CFD : Modern Applications, Challenges and Future Trends

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I delivered this lecture to the academic staff of the College of Engineering of AAST on 28/03/2012.

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CFD : Modern Applications, Challenges and Future Trends

  1. 1. Computational Fluid Dynamics Modern Applications, Challenges and Future Trends Arab Academy for Science, Technology and Maritime Transport, 28th March 2012 Dr. Khalid M. Saqr B.Sc (Alex. Uni.), M.Eng (UTM), PhD (UTM) © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.28/03/2012
  2. 2. OutlinesI. CFD in a nutshell • Tool or an engineering science? • Frame of reference of CFDII. Modern CFD codes • Building blocks of modern codes • Commercial vs. open source codesIII. Modern applications of CFD • Industrial sector • Medicine and biomechanics • Homeland securityIV. CFD for combustion applications • Modeling of turbulent vortex flamesV. Contemporary challenges • Physical models • Computational requirements • Benchmarking and validationVI. Future trends • Mesh-free methods • Low-cost HPC • Runtime validation concept © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  3. 3. I. CFD in a nutshell (definition) ?CFD: An engineering tool…? Or an independent branch of engineeringscience ? Computational homodynamic Computational Oceanography 2nd World War weaponry 1930s – 1940s 2000 – 2010s © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  4. 4. I. CFD in a nutshell (definition) Computer Science Fluid Mechanics & Software Engineering Heat Transfer CFD Electromagnetic field Processor development Chemical reaction Parallel computing Physical & Life Sciences Engineering science Geophysics Vascular medicine Oceanography21st Century definition of CFD:Solving the governing equations of fluid flow -by using computational methods-under various physical conditions (e.g. heat transfer, radiation, electromagneticfield, nuclear reaction…etc.) to study different phenomena encountered in thenumerous branches of physical science. © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  5. 5. I. CFD in a nutshell (frame of reference) Frame of reference of engineering CFDTheories of Continuum Molecular / Quantum theorymatter: hypothesis Kinetic theoryMechanics: Newtonian RelativisticChaos theory: Deterministic Random chaos chaos1. Matter (i.e. fluid) is assumed to be a continuum, and its propertiesand characteristics can be described by field functions.2. These field functions are functions in Euclidian space and time, andtheir frame of reference is an inertial one.3. The sensitive dependence on initial conditions described by thegoverning partial differential equation does not involve any randomevents © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  6. 6. II. Modern CFD Codes (theoretical basis) Formulation of field equations Eulerian Lagrangian Methods are not sufficiently FVM FEM mature for engineering applications. Commercial codes: Commercial codes: -Fluent -Lattice Boltzmann Method -COMSOL -CFX -DSMC -CFD++ -ADINA -FLACS -SPH -FloTHERM -COSMOS Open-Source: -EFDLab -Elmer No commercial codes. -FlowVision -PHOENIX Only “experimental” -… many more ! Open-Source codes ! Open-Source: -OpenFOAM -Code_Saturne -FDS -OpenFVM © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  7. 7. II. Modern CFD Codes (building blocks) What to : Building Blocks Geometry & Presume • Boundary / initial conditions • Physical models grid generation and what to : module • Physical phenomena (i.e. heat Neglect transfer, chemical reaction…etc) • Properties (i.e. compressibility, real Problem settings gas…etc) module and what to : Calculate • Unknowns • Relationships between field variables Solution module Visualization Solution methods and algorithms module • Spatial / temporal descritization schemes • Convergence criterion • Interpolation methods • …etc. © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  8. 8. II. Modern CFD Codes (Open-source vs. commercial) Feature Open-source Commercial Customization of Excellent Good physical models Customization of Excellent Poor numerical schemes Authenticity of Excellent Good physical models User friendliness Poor Excellent Free technical Poor Good support Paid technical Excellent Excellent support Academic use Excellent Poor ~ Good Industrial use Poor Excellent © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  9. 9. III. Modern Applications of CFD• Industrial sector (examples) – Electronics cooling – Chemical engineering © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  10. 10. III. Modern Applications of CFD• Medicine and biomechanicsVascular homodynamicRespiratory systemaerodynamicsAir-breathing diseasetransmissionVelocity magnitude plotted on a midplane slice of the abdominal aorta for one representativesubject under resting (left) and simulated exercise (right) conditions. © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  11. 11. III. Modern Applications of CFD• Medicine and biomechanicsVascular homodynamicRespiratory systemaerodynamicsAirborne transmission ofrespiratory infectious diseasesDeposition enhancement factors (DEFs) for a steady state inhalation flow rate of 30 L/min in acast-based model of the upper TB airways with particle sizes of (a) 40 nm and(b) 4 μm. DEF values represent the ratio of locally deposited mass to total deposited mass inthe airway. Significant enhancement in local deposition is observed for both nanometer(factor of 25) and micrometer (factor of 110) aerosols. © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  12. 