1 / 33

Velocity and Wall Pressure Correlations Over a Forward Facing Step

Velocity and Wall Pressure Correlations Over a Forward Facing Step. E. Fiorentini 1-2 , R. Camussi 1 , F. Pereira 2 , M. Felli 2 , A. Di Marco 1, G. Aloisio 2 ,. 1: Dip. Ingegneria Meccanica e Industriale, Università Roma Tre; 2: INSEAN Vasca Navale, Propulsion and Cavitation Group ;.

evan
Download Presentation

Velocity and Wall Pressure Correlations Over a Forward Facing Step

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Velocity and Wall Pressure Correlations Over a Forward Facing Step E. Fiorentini1-2, R. Camussi1,F. Pereira2, M. Felli2, A. Di Marco1, G. Aloisio2, 1: Dip. Ingegneria Meccanica e Industriale, Università Roma Tre; 2: INSEAN Vasca Navale, Propulsion and Cavitation Group;

  2. Outline • Background and motivations • Experimental set up: wall pressure fluctuations + time resolved PIV • Results and physical interpretations • Future perspectives

  3. TBL separation and wall pressure fluctuations • Steps and geometrical irregularities are recognized as potential sources of aerodynamically generated noise; • The subject is of great interest from the viewpoint of practical and basic research applications; • Fluid dynamic and aeroacoustic complexity of the phenomenon, due to the presence of fluctuating pressure connected to both acoustic and pseudo acoustic contribution.

  4. Geometrical irregularities Backward-facing step (BFS) Efimtsov et al., 2000 Lee & Sung, JFM 2003 …. Forward-facing step (FFS) Efimtsov et al. (1999) Leclerq et al. (2001) • Strong noise sourceat 5-6H, corresponding to the oscillating reattachment point of the flow • Noise 20 dB greater than the flat plate • Strong noise source: where? • Noise 30 dB greater than the flat plate

  5. The shallow cavity studies(Camussi et al., JSV 2006, Exp. Fl. 2006) • The reattachment point at 5-6H and the FFS vertical wall are the most important noise emitting sources • The FFS is the noisiest zone Sound Pseudo-sound

  6. Literature background • Efimtzov et al. (1999) studied wall pressure spectra downstream and upstream a FFS: they found that the most noisy region is just downstream the FFS • Leclerq et al. (2001) characterized a FFS-BFS sequence: they found that the largest SPL peaks are upstream the FFS Few works and contrasting results!

  7. Objectives of the present study • Understand the physical mechanisms underlying the observed wall pressure statistics (understand → control) Hydrodynamic? Acoustic? • Correlate wall pressure pointwise measurements with PIV velocity fields

  8. Experiment on a FFS • Measurements at the large scale recirculating water channel of INSEAN • Fully developed turbulent boundary layer (Camussi & Di Felice, Phys. Fl. 2006) with */h = 0.5 • Reh = U∞h/ = 440026300

  9. Wall pressure measurements set up Array of pressure transducers Acquisition system PC Hydrophones + Accelerometer U =  • fs = 1200 Hz, t = 400 sec,  = 15 mm (0,75 h)

  10. Pressure transducers flush mounted at the wall U • ENDEVCO 8510B-2 • Piezoresistive transducers • full scale range = 2 psi • sensitivity = 15050 mV/psi • resonance frequency = 70000 Hz • Ø= 3.8 mm

  11. laser camera mirror Laser sheet Spherical lens Cylindrical lens step U Simultaneous pressure/PIV measurements set up Argon 6W SPECTRAPHYSICS Stabilite 2017 • Photron LTDFastcam APX • Up to 120.000 fps • CMOS sensor • 8 GB memory • fs = 1000 Hz • t = 12 sec • 1024x512 px

  12. PIV post processing techniques • Time resolved (1000fps) • 2D FFT based cross-correlation • OFFSET method to resolve velocity gradients • Windows deformation • Multi-frame adaptive method (Romano & Di Felice)

  13. Results • Averaged velocity & vorticity: overall behavior upstream & downstream of the step • Wall pressure statistics: overall SPL + auto-spectra + convection velocities • Pressure/velocity conditional statistics: ongoing activity (next AIVELA conference…hopefully)

