Vortical structures and wakes of bluff bodies in homogenous and stratified environment are common and important in ocean engineering.Based on the Boussinesq approximation,a thermocline model is proposed to deal with the variable density stratified fluid,and implemented in the commercial software Simcenter STAR-CCM+framework.The improved delayed detached eddy simulation(IDDES)modeling method is adopted to resolve the coherent vortical structures and turbulent wakes precisely and efficiently.Four conditions consisting of one homogenous and three stratified fluid cases with different density gradient past a sphere at Reynolds number 3 700 are investigated.Results show that density stratification has a great impact on the vortical structures,the vertical motion is suppressed and internal waves will be induced and propagated,which is very different with that of homogenous situation.With the stratification strength increases,the vortical structures are gradually flattened,the asymmetry and anisotropy between vertical and horizontal motions are enhanced.