Experimental investigation of the grid-generated turbulence features in a free surface flow

The present study aims to investigate the features of a grid-generated turbulence occurring in a current flow with a free surface flow. The interest is focused on the length and time scales of the turbulence. These are the macro, the micro and the Kolmogorov scales. To analyze the flow, a 2D LDV system has been used to measure (U) over bar, (W) over bar, u' and w'. This non-intrusive and optical technique is really accurate (in terms of space and time resolution). Furthermore, it does not disturb the flow and provides a high data rate. Both horizontal and vertical velocities are recorded at the same time according to a coincidence window (tau(cw)). Bias measurements are avoided by using a filtering technique during data processing. The improved homogeneity and isotropy of the turbulence downstream of the grid allows the use of the Taylor hypothesis. Thus, all length and time scales of the flow can be estimated. Results are discussed as well as the influence of the upcoming mean velocity ((U) over bar) on the turbulence properties. (c) 2005 Elsevier Inc. All rights reserved.