1 / 17

Influence of wall roughness on near wall turbulence structure by Haigermoser C.* , Vesely L.*, La Polla M., Onorato M.,

Influence of wall roughness on near wall turbulence structure by Haigermoser C.* , Vesely L.*, La Polla M., Onorato M., Politecnico di Torino XIV A.I.VE.LA. National Meeting Roma, 6-7 novembre 2006. * Marie Curie EST fellow. Introduction Experimental Setup Results General

dino
Download Presentation

Influence of wall roughness on near wall turbulence structure by Haigermoser C.* , Vesely L.*, La Polla M., Onorato M.,

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. Influence of wall roughness on near wall turbulence structure by Haigermoser C.*, Vesely L.*, La Polla M., Onorato M., Politecnico di Torino XIV A.I.VE.LA. National Meeting Roma, 6-7 novembre 2006 * Marie Curie EST fellow

  2. Introduction Experimental Setup Results General Vertical Plane PIV Measurements Horizontal Plane PIV Measurements Summary and Conclusion Outline

  3. Turbulent boundary layer measurements on rough walls using PIV 2 different rough walls tested Aim: Influence of roughness on coherent structures with reference to a smooth wall turbulent boundary layer 1. Introduction

  4. Double pulsed Nd: YAG, Q–switched laser, with 200 mJ of energy per pulse (5-6 ns pulse duration) 1280 x 1024 pixel CCD Camera DANTEC system hub Software: DANTEC Flow Manager CCD Camera System Hub Flow Manager (PC) Laser 2. Experimental SetupPIV Setup

  5. Closed loop open-flow water tunnel with 350 x 500 x 1800 mm3 test section Mean freestream velocity 0.3 m/s (Reθ≈ 1900) Silicon Carbide Particles with 2 μm nominal diameter PIV image size: 800 Viscous units 600 Viscous units 2. Experimental SetupFlow Setup 51mm 41mm

  6. Avoiding laser deflection (image deflection) due to surface waves by covering the water surface with Plexiglas Time between two images was 1 ms Plexiglas Laser Sheet Roughness Sand Paper y FLOW x Camera 2. Experimental SetupMeasurement Setup z • 1000 recordings to ensure data convergence • Measurements in vertical and horizontal plane

  7. 2 different rough surfaces tested 3D roughness Top View Side View 2D roughness 6 1.7 Flow Direction Top View Side View 3.5 Flow Direction 5 1.3 2. Experimental SetupRoughness

  8. 4. ResultsGeneral • Mean velocity profiles: • Generic results:

  9. 4. ResultsTurbulence • Increased turbulence at y+>100 due to increased turbulence in the tunnel ([1] Tachie, Bergstrom, Balachandar, 2000). • 2D roughness shows reduced turbulence level of u-velocity close to the wall ([2] Jimenez, 2004). Due to form drag.

  10. FLOW FLOW FLOW 4. ResultsVertical Plane Smooth wall Wall 3D Roughness 2D Roughness Wall • Strong shear layer separates low and high momentum zones • Vortex heads situated in shear layer • Vortex heads belong to a package

  11. ∆y+ ∆x+ 4. ResultsVertical Plane Results of Spatial Correlation with streamwise fluctuating velocity, yref=0.2δ: Smooth wall 3D Roughness 2D Roughness + + + + Increased inclination of vortex heads in a vortex package especially for 3D roughness

  12. 4. ResultsVertical Plane Probability of a measurement point to be involved in a clockwise swirling motion Λci < 0 : • Comparable values of Pω for y+ > 100 • Higher peak values for rough walls • Peak value for 3D roughness shifted farer away from the wall • Smooth wall swirling motions appear to be weaker • 2D roughness produces strongest clockwise vortices

  13. 4. ResultsVertical Plane Positive vortices – 2 explications: Positive vortices are a part of hairpin-like vortices: Positive vortices induced by negative vortices:

  14. 4. ResultsVertical Plane Correlations Λrci\ Λpci, yref=0.2δ: • Results of a study by Natrajan, Wu and Christensen for smooth wall (TAM report 2006): Θ1= 65º, Θ2= 230º, d1=135, d2=103.5. • Similar results for 3D roughness as for smooth wall • Increased Θ2 for 2D roughness

  15. 4. ResultsHorizontal Plane 3D Roughness (y+ = 50) 2D Roughness (y+ = 50) FLOW FLOW

  16. Skin friction with 2D roughness higher than with 3D roughness in spite of smaller roughness height Essentially the same flow structure characteristics observed like for smooth wall Higher inclination of vortex packets Position of negative vortices with respect to positive vortices similar Increased low speed streak spacing with roughness Vortex strength higher especially for the 2D case Pyramids create “attached” vortices 5. Summary and Conclusion

  17. [1] Jimenez J. Turbulent flow over rough walls. Annu. Rev. Fluid Mech. 36, pp. 173-196, 2004. [2] Tachie, Bergstrom, Balachandar. Rough wall boundary layers in shallow open channel flow. J. of Fluids Engineering, Vol. 122, 2000. [3] Natrajan, Wu, Christensen. Spatial signatures of retrograde spanwise vortices in wall turbulence. TAM report 2006. References

More Related