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Stall inception and recovery in variable pitch in motion fan

Stall inception and recovery in variable pitch in motion fan

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Bianchi GT2011 Bianchi GT2011 Presentation Transcript

  • Stall Inception, Evolution and Control in a Low-Speed Axial Fan with Variable Pitch in Motion ! GT2011-45725Stefano BIANCHI, Alessandro CORSINI, Anthony G. SHEARDLuca MAZZUCCO, Lucilla MONTELEONE Flakt Woods Ltd FMGroup @ DIMA-URLS Turbo Expo Turbine Congress and Exhibition June 7 – 11, 2011, Vancouver, BC, Canada.
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Background motivations (i) • Huge amount of research works have been dedicated in the last decades to the goal of finding reliable methods to monitor the approach of fans or compressors to the stability limits while running literature review spans from ’70s&’80s (Day and Cumpsty, 1978) (Greitzer, 1980) to stall detection, management & control studies (Paduano et al., 2001) (Christensen et al., 2006) • Two questions are still under scrutiny alert methods are proposed for individual test-beds techniques for the detection of stall initiation, based on experimental observation of pre-stall behaviours, have sought to identify such behaviour as early as possible i.e. early detection period lasts less than two rotor revolutions for axial compressors and it could be ten times longer in low-speed single stage industrial fans Turbo Expo 2011, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Background motivations (ii)• Several studies suggested the presence of tip flow phenomena (in low-speed and high- speed rotors) directly responsible for the generation of those disturbances (also called ‘spikes’ or ‘pips’) causing the inception of part-span stall cells• This inception mechanism could be correlated also with a modification of the noise signal in the casing region• A number of scholars have utilised azimuthal measurements in an attempt to link the rotating unsteady patterns of flow instabilities to their acoustic signatures to detect in centrifugal turbomachines low frequency noise due to rotating stall in (Okada, 1987) or aerodynamic sound sources (Mongeau et al., 1995) In a similar vein (Kameier and Neise, 1997) established a link between tip-clearance noise and associated blade-tip flow instabilities in axial turbo-machinery by correlating rotating source and vortex mechanisms with rotating stall cells Turbo Expo 2011, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Aims • The present work was aimed to provide the background for the development of a stall detection tool in low-speed axial fans with VPIM. • In this paper, the stall characteristics of a low-speed fan are established using flush- mounted microphones placed at two azimuthal positions around the casing. • Spatial and temporal correlations between rotating instabilities are established, which facilitates a full analysis of stall inception. •  Energetic analysis on the stall cells and recovery behaviour is estabilished. •  The study is finalised to characterise the stall and the recovery of a VPIM fan, for the use of the previously patented ‘SDP stall detection tool’ (Sheard et al., J. Eng. Gas Turb and Power GTP-10-1168). Turbo Expo 2011, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Outline • Methodology Test fan and apparatus • Stall visualization technique Rationale and background information Sensitivity analysis • Discussion of the stall warning @ 700 rpm-speed Fourier and energetic analysis Visualization of the stall cell • Conclusions Turbo Expo 2011, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Methodology. Fan geometry & design • Low-speed axial fans for heavy-duty applications intended for high-temperature operations in the boilers of coal power plants. blade profiles modified ARA-D geometry type arbitrary vortex radial work distribution Turbo Expo 2011, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Methodology. Fan Variable Pitch in Motion (VPIM) System• Remotely controlled oil-dynamic actuators VPIM system @ 1.5°/s. Turbo Expo 2011, Turbine Congress and Exhibition
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Methodology. Fan test section BS 848 P I – AMCA certified Turbo Expo 2010, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Methodology. Test rig Turbo Expo 2011, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Methodology. Fan performance @ steady conditions • Total pressure-to-volume performance map @ different pitch angles Turbo Expo 2011, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Methodology. Test apparatus 10 kHz• The microphones were mounted flush with the inner wall of the casing• The microphones were mounted above the blade vane Turbo Expo 2011, Turbine Congress and Exhibition FMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Signal processing technique y • Cross Correlation Analysis between the pressure measured in two azimuthal locations The cross-correlation of functions f(t) and g(t) is equivalent to the convolution of f *(−t) and g(t): x Analogous to the convolution theorem, the cross-correlation satisfies: denotes the Fourier transform, and ’*’ indicates the complex conjugate.