The generation of grid turbulence with continuously adjustable intensity and length scales

Abstract

Studying boundary layer transition and its sensitivity to free-stream turbulence, it is often advantageous to be able to continuously adjust intensity and length scales of the turbulence. In this study, we present a new adjustable static turbulence grid and characterize the turbulence it generates. The biplane grid consists of 7 vertical and 19 horizontal, 1 mm-thick baffle plates with a spacing of 12.5 mm. Four of the vertical and ten of the horizontal baffles can be rotated by 90 $$^\circ$$ around the longitudinal axis to change their angle of attack and effective width, while the whole grid can be shifted by 410 mm in flow direction. Adjusting the baffle plate angle and axial grid displacement allows a variation of the turbulence intensity at the exit of the turbulence generator, while other parameters, such as the integral length scale or the turbulent Reynolds number, remain constant and vice versa. The turbulence intensity at the exit can be set within the range of 1.5–8%. Single and X-wire probes are used to measure the level of isotropy, decay of turbulent kinetic energy as well as characteristic length scales and energy spectra. The experiments are performed in a rectangular duct with a cross section of 100 mm $$\times$$ 250 mm embedded in a closed-loop wind tunnel. Reynolds numbers based on grid spacing vary from 11,000 to 32,500.