Measurements of decaying grid turbulence with various initial conditions

Abstract

The uniform grid, a tool commonly used to generate homogeneous and isotropic turbulence, has been the subject of many studies. Many studies have primarily focused on how initial conditions of uniform square grids, including the Reynolds number, mesh size, bar size, cross-section of bar, and solidities, affect the statistical characteristics of grid turbulence. However, the influence of mesh shape has not been studied extensively. This study deviates from the norm by examining the influence of different mesh shapes, specifically the uniform nonsquare grid, on grid turbulence. This variation in mesh shape can be easily achieved based on the traditional uniform square grid. The findings reveal that when a uniform nonsquare grid is used, the distance required for turbulence to fully develop decreases. Additionally, there is an increase in the low-frequency components of fluctuating velocity, while high-frequency components decrease. This shift leads to a difference in energy distribution. Moreover, using a uniform nonsquare grid reduces the anisotropies of decaying turbulence to a certain extent. The skewness approaches theoretical value of 0 more closely, while the flatness remains largely unchanged. The mesh shape also affects the decay exponents and power-law coefficients obtained, with the decay exponent potentially getting much closer to 1. Furthermore, larger integral length scales can be achieved at the same downstream position, without significantly modifying the turbulence intensity, by using the uniform nonsquare grid. This could better meet the requirements of large-scale turbulence in certain engineering fields, such as wind engineering, compared to the traditional uniform square grid.