Aerodynamic Noise Characteristics Research Articles

Effect of Tailing-Edge Thickness on Aerodynamic Noise for Wind Turbine Airfoil

The influence of wind turbine airfoil trailing edge thickness on aerodynamics and aerodynamic noise characteristics was studied using the computational fluid dynamics (CFD)/ Ffowcs Williams–Hawkings (FW–H) method in the present work. First, the airfoil of a DU97-W-300-flatback airfoil was chosen as the research object, and numerical method validation was performed. Three kinds of turbulence calculation methods (unsteady Reynolds average Navier-Stokes (URANS), detached eddy simulation (DES), and large eddy simulation (LES)) were investigated in detail, and three sets of grid scales were used to study the impact of the airfoil on the aerodynamic noise. Secondly, the airfoil trailing edge thickness was changed, and the impact of trailing edge thickness on aerodynamics and aerodynamic noise was investigated. Results show that three kinds of turbulence calculation methods yield the same sound pressure frequency, and the magnitude of the sound pressure level (SPL) corresponding to the mean frequency is almost the same. The calculation of the SPL of the peak value and the experimental results can match well with each other, but the calculated core frequency is slightly lower than the experimental frequency. The results of URANS and DES are closer to each other with a changing trend of SPL, and the consequences of the DES calculation are closer to the experimental results. From the comparison of two airfoils, the blunt trailing edge (BTE) airfoil has higher lift and drag coefficients than the original airfoil. The basic frequency of lift coefficients of the BTE airfoil is less than that of the original airfoil. It is demonstrated that the trailing vortex shedding frequency of the original airfoil is higher than that of the BTE airfoil. At a small angle of attack (AOA), the distribution of SPL for the original airfoil exhibits low frequency characteristics, while, at high AOA, the wide frequency characteristic is presented. For the BTE airfoil, the distribution of SPL exhibits low frequency characteristics for the range of the AOA. The maximum AOA of SPL is 4° and the minimum AOA of SPL is 15°, while, for the original airfoil, the maximum AOA of SPL is 19°, and the minimum AOA is 8°. For most AOAs, the SPL of the BTE airfoil is larger than that of the original airfoil.

Characteristics of aerodynamic noise from the bogie of a high-speed train measured linear array in the field test

Characteristics of aerodynamic noise from the bogie of a high-speed train measured linear array in the field test

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.

Experimental study on aerodynamic noise characteristics of high-lift configuration with variable gap leading-edge slat

The aircraft high-lift devices are important components to ensure the safety of take-off and landing, and it is also the main source of airframe noise in the process of take-off and landing, especially the leading-edge slat. The slat that reduces gap by rotating with the fixed axis is proposed in this paper, and experimental study of far-field aerodynamic noise characteristics of high-lift configuration with the slat is also carried out. The experimental results show that discrete tones in the low-middle frequency range disappear and the broadband frequency amplitude also slightly decline, resulting in a significant decrease in the overall sound pressure level of the high-lift configuration with slat gap of 0, compared with the configuration with conventional leading-edge slat. However, in the process of rotation from conventional slat to seamless slat, more prominent discrete tone in low-middle frequency range or humps in mid-high frequency range appear at angles of attack below 6°, which give rise to the overall increase in the sound pressure level. At angles of attack above 6°, these aero-acoustic phenomena are not obvious. Hence, the overall sound pressure levels of high-lift configuration gradually decrease with the rotation process in larger angles of attack.

Numerical Modeling and Investigation on Aerodynamic Noise Characteristics of Pantographs in High-Speed Trains

