine which of two given graphs has a given structural property and then assess which visualisation algorithm helped in identifying the correct answer. Our summarisation approach SynGraphy compares favourably to other techniques on a variety of networks.
The document describes a microstrip-fed broadband circularly polarized monopole antenna. It discusses how asymmetric feeding is used to generate two orthogonal current components with a 90 degree phase difference, producing circular polarization. A rectangular slit and stub are added to the ground plane. Simulations show the slit helps produce circular polarization but causes impedance mismatch from 2-4 GHz. The stub excites a new mode, improving impedance matching in that band and only slightly affecting the circular polarization characteristics. This allows both a broad impedance bandwidth of 6.72 GHz and an axial ratio bandwidth of 1.37 GHz to be achieved simultaneously.
Optimize Single Particle Orbital (SPO) Evaluations Based on B-splinesIntel® Software
Orbital representations that are based on B-splines are widely used in quantum Monte Carlo (QMC) simulations of solids, which historically take as much as 50 percent of the total runtime. Random access to a large four-dimensional array make it challenging to efficiently use caches and wide vector units in modern CPUs. So, we present node-level optimizations of B-spline evaluations on multicore and manycore shared memory processors.
To increase single instruction multiple data (SIMD) efficiency and bandwidth utilization, we first apply data layout transformation from an array of structures (AoS) to a structure of arrays (SoA). Then, by blocking SoA objects, we optimize cache reuse and get sustained throughput for a range of problem sizes. We implement efficient nested threading in B-spline orbital evaluation kernels, paving the way towards enabling strong scaling of QMC simulations, resulting with performance enhancements. Finally, we employ roofline performance analysis to model the impacts of our optimizations.
An Iteratively Coupled Solution Method for Partial and Super-Cavitation Predi...João Baltazar
An iteratively coupled solution method for the calculation of partial and super-cavitating flow on propellers with a potential based Boundary Element Method is presented. The solution method explores the fact that only the source strength beneath the cavity changes due to the presence of the cavity. The knowledge of the source strength change is sufficient to solve the original Neumann problem. The system is iteratively coupled to the complete cavitating system in the cavity planform iteration. The advantage is that the complete system matrix for the Neumann problem is identical to the matrix of the wetted flow problem and needs only to be inverted once. The numerical studies are carried out for the INSEAN E779A propeller with predicted partial and super-cavitation.
This document discusses evaluating reliability parameters for a power plant using algebra of logics. The power plant has two identical generators in standby redundancy to power four machines that can operate in pairs. The author develops a mathematical model representing the system configuration and operating conditions using Boolean logic. Equations are formulated to represent the conditions for successful operation of the power plant. The model is then solved using orthogonalization algorithms and algebra of logics to obtain the overall reliability function of the power plant in terms of the component reliabilities.
The document describes the design of a reversible 8-bit arithmetic logic unit (ALU) using low power reversible logic gates. It involves designing reversible logic gates, arithmetic circuits like full adders and multipliers, and a multiplexer. Reversible NAND/AND and NOR/OR gates are designed. A DKGP gate is used to design a reversible 1-bit full adder and 8-bit complementing adder. 4x4 and 8x8 multipliers are designed using compressors. A 2x1 multiplexer and 4x1 multiplexer are also designed using primitive gates. CMOS and SET implementations and their input/output waveforms are shown for the designed circuits.
PROPAN - Potential Flow Code for Foils and Rotors: PROPAN is short for Propeller Panel Method. PROPAN is a panel code for the calculation of steady and unsteady potential flow around foils, open and ducted propellers, and wind and marine current turbines. PROPAN was developed by MARETEC (Marine and Environmental Technology Research Centre) at Instituto Superior Técnico (IST) which belongs to Lisbon University.
Unsteady Potential Flow Calculations on a Horizontal Axis Marine Current Turb...João Baltazar
Three-dimensional unsteady potential flow calculations for a horizontal axis marine current turbine with a low order potential based panel method, originally developed for marine propellers, are presented. The analysis is carried out for straight and yawed flow conditions for a turbine with controllable pitch for two different pitch settings in a wide range of tip-speed-ratios. An empirical vortex model is assumed for the turbine wake which includes the variation of pitch of the helicoidal vortices behind the blades. Comparison of numerical calculations with experimental measurements available in the literature and effect of the tidal velocity profile on the turbine blade loadings are presented.
