The characteristics of internal waves generated by a revolution body in a stratified fluid with a pycnocline

Abstract

Experiments are conducted for the characteristics of both body and wake-generated internal waves due to a revolution body (aspect ratio 7:1) in a stratified fluid with a pycnocline where the revolution body is horizontally towed in forward and backward ways. Results show that the body-generated internal waves are a type of stationary multiple-mode Lee wave structures, and the wake-generated internal waves are a type of non-stationary quasi-Lee structures produced by the large-scale coherent structure in the turbulent wake acting as a moving excitation with respect to the towed revolution body. The transition between Lee and quasi-Lee waves occurs at a critical Froude number Frc which is shown to be linearly dependent on the aspect ratios of the revolution bodies where the wave patterns for FrFrc are dominated byLee waves,whereas the wave patterns forFrFrcare dominated by quasi-Lee waves,Fr is the Froude number for the characteristic diameter of the revolution body. For the quasi-Lee waves, the dimensionless peak-to-peak amplitudes linearly increase with Fr and the Froude numbers relative to the correlation velocities remain at a relatively constant value of approximately 0.8 regardless of the aspect ratios. Moreover, the head and the tail shapes of the revolution body have no remarkable influence on the critical Froude number Frc, as well as both the Froude numbers relative to the correlation velocities and the dimensionless peak-to-peak amplitudes of the quasi-Lee waves.