12. III. Modern Applications of CFD• Medicine and biomechanicsVascular homodynamicRespiratory systemaerodynamicsAirborne transmission ofrespiratory infectious diseasesAirflow streamlines of supplied and exhaled airflows in Scenario #1: (a) supplied airflow; (b)exhaled airflow of P8; (c) exhaled airflow of P12; (d) exhaled airflow of P21; (e) exhaledairflow of P27; (f) exhaled airflow of P30. © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  13. 13. III. Modern Applications of CFD• Homeland security – Simulation of atmospheric dispersion of a contaminant released in downtown Portland, Oregon. The wind is from the west and the contaminant is released at the small yellow “+.” Annu. Rev. Fluid Mech. 2006. 38:87–110 © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  14. 14. IV. CFD for combustion applications 1- Deflagration Stationary Flames Propagating flames 2- DetonationClassification according Flamesto temporal development Propagating Flames Stationary flames 1- Laminar Flames 2- Turbulent Flames 1- Laminar Flames Premixed Flames 2- Turbulent Flames 3- Propagating FlamesClassification according 1- Laminar Flamesto pre-mixing between Flames Non-premixed (diffusion) Flames 2- Turbulent Flamesfuel and air 1- Laminar Flames Partially-premixed Flames 2- Turbulent Flames Bluff-body stabilization Stable Flames Aerodynamic stabilizationClassification according 1- Swirl stabilized flames 2- Vortex stabilized flamesto stability criterion Flames 3- Flow field stabilized flames 1- Thermal instability 2- Aerodynamic instability Unstable Flames 3- Acoustic instability 4- Chemical instability 5- Electromagnetic instability © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  15. 15. IV. CFD for combustion applications• It is a fact that most of engineering combustion systems involve turbulent flames• It is also a fact that any turbulent flow problem represent a challenge for CFD !• The bottleneck of CFD combustion solvers is the modeling of turbulence- chemistry interaction Chemical Modeling kinetics problems problems Turbulence (?) Mixing Chemical reaction (?) Time scale problem ? Damköhler number Density Pressure Heat Thermal conductivity Viscosity © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  16. 16. IV. CFD for combustion applications Turbulence modeling approaches Isotropic turbulence DNS Anisotropic turbulence • Algebraic models • Reynolds stress models • Eddy viscosity models (2 • Filtering approaches (LES, equations, 4 equations) DES, VLES) Coupling Technique • PDF model • EDM • Flamelet model • Detailed chemical • EDC kinetics Eddy break-up theory Flamelet theory Detailed chemistry Chemical Reaction modeling approaches © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  17. 17. IV. CFD for combustion applications• Modeling of vortex flames Vortex flame Swirling flame 1. Enhanced flame stability Applications: - Micro gas turbines 2. Shorter flame length - Micro jet engines for miniaturized UAVs 3. Added flame controllability © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  18. 18. IV. CFD for combustion applicationsProblems that had to be Secondary recirculation solved: zones1. Turbulence modeling of the vortex flow field in this complex geometry2. Find suitable parameters to study the aerodynamic vortex field stability mechanism of the flame3. Conduct a parametric study to reveal the major characteristics of the flame © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  19. 19. IV. CFD for combustion applications• Major contributions: 1. Formulation of the Rε/k-ε turbulence model 2. The new model variant has been coded into Fluent and OpenFOAM, tested and validated for several cases of rotation flows 3. Complete description of all main-flow phenomena in the asymmetric vortex combustor 4. Identification of the aerodynamic stability mechanism of vortex flames Stoichiometric Reaction Zones © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  20. 20. V. Contemporary Challenges• Physical models Turbulence Multiphase flow Chemical reaction- Highly strained - Interaction - Optimize betweenflows between primary and physical assumptions secondary phase and correct chemical- Atmospheric flow kineticsmodeling - Integration with new turbulence - Efficient coupling- Transitional flow models with turbulenceregimes models © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  21. 21. V. Contemporary Challenges• Computational requirements – Faster processors and larger memories – Smarter software algorithms Computational requirements DNS DES LES RANS Turbulence models (example) © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  22. 22. V. Contemporary Challenges• Benchmarking and validation Error sources in CFD Physical models Numerical schemes Encountered by Encountered by grid benchmarking and independency studies validation Challenges: 1- Unavailability of sufficient experimental data for some problems (i.e. biomechanics) 2- Generalization of the validation procedure © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  23. 23. VI. Future trends in CFD research• Mesh-free methods (late 1970s – today) – Smoothed Particle Hydrodynamics (SPH) – Diffuse Element Method (DEM)• Hybrid Methods – Particle in Cell (PIC) – Lattice Boltzmann Method (LBM) – Direct Simulation Monte Carlo (DSMC) © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  24. 24. VI. Future trends in CFD research• Low-cost HPC Clustering concept Old / Unused PCs Linux OS Network Parallel CFD code HPC © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  25. 25. VI. Future trends in CFD research• Runtime validation concept (LES, DES) Problem setup Problem setup Fine tuning Solution Basic Pre-solution Validation Change Results Model(s) Solution Validation invalid Results valid Final results Final results © All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.
  26. 26. Thank you© All copyrights belong to Dr. Khalid M. Saqr. All rights reserved.

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