•  CoherenceThe coherence between two signals x(t) and y(t) is a real-valued function that is defined as: Turbo Expo 2011, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Measurements Uncertainty • The overall uncertainty on unsteady pressure measurements was estimated as: ΔV = 1000 mV ± 12 mV (20:3) on the voltage; and ΔG = 200 dB ± 2.4 dB (20:3) on the raw signal gain in the range of frequencies considered. •  The system frequency limitation of the pressure probes was calculated. •  The system response for the phase angle was carefully checked. α (deg) f (Hz)FMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Measurements uncertainty • The overall uncertainty on unsteady pressure measurements was estimated as: ΔV = 1000 mV ± 12 mV (20:3) on the voltage; and ΔG = 200 dB ± 2.4 dB (20:3) on the raw signal gain in the range of frequencies considered. •  The system frequency limitation of the pressure probes was calculated. •  The system response for the phase angle was carefully checked. α (deg) f (Hz)FMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Test Conditions dynamic testMachtip = 0.25 ARe = 106 B Pitch variation C Φstart = 0.200 Φend = 0.120 Turbo Expo 2010, Turbine Congress and Exhibition FMGroup @ DMA-Sapienza
  • Visual inspection of wall pressure low-pass filtered @ 150 HzStall inception Turbo Expo 2010, Turbine Congress and Exhibition
  • Detection of stall regions in a low-speed axial fan by visualisation of sound signals Visual inspection of wall pressure low-pass filtered @ 150 Hz Details at stall inception I1: inception spike Instabilities with similar wave structure RS1: new-born stall cell Turbo Expo 2011, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza
  • Visual inspection of wall pressure low-pass filtered @ 150 Hz Details of the stall evolution Cell leading edge Cell trailing edge Partial recovery Stall cell passage Partial recovery Stall cell passage Turbo Expo 2011, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Visual inspection of wall pressure low-pass filtered @ 150 Hz Average velocity of the stall cells Turbo Expo 2011, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Average velocity and angular estension of the stall cell Probably: part-span stall cell Turbo Expo 2011, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Cross-Correlation (Ch1-Ch2) during three different operatiing conditions Turbo Expo 2011, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Cross-Correlation (Ch1-Ch2) during three different operating conditions New-born stall cell Instabilities with similar wave structure Turbo Expo 2011, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Cross-Correlation (Ch1-Ch2) during three different operatiing conditions New-born stall cell Instabilities with similar wave structure Turbo Expo 2011, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Visual inspection of wall pressure low-pass filtered @ 150 HzStall recovery via VPIM Turbo Expo 2010, Turbine Congress and Exhibition
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Visual inspection of wall pressure low-pass filtered @ 150 Hz Stall recovery via VPIM - details Turbo Expo 2011, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in MotionStall recovery via VPIM – details of stall cell evolution @ recovery Turbo Expo 2011, Turbine Congress and Exhibition
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Spectral Density of Energy (SDE) – Stall and recovery Turbo Expo 2011, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Spectral Energy Density – details of the recovery Turbo Expo 2011, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Concluding Remarks•  The present study has established the stall characteristic of a subsonic axial fan by visual inspection of thepressure traces and acoustic correlations from two different pressure probes mounted on the casing.•  The spectral analysis detected the presence of low frequency tone components related to rotating stall. Theexistence of these tone-band modulations could be inferred as being the signature of rotating stall in this typeof fans.•  The potential of the VPIM system, operated to extend the classical stable operating range of the fan, could beextended in a ‘joint control system’ of the fan unstable operations, because the VPIM shows an immediaterecovery of the stall, when the proper pitch angle is reached.•  As a consequence, a sufficiently quick ‘stall prediction method’ should be developed. This is an ongoing workof this research group, after the stall warning system presented in the last Turbo Expo and recently patented. Turbo Expo 2011, Turbine Congress and Exhibition FMGroup @ DMA-Sapienza
  • Stall inception, evolution and control in a low speed axial fan fitted with Variable Pitch in Motion Roma – Foro Romano view Vaxjio, Sweeden– The Lake view Acknowledgement The present research was done in the context of the contract FW-DMA10-11, between Flakt Woods Ltd and Fluid Machinery Research Team @ Dipartimento di Ing. Meccanica e Aerospaziale “Sapienza” University of Rome Turbo Expo 2011, Turbine Congress and ExhibitionFMGroup @ DMA-Sapienza