FW-H Acoustic Analogy Research Articles

Pneumatic Noise Study of Multi-Stage Sleeve Control Valve

This study considers the practical issue of severe noise observed in a multi-stage sleeve control valve within an engineering project. Employing computational fluid dynamics (CFD) methodology, we initially performed numerical simulations to analyze the steady-state flow field within the control valve. Subsequently, we identified the underlying factors contributing to the noise issue within the valve. To assess the aerodynamic noise of the control valve, we applied the FW-H acoustic analogy theory and determined the intensity and distribution characteristics of the aerodynamic noise. Finally, we validated the numerical simulation results of the aerodynamic noise against theoretical calculations. Our findings indicate that the steam medium experiences high-speed flow due to disturbances caused by various components within the valve, resulting in significant turbulence intensity. This intense turbulence leads to pressure fluctuations in the steam, serving as the main catalyst for noise generation. The aerodynamic noise of the control valve exhibits a roughly symmetrical distribution along the pipe–valve system, with noticeable increases in noise levels upstream and downstream of the valve compared to other regions. The distribution cloud map obtained from the numerical simulations serves as a valuable reference for analyzing the locations where aerodynamic noise is generated. Comparing the numerical simulation results with the theoretical calculations at the noise monitoring points, we found that the noise error of the monitoring points was less than 5%, which proves the effectiveness of the numerical simulation method. These results provide essential data support for the acoustic detection of aerodynamic noise in control valves, carrying significant practical implications for engineering applications.

Hybrid Artificial Boundary Conditions for the Application of Blunt-Body Aerodynamic Noise Prediction

A hybrid artificial boundary condition (HABC) that combines the volume-based acoustic damping layer (ADL) and the local face-based characteristic boundary condition (CBC) is presented to enhance the absorption of acoustic waves near the computational boundaries. This method is applied to the prediction of aerodynamic noise from a circular cylinder immersed in uniform compressible viscous flow. Different ADLs are designed to assess their effectiveness whereby the effect of the mesh-stretch direction on wave absorption in the ADL is analysed. Large eddy simulation (LES) and FW-H acoustic analogy method are implemented to predict the far-field noise, and the sensitivities of each approach to the HABC are compared. In the LES computed propagation field of the fluctuation pressure and the frequency-domain results, the spurious reflections at edges are found to be significantly eliminated by the HABC through the effective dissipation of incident waves along the wave-front direction in the ADL. Thereby, the LES results are found to be in a good agreement with the acoustic pressure predicted using FW-H method, which is observed to be just affected slightly by reflected waves.

Marine propeller underwater radiated noise prediction with the FWH acoustic analogy Part 1: Assessment of model scale propeller hydroacoustic performance under uniform and inclined flow conditions

This paper explores hydrodynamic performance, including cavitation and URN for the benchmark model scale propeller, The Princess Royal, operating under uniform and inclined flow conditions. In the numerical calculations, the DES method and the k-ω SST turbulence model were utilised to solve the cavitating flow around the propeller and determine the source field for the sound propagation. Also, the developed V-AMR advanced meshing technique was applied for accurately solving the tip vortex flow and hence better representation of the tip vortex cavitation in the propeller slipstream. The Schnerr-Sauer mass transfer model was used to model the cavitation on and off the propeller blades, whereas the cavitating propeller URN was predicted using the permeable formulation of the FWH equation. The numerical results were first validated with the available experimental data in model scale in a wide range of operating conditions through the propeller hydrodynamic performance characteristics, cavitation extensions and URN. Then, the numerical URN predictions were extrapolated to full-scale with the aid of the ITTC procedure to compare the CFD predictions with the extrapolated measured data obtained by different testing facilities within the scope of a recently conducted international round-robin test campaign. The results showed that the sheet and tip vortex cavitation was generally modelled successfully in the numerical calculations compared to the model-scale experimental observations in different facilities. The propeller URN predictions were in good agreement with the measured data in model scale, although some URN level discrepancies (i.e., around 5 and 10 dB) were observed between numerical predictions and model-scale measurements at certain frequencies in the low-frequency region of the noise spectrum. By taking the URN level differences measured in each facility into account, the full-scale extrapolated propeller URN predictions satisfactorily agree with the extrapolated full-scale experimental test data. Therefore, this study confirms that the CFD methods, together with the acoustic analogy, can be used for predicting the propeller URN, similar to other traditional ship hydrodynamic phenomena (e.g., resistance, self-propulsion, cavitation etc.).

