CONDITIONAL SAMPLING OF DISSIPATION IN MODERATE REYNOLDS-NUMBER GRID TURBULENCE

Multi-point hot-wire measurements in grid turbulence have been used to conditionally average the dissipation over inertial-scale features of the turbulent field. Velocities were measured at 5 separate spatial p oints obtaining six simultaneous velocity components, at turbulent Rey nolds numbers Re-lambda of 160 and 230. The dissipation was approximat ed with pseudo- or surrogate dissipation epsilon(r)' based on one or t wo velocity gradients. The conditioned dissipation epsilon(r)' inside the most intense large-scale rotational regions of the flow is more th an twice as large as the expected value of epsilon(r)' over the whole domain. Conditional averaging was also carried out over strong large-s cale fronts showing smaller excess in dissipation. (C) 1996 American I nstitute of Physics.