Analysis Of Aerodynamic Noise Research Articles

Study on the aerodynamic performance and noise of windshield area in high-speed trains at a frequency of 38 hz

The noise level of a high-speed train is a crucial indicator of its operational quality. A significant low-frequency interior noise, referred to as ‘38 Hz’ in this context, has been detected during the operation of high-speed trains. This notable noise primarily occurs in the train attendant’s cabin near the windshield area. In this study, we conducted a comprehensive full-scale test to investigate the preliminary cause behind this significant ‘38 Hz’ noise. Our investigation reveals that it is associated with aerodynamic noise originating from the windshield area. To identify the root cause of this ‘38 Hz’ noise in the windshield area, we established a computational fluid dynamics (CFD) based model for aerodynamic noise analysis. The causes were found to be related to both the size and opening of the windshield cavity. Simulation results demonstrate that closing the upper opening significantly reduces the volume of ‘38 Hz’ noise compared to the original outer windshield structure design. We verified and validated these findings through an extensive full-scale test, which showed that by implementing our proposed modified windshield structure, there was approximately 7 dB reduction in significant ‘38 Hz’ noise observed within the train attendant’s cabin near the windshield area.

Aerodynamic noise analysis of the skirting board under an ultra-high-speed train based on bidimensional empirical mode decomposition

ABSTRACT The grille located in the lower part of the train often forms a grille-cavity structure in the equipment bay’s surface. The issue of flow-induced sound of this structure becomes more significant at high speeds. In this study, we focus on a skirting board with a grille, that is simplified as a grille-cavity structure. We use DDES in combination with modal decomposition, to analyze the fluidization mechanism of the structure. The results indicate that the shear oscillation at the opening of the cavity is more pronounced at ultra-high speed. Moreover, it has been shown that both POD and BEMD can accurately separate and identify coherent structures in the flow field. BEMD has higher accuracy. And the flow is primarily dominated by low-frequency acoustic oscillation. Finally, when we compare three grille configurations (V, ᴖ), we find that the grille’s presence mitigates the cavity’s aerodynamic noise, especially when using a -shaped grille.

Aerodynamic noise analysis of tilting rotor in edgewise flow conditions

This paper presents a comprehensive experimental analysis of the noise characteristics of an isolated tilt-rotor system under edgewise flight conditions. The investigation explores the effect of rotor tilt on noise and aerodynamics using flow velocity, thrust, and far-field noise measurements. Flow field results show that as the tilting angles vary, there is a change in speed over the rotor blade surface, which influences vortex formation and wake attributes. The far-field noise spectra revealed a significant decrease in sound pressure level with increasing tilt angle, predominantly evident in both the high-amplitude tonal peaks and the broadband signal within the low-to-mid frequency range. The directivity patterns of the overall sound pressure level also demonstrated a reduction in magnitude with the tilting of the rotor. This reduction was observed consistently across all top-plane observation points, with a monopole directivity trend. Meanwhile, in the side plane array, the decrease was primarily evident above the plane of rotation with a dipole directivity pattern. The radiation direction at which the minimum sound pressure level occurs was identified near the rotation plane, irrespective of the tilt angle. Furthermore, the time-dependent noise analyses revealed dominant and persistent signal characteristics at the blade passing frequency, whereas the mid-frequency range exhibited more intermittent behaviour, and the high-frequency range indicated transient characteristics.

Numerical simulation and prediction of aerodynamic noise of high-speed trains

In order to improve the efficiency of high-speed train aerodynamic noise analysis and provide a feasible method for aerodynamic noise prediction, the aerodynamic noise and its influencing factors are analyzed from the perspective of the total energy (sound power) radiated to the far field per unit time by the aerodynamic fundamental noise sources (monopole, dipole and quadrupole sources). A full-scale and a 1:8 scale-down computational fluid dynamics model of a high-speed train are established. The far-field sound pressure level at several receivers and velocities is calculated by using the transient large eddy simulation and the FW-H equation. The numerical simulation results are used to predict the aerodynamic noise under specified working conditions. The research work can achieve the prediction of aerodynamic noise at other velocities using noise data at known velocities on the same noise source case, as well as the prediction of aerodynamic noise of full-scale model using data of scale-down model, and is applicable to either bogies as local noise sources or the complete vehicle as a noise source. The maximum error between the prediction and simulation result is 0.33 dBA under various working conditions, which meets the engineering calculation requirements.