Pantographs are important devices on high-speed trains. When a train runs at a high speed, concave and convex parts of the train cause serious airflow disturbances and result in flow separation, eddy shedding, and breakdown. A strong fluctuation pressure field will be caused and transformed into aerodynamic noises. When high-speed trains reach 300 km/h, aerodynamic noises become the main noise source. Aerodynamic noises of pantographs occupy a large proportion in far-field aerodynamic noises of the whole train. Therefore, the problem of aerodynamic noises for pantographs is outstanding among many aerodynamics problems. This paper applies Detached Eddy Simulation (DES) to conducting numerical simulations of flow fields around pantographs of high-speed trains which run in the open air. Time-domain characteristics, frequency-domain characteristics, and unsteady flow fields of aerodynamic noises for pantographs are obtained. The acoustic boundary element method is used to study noise radiation characteristics of pantographs. Results indicate that eddies with different rotation directions and different scales are in regions such as pantograph heads, hinge joints, bottom frames, and insulators, while larger eddies are on pantograph heads and bottom frames. These eddies affect fluctuation pressures of pantographs to form aerodynamic noise sources. Slide plates, pantograph heads, balance rods, insulators, bottom frames, and push rods are the main aerodynamic noise source of pantographs. Radiated energies of pantographs are mainly in mid-frequency and high-frequency bands. In high-frequency bands, the far-field aerodynamic noise of pantographs is mainly contributed by the pantograph head. Single-frequency noises are in the far-field aerodynamic noise of pantographs, where main frequencies are 293 Hz, 586 Hz, 880 Hz, and 1173 Hz. The farther the observed point is from the noise source, the faster the sound pressure attenuation will be. When the distance of two adjacent observed points is increased by double, the attenuation amplitude of sound pressure levels for pantographs is around 6.6 dB.

Study on the Aerodynamic Noise Characteristics of the Pantograph of the High-speed Train

Study on the Aerodynamic Noise Characteristics of the Pantograph of the High-speed Train

Numerical Study on the Acoustic Characteristics of an Axial Fan under Rotating Stall Condition

Axial fan is an important piece of equipment in the thermal power plant that provides enough air for combustion of coal. This paper focuses on the aerodynamic noise characteristics of an axial fan in the development from stall inception to stall cells. The aerodynamic noise characteristic of monitoring region in time and frequency domains was simulated employing the large-eddy simulation (LES), with the addition of throttle setting and the Ffowcs Williams-Hawkings (FW-H) noise model. The numerical results show that, under the design condition, the acoustic pressure presents regular periodicity along with the time. The noise energy is concentrated with high energy of the fundamental frequency and high order harmonics. During the stall inception stage, the acoustic pressure amplitude starts fluctuating and discrete frequencies are increased significantly in the low frequency; among them, there are three obvious discrete frequencies: 27.66 Hz, 46.10 Hz and 64.55 Hz. On the rotating stall condition, the fluctuation of the acoustic pressure level and amplitude are more serious than that mentioned above. During the whole evolution process, the acoustic pressure peak is difficult to keep stable all the time, and a sudden increase of the peak value at the 34.5th revolution corresponds to the relative velocity’s first sudden increase at the time when the valve coefficient is 0.780.

Effect of inlet guide vanes on the performance of small axial flow fan

Effects of the inlet guide vanes on the static characteristics, aerodynamic noise and internal flow characteristics of a small axial flow fan are studied in this work. The inlet guide vanes with different outlet angle are designed, which are mounted on the casing and located at the upstream of the impeller of the prototype fan. Both steady and unsteady flow simulations are performed. The steady flow is simulated by the calculations of Navier-Stokes equations coupled with RNG k-epsilon turbulence model, while the unsteady flow is computed with large eddy simulation. According to the theoretical analysis, the inlet guide vanes with outlet angle of 60° are regarded as the optimal inlet guide vanes. The static characteristic experiment is carried out in a standard test rig and the aerodynamic noise is tested in a semi-anechoic room. Then, performances of the fan with optimal inlet guide vanes are compared with those of the prototype fan. The results show that there is reasonable agreement between the simulation results and the experimental data. It is found that the static characteristics of small axial flow fan is improved obviously after installing the optimal inlet guide vanes. Meanwhile, the optimal inlet guide vanes have effect on reducing noise at the near field, but have little effect on the noise at the far field.

Robust Navier-Stokes method for predicting unsteady flowfield and aerodynamic characteristics of helicopter rotor

