The surface correction to the quadrupole source term of the Ffowcs Williams and Hawkings integral in the frequency domain suffers from the computation of high-order derivatives of Green’s function.The far-field appro...The surface correction to the quadrupole source term of the Ffowcs Williams and Hawkings integral in the frequency domain suffers from the computation of high-order derivatives of Green’s function.The far-field approximations to the derivatives of Green’s function have been used without derivation and verification in previous work.In this work,we provide the detailed derivations of the far-field approximations to the derivatives of Green’s function.The binomial expansions for the derivatives of Green’s function and the far-field condition are employed during the derivations to circumvent the difficulties in computing the high-order derivatives.The approximations to the derivatives of Green’s function are systemically verified by using the benchmarks two-dimensional convecting vortex and the co-rotating vortex pair.In addition,we provide the derivations of the approximations to the multiple integrals of Green’s function by using the far-field approximations to the derivatives.展开更多
A numerical study on the acoustic radiation of a propeller interacting with non-uniform inflow has been conducted. Real geometry of a marine propeller DTMB 4118 is used in the calculation, and sliding mesh technique i...A numerical study on the acoustic radiation of a propeller interacting with non-uniform inflow has been conducted. Real geometry of a marine propeller DTMB 4118 is used in the calculation, and sliding mesh technique is adopted to deal with the rotational motion of the propeller. The performance of the DES （Detached Eddy Simulation） approach at capturing the unsteady forces and moments on the propeller is compared with experiment. Far-field sound radiation is predicted by the formation 1A developed by Farassat, an integral solution of FW-H （Ffowcs Williams-Hawkings） equation in time domain. The sound pressure and directivity patterns of the propeller operating in two specific velocity distributions are discussed.展开更多
Aeroacoustic performance of fans is essential due to their widespread application. Therefore, the original aim of this paper is to evaluate the generated noise owing to different geometric parameters. In current study...Aeroacoustic performance of fans is essential due to their widespread application. Therefore, the original aim of this paper is to evaluate the generated noise owing to different geometric parameters. In current study, effect of five geometric parameters was investigated on well performance of a Bladeless fan. Airflow through this fan was analyzed simulating a Bladeless fan within a 2 m×2 m×4 m room. Analysis of the flow field inside the fan and evaluating its performance were obtained by solving conservations of mass and momentum equations for aerodynamic investigations and FW-H noise equations for aeroacoustic analysis. In order to design Bladeless fan Eppler 473 airfoil profile was used as the cross section of this fan. Five distinct parameters, namely height of cross section of the fan, outlet angle of the flow relative to the fan axis, thickness of airflow outlet slit, hydraulic diameter and aspect ratio for circular and quadratic cross sections were considered. Validating acoustic code results, we compared numerical solution of FW-H noise equations for NACA0012 with experimental results. FW-H model was selected to predict the noise generated by the Bladeless fan as the numerical results indicated a good agreement with experimental ones for NACA0012. To validate 3-D numerical results, the experimental results of a round jet showed good agreement with those simulation data. In order to indicate the effect of each mentioned parameter on the fan performance, SPL and OASPL diagrams were illustrated.展开更多
In this paper,an analytical time domain formulation based on Ffowcs Williams-Hawkings(FW-H)equation is derived for the prediction of the acoustic velocity field generated by moving bodies.This provides the imposition ...In this paper,an analytical time domain formulation based on Ffowcs Williams-Hawkings(FW-H)equation is derived for the prediction of the acoustic velocity field generated by moving bodies.This provides the imposition of the Neumann boundary condition on a rigid scattering surface.In order to calculate the scattering sound pressure of the duct,a thin-body boundary element method(BEM)has been proposed.The radiate sound pressure is calculated using the acoustic analogy FW-H equation.The scattering effect of the duct wall on the propagation of the sound wave is presented using the thin-body BEM.Computational results for a pulsating sphere,dipole source,and a tail rotor verify the method.The sound pressure directivity and scattering effect are shown to demonstrate the applicability and validity of the approach.展开更多
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
