Internal gravity waves spectrum generated by a hydrofoil body moving in a stratified fluid

The movement of subsurface objects in the stratified fluid causes the formation of internal waves. In this paper Internal gravity waves spectrum generated by a hydrofoil body moving in a stratified fluid is investigated. In a glass tank with dimensions 3×1×0.5 (m), a linear stratification with buoyancy frequency (N) equal to 0.44 per second, was set up. Then a hydrofoil body with 6 cm in diameter, 20 cm at length and 12 cm wide was towed in the fluid. While changing the Froude (from 0.19 to 1.7) and Reynolds numbers of the flow, the effects of these changes were examined on the formation of the internal waves and wake of the hydrofoil. By using shadowgraph technique and signal fluctuations record, the internal waves with a length of about half a meter were identified. In this study, the signals are recorded in domain of frequency at a certain distance from the model. Using an ultra-fast salinity meter (densitometer) for recording signal frequencies it was found that increasing Froude number results in more combination of frequencies occurred in the environment. The energy of wave spectrum increased up to a critical Froude number, and then decreased due to turbulence.