In this paper, experiments are conducted for the characteristics of internal waves generated by a self-propelled model translating horizontally below the strong pycnocline of a density stratified fluid. The translational speed of the self-propelled model ranges from 0.06 to 1.4 m/s, the corresponding Froude number Fr from 0.44 to 10.33. Two cross-track conductivity probe arrays are arranged at two along-track positions to obtain the density fluctuation characterizing the internal wave. Two regimes of the internal wave are distinguished by the critical Froude number Frc. For Fr<Frc, the correlation velocity of internal wave Uiw is nearly equal to the translational speed U of the model, indicating that the internal waves are stationary to the model and usually called body-generated waves. For Fr>Frc, the correlation velocities are noticeably lower than the translational speeds of the model and the Froude number Friw associated with Uiw varies within the range 0.4~1.5, showing that such internal waves are non-stationary to the body and termed as wake-generated waves. For the variation of the maximum peak-peak amplitudes Am versus Fr, Am reaches its maximum when Frp=1.03. For Fr<Frp, the maximum peak-peak amplitude Am increase with Fr and the wave patterns for such waves are dominated by stationary body-generated waves. For Frp<Fr<Frc, the maximum peak-peak amplitude Am decreases with Fr and the influence of wake-generated waves gradually increases, but the wave patterns for such waves are still dominated by stationary body-generated waves. For Fr>Frc, the dimensionless maximum peak-peak amplitude Am do not have an explicit growth trend with Fr but change within the range 0.04~0.07, and the internal waves under such conditions are dominated by non-stationary wake-generated waves.
Internal waves (IWs) generated by a submerged model such as a towed sphere, a cylinder or a self-propelled body and its associated turbulent wake in a stratified fluid are of great interests in oceanic hydrodynamics. Several classifications of IWs are proposed based on experimental observations. Lin et al. (1993) indicated that three regimes of IWs generated by a towed sphere could be identified, i.e. Lee waves, forced waves and waves generated by the gravitational collapse of the turbulent wake. Bonneton et al. (1993) classified the IWs into four regimes with respect to the different sources, i.e. sphere itself, wake collapse, excitation from the recirculation zone and the random turbulence. Robey (1997) proposed a more general classification consisting only two types, body-generated and wake-generated IWs. The body-generated IWs are Lee waves, generated by the sphere itself and the following stationary separation bubble whose area is nearly equivalent to the recirculation zone. The wake-generated IWs are highly non-stationary and the sources are complicated.