Direct numerical simulations are performed to study single gas/vapor bubble and spherical bubble clusters containing 13–352 vapor bubbles in compressible flow fields.The numerical results show that the single cavitat...Direct numerical simulations are performed to study single gas/vapor bubble and spherical bubble clusters containing 13–352 vapor bubbles in compressible flow fields.The numerical results show that the single cavitation bubble keeps spherical during the collapse process,and the far-field acoustic pressure calculated by the Ffowcs William-Hawkings(FW-H)formulation is basically consistent with the analytical solution obtained based on the volume acceleration calculation.However,the spherical bubble cluster collapses layer by layer due to the strong coupling between bubbles.The closer to the center of the bubble cluster,the shorter the collapse time and the stronger the non-spherical deformation.The collapse of a bubble cluster would generate multiple acoustic pressure peaks,which cannot be accurately predicted by the volume fluctuation sound source theory.The size and volume fraction of the bubble cluster have a significant influence on the collapse time and the distribution of sound pressure.We found that when the volume fraction of a bubble cluster is large,the total collapse time is basically the same as that of its corresponding single bubble with the equal volume.The frequency distribution of sound pressure of a dense bubble cluster is also close to that of its corresponding single bubble.In addition,we found that a bubble cluster with randomly distributed bubble diameters collapses asymmetrically and rebounds in the late stage of the collapse process.The above study reveals part of the mechanism of bubble cluster collapse and sound generation,and provides a theoretical basis for the establishment of cavitation noise model.展开更多
Cavitation noise around propellers has many adverse effects.It is still very limited nowadays to inhibit propeller cavitation noise in engineering.In this study,the cavitation noise around a PPTC propeller is simulate...Cavitation noise around propellers has many adverse effects.It is still very limited nowadays to inhibit propeller cavitation noise in engineering.In this study,the cavitation noise around a PPTC propeller is simulated using the large eddy simulation(LES)coupled with the porous Ffowcs Williams-Hawkings(PFW-H)equation.The investigation aims to find a strategy to suppress cavitation noise and analyze the noise suppression mechanism.The predicted hydrodynamic results agree well with the experimental data and are utilized in the hydroacoustic analysis.The hydroacoustic results indicate that the pseudo-thickness noise dominates the dominant frequency component of the total cavitation noise due to the effect of cavity evolution,which is one of the reasons why the pseudo-thickness noise dominates the total cavitation noise.A method is found to weaken the cavitation noise through ventilation at the generation location of the sheet cavity(SC).It is worth noting that ventilation inhibits the generation and development of SC by changing the pressure distribution on the suction surface of the blade and pushing away the cavities around the ventilation holes.Moreover,cavity evolution noise dominates the fluid volume evolution noise under the ventilated cavitating condition.Ventilation significantly attenuates the vapor volume pulsation and thus the cavity evolution noise,which leads to a reduction in pseudo-thickness noise and total cavitation noise.The ventilation mainly reduces noises at the dominant frequency of the pseudo-thickness noise and the total cavitation noise.展开更多
基金National Numerical Windtunnel project,and the National Natural Science Foundation of China(Nos.11922214,91752118).
文摘The surface correction to the quadrupole source term of the Ffowcs Williams and Hawkings integral in the frequency domain suffers from the computation of high-order derivatives of Green’s function.The far-field approximations to the derivatives of Green’s function have been used without derivation and verification in previous work.In this work,we provide the detailed derivations of the far-field approximations to the derivatives of Green’s function.The binomial expansions for the derivatives of Green’s function and the far-field condition are employed during the derivations to circumvent the difficulties in computing the high-order derivatives.The approximations to the derivatives of Green’s function are systemically verified by using the benchmarks two-dimensional convecting vortex and the co-rotating vortex pair.In addition,we provide the derivations of the approximations to the multiple integrals of Green’s function by using the far-field approximations to the derivatives.
基金supported by the National Natural Science Foundation of China (Grant No. 11272213)
文摘A numerical study on the acoustic radiation of a propeller interacting with non-uniform inflow has been conducted. Real geometry of a marine propeller DTMB 4118 is used in the calculation, and sliding mesh technique is adopted to deal with the rotational motion of the propeller. The performance of the DES （Detached Eddy Simulation） approach at capturing the unsteady forces and moments on the propeller is compared with experiment. Far-field sound radiation is predicted by the formation 1A developed by Farassat, an integral solution of FW-H （Ffowcs Williams-Hawkings） equation in time domain. The sound pressure and directivity patterns of the propeller operating in two specific velocity distributions are discussed.
