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 points obtaining six simultaneous velocity components, at turbulent Rey‐ nolds numbers Re _λ of 160 and 230. The dissipation was approximated with pseudo‐ or surro‐ gate dissipation ε _r ^′ based on one or two velocity gradients. The conditioned dissipation ε _r ^′ inside the most intense large‐scale rotational regions of the flow is more than twice as large as the expected value of ε _r ^′ over the whole domain. Conditional averaging was also carried out over strong large‐scale fronts showing smaller excess in dissipation.