Turbulence budgets in time-resolved variable density round jets*

Variable density turbulence occurs in flows with large density gradients and plays an important role in natural and engineered systems from the astrophysical (stellar evolution, supernovae) to the very small (inertial confinement fusion). The Turbulent Mixing Tunnel at Los Alamos National Laboratory was built to study this problem using simultaneous time-resolved planar density and stereoscopic velocity measurements (Particle Image Velocimetry and Laser-Induced Fluorescence). Because of the density field’s active role simultaneous measurements are critical for testing turbulence models such as LANL’s BHR. We made measurements of two momentum-matched jets in air and SF₆ (At = 0.16 and 0.6; Re = 7,000 and 12,000) and the flow was sampled at locations ranging from 2-16 initial jet diameters with 10,000 snapshots taken at each. Applying Taylor’s frozen turbulence hypothesis the full velocity gradient tensor was estimated and the pressure fields calculated using omni-directional integration, allowing the computation of the complete turbulence budgets. The effect of variable density conditions will be explored and compared to previous experiments on the same facility at Re = 20,000, and the validity of Lumley’s model for pressure-velocity correlations will be examined.