Application of the complex differentiation method to the sensitivity analysis of aerodynamic noise

The complex differentiation method (CDM) is applied to the sensitivity analysis of the noise generated by two-dimensional mixing layers, simulated by Direct Numerical Simulation (DNS), in order to investigate its capabilities to highlight the effects of a key parameter on the aerodynamic noise. For this purpose, simulations are carried out using the CDM for different flow Mach numbers, Reynolds numbers and mesh spacings. In each case, the derivatives of the noise levels with respect to one of the three parameters are obtained using the CDM, implemented by adding a small imaginary perturbation to the parameter under study. In most cases, vortex pairings occur in the mixing layers and produce acoustic waves at a single frequency. The derivatives of the acoustic intensity obtained using the CDM show that the sound radiation is stronger and less directed downstream as the Mach number increases, in agreement with dimensional analyses. They also indicate that the radiation is more intense and directive as the Reynolds number increases. The magnitude of the derivatives of the acoustic intensity with respect to the mesh size decreases for finer meshes, showing that the grid sensitivity of the radiated noise is reduced for the latter meshes, as expected. In all cases, the derivatives obtained using the CDM are in good agreement with results from parametric studies. This suggests that the CDM can be used to describe the effects of physical parameters and of the grid resolution on the sound produced by a high-speed flow.

Flow behavior and aerodynamic noise characteristics of ultra-high-speed elevator based on large eddy simulation

PurposeThis paper aims to guide the implementation of noise reduction measures in hoistway and reduce the aerodynamic noise generated by elevator operation, this paper aims to propose an aerodynamic noise analysis method that can solve the flow field in hoistway.Design/methodology/approachA turbulence-acoustic model solving the flow field in a hoistway and a numerical wind hoistway model of the ultra-high-speed elevator were established by using large eddy simulation (LES) and Curle acoustic theory.FindingsThe characteristics of pulsating flow field and aerodynamic noise around ultra-high-speed elevator are analyzed. The asymmetric characteristics of the flow field could be observed using the turbulent kinetic energy and the instantaneous vortexes in the wind hoistway model. Vortex shedding, air flow separation and recombination around the car were the key factors for aerodynamic noise generation. The sound pressure level was approximately linear to the logarithm of car speed. The increase of car deflection angle in a certain range would reduce the peak frequency of wake noise and increase the sound pressure level (SPL) value.Originality/valueThis paper provides important guidance for researches studying the aerodynamic noise in the hoistway and the technical personnel that look for the reduction measures, which greatly improves the shortcomings in the numerical simulation of the aerodynamic noise of the hoistway.

Identification of Aerodynamic Tonal Noise Sources of a Centrifugal Compressor of a Turbocharger for Large Stationary Engines

The aerodynamics of centrifugal compressors is a topical issue, as the vibrations and noise reduce the comfort of people who are in proximity to the compressor. The current trend in rotating machinery research is therefore not only concerned with performance parameters but also increasingly with the effect on humans. An analysis of aerodynamic noise based on external acoustic field measurements may be a way to assess the nature of aerodynamic excitation. In this research, the experimental measurements at 20 operating points covered the entire characteristic operating range of the selected centrifugal compressor. The dominant noise arising at blade-passing frequency (BPF) was identified at all the operational points, and the dominant effect of the buzz-saw noise was identified at the maximum rotor speed. The determination of the total sound pressure level LPA showed a trend towards an increasingly higher rotor speed and compressor surge line. In the amplitude-frequency characteristics, the sound pressure was found to be dependent on the rotor speed for BPF. On the other hand, non-monotonicity was detected between the operational points at given speed lines, confirming the complexity of the aerodynamics of rotating machines. The metric chosen to identify prominent tones determined by the tonality of individual tones in the frequency spectrum showed a clear effect of integer multiples of the rotational frequency on the overall noise. Thus, the results presented here confirm the dominant influence of BPF in terms of the psychoacoustic impact on humans.

