1 / 36

An Experimental Investigation of Turbulent Boundary Layer Flow over Surface-Mounted Circular Cavities

An Experimental Investigation of Turbulent Boundary Layer Flow over Surface-Mounted Circular Cavities. Jesse Dybenko Eric Savory Department of Mechanical and Materials Engineering University of Western Ontario, London, ON May 24, 2006. Flow Geometry. Motivation.

erv
Download Presentation

An Experimental Investigation of Turbulent Boundary Layer Flow over Surface-Mounted Circular Cavities

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. An Experimental Investigation of TurbulentBoundaryLayerFlow over Surface-Mounted Circular Cavities Jesse Dybenko Eric Savory Department of Mechanical and Materials Engineering University of Western Ontario, London, ON May 24, 2006

  2. Flow Geometry

  3. Motivation • Cavities are found on aircraft and automobiles • Landing gear wheel wells • Recessed windows • Sun roofs • Symmetric geometry, asymmetric mean flow • Not well researched • A better understanding of these flows could lead to drag and noise reduction for airframes

  4. Background • Peak in cavity drag at h/D 0.5

  5. Background • Cavity Feedback Resonance (Rossiter, 1964)

  6. Background • Vortices shed from upstream cavity lip

  7. Background • Vortices convected downstream

  8. Background • Vortex impinges on downstream lip

  9. Background • Acoustic pulse radiates upstream

  10. Background • Pulse disturbs shear layer – causes vortex to be shed. Feedback loop is closed.

  11. Background • Frequency associated with this mechanism can be estimated using Rossiter’s Formula (Rossiter, 1964): • f is predicted oscillation frequency, m is integer mode number, is vortex-sound pulse lag-time factor, M is free stream Mach number, is ratio of vortex convection velocity to free stream velocity

  12. Background • Oscillation can also occur according to the depth scale of the cavity: depth-mode resonance • Can also estimate frequency due to this mechanism: • f is predicted oscillation frequency, N is odd-integer mode number, c is speed of sound in air, h is cavity depth

  13. Major Objectives • To understand the causes of abnormal flow in cavity and in its wake for h/D 0.5 • What causes this flow to differ from flow at other depth configurations? • To investigate the fluctuating nature of the flows at various cavity depths and their relationship with resulting cavity drag

  14. Experimental Setup

  15. Experimental Techniques • Three cavity depth ratios were used for measurements: • h/D = 0.20, 0.47 and 0.70 • Cavity depth was only variable • Three systems were used for measurements: • Pressure transducers • Surface pressure distribution • Microphones • Acoustic response of cavity • Two-component hot-wire anemometry • Mean Velocity and Turbulence Profiles in wake

  16. Experimental Variables • U0 = 27.0 m/s, δ = 55 mm (δ/D = 0.72), ReD = 1.3 x 105

  17. Results and Discussion • Mean pressure distributions on sidewall

  18. Results and Discussion • Mean surface pressure distributions on cavity base

  19. Results and Discussion • Vortex Skeleton Diagrams – h/D = 0.2

  20. Results and Discussion • Vortex Skeleton Diagrams – h/D = 0.47

  21. Results and Discussion • Vortex Skeleton Diagrams – h/D = 0.70

  22. Results and Discussion • RMS pressure distributions on sidewall

  23. Results and Discussion • RMS pressure distributions on cavity base

  24. Results and Discussion • Drag coefficient comparison

  25. Results and Discussion • Wake velocity profiles – Stream-wise velocity

  26. Results and Discussion • Wake velocity profiles – Stream-wise turbulence

  27. Results and Discussion • Frequency analysis • Estimate Frequencies • Cavity Feedback Resonance: • Predicted first-mode f = 145.5 Hz

  28. Results and Discussion • Frequency analysis • Estimate Frequencies • Depth Mode Resonance: • Predicted first-mode frequencies are depth-dependent, for three depths tested: • h/D = 0.20  f = 2329 Hz • h/D = 0.47  f = 1512 Hz • h/D = 0.70  f = 1164 Hz

  29. Results and Discussion • Frequency analysis – Microphone in base

  30. Results and Discussion • Frequency analysis – Microphone in base

  31. Conclusions • Pressure Measurements • RMS pressure patterns show maxima at shear layer reattachment points and vortex centres • Mean pressure patterns agree well with those done by previous investigators • Integrated drag coefficients also match well with previous data

  32. Conclusions • Wake Flow Analysis • Symmetric velocity and turbulence profiles for h/D = 0.20 • Asymmetric for h/D = 0.47, showing clear, circular trailing vortex feature, which can be disturbed to switch sides • In this feature, mean streamwise velocity is at a minimum, turbulence at a maximum

  33. Conclusions • Frequency analysis • Possible link between cavity feedback resonance and abnormal flow behaviour at h/D = 0.47 • Depth mode oscillations occur for h/D = 0.47 and 0.70; 0.20 not deep enough

  34. Recommendations • Aerodynamic Design • If circular cavity required on vehicle frame, shallow holes are best (h/D = 0.20 or less) • low drag, low noise in high frequency band, no resonances

  35. Acknowledgements • Technicians at BLWTL • Prof. Gregory Kopp • University Machine Shop • Advanced Fluid Mechanics Research Group • Tom Hering and Rita Patel

  36. Questions? For additional information on research done by the AFM Research Group, try our website: http://www.eng.uwo.ca/research/afm

More Related