Effect of exit Reynolds number on self-preservation of a plane jet

Abstract

We investigated in experiment the effect of exit Reynolds number on self-preservation of a turbulent plane jet. Centerline velocity statistics were measured in plane jets issuing from the same nozzle but, respectively, with seven Reynolds numbers varying between Re=4,582 and Re=57,735, where Re≡Ujh/ν (Uj being the momentum-averaged exit mean velocity, h the slot height and ν the kinematic viscosity). All measurements were conducted using single hot-wire anemometry and over an axial distance (x) of 40 h. These measurements revealed a significant Re-dependence of either the mean or turbulent flow field. As Re increases, the pace of the jet development decreases and, as a result, both the mean and turbulent properties reach their self-preserving states over a longer downstream distance (x). The centerline integral scale L for all jets grows linearly with x and the growth rate decreases as Re is increased. It is also found that the local Reynolds number ReL scales with x as ReL∝x1/2. The study suggests that differences of the self-preserving states observed may be related to the differences in the underlying turbulence structures in the near field of the seven jets.