Effects of Porous Parameters on the Aerodynamic Noise of the Blowing Device of Guardrails

To solve the problem of the strong noise generated in the galvanizing process on the surface of the guardrail board, optimal design of the outlet structure of the blowing device is carried out according to the sound absorption and noise reduction theory of microperforated plates. The aerodynamic characteristics and aerodynamic noise analysis of the blowing device are investigated by large eddy simulation with dynamic grid technology. The oblique surface of the outlet is processed with blind holes, and then the influence of blind holes on the aerodynamic noise of the blowing device is explored, including different shapes, porosities and depths. The spectral study reveals that when the guardrail board just enters the blowing device, there is greater noise compared to other working conditions. The place with the highest noise sound pressure level (SPL) is at the outlet of the blowing device at the monitoring point of R=1 m and the direction of 90°. The SPLs of the monitoring points at 0° and 180° are smaller than those in other directions, while the SPL distribution of the monitoring points in other directions is relatively even. Compared with the original blowing device, the best noise reduction performance is achieved when the blowing device has cylindrical holes, with a porosity of 10% and a hole depth of 3 mm. The noise reduction value reaches up to 28.4 dB. In addition, an aerodynamic noise test was carried out on the blowing device in the corrugated board galvanizing workshop to demonstrate the correctness of the results of the numerical simulation.

Theoretical and Experimental Analysis of Aerodynamic Noise in Small Wind Turbines

This paper presents an analysis of sound pressure levels through theoretical modeling and experimental validation in a 1 kW small wind turbine. The models used in the theoretical analysis are BPM (Brooks, Pope, and Marcolini) and BM (Brooks and Marcolini), where wind turbine blades are divided in sections, and each section has its own contribution with respect to the total emitted sound pressure level. The noise propagation study and its experimental validation were accomplished within the requirements of the standard IEC 61400-11 Ed.3 and the standard NOM-081-SEMARNAT-1994. The comparative study of theoretical and experimental results showed that the BPM and BM methods have a maximum error of 5.5% corresponding to the rated wind speed of 10 m/s. However, at low wind speeds, the theoretical models fit well to experimental data, for example, in the range from 5 to 8 m/s. The experimental data showed that the rotor’s aerodynamic noise is more evident at low wind speed, because under these conditions, environmental noise is much less than wind turbine noise. Finally, to prevent possible negative effects on people’s health, there is a recommended minimum and suitable distance between small wind turbine installations and buildings.

Numerical analysis of aerodynamic noise from pantograph in high-speed trains using lattice Boltzmann method

A pantograph in contact with a catenary for power supply is one of the major aerodynamic noise sources in high-speed trains. To reduce pantograph noise, it is essential to understand the noise generation mechanism of the pantograph. However, it is difficult to determine this mechanism through measurement. Therefore, in this study, the aerodynamic and acoustic performances of a pantograph in a high-speed train were investigated through numerical analysis using the lattice Boltzmann method. First, a real-scaled pantograph was modeled through computer-aided design. Then, the surface and volume meshes of the pantograph model were generated for simulation analysis. Numerical simulation was conducted at a speed of 300 km/h based on the lattice Boltzmann method. Based on the time derivative analysis of flow pressures, it was concluded that the panhead, joint, and base were the dominant noise sources in the pantograph. In particular, various vortexes were generated from the metalized carbon strip of the panhead. The peaks of the sound pressure level propagated from the panhead were 242, 430, and 640 Hz. The noise generation mechanism was analyzed through numerical simulation using noise characteristics.

Streamline Computation Study on Rotation Aerodynamic Noise Prediction of Cross-flow Fan

The approach of resolving analysis the cross-flow relative motion streamline on the cross-flow straight blade is presented to predict the rotation aerodynamic noise performance of cross-flow fan by solving the dipole source term of Ffowcs Williams and Hawkings equation, while the cross-flow fan is applied in the indoor unit of split-type air-conditioner and operated in the rated condition. The calculating results of the method are respectively drawn by programming in Matlab computational language, and compared with the results of CAA numerical simulation and noise experiment. There are some differences in the distribution condition of aerodynamic force fluctuation amplitude on the blade surface, and sound pressure in the related frequency on the indoor unit casing, or on the sphere far field, between the streamline computation approach and numerical simulation. The orders of magnitudes of these calculating results solved by the analysing streamline method are similar with that attained by the numerical simulation. The resolving analysis approach has the characteristics of decreasing the computing cost and not constructing the acoustics grid model of fan, compared with the numerical simulation. The error between the result of numerical simulation and noise test is larger than that between the result of theoretical calculation and noise test, so the approach could be used for the rotation aerodynamic noise analysis of the cross-flow fan.

