Analyzing and benchmarking an active grid turbulence generator in a laboratory water tunnel

Active grid turbulence generators used to produce turbulent flow in laboratories have become commonplace in wind tunnels. However, usage of active grids in water tunnels is rare, and our facility at Lehigh University is one of the few water tunnels that allow for active grid turbulence generation. We will discuss results from an extensive experimental campaign where we explore the influence of parameters including grid operating protocol, free-stream inlet velocity (mesh Reynolds number, Re_M), winglet rotational velocity (Rossby number, Ro), and winglet blockage ratios on produced turbulent flow. Turbulence is characterized by turbulence intensities, integral length scales, Taylor Reynolds numbers, and anisotropic ratios. Results suggest the three most influential parameters include the winglet blockage ratio, Re_M, and Ro. Similar to trends in wind tunnel studies, a larger blockage ratio contributes to larger turbulence intensities. However, unlike in wind tunnel experiments, there is little evidence that Ro impacts turbulence intensities despite directly influencing integral length scales. Results of this study encourage the plausibility of tailoring desired turbulent flows by carefully manipulating active grid operating conditions.