The impact of upstream turbulence on a plane jet

Abstract

The influence of upstream turbulence on the flow produced by a plane jet is investigated experimentally with hot-wire anemometry and smoke flow visualisation. An innovative active grid, where each wing can be independently controlled, is used to change the upstream turbulence conditions. Three cases are investigated: a canonical reference case, a case with the same integral scale as the reference case but an order of magnitude increase in turbulence intensity, and a case with both an order of magnitude increase in turbulence intensity and an order of magnitude increase in integral scale compared to the reference case. It is demonstrated that the wake width increases with turbulence intensity, but decreases with integral scale for constant turbulence intensity. In addition, the positional variability of the wake width is highest with high turbulence intensity and a short integral scale. Along the jet centreline, the potential core region is shorter with elevated upstream turbulence intensity; this is reflected in both the mean velocity and the variance. The decay of the centreline mean velocity is also retarded by incoming turbulence. In all, increased incoming turbulence results in increased jet spreading, and a shorter integral scale further increases the spreading.