Improving the design of the traction motor of trains to reduce the aerodynamic noise

The traction motor of trains, which is the core equipment in the railway industry, is a major noise source. As the protection of the environment becomes increasingly more important, the regulations regarding acceptable train noise are becoming stricter. Therefore, more studies on the traction motor of trains are required to find a method to reduce the noise. The existing studies on this topic are insufficient because of the high cost of producing prototypes and the absence of an aerodynamic noise analysis scheme with proven reliability. In this study, the noise performance of the traction motor of trains was evaluated using the numerical analysis of the lattice Boltzmann method, and its effect on the design variables of the traction motor was analyzed. To conduct this study, a reliable numerical analysis scheme was established by evaluating the performance of the base model through an experiment and numerical analysis and comparing the two results. In addition, seven major noise sources, including the size of the cooling fan, blade shape, number of blades, slot wedge shape, and clamp shape, were selected by analyzing the result of the numerical analysis of the base model. The effect of each design variable on the performance of the base model was analyzed by assessing the performance of cases that reflect the design modification of the chosen design variables. Based on the result, a complementary design model was designed to reduce noise, and the performance of this model was evaluated using numerical analysis and compared with that of the base model. From the results, it was confirmed that the newly created model produces much lower noise than the base model.

UH-1H 로터 블레이드의 제자리 비행 시 투과면을 이용한 원방 소음 해석

본 연구에서는 투과면을 이용하는 음향상사법으로 제자리 비행하는 UH-1H 로터 블레이드 주위의 원방 소음을 예측하였다. 두께 소음과 하중 소음, 그리고 충격파 및 끝단 후류 등에 의해 발생하는 유동 소음을 예측하기 위해 블레이드 표면을 포함하는 투과면을 구성하였다. 3차원 압축성 Euler 방정식 및 Navier-Stokes 방정식을 적용하여 공력 해석을 수행하고 비교하였다. 투과면의 위치에 따라 High Speed Impulsive 소음을 예측 및 검증하였다. 블레이드 끝단에서 발생하는 충격파에 의한 소음원이 지배적인 요소임을 확인하였으며, 충격파를 온전히 포함하도록 투과면을 구성하는 것이 중요함을 보였다.

Numerical Analysis of Aerodynamic Noise Generated by Interaction between Karman Vortex and Cylinder Blade

Numerical Analysis of Aerodynamic Noise Generated by Interaction between Karman Vortex and Cylinder Blade

Aerodynamic noise analysis of a portable pneumatic extinguisher

The portable pneumatic extinguisher is one of the most important pieces of equipment for forest fire fighting in China. However, the working noise of the equipment is detrimental to the physiological and psychological health of people in terms of noise exposure. Few research studies have addressed the noise of portable pneumatic extinguishers. Changes of the geometric parameters of the fan can induce variations in the airflow field, thus modulating the resulting aerodynamic noise. This article describes how certain parameters influence the aerodynamic noise of a portable pneumatic extinguisher; the research object of this study was the 6MF-30 portable pneumatic extinguisher. Based on the literature, three parameters that influence the airflow in the fan were chosen for investigation: the stagger angle, exit installation angle and curvature ratio. Models of the portable pneumatic extinguisher fan were developed using SolidWorks, and the values of the geometric parameters were calculated using formulas incorporating trigonometric functions. The noise simulation was conducted via FLUENT based on the FW-H equation, and ten two-dimensional models with different parameters were investigated. The results show that the exit installation angle has essentially no effect on aerodynamic noise. In contrast, the stagger angle and the curvature ratio can have a large influence on aerodynamic noise. The optimal model differs for different frequency bands; for example, at frequencies below 80 Hz, a fan with a stagger angle of 30 exhibits better noise performance, and at frequencies in the range of 80 Hz to 1000 Hz, a fan with a stagger angle of 40 produces lower working noise. The results are clearly different from those of an aerodynamic performance analysis.