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Similar to On the Use of the \gamma-Re_\theta Transition Model for the Prediction of the Propeller Performance at Model-Scale
The primary objective of this project is to extend the conveniences of
deconvolution to non-linear problems of fluid flow in porous media. Unlike
conventional approaches, which are based on an approximate linearization of the
problem, here the solution of the non-linear problem is linearized by a perturbation
approach, which permits term-by-term application of deconvolution. Because the
proposed perturbation solution is more conveniently evaluated in the Laplacetransform
domain and the standard deconvolution algorithms are in the time-domain,
an efficient deconvolution procedure in the Laplace domain is a prerequisite.
For this research objective, a new algorithm is introduced which uses inverse
mirroring at the points of discontinuity and adaptive cubic splines to approximate rate
or pressure versus time data. This algorithm accurately transforms sampled data into
Laplace space and eliminates the Numerical inversion instabilities at discontinuities
or boundary points commonly encountered with the piece-wise linear approximations
of the data.
Applying the algorithm to the field data obtained from published works, we can
unveil the early-time behavior of a reservoir system masked by wellbore-storage
effects. The wellbore-storage coefficient can be variable in the general case. The new
method thus provides a powerful tool to improve pressure-transient-test
interpretation.
Practical use of the algorithm presented in this research has applications in a
variety of Pressure Transient Analysis (PTA) and Rate Transient Analysis (RTA)
problems. A renewed interest in this procedure is inspired from the need to evaluate
production performances of wells in unconventional reservoirs. With this approach,
ESTIMATE OF THE HEAD PRODUCED BY ELECTRICAL SUBMERSIBLE PUMPS ON GASEOUS PETR...ijaia
This paper reports successful development of an exact and an efficient radial basis function network (RBFN) model to estimate the head of gaseous petroleum fluids (GPFs) in electrical submersible pumps (ESPs). Head of GPFs in ESPs is now often estimated using empirical models. Overfitting and its consequent lack of model generality data is a potentially serious issue. In addition, available data series is fairly small, including the results of 110 experiments. All these limits were considered in RBFN design process, and highly accurate RBFNs were developed and cross validated.
This document presents a new approach for dense non-rigid structure from motion (NRSfM) using monocular video. Previous NRSfM methods provided sparse 3D reconstructions, while this new approach enables dense 3D reconstruction for every frame. It formulates NRSfM as a variational energy minimization problem that estimates projection matrices and 3D shapes by minimizing reprojection error with spatial smoothness and low-rank priors. The energy is optimized iteratively to estimate rotations and refine shapes. Results on real sequences demonstrate improved accuracy over previous sparse NRSfM methods.
This document summarizes a study that compares the performance of three different single expansion ramp nozzles (AP1, BP1, and CP1) at various nozzle pressure ratios (NPRs). The nozzles have different initial ramp angles. Computational fluid dynamics is used to analyze the flow and pressure variations inside the nozzles. Meshing is performed on the nozzle geometries at different NPR conditions. Parameters like centerline Mach number, wall shear stress, thrust, and efficiency are compared for the three nozzle designs at various operating pressures to determine the most efficient configuration. The effect of initial ramp angle on nozzle performance is also investigated.
Statistical issues in global fits: Lessons from PDF determinationsJuan Rojo
The document discusses statistical issues that arise in global fits to determine parton distribution functions (PDFs) from experimental data. It notes that PDF fits must combine data from different collision types and experiments, which can have inconsistent measurements. Traditional PDF fitting methods make restrictive assumptions that introduce bias, while the NNPDF approach uses neural networks and Monte Carlo replicas to avoid biases and faithfully represent uncertainties, including in regions with limited data. Inconsistent data poses challenges and requires delicate handling in global fits to obtain statistically sound PDF results.
This document is a thesis submitted by Aad Vijn to the Delft University of Technology in partial fulfillment of the requirements for a Master of Science degree in Applied Mathematics. The thesis investigates inverse modeling techniques to predict the magnetic signature of naval ships based on onboard measurements of the magnetic field and an accurate description of the ship's steel geometry. The thesis first derives the relevant forward and inverse problems and discusses the ill-posed nature of the inverse problem. It then presents methods for discretizing and solving the inverse problem, including regularization techniques. The performance of the resulting prediction model is analyzed using both simulated and real measurement data obtained from a measurement campaign on a mock-up model. While initial results are promising, the thesis identifies several
This document outlines José Cupertino Ruiz Vargas's PhD thesis on searching for diboson resonances in CMS data. It begins with an introduction to the standard model of particle physics and motivations for physics beyond the standard model, including the Randall-Sundrum model with extra dimensions. It then describes the CMS detector and object identification techniques. The analysis strategy is to select events with two opposite-sign leptons and two jets, and estimate backgrounds using Monte Carlo simulations and data-driven techniques. Unblinded results show agreement between data and background predictions in control regions.
