Shock-driven variable density mixing experiments at the Vertical Shock Tube

The Vertical Shock Tube (VST) facility at Los Alamos National Laboratory is studying shock driven mixing of a perturbed air-SF6 interface using simultaneous Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF). We are examining the effects of incident Mach number in the range 1.2 to 2, and the effects of changing the amplitude and wavelength of 3D perturbations on the air-SF6 interface. Through measurements of density fields, velocity fields, vorticity, strain rate, and Reynolds stress, we are examining differences in the largest and smallest scales of turbulent mixing. Results of Mach number and initial condition effects will be presented, including characterization of the initial conditions using spectra and proper orthogonal decomposition, and understanding the dynamic behavior of the evolving flow in an instantaneous as well as a statistical sense. Our observations indicate differences in both the large-scale mixing features as well as earlier development of smaller scales of mixing that are impacted by both initial Mach number and the modal nature of the initial conditions. Calculations of Taylor microscales based upon both density and velocity fields will also be presented in the context of understanding the development of the mixing.