Validation scheme for small effect of wind tunnel blockage on decaying grid-generated turbulence

Abstract

This paper proposes a validation scheme for the effect of wind tunnel blockage on decaying grid-generated turbulence. This validation scheme was derived from the governing equations of the k-∈ model. Analytical solutions for the validation scheme were derived by introducing a model of the difference between the rate of change of the effect of fluid acceleration on the turbulent kinetic energy and that of the effect on its dissipation. The derived solutions include a decay exponent that excludes the acceleration effect, a parameter characterizing the acceleration, the initial anisotropy, and the model coefficient of the k-∈ model, and can be quantified by parameters which can be known. The physical meaning of the model was clarified. The derived solutions and model were confirmed to be accurate through numerical simulation. An equation for the decay exponent, which is also affected by the fluid acceleration, was developed using the derived solutions. This scheme was applied to the examination of the reduced fluid acceleration effect in a moderate-sized wind tunnel to measure the grid-generated turbulence. The fluid acceleration effect in the wind tunnel was confirmed to be small using the derived equations. The decay characteristics of the grid-generated turbulence in the wind tunnel were measured and were found to agree with those obtained in previous experiments.

Keywords

• turbulent flow
• wind tunnel blockage
• grid-generated turbulence
• k-∈ model