A robust unsteady rotor flowfield solver CLORNS code is established to predict the complex unsteady aerodynamic characteristics of rotor flowfield. In order to handle the difficult problem about grid generation around rotor with complex aerodynamic shape in this CFD code, a parameterized grid generated method is established, and the moving-embedded grids are constructed by several proposed universal methods. In this work, the unsteady Reynolds-Averaged Navier-Stokes (RANS) equations with Spalart-Allmaras are selected as the governing equations to predict the unsteady flowfield of helicopter rotor. The discretization of convective fluxes is accomplished by employing the second-order central difference scheme, third-order MUSCL-Roe scheme, and fifth-order WENO-Roe scheme. Aimed at simulating the unsteady aerodynamic characteristics of helicopter rotor, the dual-time scheme with implicit LU-SGS scheme is employed to accomplish the temporal discretization. In order to improve the computational efficiency of hole-cells and donor elements searching of the moving-embedded grid technology, the “disturbance diffraction method” and “minimum distance scheme of donor elements method” are established in this work. To improve the computational efficiency, Message Passing Interface (MPI) parallel method based on subdivision of grid, local preconditioning method and Full Approximation Storage (FAS) multi-grid method are combined in this code. By comparison of the numerical results simulated by CLORNS code with test data, it is illustrated that the present code could simulate the aerodynamic loads and aerodynamic noise characteristics of helicopter rotor accurately.

Numerical study on the aerodynamic noise characteristics of CRH2 high-speed trains

The aerodynamic noise of high-speed trains not only causes interior noise pollution and reduces the comfort of passengers, but also seriously affects the normal life of residents. With the increase of running speed of trains, aerodynamic noises will be more than wheel-rail noises and become the main noise source of high-speed trains. This paper established a computational model for the aerodynamic noise of a CRH2 high-speed train with 3-train formation including 3 train bodies and 6 bogies, adopted the detached eddy simulation (DES) to conduct numerical simulation for the flow field around the high-speed train, applied Ffowcs Williams-Hawkings acoustic model to conduct unsteady computation for the aerodynamic noise of high-speed trains, and analyzed the far-field aerodynamic noise characteristics of high-speed trains. Studied results showed: The main energy of the complete train was mainly within the range of 613 Hz-2500 Hz when the high-speed train ran at the speed of 350 km/h. In the whole frequency domain, it was a broadband noise. Regarding the longitudinal observation point which was 25 m away from the center line of track and 6m away from the nose tip of head train, the sound pressure level of total noises reached the maximum value 88.9 dBA. The maximum sound pressure level of the noise observation point which was 7.5 m away from the center line of track was around the first bogie of head train. Various components made different contributions to the aerodynamic noise of the complete train, and the order was head train, mid train, bogie system (6 bogies) and tail train. The first bogie of head train made the greatest contribution to bogie system and was the main aerodynamic noise source of the complete train.

A comparative study on aerodynamic performance and noise characteristics of two kinds of long-eared owl wing models

The camber line, chord length and thickness of the airfoil are important factors affecting the aerodynamic performance and noise characteristics of the blade. In this research, the long-eared owl wing as bionic prototype and two bionic blades were constructed by using bionic reconstruction method. The one named bionic blade A is based on the long-eared owl wing, which is reconstructed according to section theory and fitting formula of the measured long-eared owl wing. The other is the three-dimensional stretched cross-sectional bionic blade B. To compare the aerodynamic performance and noise characteristics of two bionic blades, the LES method coupled with FW-H equation was adopted to simulate the flow fields and the corresponding sound fields numerically at low Reynolds number condition. The results show that the lift coefficient for the bionic blade B is larger than that for the bionic blade A when the angle of attack is in the range of 0° ~ 30°. The pressure curve of bionic blade B indicates that the pressure generated from the suction side makes a greater contribution to lift force than the pressure side, especially at the leading edge. The location of the separation bubble moves from the trailing edge to the leading edge in the suction side of the blade at α =15°. The size of vortex shedding near the surface of the bionic blade A is smaller than the bionic blade B at α = 0° and it’s caused by the deeply concaved lower surface near the wing root probably. The range of the separation bubble acts as the main influence on the noise generation. Compared with the bionic blade B, the aerodynamic noise generated by the blade A is lower and the minimum value of sound pressure level is even 12.88 dB on the y-direction. That means the special construction of the natural long-eared owl wing could suppress the unsteady pressure fluctuation on the blade surface efficiently to decrease the aerodynamic noise.

