Turbulent characteristics and energy transfer in the far field of active-grid turbulence

Turbulent characteristics in the far field of active-grid turbulence have been investigated through wind tunnel experiments using hot-wire anemometry. Two forcing protocols are employed following previous studies: one is the double-random mode and the other is the open mode with the grid remaining static with minimum blockage. The integral length scale L for the double-random modes slightly decreases with streamwise distance in the far field as observed in the near field of the active-grid turbulence. The nondimensional dissipation rate C-e for the double-random modes is around 0.5. This asymptotic value is different from those reported in previous active-grid turbulence experiments and could be nonuniversal. The equilibrium scaling L / ? = CeRe?/15 (? is the Taylor microscale and Re-? is the turbulent Reynolds number) with a constant C-e is established in the far field of the double-random modes regardless of active-grid motions. The sum of production and destruction terms in the enstrophy budget equation for homogeneous and isotropic turbulence S + 2 G / Re-? (S is the skewness of the longitudinal velocity derivative and G is the destruction coefficient) is proportional to Re-?(-1) and close to zero in the present active-grid turbulence, suggesting that the equilibrium scaling is possibly related to the balance between the production and destruction of the enstrophy.

Automated summary

Turbulent characteristics in the far field of active-grid turbulence were investigated using hot-wire anemometry in wind tunnel experiments. The integral length scale slightly decreases with streamwise distance in the far field for the double-random modes, while the nondimensional dissipation rate is around 0.5. Regardless of active-grid motions, an equilibrium scaling with a constant C-e is established in the far field of the double-random modes.