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Influence of wall roughness on Influence of wall roughness on near wall turbulence structurenear wall turbulence structure
bybyHaigermoser C.*Haigermoser C.*, Vesely L.*, La Polla M., , Vesely L.*, La Polla M.,
Onorato M., Onorato M., Politecnico di TorinoPolitecnico di Torino
XIV A.I.VE.LA. National Meeting XIV A.I.VE.LA. National Meeting Roma, 6-7 novembre 2006Roma, 6-7 novembre 2006
Influence of wall roughness on Influence of wall roughness on near wall turbulence structurenear wall turbulence structure
bybyHaigermoser C.*Haigermoser C.*, Vesely L.*, La Polla M., , Vesely L.*, La Polla M.,
Onorato M., Onorato M., Politecnico di TorinoPolitecnico di Torino
XIV A.I.VE.LA. National Meeting XIV A.I.VE.LA. National Meeting Roma, 6-7 novembre 2006Roma, 6-7 novembre 2006
* Marie Curie EST fellow
Roma, 6-7 November 2006Roma, 6-7 November 2006XIV A.I.VE.LA. National Meeting XIV A.I.VE.LA. National Meeting
OutlineOutlineOutlineOutline
1. Introduction2. Experimental Setup3. Results
1. General2. Vertical Plane PIV Measurements3. Horizontal Plane PIV Measurements
4. Summary and Conclusion
1. Introduction2. Experimental Setup3. Results
1. General2. Vertical Plane PIV Measurements3. Horizontal Plane PIV Measurements
4. Summary and Conclusion
Roma, 6-7 November 2006Roma, 6-7 November 2006XIV A.I.VE.LA. National Meeting XIV A.I.VE.LA. National Meeting
1. Introduction1. Introduction1. Introduction1. Introduction
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
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
Roma, 6-7 November 2006Roma, 6-7 November 2006XIV A.I.VE.LA. National Meeting XIV A.I.VE.LA. National Meeting
2. Experimental Setup2. Experimental SetupPIV SetupPIV Setup
2. Experimental Setup2. Experimental SetupPIV SetupPIV Setup
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
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 CameraCCD Camera
LaserLaser
System HubSystem Hub Flow Manager (PC)Flow Manager (PC)
Roma, 6-7 November 2006Roma, 6-7 November 2006XIV A.I.VE.LA. National Meeting XIV A.I.VE.LA. National Meeting
2. Experimental Setup2. Experimental SetupFlow SetupFlow Setup
2. Experimental Setup2. Experimental SetupFlow SetupFlow Setup
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:
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:
0 5 10 15 20 25 30 35 40 45mm
0
5
10
15
20
25
30
35
mm
51mm
41mm60
0 V
isco
us
unit
s
800 Viscous units
Roma, 6-7 November 2006Roma, 6-7 November 2006XIV A.I.VE.LA. National Meeting XIV A.I.VE.LA. National Meeting
2. Experimental Setup2. Experimental SetupMeasurement SetupMeasurement Setup
2. Experimental Setup2. Experimental SetupMeasurement SetupMeasurement Setup
Laser Sheet
Avoiding laser deflection (image deflection) due to surface waves by covering the water surface with Plexiglas
Time between two images was 1 ms
Avoiding laser deflection (image deflection) due to surface waves by covering the water surface with Plexiglas
Time between two images was 1 ms 1000 recordings to ensure data convergence
Measurements in vertical and horizontal plane
1000 recordings to ensure data convergence Measurements in vertical and horizontal plane
z
FLOW
Sand Paper
Roughness
Camera
Plexiglas
xy
Roma, 6-7 November 2006Roma, 6-7 November 2006XIV A.I.VE.LA. National Meeting XIV A.I.VE.LA. National Meeting
2. Experimental Setup2. Experimental SetupRoughnessRoughness
2. Experimental Setup2. Experimental SetupRoughnessRoughness
2 different rough surfaces tested 2 different rough surfaces tested
FlowDirection
5
6 1
.7
Top View Side View
3D roughness
3.5
1.3
Side ViewTop View
FlowDirection
2D roughness
Roma, 6-7 November 2006Roma, 6-7 November 2006XIV A.I.VE.LA. National Meeting XIV A.I.VE.LA. National Meeting
4. Results4. ResultsGeneralGeneral
4. Results4. ResultsGeneralGeneral
0
5
10
15
20
25
1 10 100 1000 10000
y+
U+
Smooth2D Roughness3D Roughness
Mean velocity profiles:
Mean velocity profiles:
Generic results: Generic results:
Roma, 6-7 November 2006Roma, 6-7 November 2006XIV A.I.VE.LA. National Meeting XIV A.I.VE.LA. National Meeting
4. Results4. ResultsTurbulenceTurbulence4. Results4. Results
TurbulenceTurbulence
0
1
2
3
4
5
6
7
8
9
10
1 10 100 1000y+
U'2
+ ,
V'2+
Smooth Wall (DeGraff) V'̂ 2+ 2D Roughness U'̂ 2+ Smooth (DeGraff) U'̂ 2+ 2D Roughness V'̂ 2+
Smooth U'̂ 2+ Smooth V'̂ 2+ 3D Roughness U'̂ 2+ 3D Roughness v'̂ 2+
•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.