Anomalous Synchronization Stability of Power-grid NetworkHeetae Kim
The document summarizes research on the synchronization stability of power grid networks. It presents analysis of a toy model that shows an anomalous peak in stability during a transition as the transmission capacity increases. Real data is also presented on the Chilean power grid network, which includes information on different power sources. The research aims to better understand stability at both the community and individual node levels between theoretical analysis and real-world applications.
This document discusses polyhedral computation techniques for characterizing regions of entropic vectors and computing achievable rate regions of coded networks. It begins with background on polyhedra, including representations and conversions between representations. It then discusses two algorithms - lexicographic reverse search and the double description method - for performing representation conversions. The document outlines applying polyhedral projection techniques like the convex hull method to these network coding problems.
Variation aware design of custom integrated circuits a hands on field guideSpringer
This document discusses different process-voltage-temperature (PVT) design flows and compares their speed and accuracy. It introduces a "Fast PVT" flow that can quickly extract the most relevant worst-case PVT corners through a global optimization algorithm. This flow allows for fast and accurate iterative design and verification, completing on average 5 times faster than simulating all PVT corners while still reliably finding the true worst-case corners. The document provides details on the Fast PVT algorithm and shows results from its use in industrial circuit design projects.
Numerical Studies for Verification and Validation of Open-Water Propeller RAN...João Baltazar
In this paper, viscous flow calculations using a RANS method are presented for two marine propellers in open-water conditions at model-scale. A verification study from a range of geometrically similar grids with different grid densities is made. The results show that the numerical uncertainties for the propeller forces are in the order of 0.4%-2.2%. The influence of the domain size and boundary conditions on the prediction of the propeller forces is analysed. The numerical predictions are compared with the experimental results. These differences (comparison error) are larger than the numerical uncertainty, suggesting that the comparison error is dominated by the modelling error.
Succinct Summarisation of Large Networks via Small Synthetic Representative G...Jérôme KUNEGIS
Talk by Jérôme Kunegis at BeNet'17 in Gent.
In this talk, Jérôme Kunegis presented ongoing work, see the abstract below.
Abstract: We describe a method for visually summarising the structure of large network datasets that works by drawing smaller graphs generated to have similar structural properties to the input graphs. Visualising complex networks is crucial to understand and make sense of networked data and the relationships it represents. Due to the large size of many networks, visualisation is extremely difficult; the simple method of \emph{drawing} large networks like those of Facebook or Twitter leads to graphics that convey little or no information. While modern graph layout algorithms can scale computationally to large networks, their output tends to a common \emph{hairball} look, which makes it difficult to even distinguish different graphs from each other. Graph sampling and graph coarsening techniques partially address these limitations but they are only able to preserve a subset of the properties of the original graphs. In this paper we take the
problem of visualising large graphs from a novel perspective: we leave the original graph's nodes and edges behind, and instead summarise its properties such as the clustering coefficient and bipartivity by generating a completely new graph whose structural properties match that of the original graph. To verify the utility of this approach as compared to other graph visualisation algorithms, we perform an experimental evaluation in which we repeatedly asked experimental subjects (professionals in graph mining and related areas) to determine which of two given graphs has a given structural property and then assess which visualisation algorithm helped in identifying the correct answer. Our summarisation approach SynGraphy compares favourably to other techniques on a variety of networks.
The document describes a microstrip-fed broadband circularly polarized monopole antenna. It discusses how asymmetric feeding is used to generate two orthogonal current components with a 90 degree phase difference, producing circular polarization. A rectangular slit and stub are added to the ground plane. Simulations show the slit helps produce circular polarization but causes impedance mismatch from 2-4 GHz. The stub excites a new mode, improving impedance matching in that band and only slightly affecting the circular polarization characteristics. This allows both a broad impedance bandwidth of 6.72 GHz and an axial ratio bandwidth of 1.37 GHz to be achieved simultaneously.
