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

The evolution of the velocity derivative skewness, S(partial derivative u/partial derivative 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 C-is an element of similar to Re-M(alpha)/Re-L(beta). In the far-field, the turbulence agrees with canonical grid turbulence results and C-is an element of is approximately constant. It is found that in the non-equilibrium region, the value of -S(partial derivative u/partial derivative 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 C-is an element of approximately corresponds to that of -S(partial derivative u/partial derivative x), which is suggestive that some of the non-equilibrium properties are likely a result of residual strain from the turbulence generating conditions. (C) 2015 AIP Publishing LLC.