Numerical study of surface thermal signatures of lee waves excited by moving underwater sphere at low Froude number

Abstract A submerged body moving in density-stratified water, such as in oceans, disturbs the surrounding water layers. Furthermore, the internal waves generate and modulate the flow field on the water surface. Thereafter, the thin water surface layer and underlying water, which differ in temperatures because of factors such as solar radiation and water vapor exchange, mix. Consequently, thermal signatures could be generated on the water surface and detected by high-resolution infrared equipment; hence, the presence of a submerged moving body could also be deduced. To thoroughly examine this phenomenon, a submerged sphere moving horizontally in linearly density-stratified water with a “hot skin” layer on its surface was numerically studied in this work. A suitable solver, i.e., “twoLiquidMixing_skin_Foam” , based on the well-known open-source computational fluid dynamics code, “Open-Source Field Operation and Manipulation”, was developed for the aforementioned problem. The internal waves excited by the sphere were validated by experimental results to illustrate the accuracy of the developed solver. Then, the impact of lee waves on the water surface thermal signatures was investigated in detail for the towed submerged sphere moving at various depths in fluid with different internal Froude numbers.