Optimize Single Particle Orbital (SPO) Evaluations Based on B-splinesIntel® Software
Orbital representations that are based on B-splines are widely used in quantum Monte Carlo (QMC) simulations of solids, which historically take as much as 50 percent of the total runtime. Random access to a large four-dimensional array make it challenging to efficiently use caches and wide vector units in modern CPUs. So, we present node-level optimizations of B-spline evaluations on multicore and manycore shared memory processors.
To increase single instruction multiple data (SIMD) efficiency and bandwidth utilization, we first apply data layout transformation from an array of structures (AoS) to a structure of arrays (SoA). Then, by blocking SoA objects, we optimize cache reuse and get sustained throughput for a range of problem sizes. We implement efficient nested threading in B-spline orbital evaluation kernels, paving the way towards enabling strong scaling of QMC simulations, resulting with performance enhancements. Finally, we employ roofline performance analysis to model the impacts of our optimizations.
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Prediction of Sheet Cavitation on Marine Current Turbines With a Boundary Ele...João Baltazar
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On the Use of the \gamma-Re_\theta Transition Model for the Prediction of the Propeller Performance at Model-Scale
1. On the Use of the γ − ˜Reθ Transition Model
for the Prediction of the Propeller Performance
at Model-Scale
J. Baltazar1, D. Rijpkema2, J.A.C. Falc˜ao de Campos1
1Instituto Superior T´ecnico, Universidade de Lisboa, Portugal
2Maritime Research Institute Netherlands, Wageningen, the Netherlands
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4. Introduction
Full-scale prediction propellers mostly based on simple
extrapolation methods from model-scale experiments
RANS solvers may be used at both model and full scale and
offer an alternative scaling method
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5. Introduction
Full-scale prediction propellers mostly based on simple
extrapolation methods from model-scale experiments
RANS solvers may be used at both model and full scale and
offer an alternative scaling method
Requires accurate prediction at both Reynolds numbers
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6. Introduction
Turbulence models (k − ω, SST, k −
√
kL, etc.) are known to
provide a good prediction for fully developed turbulent flows
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7. Introduction
Turbulence models (k − ω, SST, k −
√
kL, etc.) are known to
provide a good prediction for fully developed turbulent flows
However, these models predict transition at lower Reynolds
number than seen in experiments
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8. Introduction
Turbulence models (k − ω, SST, k −
√
kL, etc.) are known to
provide a good prediction for fully developed turbulent flows
However, these models predict transition at lower Reynolds
number than seen in experiments
Model-scale experiments in critical Reynolds number regime
smp’17 Espoo, Finland June 12-15 3
9. Introduction
Turbulence models (k − ω, SST, k −
√
kL, etc.) are known to
provide a good prediction for fully developed turbulent flows
However, these models predict transition at lower Reynolds
number than seen in experiments
Model-scale experiments in critical Reynolds number regime
Improve the prediction of the propeller performance prediction at
model-scale using the RANS equations complemented with the
k − ω SST turbulence model and the γ − ˜Reθ transition model
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12. Overview
Two marine propellers: conventional and skewed propellers
Estimation of the numerical errors: round-off error (negligible),
iterative error and discretisation error
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13. Overview
Two marine propellers: conventional and skewed propellers
Estimation of the numerical errors: round-off error (negligible),
iterative error and discretisation error
Influence of the turbulence inlet quantities
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14. Overview
Two marine propellers: conventional and skewed propellers
Estimation of the numerical errors: round-off error (negligible),
iterative error and discretisation error
Influence of the turbulence inlet quantities
Comparison with paint-tests
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15. Overview
Two marine propellers: conventional and skewed propellers
Estimation of the numerical errors: round-off error (negligible),
iterative error and discretisation error
Influence of the turbulence inlet quantities
Comparison with paint-tests
Boundary-layer analysis
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16. Overview
Two marine propellers: conventional and skewed propellers
Estimation of the numerical errors: round-off error (negligible),
iterative error and discretisation error
Influence of the turbulence inlet quantities
Comparison with paint-tests
Boundary-layer analysis
Prediction of open-water performance
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18. RANS Code ReFRESCO
Viscous flow CFD solver developed within a cooperation led by