Marine propeller underwater radiated noise prediction with the FWH acoustic analogy Part 2: Assessment of model scale propeller hydroacoustic performance under non-uniform flow conditions

This study presents the model scale benchmark, The Princess Royal, propeller's hydrodynamic performance, including cavitation extensions and URN operating in a non-uniform wake field. The developed V-AMR technique was used in the numerical calculations to accurately solve the tip vortex flow and better representation the tip vortex cavitation (TVC) in the propeller slipstream. The sheet and tip vortex cavitation was modelled using the Schnerr-Sauer cavitation model. A hybrid method, combining the DES and permeable formulation of the FWH equation, was used for predicting the propeller URN at four different operating conditions corresponding to full-scale operating conditions. The numerical results were first validated with the experimental data obtained in the cavitation tunnel through the propeller hydrodynamic characteristics, cavitation extension and URN in model scale. Then, the propeller URN predictions using a hybrid method were extrapolated to full-scale with the ITTC extrapolation procedure to compare the numerical results with the extrapolated experimental data and full-scale measurements. The results showed that the cavitation extensions on and off the blades were satisfactorily predicted in the numerical calculations compared to the model-scale campaigns and full-scale sea trial observations. However, the same cavitation dynamics and TVC could not be predicted in conditions where the weak and incipient TVC were present between the numerical calculations and model-scale test campaign. Also, the numerical calculations underpredicted the model scale propeller URN at certain frequencies compared to model scale experimental data, except for the highest loading condition. Akin to the comparisons of model scale propeller URN between the numerical calculations and model-scale test data, the extrapolated propeller URN was generally underpredicted at a certain frequency range of the noise spectrum in the numerical calculations compared to the full-scale measurements. This underprediction in the numerical calculations can be associated with the lack of cavitation dynamics, especially TVC, compared to experimental and full-scale observations.

Influence of Stern Rudder Type on Flow Noise of Underwater Vehicles

The stern rudder of an underwater vehicle has a significant impact on the wake field and the flow noise. Hence, it is important to optimize the design of the stern rudder for reducing the radiated noise. In this work, a numerical model is set up to predict the flow noise of the underwater vehicle, based on the LES turbulence model and FW-H acoustic analogy method. After the verification study, the numerical prediction of the flow noise is compared with the experimental measurements to verify the accuracy of the numerical model. Then, the influence of sails on the flow noise is explored. It is observed that the existence of the sail significantly increases the noise at the low frequency. Furthermore, to examine the influence of the stern rudder type, the sound pressure levels of underwater vehicles with three full appendages having cross-type rudders, X-type rudders, and T-type rudders, are compared. The strong interaction between the sail’s wake and the stern rudder is evident. The underwater vehicle with T-type rudders exhibits the lowest sound pressure. In addition, the influence of the stern rudder type on the directivity of sound pressure levels is also presented.

Marine propeller underwater radiated noise prediction with the FWH acoustic analogy part 3: Assessment of full-scale propeller hydroacoustic performance versus sea trial data