文摘Aeroacoustic performance of fans is essential due to their widespread application. Therefore, the original aim of this paper is to evaluate the generated noise owing to different geometric parameters. In current study, effect of five geometric parameters was investigated on well performance of a Bladeless fan. Airflow through this fan was analyzed simulating a Bladeless fan within a 2 m×2 m×4 m room. Analysis of the flow field inside the fan and evaluating its performance were obtained by solving conservations of mass and momentum equations for aerodynamic investigations and FW-H noise equations for aeroacoustic analysis. In order to design Bladeless fan Eppler 473 airfoil profile was used as the cross section of this fan. Five distinct parameters, namely height of cross section of the fan, outlet angle of the flow relative to the fan axis, thickness of airflow outlet slit, hydraulic diameter and aspect ratio for circular and quadratic cross sections were considered. Validating acoustic code results, we compared numerical solution of FW-H noise equations for NACA0012 with experimental results. FW-H model was selected to predict the noise generated by the Bladeless fan as the numerical results indicated a good agreement with experimental ones for NACA0012. To validate 3-D numerical results, the experimental results of a round jet showed good agreement with those simulation data. In order to indicate the effect of each mentioned parameter on the fan performance, SPL and OASPL diagrams were illustrated.
文摘In this paper,an analytical time domain formulation based on Ffowcs Williams-Hawkings(FW-H)equation is derived for the prediction of the acoustic velocity field generated by moving bodies.This provides the imposition of the Neumann boundary condition on a rigid scattering surface.In order to calculate the scattering sound pressure of the duct,a thin-body boundary element method(BEM)has been proposed.The radiate sound pressure is calculated using the acoustic analogy FW-H equation.The scattering effect of the duct wall on the propagation of the sound wave is presented using the thin-body BEM.Computational results for a pulsating sphere,dipole source,and a tail rotor verify the method.The sound pressure directivity and scattering effect are shown to demonstrate the applicability and validity of the approach.
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.
基金supported by the National Natural Science Foundation of China(Grant No.12272343)the State Key Program of National Natural Science of China(Grant Grant No.91852204).
文摘Direct numerical simulations are performed to study single gas/vapor bubble and spherical bubble clusters containing 13–352 vapor bubbles in compressible flow fields.The numerical results show that the single cavitation bubble keeps spherical during the collapse process,and the far-field acoustic pressure calculated by the Ffowcs William-Hawkings(FW-H)formulation is basically consistent with the analytical solution obtained based on the volume acceleration calculation.However,the spherical bubble cluster collapses layer by layer due to the strong coupling between bubbles.The closer to the center of the bubble cluster,the shorter the collapse time and the stronger the non-spherical deformation.The collapse of a bubble cluster would generate multiple acoustic pressure peaks,which cannot be accurately predicted by the volume fluctuation sound source theory.The size and volume fraction of the bubble cluster have a significant influence on the collapse time and the distribution of sound pressure.We found that when the volume fraction of a bubble cluster is large,the total collapse time is basically the same as that of its corresponding single bubble with the equal volume.The frequency distribution of sound pressure of a dense bubble cluster is also close to that of its corresponding single bubble.In addition,we found that a bubble cluster with randomly distributed bubble diameters collapses asymmetrically and rebounds in the late stage of the collapse process.The above study reveals part of the mechanism of bubble cluster collapse and sound generation,and provides a theoretical basis for the establishment of cavitation noise model.
基金Project supported by the National Key Research and Development Program of China(Grant No.2022YFB3303501),the National Natural Science Foundation of China(Grant No.52176041)supported by the National Key Laboratory of Ship Vibration and Noise,China Ship Development and Design Center(Grant No.JCKY2021207CI01).
文摘Cavitation noise around propellers has many adverse effects.It is still very limited nowadays to inhibit propeller cavitation noise in engineering.In this study,the cavitation noise around a PPTC propeller is simulated using the large eddy simulation(LES)coupled with the porous Ffowcs Williams-Hawkings(PFW-H)equation.The investigation aims to find a strategy to suppress cavitation noise and analyze the noise suppression mechanism.The predicted hydrodynamic results agree well with the experimental data and are utilized in the hydroacoustic analysis.The hydroacoustic results indicate that the pseudo-thickness noise dominates the dominant frequency component of the total cavitation noise due to the effect of cavity evolution,which is one of the reasons why the pseudo-thickness noise dominates the total cavitation noise.A method is found to weaken the cavitation noise through ventilation at the generation location of the sheet cavity(SC).It is worth noting that ventilation inhibits the generation and development of SC by changing the pressure distribution on the suction surface of the blade and pushing away the cavities around the ventilation holes.Moreover,cavity evolution noise dominates the fluid volume evolution noise under the ventilated cavitating condition.Ventilation significantly attenuates the vapor volume pulsation and thus the cavity evolution noise,which leads to a reduction in pseudo-thickness noise and total cavitation noise.The ventilation mainly reduces noises at the dominant frequency of the pseudo-thickness noise and the total cavitation noise.
