High Reynolds Number Wall Turbulence: Facilities, Measurement Techniques and Challenges

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1 High Reynolds Number Wall Turbulence: Facilities, Measurement Techniques and Challenges Beverley McKeon Graduate Aeronautical Laboratories California Institute of Technology

2 Chapter 7: HIGH REYNOLDS NUMBER WALL TURBULENCE: FACILITIES AND MEASUREMENT TECHNIQUES 7.1 Why study high Re wall turbulence? Why do we continue to study wall turbulence after an investment of 50+ years and little progress? Understand behavior of mean properties as the Reynolds number becomes infinite Understand structure of wall turbulence Understand dynamics of wall turbulence Formulate low order models for specific flows Develop predictive and control capabilities Extend al the above to complex turbulent flows

3 7.2 Experimental facilities Comparison of some large scale boundary layer wind tunnel facilities From The Nordic Wind Tunnel proposal to build a very large turbulence research facility by W.K. George et al, circa

4 Footprint of large scale wind tunnel facilities National Diagnostic Facility at IIT Chicago NASA Ames Full Scale Wind Tunnel (Saddoughi & Veeravalli 1994) Near neutral atmospheric surface layer

5 High Reynolds number pipe flow facilities Princeton/ONR Superpipe Closed loop facility Air at pressures up to 200 atmospheres (20 MPa) Change in kinematic viscosity, ν, x 160 Test leg diameter D = m Development length > 160D Re D = 31 x 10 3 to 35 x 10 6 Surface roughness 0.15μm rms Comparison of friction factors in Superpipe and Oregon liquid helium facility (mass ratio 25 tonnes/1oz!)

6 High Reynolds number pipe flow facilities, cont. Proposed CICLOPE facility, Bologna, Italy Closed loop facility Osborne Reynolds original pipe flow experiment, Manchester, England. Re D ~ 3x10 3 Air at atmospheric pressure Test leg diameter D = m Re D = 31 x 10 3 to 35 x 10 6 Yamal Europe Natural Gas Pipeline Re D ~ 10 7

7 7.3 Requirements on experimental facilities Temperature Surface condition Flow development (inlet and outlet boundary condition) issues Pressure gradient Freestream turbulence/vibration Two dimensionality Spatial resolution Stability (temporal resolution)

8 7.4 How do we interrogate wall turbulence? Measurement techniques (not exhaustive) Flow visualization (Traversing) dynamic pressure profiles Hot wires Sonic anemometry Laser Doppler Velocimetry/Anemometry Particle Image Velocimetry Wall pressure Wall shear stress

9 Visualization: Planar Laser Induced Fluorescence (PLIF) Smoke visualization Fluorescent dye illuminated using a laser sheet. Low Reynolds number boundary layer, Re θ =725, generated by towing a flat plate in a water tank. Side and top views. Gad el Hak (2000) Smoke illuminated using a laser sheet in the atmospheric surface layer, showing ramp like structures. Comparison with low Reynolds number laboratory boundary layer. Hommema & Adrian (2003)

10 Measurement of dynamic pressure 2 2 U ( y) = [ p ( y) p( y)] [ p0( y) p ρ ρ 0 w ]

11 Corrections to dynamic pressure measurements: Pitot static probes

12 Corrections to stagnation pressure measurements 25 Pitot pressure Displacement effect of mean shear, O(15%d probe ) u Turbulence intensity U + y+ Viscous effects y + New displacement correction only New displacement correction plus wall term What mattered for this study was the slope of the velocity profile (1/κ)

13 Corrections to wall static pressure measurements finite size of tapping, ΔU = O(1%U) Π=Δp static /τ w

14 Effect of M c Keon & Smits static pressure correction 36 McKeon & Smits, Meas. Sci. Tech., 13, u Re = 3M Re = 13M k=0.421, B= y+

15 Effect of M c Keon & Smits static pressure correction 36 McKeon & Smits, Meas. Sci. Tech., 13, Re = 3M u Re = 13M k=0.421, B= y+

16 Effect of corrections on overlap region scaling With wall term If you only have low Reynolds number data then appropriate Pitot probe corrections are crucial. Old static pressure correction and new displacement correction With high Reynolds number data the corrections become small New static pressure correction and new displacement correction

17 Hot wire anemometry (From Dantec Dynamics) Li et al, 2002 Quadrant analysis

18 Hot wire anemometry, cont. Issues associated with calibration frequency response of combined wire/circuit system noise floor temperature drift spatial resolution (From Dantec Dynamics) h 0.97 h 1 f c = 1.3 τw τ w t 0.15 h NSTAP Kunkel, Arnold & Smits 2006 (From Bruun 1995)

19 Particle Image Velocimetry 5s sample of synchronous hot wire measurements over the first 5m of the atmospheric surface layer, Metzger et al 2007 Hambleton et al, < z < 0.48m, x=2m Temporal to spatial conversion from Taylor s hypothesis Spatial equivalent would be R L flow PIV field of view of Morris et al (2007)

20 Laser Doppler Velocimetry Wei & Willmarth 1989 Courtesy of Dantec Dynamics

21 Wall pressure Wall shear stress Klewicki et al, 2008 ѵ kinematic viscosity of oil at 22.5 C [72.5 F] =55E 6 m^2/s λ wavelength of sodium light source = 589 nm n index of refraction for oil = ρ density of oil = kg/l ds/dt rate of change of fringe width Jacobi et al, 2009! Kalvesten thesis, 1996 Chandrasekan et al, 2005