Grid turbulence in air and water

Abstract

An experimental comparison of grid turbulence performed in a wind tunnel and in a water tunnel is described. The measurements were made in the initial stage of decay with mesh Reynolds numbers ranging from 12 800 to 81 000. Hot‐wire and hot‐film instrumentation combining analog and digital computing methods were used to measure higher‐order correlations of the longitudinal component of turbulent velocity and higher‐order moments of longitudinal turbulent velocity gradients. A comparison of the latter is obtained for an increase in Reynolds number without having to alter the flow geometry. Apart from the intrinsic interest of such measurements in water, the results show the non‐Gaussian character of the turbulent fluctuation and compare the behavior of higher‐order moments of turbulent velocity gradients to theoretical considerations for the small scale turbulent structure.