Experimental Investigation On Propeller Effect On Internal Waves Generated By A Moving Submarine In A Stratified Fluid

The internal wave?IW?is a common phenomenon in a stratified ocean.When a submerged object moves in the stratified fluid,its body and wake deviate water clusters from the equilibrium position,triggering the oscillations of water clusters and generating the internal waves behind its track.Experiments are performed on the internal waves generated by a towed model with a rotating propeller in a density stratified fluid with a linear halocline.The Reynolds number Re=UD/?ranges from 7000 to 84000,and the Froude number Fr=U/DN_max ranges from 0.7 to 8.1.Based on the multi-channel conductivity probe arrays technology and the cross correlation analysis method,the wave speed,amplitude and patterns are investigated.It is shown that the propeller advances the transition from body-generated waves to wake-generated waves.Besides,observations show that the propeller-generated wave is a kind of inner V shaped wave on the horizontal plane,composed of symmetrical structure and asymmetrical structure.Before the transition,there exists a critical point of thrust momentum and the critical point advances with the increase of Fr.An extra V-shaped wave pattern with a narrow opening angle is generated by the propeller and the wave amplitude becomes larger with the increase of thrust momentum,indicating that the propeller produces body and wake effect at the same time before the transition.The internal waves are stationary to the translating model before the critical point,indicating that the excitation source is the volume effect.The dominant internal waves are nonstationary and have a poor repeatability after the critical point,indicating that the excitation source is the wake effect.Dimensionless peak-to-peak amplitudes increase with J_ndd linearly and only the ratio differs.After the transition,the wave speed Fr_iw drops down and fluctuates within a range of 0.4-1.5,showing that the internal waves are non-stationary to the model.The interaction of the drag and thrust momentum change the characteristics of the wave amplitudes and patterns.The wave amplitude no longer simply grows with the Fr but depends on the contrast of the two momentums.The highest contrast of the wave pattern contour maps appears when the two momentums have the largest difference if other conditions are the same.The range 1<J_D/J_T<10 is considered a region of non-momentum wake,meaning that the momentum difference is not enough to generate large scale structures in the wake.Furthermore,different with the drag momentum,the thrust momentum in the wake effect can generate enough net momentum when J_T/J_D>1.