Thermally stratified flow around a circular cylinder in a finite-depth channel at a moderate Reynolds number

Large-eddy simulation is introduced to investigate the effects of finite-depth thermal stratification on flow around a circular cylinder at a Reynolds number of 500 and multiple stratification coefficients K (ratio of fastest linearly vertical internal-wave speed to inflow velocity). Thermal stratification affects the cylinder wake and loading in a two-stage transition form, in which three distinct flow regimes are identified. Regime I ( K = 0 to 1): under weakly stratified conditions, the flow retains features of periodic vortex shedding, and the aerodynamic coefficients show weak variations. Regime II ( K = 1 to 2): as K increases, buoyancy suppresses vertical fluid motions, driving reductions in both the Strouhal number St and the drag coefficient C D , reaching their minima at K ≈ 2. Regime III ( K = 2 to 3): when K > 2, both St and C D increase with K due to internal gravity waves, and the instantaneous vortex structures further show that the wake gradually transitions from a three-dimensional vortex-shedding dominated state to a more two-dimensional, internal-wave-controlled pattern. The critical thermal impacts on aerodynamic forces and near-wake patterns found in this paper could be helpful in engineering applications like energy harvesting, wind turbines, and urban pollutant dispersion.