Numerical study on the wake structures of a sphere in linearly stratified flow

In this study, numerical simulations have been carried out to evaluate the influence of internal Froude number (Fr) on the wake characteristics of a sphere in linearly stratified flow. Five models with different levels of Fr (Fr = 0.05, 0.2,0.25,0.5 and 1) at a Reynolds number of Re = 3700 have been selected for comparative study. UDF (User Defined Function) is employed to establish linear density stratification. The influences of stratification on wake characteristics are studied by analyzing the wake patterns, vortical structures, velocity distributions, and lee waves. The results of the study demonstrate that reduced Fr values lead to heightened vertical suppression of the near wake, while increased stratification prompts a transformation of the wake's three-dimensional coherent structures towards quasi-two-dimensionality. Furthermore, the presence of stratification notably impacts the length and amplitude of the lee wave.