Experimental Study of Initial Condition Dependence for Turbulence Design in Shock Driven Flows

1. Experimental Study of Initial Condition Dependence for Turbulence Design in Shock Driven Flows Sridhar Balasubramanian, K. Prestridge, B.J. Balakumar, G. Orlicz P-23 Neutron Science and Technology Group, Extreme Fluids Team Los Alamos National Laboratory Acknowledgments: Malcolm Andrews, Ray Ristorcelli, Rob Gore, Fernando Grinstein & Akshay Gowardhan Research supported by Los Alamos National Laboratory Directed Research and Development Program (LDRD-DR)

2. How is shock-driven (Richtmyer-Meshkov) turbulence affected by initial conditions? • Buoyancy-driven turbulence can be affected at late-time by initial conditions, and memory of the IC’s are not lost (Dimonte et al., Phys Fluids 2004, Ramaprabhu et al., JFM 2005). • Carefully imposed initial conditions effect the growth rate of turbulent Rayleigh-Taylor (R-T) mixing (Banerjee & Andrews, 2009, Ramaprabhu et al., 2005, Dimonte et al., 2004, Mueschke, 2004). • Work has not yet been done to test the dependence of initial conditions on shock-driven turbulent flows.

3. Current shock tube configuration allows diagnostic access for simultaneous PIV/PLIF measurements Nozzle to create curtain • Layer Configuration: Light-Heavy-Light (Air-SF6-Air) • Atwood Number = 0.67 • Incident Shock Mach Number = 1.2 • Primary Wavelength,  = 3.6 mm • PLIF Resolution ~ 54 m/pixel • (to resolve scalar concentration gradients) • PIV Resolution ~ 156 m/vector

4. New, longer test section allows observation of late-time flow structures Reflected shock Reflected Expansion fan Incident shock Initial Condition Expansion fan New Test Section (L~0.45m)

5. y x z New stereo PIV diagnostic has been added to capture 3-D velocity field in a plane x y z Side view of IC’s End view of the IC’s

6. PIV through the initial conditions shows the exit and peak velocities of the curtain for input into simulations y x z (mm) 0 z 10 30 50 70 Only select vectors shown for clarity d

7. Detailed IC measurements are critical to understanding the sensitivity of the late-time flow to initial conditions y x Experimental velocity profiles at 9 vertical planes 3-D Numerical ICs SF6 Volume Fraction x z (mm) 0 y z 10 x 30 z 50 Centerline of curtain 70 d Experimental concentration profiles at 20 mm from nozzle exit A=0.50, B=0.198, k=1745.3, a=-0.0398, =835.6

8. We can control the initial conditions and observe late-time modes and turbulence after reshock IC formed by nozzle geometry Reshocking late-time structures Dependence of growth patterns and mixing width on initial conditions in RM unstable fluid layers. Physica Scripta 2008. Balakumar, Orlicz, Tomkins, Prestridge

9. Can amplitude & wavelength in IC’s allow us to predict the late-time flow behavior? Will either of these morphologies become turbulent upon reshock?? Question: Can we predict the onset and nature of the turbulence and somehow link that to the initial conditions?? We know that morphologies with multiple wavelengths, such as this, lead to turbulence upon reshock. Varicose curtain, Reshocked at 615µs,(Balakumar et al. POF 2008) Reynolds number  4000 at t=565 s  12,000 at t=800 s

10. The power spectral density gives us a metric for when the flow has enough modes to become turbulent upon reshock 2-D FFT of concentration signal (avg over span) Transition? No transition? Widths of k=1.5 peaks

11. A series of experiments was performed to test the predictions of turbulent transition from the PSD analysis FIRST SHOCK RESHOCK Reshock times 90 µs 170 µs Can we quantify these observable differences? 280 µs

12. The PSD of structures after reshock show a broadening and loss of features indicating transition to turbulence 2-D FFT of concentration signals, 250 µs after reshock Reshock timings Reshock at late times gives lower value of Isuggesting that there is more mixing Differences in the amount of mixing are seen between early time reshock (90s, 170 s) and late time reshock (280 s, 600 s).

13. First 3-D simulations of the gas curtain capture many of the large-scale features, but validation is ongoing Reshock at 90 µs, Experiment & Simulation 3-D Initial Conditions Experiment Simulation Reshock at 170 µs, Experiment & Simulation Experiment 3-D ILES simulations performed at LANL by Akshay Gowardhan & Fernando Grinstein Simulation

14. We can form complex initial conditions using new nozzle designs that will become turbulent after first shock, instead of after reshock Varicose initial conditions Reshocked at 90µs Wavelength=3.6mm Amplitude=3.2mm Sinuous initial conditions Shocked once Wavelength=7mm Amplitude=6.5mm (sinuous data from Balakumar et al., 2008, PhysicaScripta)

15. Summary & Future Plans • Measured 3-D characteristics of our well-controlled experimental initial conditions, providing (for the first time) enough constraints on 3-D simulations for IC sensitivity studies. • Preliminary PLIF measurements have helped us understand which multi-mode conditions will lead to the development of turbulence. • Velocity field measurements (PIV) of the turbulence will allow us to characterize the turbulent fluctuations to determine the extent of the impact of the initial modes on the turbulence quantities. • Feasibility of designing multi-mode nozzles with initial conditions that will transition to turbulence upon first shock.