MARIN
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19. RANS Code ReFRESCO
Viscous flow CFD solver developed within a cooperation led by
MARIN
Solves the incompressible RANS equations, complemented with
turbulence/transition models
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20. RANS Code ReFRESCO
Viscous flow CFD solver developed within a cooperation led by
MARIN
Solves the incompressible RANS equations, complemented with
turbulence/transition models
The equations are discretised using a finite-volume approach
with cell-centred collocation variables
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22. Performance Prediction at Model-Scale
Turbulence model: k − ω SST 2-equation model proposed by
Menter et al. (2003)
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23. Performance Prediction at Model-Scale
Turbulence model: k − ω SST 2-equation model proposed by
Menter et al. (2003)
Transition model: γ − ˜Reθ model proposed by Langtry and
Menter (2009)
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24. Performance Prediction at Model-Scale
Turbulence model: k − ω SST 2-equation model proposed by
Menter et al. (2003)
Transition model: γ − ˜Reθ model proposed by Langtry and
Menter (2009)
Second-order convection scheme (QUICK) is used for the
momentum equations
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25. Performance Prediction at Model-Scale
Turbulence model: k − ω SST 2-equation model proposed by
Menter et al. (2003)
Transition model: γ − ˜Reθ model proposed by Langtry and
Menter (2009)
Second-order convection scheme (QUICK) is used for the
momentum equations
First-order upwind scheme is used for the turbulence/transition
models
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26. Performance Prediction at Model-Scale
Turbulence model: k − ω SST 2-equation model proposed by
Menter et al. (2003)
Transition model: γ − ˜Reθ model proposed by Langtry and
Menter (2009)
Second-order convection scheme (QUICK) is used for the
momentum equations
First-order upwind scheme is used for the turbulence/transition
models
No wall functions are used (y+
∼ 1)
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27. Test Cases
Propellers S6368 (left) and S6698 (right)
S6368 S6698
Diameter D [m] 0.2714 0.233
Chord length at r = 0.7R [m] 0.0694 0.121
Number of blades 4 4
Pitch ratio P/D at r = 0.7R 0.757 1.224
Blade-area ratio AE /A0 0.456 0.729
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28. Mesh and Numerical Set-up
Multi-block structured grids (GridPro)
Cylindrical Domain (5D):
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31. Estimation of Numerical Errors
Iterative errors: monitored from the residuals
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32. Estimation of Numerical Errors
Iterative errors: monitored from the residuals
Turbulence model: residuals ∼ 10−4 to 10−6
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33. Estimation of Numerical Errors
Iterative errors: monitored from the residuals
Turbulence model: residuals ∼ 10−4 to 10−6
Transition model: residuals ∼ 10−3 to 10−5, γ ∼ 10−1
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34. Estimation of Numerical Errors
Iterative errors: monitored from the residuals
Turbulence model: residuals ∼ 10−4 to 10−6
Transition model: residuals ∼ 10−3 to 10−5, γ ∼ 10−1
The transition model is not as numerically robust as the
turbulence model: iterative convergence becomes more difficult!
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35. Estimation of Numerical Errors
Iterative errors: monitored from the residuals
Turbulence model: residuals ∼ 10−4 to 10−6
Transition model: residuals ∼ 10−3 to 10−5, γ ∼ 10−1
The transition model is not as numerically robust as the
turbulence model: iterative convergence becomes more difficult!
Fast iterative convergence of the propeller forces
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36. Estimation of Numerical Errors
Iterative errors: monitored from the residuals
Turbulence model: residuals ∼ 10−4 to 10−6
Transition model: residuals ∼ 10−3 to 10−5, γ ∼ 10−1
The transition model is not as numerically robust as the
turbulence model: iterative convergence becomes more difficult!
Fast iterative convergence of the propeller forces
Dicretisation errors: estimated from a numerical uncertainty
analysis
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37. Estimation of Numerical Errors
Iterative errors: monitored from the residuals
Turbulence model: residuals ∼ 10−4 to 10−6
Transition model: residuals ∼ 10−3 to 10−5, γ ∼ 10−1
The transition model is not as numerically robust as the
turbulence model: iterative convergence becomes more difficult!
Fast iterative convergence of the propeller forces
Dicretisation errors: estimated from a numerical uncertainty
analysis
Convergence of the propeller forces with grid density.
Differences lower than 1% for grids with 8M cells
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38. Estimation of Numerical Errors
Iterative errors: monitored from the residuals
Turbulence model: residuals ∼ 10−4 to 10−6
Transition model: residuals ∼ 10−3 to 10−5, γ ∼ 10−1
The transition model is not as numerically robust as the
turbulence model: iterative convergence becomes more difficult!