  14. Examples of averaged velocity fields Separations and reattachments upstream and downstream of the step

  15. Averaged fields upstream of the step: streamlines and vorticity • Upstream separation point: xr h [Leclercq et al.: xr 0,8 h] • Reattachment at the vertical wall: • hr 0,5 h • [Leclercq et al.: hr 0,6 h] hr Reh = 4400 U∞ = 0,25 m/s xr

  16. Averaged fields upstream of the step: streamlines and vorticity • Upstream separation point: xr h [Leclercq et al.: xr 0,8 h] • Reattachment at the vertical wall: • hr 0,5 h • [Leclercq et al.: hr 0,6 h] • xr and hr about constant with Re hr Reh = 17500 U∞ = 1 m/s xr

  17. Averaged fields upstream of the step: vorticty and li structures Reh= 4400 Same behaviour for different Re

  18. Wall pressure fluctuations upstream of the step: auto-spectra What we may expect? • Far from the step: quasi-equilibrium conditions inducing a power law with -1 exponent as an effect of turbulent structures in the outer layer (Bradshaw, 1967, Farabee & Casarella, 1991) • Close to the step: recirculation region with no advection effects – the classical -7/3 exponent should be present

  19. Wall pressure fluctuations upstream of the step: auto-spectra U

  20. Wall pressure fluctuations upstream of the step: auto-spectra U

  21. Wall pressure fluctuations upstream of the step: auto-spectra U

  22. Averaged fields downstream of the step: streamlines and vorticity • reattachment at xb 2,5 h • xb about constant with Re • Mohesen: xb  22,5 h • Leclercq et al.: xb  3,2 h • Farabee & Casarella: xb  34 h Reh = 4400 U∞ = 0,25 m/s xb

  23. Averaged fields downstream of the step: streamlines and vorticity • reattachment at xb 2,5 h • xb about constant with Re • Mohesen: xb  22,5 h • Leclercq et al.: xb  3,2 h • Farabee & Casarella: xb  34 h Reh = 17500 U∞ = 1 m/s xb

  24. Wall pressure fluctuations downstream of the step: auto-spectra • The slope decreases from -2.5 to -2 (in agreement with Leclerq et al.) - 2,5 - 2,5 U

  25. Wall pressure fluctuations downstream of the step: auto-spectra • The slope decreases from -2.5 to -2 (in agreement with Leclerq et al.) - 2 - 2 U

  26. Overall sound pressure level Maximum noise level • SPL increases close to the wall • Same trend for different Reynolds numbers U

  27. Wall pressure fluctuations : further issues • Cross-correlations reveal acoustic (peak at 0 time shift due to the very high speed of sound) and hydrodynamic perturbations • The hydrodynamic convection velocity varies from 0,5  0,7 U∞ both upstream and downstream the step: the lowest magnitudes occur in the recirculation regions

  28. Conclusions and future perspectives • An extensive data base has been generated: preliminary results clarify the overall dynamics • The Reynolds number seems to have a weak influence upon the separation/reattachment points • Wall pressure spectra reflect the influence of the recirculation regions as well as the hydrodynamic advection • The SPL reveals that the most noisy region is located downstream the step at the reattachment region! • Pressure-PIV data analysis: conditional analysis and ensemble averages would clarify the physical nature of the observed large SPL (also by the application of signal-processing advanced methodologies: Wavelet transform & POD)

  29. laser camera mirror Laser sheet Spherical lens Cylindrical lens step U Simultaneous pressure/PIV measurements set up Array of pressure transducers Acquisition system PC Hydrophones+ accelerometer High speed camera Optics + mirror laser • fs = 1000 Hz • t = 12 sec • 1024x512 px

  30. laser camera mirror Laser sheet Spherical lens Cylindrical lens step U Simultaneous pressure/PIV measurements set up • SPECTRA-PHYSICS Stabilite 2017 • Argon • max Power = 6 W

  31. laser camera mirror Laser sheet Spherical lens Cylindrical lens step U Simultaneous pressure/PIV measurements set up • Photron LTDFastcam APX • Up to 120.000 fps • CMOS sensor • 8 GB memory

  32. CONFIGURAZIONE DI MISURA: idrofoni idrofono a monte idrofono vicino al gradino

More Related