Contraction Effects on Turbulent Inflow Produced by an Active Grid

Applications such as wind energy have provided motivation for generating realistic turbulent inflows in wind tunnels. Facilities with the ability to produce such inflows allow for studies of the interaction between the inflow turbulence and the flow of interest. An example flow is the effect of atmospheric turbulence on the behavior of a wind turbine wake. Active grids – systems of actively driven elements - have the ability to tailor the inflow turbulence quantities (e.g. turbulence intensities, integral length scale, and turbulence spectrum). An active grid with 40 independent axes located within the forward contraction of a low speed, open return wind tunnel has been developed with the intent to allow the generated turbulence to evolve before entering the test section thereby producing a better conditioned turbulent inflow. The effects of the contraction on the turbulent inflow is thus of interest. Surveys using hot-wire anemometry within the contraction have been conducted to investigate the evolution of the turbulence as it propagates downstream. The turbulence characteristics at the grid and those at the test section entrance will be compared.