Analysis of Aerodynamic Noise at Inter-coach Space of High Speed Trains

A numerical analysis method for predicting aerodynamic noise at inter-coach space of high-speed trains, validated by wind-tunnel experiments for limited speed range, is proposed. The wind-tunnel testing measurements of the train aerodynamic sound pressure level for the new generation Korean high-speed train have suggested that the inter-coach space aerodynamic noise varies approximately to the 7.7th power of the train speed. The observed high sensitivity serves as a motivation for the present investigation on elucidating the characteristics of noise emission at inter-coach space. As train speed increases, the effect of turbulent flows and vortex shedding is amplified, with concomitant increase in the aerodynamic noise. The turbulent flow field analysis demonstrates that vortex formation indeed causes generation of aerodynamic sound. For validation, numerical simulation and wind tunnel measurements are performed under identical conditions. The results show close correlation between the numerically derived and measured values, and with some adjustment, the results are found to be in good agreement. Thus validated, the numerical analysis procedure is applied to predict the aerodynamic noise level at inter-coach space. As the train gains speed, numerical simulation predicts increase in the overall aerodynamic sound emission level accompanied by an upward shift in the main frequency components of the sound. A contour mapping of the aerodynamic sound for the region enclosing the inter-coach space is presented.

GS32 ポリマー型感圧塗料を用いた低速流れ場における非定常圧力計測技術

Pressure sensitive paint (PSP) is a useful noncontact measurement technique to obtain continuous pressure distribution on solid surfaces. The application of PSP to low speed flows in mechanical engineering fields, including unsteady flow measurement related to analysis of aerodynamic noise, is highly demanded. Polymer-based PSP has high pressure sensitivity for low-speed flow field, but the unsteady response of the polymer-based PSP is not examined enough. In this study, we investigate the unsteady response of the polymer-based PSP, to evaluate the feasibility of the polymer-based PSP as a measurement tool for unsteady low-speed flows. We have applied the polymer-based PSP in low-speed flow to measurement of unsteady pressure distribution around a circular cylinder, and compared the amplitude spectra of PSP and that of pressure probe, which are obtained by FFT analysis. Furthermore we have visualized the distribution of the integrated intensity of the PSP amplitude spectrum around the peak, to visualize the area with large pressure fluctuation on the cylinder.

Computational Aeroacoustic Simulation of Landing Gear

RANS / NLAS numerical simulation method is adopted in this paper to carry out study on the aerodynamic noise analysis of basic landing gear configuration. Reynolds average N-S equation is solved with nonlinear turbulence model to establish the landing gear initial flow field, based on which, the NLAS (nonlinear acoustic solver) processed the turbulence fluctuation reconstruction to obtain the near-field acoustic characteristics of landing gear. Combined with the flow characteristics and the associated noise spectrum analysis, aerodynamic noise characteristics of landing gear are achieved. The work in this paper can provide useful research foundation on the following noise reduction design of landing gear.

Numerical Analysis of Aerodynamic Noise of a New High-Speed Train

Along with the raising of the train speed, aerodynamic noise of the high-speed train is generated more and more significantly and their reduction has become one of the key factors to control noise of the high-speed train. Aerodynamic noise radiated from the high-speed train surface was analyzed numerically. The mathematical and physical models of the three dimensional flow field of the high-speed train were established and the external steady and unsteady flow fields of the high-speed train were calculated by using the standard "k-ε" turbulence model and large eddy simulation (LES) respectively. On the basis of the steady flow field, aerodynamic noise sources on the car body surface of the high-speed train are calculated by using the broadband noise source model. On the basis of the unsteady flow field, the time domain characteristics of fluctuating pressures on the car body surface are analyzed. The sound pressure level on the surface pressure demonstrating is calculated and the flow field of some critical parts is analyzed.

10803 角柱周りから発生する空力騒音に関する数値解析(GS-03【流体(1)】)

An aim of this study is to establish the analysis methodology of aerodynamic noise. In this study as preliminary, aerodynamic noise analysis of flow around a square cylinder was conducted. In this study, acoustic field and flow field are calculated separately. In addition, large eddy simulation is employed for the turbulence model. As a result, calculated drag and lift coefficient are showed the same tendency of experimental result. Therefore, the same tendency of turbulent flow field as an experiment is reproduced. Also, spectra of aerodynamic noise have peak value of about 200 Hz, and the same tendency of experimental result showed.