The prediction of the flow-induced noise level is a key issue in the fluid–dynamic acoustics. In the hydroacoustics field, the complicated feedback induced by the flow past open cavities can amplify the convection in...The prediction of the flow-induced noise level is a key issue in the fluid–dynamic acoustics. In the hydroacoustics field, the complicated feedback induced by the flow past open cavities can amplify the convection instability in the shear layer which further leads to important noise radiations. The noise consists of intense narrowband and broadband components. In this paper, the level of the noise radiated by a subsonic cavity flow is calculated by using numerical flow computations based on the large eddy simulation（LES） and by solving the Ffowcs Williams-Hawkings equation. A series of three-dimensional open cavity models with overset grids and appropriate boundary conditions are developed for the hydroacoustic numerical computation. The self-sustained oscillation characteristics of the cavity flow are investigated, together with the mechanisms of the cavity noise generation. The distinguishing features of the flow-induced noise of the underwater structure cavities are studied with respect to the parameters of the cavity models, such as the free stream velocity, the dimensions of the cavity mouth, the angle of the cavity neck, the horizontal and vertical porous cavity models and the actual submarine open cavity model with an incoming flow attack angle. It is shown that it may be feasible to reduce the flow-induced noise by appropriate optimal parameters of the underwater structure cavities.展开更多
Experiments and large-eddy simulations(LESs)are conducted to study the effectiveness and the underlying physical mechanisms of a passive control technique for suppressing the self-sustained oscillations of incompressi...Experiments and large-eddy simulations(LESs)are conducted to study the effectiveness and the underlying physical mechanisms of a passive control technique for suppressing the self-sustained oscillations of incompressible flow over aperture-cavities.The control technique is implemented by installing a wedge block above the chamfered leading-edge.The experiments are carried out in a low-speed water tunnel with the freestream velocity ranging from 0.4 m/s to 4.4 m/s,while the large-eddy simulations are carried out corresponding to the experiment at a velocity of 4.0 m/s.The wall pressure fluctuations measured along the cavity floor show that a significant suppression of the self-sustained oscillations of the shear layers can be achieved by the control device.Furthermore,the suppression performance is improved as the freestream velocity increases,not limited to the design point of the control device.The analysis of numerical simulation results focuses on three aspects,the vorticity fields,the velocity fields and the pressure fields,and the physical effects of the control device on the incompressible aperture-cavity flow are visualized.Three mechanisms of suppressing the cavity oscillations are identified from the numerical results,which are the destruction of the large vortex structures by the high frequency vortical excitations,the inhabitation of the intracavity recirculation feedback by introducing the lower shunt flow,and the attenuation of the trailing-edge impingement by thickening the shear layer.展开更多
文摘The prediction of the flow-induced noise level is a key issue in the fluid–dynamic acoustics. In the hydroacoustics field, the complicated feedback induced by the flow past open cavities can amplify the convection instability in the shear layer which further leads to important noise radiations. The noise consists of intense narrowband and broadband components. In this paper, the level of the noise radiated by a subsonic cavity flow is calculated by using numerical flow computations based on the large eddy simulation（LES） and by solving the Ffowcs Williams-Hawkings equation. A series of three-dimensional open cavity models with overset grids and appropriate boundary conditions are developed for the hydroacoustic numerical computation. The self-sustained oscillation characteristics of the cavity flow are investigated, together with the mechanisms of the cavity noise generation. The distinguishing features of the flow-induced noise of the underwater structure cavities are studied with respect to the parameters of the cavity models, such as the free stream velocity, the dimensions of the cavity mouth, the angle of the cavity neck, the horizontal and vertical porous cavity models and the actual submarine open cavity model with an incoming flow attack angle. It is shown that it may be feasible to reduce the flow-induced noise by appropriate optimal parameters of the underwater structure cavities.
文摘Experiments and large-eddy simulations(LESs)are conducted to study the effectiveness and the underlying physical mechanisms of a passive control technique for suppressing the self-sustained oscillations of incompressible flow over aperture-cavities.The control technique is implemented by installing a wedge block above the chamfered leading-edge.The experiments are carried out in a low-speed water tunnel with the freestream velocity ranging from 0.4 m/s to 4.4 m/s,while the large-eddy simulations are carried out corresponding to the experiment at a velocity of 4.0 m/s.The wall pressure fluctuations measured along the cavity floor show that a significant suppression of the self-sustained oscillations of the shear layers can be achieved by the control device.Furthermore,the suppression performance is improved as the freestream velocity increases,not limited to the design point of the control device.The analysis of numerical simulation results focuses on three aspects,the vorticity fields,the velocity fields and the pressure fields,and the physical effects of the control device on the incompressible aperture-cavity flow are visualized.Three mechanisms of suppressing the cavity oscillations are identified from the numerical results,which are the destruction of the large vortex structures by the high frequency vortical excitations,the inhabitation of the intracavity recirculation feedback by introducing the lower shunt flow,and the attenuation of the trailing-edge impingement by thickening the shear layer.