Fast iterative convergence of the propeller forces
Dicretisation errors: estimated from a numerical uncertainty
analysis
Convergence of the propeller forces with grid density.
Differences lower than 1% for grids with 8M cells
Numerical uncertainties are in the order of 1%-2%
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40. Influence of Turbulence Inlet Quantities
Turbulence models predict strong decay of turbulence quantities
from the inlet along the streamwise direction. Analytical solution
for uniform axial flow
smp’17 Espoo, Finland June 12-15 10
41. Influence of Turbulence Inlet Quantities
Turbulence models predict strong decay of turbulence quantities
from the inlet along the streamwise direction. Analytical solution
for uniform axial flow
Small influence of the turbulence inlet quantities for common
turbulence models. Default values of Tu=1% and µt/µ = 1
smp’17 Espoo, Finland June 12-15 10
42. Influence of Turbulence Inlet Quantities
Turbulence models predict strong decay of turbulence quantities
from the inlet along the streamwise direction. Analytical solution
for uniform axial flow
Small influence of the turbulence inlet quantities for common
turbulence models. Default values of Tu=1% and µt/µ = 1
γ − ˜Reθ model shows a strong sensitivity to the turbulence inlet
quantities
smp’17 Espoo, Finland June 12-15 10
43. Influence of Turbulence Inlet Quantities
Turbulence models predict strong decay of turbulence quantities
from the inlet along the streamwise direction. Analytical solution
for uniform axial flow
Small influence of the turbulence inlet quantities for common
turbulence models. Default values of Tu=1% and µt/µ = 1
γ − ˜Reθ model shows a strong sensitivity to the turbulence inlet
quantities
Sensitivity study of the turbulence inlet quantities for
turbulence/transition models
smp’17 Espoo, Finland June 12-15 10
44. Influence of Turbulence Inlet Quantities
Turbulence models predict strong decay of turbulence quantities
from the inlet along the streamwise direction. Analytical solution
for uniform axial flow
Small influence of the turbulence inlet quantities for common
turbulence models. Default values of Tu=1% and µt/µ = 1
γ − ˜Reθ model shows a strong sensitivity to the turbulence inlet
quantities
Sensitivity study of the turbulence inlet quantities for
turbulence/transition models
May result in unrealistic turbulence levels at the inlet for
γ − ˜Reθ model
smp’17 Espoo, Finland June 12-15 10
45. Influence of Turbulence Inlet Quantities
Propeller S6368 at J = 0.568 and Re=4.5×105
Inlet x/R = 10 x/R = 1 Forces
Model Tu µt/µ Tu µt/µ KT 10KQ
k − ω SST 1.0% 1 0.2% 0.8 0.112 0.166
k − ω SST 1.0% 500 1.0% 115.3 0.112 0.166
k − ω SST 2.5% 500 2.2% 489.2 0.112 0.166
γ − ˜Reθ 1.0% 1 0.2% 0.8 0.121 0.163
γ − ˜Reθ 1.0% 500 1.0% 109.3 0.121 0.163
γ − ˜Reθ 2.5% 500 2.2% 489.4 0.117 0.164
γ − ˜Reθ 5.0% 500 3.3% 467.3 0.116 0.167
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46. Influence of Turbulence Inlet Quantities
γ − ˜Reθ Model: Propeller S6368 at J = 0.568 and Re=4.5×105
Tu=1.0% Tu=1.0% Tu=2.5% Tu=5.0%
µt/µ = 1 µt/µ = 500 µt/µ = 500 µt/µ = 500
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47. Influence of Turbulence Inlet Quantities
γ − ˜Reθ Model: Propeller S6368 at J = 0.568 and Re=4.5×105
Tu=1.0% Tu=1.0% Tu=2.5% Tu=5.0%
µt/µ = 1 µt/µ = 500 µt/µ = 500 µt/µ = 500
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48. Influence of Turbulence Inlet Quantities
γ − ˜Reθ Model: Propeller S6368 at J = 0.568 and Re=4.5×105
Tu=1.0% Tu=1.0% Tu=2.5% Tu=5.0%
µt/µ = 1 µt/µ = 500 µt/µ = 500 µt/µ = 500
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49. Influence of Turbulence Inlet Quantities
γ − ˜Reθ Model: Propeller S6368 at J = 0.568 and Re=4.5×105
Tu=1.0% Tu=1.0% Tu=2.5% Tu=5.0%
µt/µ = 1 µt/µ = 500 µt/µ = 500 µt/µ = 500
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50. Influence of Turbulence Inlet Quantities
γ − ˜Reθ Model: Propeller S6368 at J = 0.568 and Re=4.5×105
Tu=1.0% Tu=1.0% Tu=2.5% Tu=5.0%
µt/µ = 1 µt/µ = 500 µt/µ = 500 µt/µ = 500
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51. Influence of Turbulence Inlet Quantities
s/c
0.0 0.2 0.4 0.6 0.8 1.0
0.00
0.03
0.05
0.08
0.10
r/R=0.70
Cf