This paper assesses the full-scale The Princess Royal vessel Underwater Radiated Noise (URN) characteristics using a CFD method. Also, the cavitation extensions and propeller hydrodynamic characteristics are explored over a wide range of operating conditions. The numerical calculations were carried out using a hybrid method combining the DES and permeable formulation of the FWH equation. In the numerical calculations, two different permeable noise surfaces encapsulating the complete hull and only the propeller and its slipstream were utilised. In order to accurately solve the tip vortex flow and model the tip vortex cavitation (TVC) in the propeller slipstream, the developed V-AMR technique was applied in the numerical calculations together with the Schnerr-Sauer mass transfer model to model the cavitation. The results were validated with the full-scale measurements in terms of propeller hydrodynamic characteristics, cavitation extension and URN. The results showed that the sheet cavitation extensions predicted in the numerical calculations agreed with the sea trial observations despite the differences in the violent cavitation dynamics. Similarly, TVC was somewhat observed in the numerical calculations using the V-AMR technique with a lack of dynamics and extension in the propeller slipstream compared to the full-scale observations. The comparison of noise spectra at two different operating conditions, where similar cavitations were observed between the numerical calculations and full-scale observations, showed an agreement with the full-scale measurements. The lack of TVC and possible bursting phenomena predicted in the numerical calculations caused the underprediction of propeller URN levels up to 20 dB at certain frequencies over the noise spectrum at the lowest blade loading conditions. When the two different permeable noise surfaces were compared, it can be concluded that the permeable noise surface, encapsulating the complete hull, captures more noise information in the noise spectrum than the permeable surface, encapsulating only the propeller and its slipstream. Also, a more distinct spectral hump triggered by the tip vortex was observed using the permeable noise surface around the complete hull compared to one around the propeller. The results showed that the interaction between the cavitation and nonlinear noise sources occurring around the hull might influence the amplitude of the characteristic hump, apart from the possible hull interference on the ship hull and appendages induced by the propeller.

A fast and storage-saving method for direct volumetric integration of FWH acoustic analogy

This paper proposes a new method that makes the direct volume integration of the Lighthill stress term in FWH acoustic analogy affordable in terms of both computational time and disk storage requirement. The method is based on a dual mesh concept, i.e. while a fine mesh is used in CFD, a relatively coarse mesh is used for the acoustic calculation. The terms being independent of the observer positions in the integral formula of FWH acoustic analogy are calculated on the CFD mesh and mapped onto the acoustic mesh during the simulation. These sound source terms are used for the on-the-fly acoustic computation or saved for later use in the post-processing. A formulation of the Lighthill stress tensor in cavitating flow is also derived. The method is verified with the acoustic assessment of an inclined marine propeller case. A reduction of the calculation time by 98% and disk storage by 99% is achieved while maintaining small acoustic error.

Investigations on prediction of ship noise using the FWH acoustic analogy with incompressible flow input

Ship noise predictions using FWH acoustic analogy with incompressible flow solution inputs are investigated for a model scale container vessel with a cavitating propeller. Numerical predictions of cavitation and hull pressure pulse predictions are validated first, comparing simulations performed for the tunnel test section and experimental measurements inside a large-size cavitation tunnel. The predictions agree well including the sheet cavitation development, tip vortex cavitation (TVC) bursting, convex shaped sheet cavitation closure line and the traveling re-entrant jet underneath the sheet cavity triggers the TVC bursting behavior.Noise predictions are performed within a large open simulation domain instead of the cavitation tunnel test section. With incompressible solutions, noise levels are predicted based on two different placements of Permeable/Porous Data Surfaces (PDS) where one encloses the cavitating propeller, rudder and downstream wake (PDS−L1) and one encloses the whole ship as a rectangular box (PDS−L2). The FWH noise predictions with impermeable surfaces (S−FWH) are also studied. Differences between predictions using PDS−L1, PDS−L2, and S−FWH are discussed.To compare calculated noise source level (Ls) at different noise receivers at varying distances, normalization assuming spherical spreading acoustic wave is used. In certain combinations of receiver point and method of acoustic computation, the predicted Ls agreed well comparing to experimental measurements, including the prediction with PDS−L2 and receiver close to the PDS and direct probed incompressible hydrodynamic pressure at similar receiver locations. However, with increasing distance to the receiver, the predicted Ls increases for higher frequencies and levels out at unrealistically high levels. To study this phenomenon, a free-field monopole representing the cavity structure dynamics is tested with different combination of PDS and receiver placements, using both incompressible and compressible input. This analysis gives a clear indication that the origin of this erroneous effect is the combination of the FWH acoustic analogy with an incompressible solver.

