Characterization of turbulence generated by an active grid with individually controllable paddles

Abstract

An active grid with individually controllable paddles was constructed to generate strong turbulence (Reλ>200). Measurements of turbulence quantities using the hot-wire technique were conducted in a wind tunnel along the flow on the centre line and on an off-centred line in the wake of this grid. The effect of two different motion sequences of the active grid paddles as well as the influence of the clock rate of the paddles were tested. Finally, measurements with a fixed paddle angle were carried out. The results confirmed that the active grid is suitable to generate the intended strong turbulence. Maximum Reλ was obtained when the uniform probability density distribution was used. Turbulence generated with fixed paddle angle still delivered turbulence with Reλ~100.