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61. Comparison with Paint-Tests
Propeller S6698 at J = 0.87 and Re=7.3×105
k − ω SST Paint
Tu=1.0% Tests
µt/µ = 1
(Suction Side)
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62. Comparison with Paint-Tests
Propeller S6698 at J = 0.87 and Re=7.3×105
γ − ˜Reθ Paint
Tu=2.5% Tests
µt/µ = 500
(Suction Side)
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63. Comparison with Paint-Tests
Propeller S6698 at J = 0.87 and Re=7.3×105
k − ω SST Paint
Tu=1.0% Tests
µt/µ = 1
(Pressure Side)
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64. Comparison with Paint-Tests
Propeller S6698 at J = 0.87 and Re=7.3×105
γ − ˜Reθ Paint
Tu=2.5% Tests
µt/µ = 500
(Pressure Side)
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68. Conclusions
Turbulence model is insensitive to the inlet turbulence
parameters. A (fully) turbulent flow solution is obtained
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69. Conclusions
Turbulence model is insensitive to the inlet turbulence
parameters. A (fully) turbulent flow solution is obtained
A strong sensitivity to the inlet turbulence parameters
(Tu and µt/µ) is found for the transition model
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70. Conclusions
Turbulence model is insensitive to the inlet turbulence
parameters. A (fully) turbulent flow solution is obtained
A strong sensitivity to the inlet turbulence parameters
(Tu and µt/µ) is found for the transition model
Inlet turbulence values are recommended (Tu=2.5% and
µt/µ = 500) for the transition model. A qualitative agreement
is found between the paint-tests and the limiting streamlines
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71. Conclusions
Turbulence model is insensitive to the inlet turbulence
parameters. A (fully) turbulent flow solution is obtained
A strong sensitivity to the inlet turbulence parameters
(Tu and µt/µ) is found for the transition model
Inlet turbulence values are recommended (Tu=2.5% and
µt/µ = 500) for the transition model. A qualitative agreement
is found between the paint-tests and the limiting streamlines
Transition model versus turbulence model:
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72. Conclusions
Turbulence model is insensitive to the inlet turbulence
parameters. A (fully) turbulent flow solution is obtained
A strong sensitivity to the inlet turbulence parameters
(Tu and µt/µ) is found for the transition model
Inlet turbulence values are recommended (Tu=2.5% and
µt/µ = 500) for the transition model. A qualitative agreement
is found between the paint-tests and the limiting streamlines
Transition model versus turbulence model:
Increase in thrust (2-4%) due to higher lift forces (cambering)
and lower shear stresses
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73. Conclusions
Turbulence model is insensitive to the inlet turbulence
parameters. A (fully) turbulent flow solution is obtained
A strong sensitivity to the inlet turbulence parameters
(Tu and µt/µ) is found for the transition model
Inlet turbulence values are recommended (Tu=2.5% and
µt/µ = 500) for the transition model. A qualitative agreement
is found between the paint-tests and the limiting streamlines
Transition model versus turbulence model:
Increase in thrust (2-4%) due to higher lift forces (cambering)
and lower shear stresses
Small variation in torque due to higher lift and lower friction
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74. Conclusions
Turbulence model is insensitive to the inlet turbulence
parameters. A (fully) turbulent flow solution is obtained
A strong sensitivity to the inlet turbulence parameters
(Tu and µt/µ) is found for the transition model
Inlet turbulence values are recommended (Tu=2.5% and
µt/µ = 500) for the transition model. A qualitative agreement
is found between the paint-tests and the limiting streamlines
Transition model versus turbulence model:
Increase in thrust (2-4%) due to higher lift forces (cambering)
and lower shear stresses
Small variation in torque due to higher lift and lower friction
Better agreement (1-10%) for the conventional propeller
(S6368) with transition model and similar results
(1-9%) for skewed propeller (S6698)
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