A REVIEW OF METHODS FOR HYDRO-ACOUSTIC ANALYSIS OF NON-CAVITATING MARINE PROPELLERS

Underwater Radiated Noise (URN) emanating from surface and underwater marine platforms has become a significant concern for all the Nations in view of the global requirement to minimise the increasing adverse impact on marine mammals and fishes and maintain ecological balance in the ‘Silent’ ocean environment. Ambient noise level in the sea, in 10 to 300 Hz frequency band, has increased by 20 to 30 dB due to shipping (Wittekind, 2009). Marine propeller (in non- cavitating and cavitating regime) is a potential contributor to the ships noise and a lot of scientific research has been undertaken and considerable progress has been achieved in estimating the hydro-acoustic performance of marine propellers. In light of this, the scope of this paper is to review and critically examine the various methods used for estimating the hydro-acoustic performance of marine propellers, particularly in the non-cavitating regime, over the past many years. This review paper brings out the details, applicability, merits and demerits of various methods, extrapolation laws to obtain full scale results, scientific conclusion of all the know-how on this subject and the scope of further research as perceived by the authors. This paper also presents a numerical methodology to estimate the noise radiated by a DTMB 4119 model propeller in the non-cavitating regime in open water condition. The hydrodynamic analysis of the propeller was performed using commercial CFD software STARCCM+, closure was achieved using standard k-ε turbulence model and hydro-acoustic predictions have been performed using FWH acoustic analogy. The results compare very well with the published literature.

Noise prediction research of a scaled turboprop aircraft

Aerodynamic noise level has become an important performance index of civil aircraft, and it is drawing more and more attention. Most airframe noise research based on CFD method is aimed at aircraft individual parts at present, while lack of noise prediction for the complex high fidelity full aircraft model. Due to the interaction between aircraft parts, noise prediction between single part and the actual configuration are very different in the aspect of calculation conditions, noise generation and propagation. Only by using more realistic model can the noise be accurately predicted. In this paper, high-resolution mesh and high-precision hybrid RANS/LES method, combined with the FW-H acoustic analogy method, are employed to predict the noise of a turboprop's high-fidelity 1/6 scale model of landing configure. The improved delayed detached eddy simulation (IDDES) method was used to simulate the flow in the near-field sound source region, and the sound source characteristics of the whole turboprop are obtained. In addition to the two important noise sources-flap side edge and wing tip, numerical simulation also found other two important noise sources resulting from the interaction between parts-interaction between nacelle wake and flap, and the complex flow between flap inner side and fuselage. Results of far-field noise show that in the longitudinal symmetry plane of the fuselage, the noise mainly propagates to the lower front and over back direction, and the dipole characteristics are very obvious. In the plane perpendicular to the incoming flow, the noise in the transverse direction is weaker.

Investigation of noise characteristics of periodic jet impinging on a flat plate

Noise characteristics of periodic jet impinging on a flat plate are investigated. The numerical model is established by large eddy simulation and FW-H acoustic analogy method. Compared with experimental data obtained by noise measurement experiment, the effects of acoustic integral surface and different subgrid-scale models on noise simulation results are studied. The accuracy of the optimized numerical model is also validated by verification experiment. Further, the present numerical model is applied to numerical prediction of noise directivity and spectrum distribution with different waveforms and periodic frequency. Compared with the steady impinging jet, noise characteristic of periodic jet impinging on a flat plate are presented and the mechanism of acoustic source is analyzed. The present work provides a reference value for the analysis and control of noise of periodic jet impinging on a flat plate.

Reduction of Aeroacoustic Sound and Aerodynamic Drag Using Porous Cover

The application of a porous media on square cylinders to reduce drag in cross-flow is an active research area. Be that as it may, the related stream incited sound in the encompassing flow likewise experiences decrease, an angle which has gotten less consideration. This paper exhibits a numerical strategy for coupled streamlined and aero acoustic estimations for low Mach number flow current pass a square cylinder with permeable cover. Computations are performed at a subcritical Re of 54,800 using URANS technique and FW-H acoustic analogy. The cylinder without porous cover is subjected to an incoming flow is considered for validation against measurements. A significant drag reduction and sound reduction is observed with the presence of the porous layer. Comparisons are made among the modified cylinder and its unmodified counterpart.