Numerical simulation and experimental research on the aerodynamic performance of large marine axial flow fan with a perforated blade

In this study, some of the optimal parameters for a new-style marine axial flow fan are defined by using numerical simulation and experimental tests with a large marine axial flow fan, based on the analysis of the blade perforation’s influences on its internal flow field and aerodynamic noise characteristics. Test result shows that the noise reduction for the axial flow fan with perforated blade is about 3 dB when the blade perforation diameter D is 10 mm and its deflection angle α is 45°. The results of the study show that there is an inhibitory effect on the discrete noise of axial flow fan with perforated blade on the tip area, and its total noise level emerged as the fluctuated distribution characteristics with the increase in the perforation diameter D and reduced along with the increase in the deflection of perforation angle α, at the same time varied as a linear characteristics, which can be reasonably explained by the acoustic interference theory. The results of the study have also further confirmed that the improvement of the flow of axial flow fan with perforated blade helps to reduce the pressure pulsation amplitude caused by the turbulence of the blade surface boundary layer, thereby suppressing the back-flow and vortex from the pressure surface to the suction surface efficiently. It is indicated that the improved vortex shedding phenomenon at the blade trailing edge after perforation on the area of blade tip is the main reason for the aerodynamic noise reduction of axial flow fan.

Numerical research on aerodynamic radiation noises of alternators in vehicles

To study the aerodynamic noise characteristics of alternators in vehicles, this paper established a computational model for the aerodynamic noise of an alternator based on computational fluid dynamics (CFD). The alternator adopted a non-scaling model and considered the detailed structure of collectors and other parts. Based on Lighthill acoustic theory, this paper adopted three-dimensional and large eddy simulation (LES) to conduct an unsteady numerical simulation for the flow field around the alternator, and Ffowcs Williams-Hawkings (FW-H) model was then adopted to conduct an unsteady computation for the aerodynamic noise of the alternator in the far field. When the rotational speed of the alternator was 10000 r/min, this paper obtained the aerodynamic noise characteristics of the alternator and the unsteady flow field structure around the alternator. Studied results showed: The main aerodynamic noise sources of the alternator were front fan, rear fan and stator structure; main influence orders of aerodynamic noises were the 6th, 8th, 10th, 12th, 18th, 24th, 30th and 36th orders. Similarly, this paper also conducted an experimental test on the noise of vehicle alternators. The main influence orders of aerodynamic noises of alternators were the 6th, 8th, 10th, 12th, 18th, 24th, 30th and 36th orders, which was consistent with the working condition of numerical simulation. It showed the correctness of computational results in this paper. In addition, this paper adopted the method of vector synthesis and the distribution of fan blades of the alternator to explain the cause of various orders and provided engineering application foundation for further reducing the noise of main orders.

Research on the radiation characteristics of aerodynamic noises in the connection position of high-speed trains

To study unsteady aerodynamic noise characteristics in the connection position of high-speed trains, this paper established a computational model for aerodynamic noises in the connection position of high-speed trains based on computational fluid dynamics theories. This model included 2 middle trains and 1 connection structure. The detached eddy simulation (DES) was adopted to conduct a numerical simulation for the flow field around high-speed trains which were running in the open air without crosswind. The acoustic model of Ffowcs Williams-Hawkings (FW-H) was used to conduct an unsteady computation for far field aerodynamic noises in the connection position of high-speed trains. In the meanwhile, the boundary element method (BEM) was also applied to conduct an unsteady computation for the radiation of near field aerodynamic noises in the connection position. When the running speed was 250 km/h, time-domain characteristics, frequency-domain characteristics and sound propagation characteristics of aerodynamic noises in the connection position and the unsteady flow field around the connection position were obtained. Studied results showed that: vortex shedding and fluid separations in the connection position were main reasons for aerodynamic noises. In addition, main aerodynamic noise sources were at the recess and rear (the second train) in the connection position, and the first train was not an aerodynamic noise source. Peak frequencies of aerodynamic noises in the far field were 34 Hz, 79 Hz, 124 Hz and 170 Hz. When observation points were 7.5 m away from the center line of track, the maximum sound pressure level was 83.6 dB. When observation points were 25 m away from the center line of track, the maximum sound pressure level was 75.9 dB.

