Experimental investigation of the large-scale velocity statistics in homogeneous turbulent shear flow

Abstract

Motivated by the numerical results of Isaza and Collins [“On the asymptotic behaviour of large-scale turbulence in homogeneous shear flow,” J. Fluid Mech. (in press)], the sensitivity of the self-similar behavior of the large-scale velocity statistics in an homogeneous turbulent shear flow to the initial value of the shear parameter and Reynolds number is investigated in a wind tunnel. Using an active grid, the initial value of Reynolds number based on the Taylor microscale is varied over the range 100≤Rλ≤250. The shear is generated using screens of different solidities followed by a series of straightening channels [S. Garg and Z. Warhaft, Phys. Fluids 10, 662 (1998)], allowing us to vary the initial value of the shear parameter over the modest range 6≤S0*≤12. We find that the longtime behavior of the shear parameter depends on its initial value over the nondimensional time interval 5≤St≤25, but is less sensitive to the initial value of the Reynolds number. The ratio of the turbulent kinetic energy production over dissipation rate appears to show a similar dependence on the initial value of the shear parameter, but there is more significant scatter in the data. We find that the turbulent kinetic energy grows with downstream distance, in agreement with previous work, and that its growth rate too is a stronger function of the initial shear parameter than the initial Reynolds number. The experimental results for all of the large-scale velocity statistics are consistent with the earlier direct numerical simulation study.