Presentation on theme: "IWPCTM 12, Moscow, Russia 12 July 2010 0/14 Experimental Study of Initial Condition Dependence for Turbulence Design in Shock Driven Flows Sridhar Balasubramanian,"— Presentation transcript:
IWPCTM 12, Moscow, Russia 12 July /14 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)
IWPCTM 12, Moscow, Russia 12 July /14 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.
IWPCTM 12, Moscow, Russia 12 July /14 Current shock tube configuration allows diagnostic access for simultaneous PIV/PLIF measurements Layer Configuration: Light-Heavy-Light (Air-SF 6 -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 Nozzle to create curtain
IWPCTM 12, Moscow, Russia 12 July /14 New, longer test section allows observation of late-time flow structures Initial Condition New Test Section (L~0.45m) Incident shock Reflected shock Expansion fan Reflected Expansion fan
IWPCTM 12, Moscow, Russia 12 July /14 New stereo PIV diagnostic has been added to capture 3-D velocity field in a plane Side view of IC’s End view of the IC’s y z x x z y
IWPCTM 12, Moscow, Russia 12 July /14 PIV through the initial conditions shows the exit and peak velocities of the curtain for input into simulations x z y d z (mm) Only select vectors shown for clarity
IWPCTM 12, Moscow, Russia 12 July /14 Detailed IC measurements are critical to understanding the sensitivity of the late-time flow to initial conditions x z y 3-D Numerical ICs SF 6 Volume Fraction x z y d z (mm) x Experimental velocity profiles at 9 vertical planes A=0.50, B=0.198, k=1745.3, a= , =835.6 Experimental concentration profiles at 20 mm from nozzle exit Centerline of curtain
IWPCTM 12, Moscow, Russia 12 July /14 Dependence of growth patterns and mixing width on initial conditions in RM unstable fluid layers. Physica Scripta Balakumar, Orlicz, Tomkins, Prestridge We can control the initial conditions and observe late- time modes and turbulence after reshock IC formed by nozzle geometry Reshocking late-time structures
IWPCTM 12, Moscow, Russia 12 July /14 Can amplitude & wavelength in IC’s allow us to predict the late-time flow behavior? Varicose curtain, Reshocked at 615µs, (Balakumar et al. POF 2008) We know that morphologies with multiple wavelengths, such as this, lead to turbulence upon reshock. 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?? Reynolds number 4000 at t=565 s 12,000 at t=800 s
IWPCTM 12, Moscow, Russia 12 July /14 The power spectral density gives us a metric for when the flow has enough modes to become turbulent upon reshock Transition? No transition? 2-D FFT of concentration signal (avg over span) Widths of k=1.5 peaks
IWPCTM 12, Moscow, Russia 12 July /14 A series of experiments was performed to test the predictions of turbulent transition from the PSD analysis Reshock times 90 µs 170 µs 280 µs FIRST SHOCKRESHOCK Can we quantify these observable differences?
IWPCTM 12, Moscow, Russia 12 July /14 The PSD of structures after reshock show a broadening and loss of features indicating transition to turbulence Differences in the amount of mixing are seen between early time reshock (90 s, 170 s) and late time reshock (280 s, 600 s). Reshock timings Reshock at late times gives lower value of I suggesting that there is more mixing 2-D FFT of concentration signals, 250 µs after reshock
IWPCTM 12, Moscow, Russia 12 July /14 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 Reshock at 170 µs, Experiment & Simulation Experiment Simulation 3-D ILES simulations performed at LANL by Akshay Gowardhan & Fernando Grinstein Experiment Simulation 3-D Initial Conditions
IWPCTM 12, Moscow, Russia 12 July /14 Sinuous initial conditions Shocked once 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 data from Balakumar et al., 2008, PhysicaScripta) Wavelength=7mm Amplitude=6.5mm
IWPCTM 12, Moscow, Russia 12 July /14 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.