Numerical simulation of aerodynamic noises in the far field of the high-speed train with considering bogies and connection windshields

The paper established a computational model of aerodynamic noises for 3-train formation including 3 trains, 6 bogies and 2 windshields. Based on Lighthill acoustic theories, a wideband noise source model was used to recognize the aerodynamic noise source of the high-speed train. Aerodynamic pressures of the high-speed train were extracted and compared with experimental results. The change trends and values presented a good consistency, which indicated that the computational model in this paper was effective. Large Eddy Simulation (LES) and FW-H acoustic model was then used to conduct numerical simulation of aerodynamic noises of the high-speed train. Aerodynamic noise characteristics in the far field of the high-speed train were analyzed. Analyzed results showed that when the high-speed train was running at the speed of 250 km/h, main energy was concentrated within 1250-3150 Hz, and the noise was a wideband noise in the analyzed frequency. The longitudinal observation point was 25 m away from the track center line and 25 m away from the nose tip, and its sound pressure level reached the maximum value of 89.7 dBA, while the sound pressure level around six bogies reached local maximum. With the larger distance from the track center line, the sound pressure level at horizontal observation points presented a smaller attenuation. Incoming flow had a larger impact on aerodynamic noises around the train than the tail flow. The main noise sources of a high-speed train were located at nose tip and pilot of head train, the second noise source was bogies, and the third noise source was located at train connections.

Parameterization and optimization of broadband noise for high-lift devices

The multi-objective optimization of both aerodynamic and broadband noise characteristics of a high-lift device is studied. The optimization is based on combining a recently developed parameterized Navier-Stokes approach as a surrogate model for solution reconstructions to a genetic algorithm for Pareto front construction. The parameterized Navier–Stokes solver Turb’Opty is a high-order sensitivity method around a reference Reynolds-Averaged Navier–Stokes (RANS) flow field. The present implementation takes into account up to the second-order partial derivatives including cross-derivatives of the RANS solver with respect to the optimization parameters. Acoustic predictions are based on Amiet’s airfoil models and their extensions for turbulence interaction noise and self-noise respectively. The needed temporal data are reconstructed from wall-resolved RANS simulations or estimate through the surrogate model. The use of the parameterized Navier–Stokes approach and the self-noise model are validated with both experimental and detailed simulation data on a NACA0012 configuration. The whole optimization process is then applied to the L1T2 high-lift device. The application of these noise models seems to qualitatively capture the broadband noise generated in gaps between the elements. The study of the Pareto front exhibits optimal solutions with the expected trends: for instance decreasing the Mach number and the camber reduces the noise and yields a lift reduction. Details of two optimal solutions are finally provided.

新幹線から発生する集電系空力騒音に関する音響特性

新幹線から発生する集電系空力騒音に関する音響特性

Investigation into Aerodynamic Noise Characteristics of Train Head Car Bogie Based on Simplified Models

Investigation into Aerodynamic Noise Characteristics of Train Head Car Bogie Based on Simplified Models

Aerodynamic and aero noise of stationary tire

The characteristics of aerodynamic and aero noise of stationary tire are investigated using computational fluid dynamics (CFD) and wind tunnel tests. A positive lift coefficient of almost 0.27 was found at all tested Reynolds numbers, while the drag coefficient was twice as large. The averaged pressure coefficient computed agrees with the measured, while the separation point predicted by numerical simulation is brought forward. The aero-noise numerical results using hybrid method based on large eddy simulation (LES) and FW-H formulations compares well with results from the wind tunnel test for total sound pressure level and noise spectra. Due to the defects of turbulence model and limited computer resources, the agreement of noise spectra for some test points in the frequency above 600 Hz is not the best. Sound energy of sound source and sound energy radiated from sound source are nearly proportional to the fourth power and sixth power of wind speed, respectively. At the simulated speeds, about 2.7% of sound energy comes from quadrupole sources, while 97.3% of sound energy comes from the dipole sources, which is the first time a quantitative description has been given. It should be pointed out that due to the different phases of dipole and quadrupole, the contribution of quadrupole to radiation is different at the receivers.

Noise Influence of High-Speed Train Based on Air Dynamics

How to control aerodynamic noise of high speed motor train, this paper starts from the basic theory of hydrodynamics and acoustics, it adopts method of numerical simulation and applies Fluent and VirtuaUab Acousticsand software to make study on characteristics of aerodynamic noise for high speed motor train, the test results indicates that in the stable flow distribution, the baric gradient is relatively larger when its surface pressure is in area with large change in curve curvature, when it is in the area with even curve change, the baric gradient is relatively smaller. In different gradient, the train head, the maximum pressure and the maximum negative pressure ratio of air-conditioner air deflector predicate are in proportion to the square of train speed.