Roma, 6-7 November 2006Roma, 6-7 November 2006XIV A.I.VE.LA. National Meeting XIV A.I.VE.LA. National Meeting
4. Results4. ResultsVertical PlaneVertical Plane
4. Results4. ResultsVertical PlaneVertical Plane
2D Roughne
ss
2D Roughne
ss
Strong shear layer separates low and high momentum zones
Vortex heads situated in shear layer Vortex heads belong to a package
Strong shear layer separates low and high momentum zones
Vortex heads situated in shear layer Vortex heads belong to a package
FLOW
3D Roughne
ss
3D Roughne
ss
FLOWFLOW
Smooth wallSmooth wall Wall
Wall
Roma, 6-7 November 2006Roma, 6-7 November 2006XIV A.I.VE.LA. National Meeting XIV A.I.VE.LA. National Meeting
4. Results4. ResultsVertical PlaneVertical Plane
4. Results4. ResultsVertical PlaneVertical Plane
Results of Spatial Correlation with streamwise fluctuating velocity, yref=0.2δ:
Results of Spatial Correlation with streamwise fluctuating velocity, yref=0.2δ:
3D Roughness3D Roughness 2D Roughness2D Roughness
Increased inclination of vortex heads in a vortex package especially for 3D roughnessIncreased inclination of vortex heads in a vortex package especially for 3D roughness
+
+
+
+
∆y+
∆x+
Smooth wallSmooth wall
Roma, 6-7 November 2006Roma, 6-7 November 2006XIV A.I.VE.LA. National Meeting XIV A.I.VE.LA. National Meeting
4. Results4. ResultsVertical PlaneVertical Plane
4. Results4. ResultsVertical PlaneVertical Plane
Probability of a measurement point to be involved in a clockwise swirling motion Λci < 0 :
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
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
Smooth wall swirling motions appear to be weaker
2D roughness produces strongest clockwise vortices
Roma, 6-7 November 2006Roma, 6-7 November 2006XIV A.I.VE.LA. National Meeting XIV A.I.VE.LA. National Meeting
4. Results4. ResultsVertical PlaneVertical Plane
4. Results4. ResultsVertical PlaneVertical Plane
Positive vortices – 2 explications:Positive vortices – 2 explications:
Positive vortices induced by negative vortices:
Positive vortices are a part of hairpin-like vortices:
Roma, 6-7 November 2006Roma, 6-7 November 2006XIV A.I.VE.LA. National Meeting XIV A.I.VE.LA. National Meeting
4. Results4. ResultsVertical PlaneVertical Plane
4. Results4. ResultsVertical PlaneVertical Plane
Correlations Λrci\ Λp
ci, yref=0.2δ:Correlations Λrci\ Λp
ci, 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
Roma, 6-7 November 2006Roma, 6-7 November 2006XIV A.I.VE.LA. National Meeting XIV A.I.VE.LA. National Meeting
4. Results4. ResultsHorizontal PlaneHorizontal Plane
4. Results4. ResultsHorizontal PlaneHorizontal Plane
3D Roughness (y+
= 50)3D Roughness (y+
= 50)2D Roughness (y+
= 50)2D Roughness (y+
= 50)
FLOW FLOW
Roma, 6-7 November 2006Roma, 6-7 November 2006XIV A.I.VE.LA. National Meeting XIV A.I.VE.LA. National Meeting
5. Summary and Conclusion5. Summary and Conclusion5. Summary and Conclusion5. Summary and Conclusion
Skin friction with 2D roughness higher than Skin friction with 2D roughness higher than with 3D roughness in spite of smaller with 3D roughness in spite of smaller roughness heightroughness height
Essentially the same flow structure Essentially the same flow structure characteristics observed like for smooth wallcharacteristics observed like for smooth wall
Higher inclination of vortex packets Higher inclination of vortex packets Position of negative vortices with respect to Position of negative vortices with respect to
positive vortices similar positive vortices similar Increased low speed streak spacing with Increased low speed streak spacing with
roughnessroughness Vortex strength higher especially for the 2D Vortex strength higher especially for the 2D
casecase Pyramids create “attached” vorticesPyramids create “attached” vortices
Roma, 6-7 November 2006Roma, 6-7 November 2006XIV A.I.VE.LA. National Meeting XIV A.I.VE.LA. National Meeting
ReferencesReferencesReferencesReferences
[1] Jimenez J. Turbulent flow over rough walls. Annu. Rev. Fluid Mech. 36, pp. 173-196, 2004.
[2] Tachie, Bergstrom, Balachandar. [2] Tachie, Bergstrom, Balachandar. Rough wall boundary layers in Rough wall boundary layers in shallow open channel flowshallow open channel flow. J. of Fluids Engineering, Vol. 122, 2000.. J. of Fluids Engineering, Vol. 122, 2000.
[3] Natrajan, Wu, Christensen. [3] Natrajan, Wu, Christensen. Spatial signatures of retrograde Spatial signatures of retrograde spanwise vortices in wall turbulence.spanwise vortices in wall turbulence. TAM report 2006. TAM report 2006.