Simulation Analysis on Noise Reduction Effect of Sound Barriers with Different Geometric Shapes for High-Speed Train

In order to study the noise reduction effect of different geometrical sound barriers on high-speed train aerodynamic noise, simulation studies were carried out on three shapes of sound barriers. The RNG k-epsilon turbulence model was used to calculate the aerodynamic drag of the high-speed train. Based on the large eddy simulation LES method and the FW-H acoustic analogy equation, the pulsating pressure of the train was extracted as the far-field noise source, and the noise reduction capabilities of the upright, semi-circular, and quarter-circular sound barriers were compared. The results show that the semi-circular sound barrier has the largest average insertion loss in far field, and its frequency response characteristics present the best match to the aerodynamic noise of high-speed train. Therefore, the semicircular sound barrier has the best noise reduction effect.

A Review of Methods for Hydro-Acoustic Analysis of Non-Cavitating Marine Propellers

Underwater Radiated Noise (URN) emanating from surface and underwater marine platforms has become a significant concern for all the Nations in view of the global requirement to minimise the increasing adverse impact on marine mammals and fishes and maintain ecological balance in the ‘Silent’ ocean environment. Ambient noise level in the sea, in 10 to 300 Hz frequency band, has increased by 20 to 30 dB due to shipping (Wittekind, 2009). Marine propeller (in non-cavitating and cavitating regime) is a potential contributor to the ships noise and a lot of scientific research has been undertaken and considerable progress has been achieved in estimating the hydro-acoustic performance of marine propellers. In light of this, the scope of this paper is to review and critically examine the various methods used for estimating the hydro-acoustic performance of marine propellers, particularly in the non-cavitating regime, over the past many years. This review paper brings out the details, applicability, merits and demerits of various methods, extrapolation laws to obtain full scale results, scientific conclusion of all the know-how on this subject and the scope of further research as perceived by the authors. This paper also presents a numerical methodology to estimate the noise radiated by a DTMB 4119 model propeller in the non-cavitating regime in open water condition. The hydrodynamic analysis of the propeller was performed using commercial CFD software STARCCM+, closure was achieved using standard k-ε turbulence model and hydro-acoustic predictions have been performed using FWH acoustic analogy. The results compare very well with the published literature.

Numerical study of a control scheme on flow-induced cavity noise

A numerical procedure for flow induced cavity noise is established in the paper. The procedure is based on large eddy simulation and FW-H acoustic analogy. The computational scheme is validated by comparing with experimental data. The change of flow induced noise along with cavity length, cavity depth and velocity is studied. A noise control scheme, which includes upright grille and oblique grille, is designed for reducing the flow-induced cavity noise. It turns out that the oblique grille shows superiority in the reduction of cavity noise by modifying the flow structure of the sheat layer.

DES와 FW-H 음향상사법을 이용한 탠덤 실린더의 공력소음 특성 연구

본 연구에서는 항공기 랜딩 기어와 유사한 형태의 탠덤 실린더에 대해 DES (Detached Eddy Simulation)와 FW-H(Ffowcs Williams and Hawkings) 음향상사법을 이용한 전산공력 소음해석을 수행하였다. 실린더 중심 간 거리 3.7D 조건에 대한 전산공력소음해석 결과를 탠덤 실린더를 지나는 외부 유동 특성 및 원거리 소음을 계측한 선행 연구 결과와 비교하였다. 전방 실린더의 상/하부에서 발생한 와류(Vortex)가 특징적인 주파수를 갖고 후방실린더에 충돌하면서 소음 발생원이 되는 것을 확인하였다. DES와 FW-H 음향상사법을 이용한 전산공력소음해석 방법의 타당성을 확인한 후, 전방 실린더의 후방에 분할판을 적용한 경우의 전산공력소음해석을 수행하였다. 전방 실린더의 후방에 분할판이 적용되면 전방실린더의 상/하부에서 발생하는 와류의 특징을 변화시키고 이극자 소음원 크기를 감소시켜 특정 주파수 대역에서 발생하는 소유 크기가 감소하는 것을 확인하였다.

