Velocity derivative skewness in fractal-generated, non-equilibrium grid turbulence

Abstract

The evolution of the velocity derivative skewness, S(∂u/∂x), is investigated along two streamwise axes and four transverse positions in the wake of a square-fractal-element grid. In the near-field, the produced turbulence exhibits non-equilibrium characteristics including Cϵ∼ReMα/ReLβ. In the far-field, the turbulence agrees with canonical grid turbulence results and Cϵ is approximately constant. It is found that in the non-equilibrium region, the value of −S(∂u/∂x) is dependent on both streamwise and transverse positions, but after a sufficient decay period, it takes on a near constant value in the far-field. It is demonstrated that the evolution Cϵ approximately corresponds to that of −S(∂u/∂x), which is suggestive that some of the non-equilibrium properties are likely a result of residual strain from the turbulence generating conditions.