Numerical Simulation Of Wall Pressure Fluctuations And Flow-induced Noise Performance With Submarine Based On The Large Eddy Simulation Method

The flow-induced noise, propagated when the submarine is sailingunderwater, is generally generated by the wall pressure fluctuations andthe disturbance in the turbulent boundary layer, so that we can not simplyreduce it by common methods, but have to improve it by studying themechanism and changing the shape of the submarine's body. Therefore,in order to enhance the submarine's sound-stealthy capability, it isnecessary to deeply research the wall pressure fluctuations and theflow-induced noise.As an important dipole source, the computation of the wall pressurefluctuation is always constrained by the conflict between the accuracyand the complexity of the numerical methods. In this paper, we introducethe Large Eddy Simulation (LES) theory to simulate the turbulence modelafter investigated several numerical methods that are usually used.Numerical simulations of the flow-field with two types of submarinemodels which include the water-drop type and the dish-type that are sameof cross-sectional area with of the former are presented based on theunsteady incompressible Navier-Stokes equation. The distributions of thesurface wall pressure fluctuations under frequency domain are obtainedfor comparing with the experimental data of the submarine models, sothat we can validate the reliability of the LES methods and discuss thecharacter and difference of the pressure spectrums between these twomodels. ?Lighthill's acoustic analogy forms the starting point for thederivation of the flow-induced noise prediction. Traditionally we calculate the sound by using the Ffowcs Williams and Hawkings (FW-H)acoustics equations. Since it has the compact acoustic source assumptionswhen derived, which means the flow-field is approximately divide intotwo parts: the near-field and the far-field., and we can only obtain theinformation of the far-field sound. Recently a alternative approach thatcombine the Boundary Element Method (BEM) with the Lighthill'sacoustic analogy is widely put in application, and it can predict the noiseresults of each point in the field. The discipline of these two methods willbe explained, and after that, the information of the flow is taken as thesound sources and the acoustic results of the submarine models arestudied by using these two, respectively. The results show that theflow-induced noise performance of the dish type submarine is better thanthe water-drop type's, which is consistent with the comparison of .thepressure fluctuation. We also find that in some directions, where thevariations of the body-curves are approximate to the streamline, the valueof the noise is lower. Otherwise, it tends to be higher.There also put all the results of the wall pressure fluctuations and theflow-induced noise calculated before into a summary. The relationshipbetween the pressure fluctuations and the flow-induced noise near-by isinvestigated, and the distinction of these two noise computation methodsis also discussed. The results show that in the simulation of the flow-fieldwith submarine models, the wall pressure fluctuations have importantinternal relations with the flow-induced noise performance nearby. On theother hand, in the sound computation case, these two methods cansuccessfully predict the variation of the radiate sound spectrum in thefar-field, but on the surface of the marine or in the near wall condition,we'd better choose the BEM-Lighthill method.