Numerical Study of Controlling Jet Flow and Noise using Pores on Nozzle Inner Wall

In this paper, the feasibility of controlling the subsonic jet flow and its noise using pores of blind holes added on the nozzle inner wall is explored numerically. These pores are intended to introduce disturbances to the shear layer so as to change the flow mixing. This passive strategy has not been attempted so far. A convergent nozzle with a cylindrical extension is selected as the baseline case. Three nozzles with pores on the inner wall are set up. Validations of the numerical settings are carried out, then the compressible turbulent jets at the exit Mach number M j = 0.6 in the four nozzles are calculated by large eddy simulations (LES), while the radiated sounds are predicted by the FW-H acoustic analogy. The results show that the blind holes have produced some effects on weakening the turbulence intensity in the shear layer. Comparison reveals that both temporal and spatial correlations of the turbulent fluctuations in the modified cases are suppressed to some extent. Meanwhile, the porous nozzles are shown to suppress the pairing of vortices and enhance the flow mixing, and therefore, the development of shear layer and the fragmentation of large scale vortices are accelerated.

Computation of vortical flow and flow induced noise by large eddy simulation with FW-H acoustic analogy and Powell vortex sound theory

The sound generated by a NACA0012 airfoil in the wake of a rod is numerically simulated by two approaches, one is the large eddy simulation (LES) with the FW-H acoustic analogy and the other is the LES with the Powell vortex sound theory, in order to compare the accuracies of their predictions. The vortical structures around the rod-airfoil are computed by the LES and captured by the vortex identification (Q). The acoustic predictions are verified by the measurements. It is shown that the computed results by the two hybrid approa- ches (LES and FW-H, LES and Powell) are very similar. Both are shown to be satisfactory in the prediction of the noise generated by an unsteady flow. Subsequently, the numerical simulations of the wall pressure fluctuations and the flow-induced noise of a NACA0015 airfoil are made by the two hybrid approaches. At two angles of attack (0° and 8°), the wall pressure fluctuations of the NACA0015 airfoil are computed. The obtained power spectra of the wall pressure fluctuations are analyzed and compared with the measured data. And the vortical structures around the airfoil at two angles of attack are simulated and analyzed. After that, the flow induced noises of the NACA0015 airfoil at two angles of attack are predicted by the two hybrid approaches (LES and FW-H, LES and Powell). The radiated sound spectra are analyzed and compared with the experimental data. Comparisons show that both are robust, credible and satisfactory in the numerical prediction of the flow induced noise. All numerical simulations are carried out by parallel processing in the Wuxi supercomputing center.

Feasibility study into a computational approach for marine propeller noise and cavitation modelling

There is increased interest in the ability to predict the noise associated with commercial ship propellers. Key components of the computational analysis process are considered for two test cases and the future direction in resolving the associated challenges is presented. Firstly, the Potsdam Propeller Test Case is used to compute tonal blade passage noise using the Ffowcs Williams–Hawkings acoustic analogy. Cavitation extents predicted using the Sauer and Schnerr mass transfer model agree well with the experiment but show little unsteadiness due to URANS being used. A complementary study of initial results from the study of cavitation noise modelling attempt is presented for a NACA0009 section, used as a simplified representation of a propeller blade. Large Eddy Simulation and FW-H acoustic analogy are used in order to estimate the cavitation-induced noise. Results indicate that the discussed approach provides the means for identifying low-frequency noise generation mechanisms in the flow, but does not allow for the fine-scale bubble dynamics or shockwave formation to be resolved. It is concluded that the discussed approach is a viable option to predict large parts of the marine propeller noise spectra but still further work is needed in order to account for the broadband components.

Large Eddy Simulation and FW-H Acoustic Analogy of Flow-Induced Noise in Elbow Pipe

Large Eddy Simulation and FW-H Acoustic Analogy of Flow-Induced Noise in Elbow Pipe