Broadband Noise Source Model Research Articles

Study of hydraulic turbine flow-induced noise distribution law based on defective runner blade

Abstract In order to analyse flow-induced noise distribution law under the defective runner blade, this paper performs defective treatment on the runner blade according to the HLA855a-LJ-250 hydraulic turbine model. Two kinds of blade models, intact blade and outlet side abrasive blade, are established respectively, and the Realizable k-ε turbulence model and broadband noise source model are used to simulate the hydraulic turbine under rated operating conditions. The simulation results show: 1)Double-row leaf grilles and runner blade are the main dipole flow-induced noise sources; 2)Significant differences in the distribution of the acoustic power levels of the double-row leaf grilles’ characteristic blades and the runners’ characteristic blades under different Schemes; 3)Runner defective blades have less effect on the acoustic power level of spiral case, the rest of the overflow components acoustic power level has a tendency to increase, especially the runner has the greatest impact. The maximum increase in acoustic power level of the runner is almost 17 dB, followed by double-row leaf grilles with an increase of around 8 dB. Therefore, critical attention needs to be paid to the abnormal noise signals of runner and double-row leaf grilles.

Transient flow and noise characteristics of accelerated flow past a hydrofoil with special emphasis on vortex-turbulence-noise interaction

The transient process is widely existed in hydraulic machinery and engineering application, which is closely related to the flow and noise characteristics. In the present work, the large eddy simulation turbulence model is employed to simulate the transient flow of accelerated flow past a NACA0015 hydrofoil. The Reynolds number is 8000, the attack angle is 30°, the inlet velocity accelerates from zero to 0.1 m/s with acceleration of 0.1 m/s2, the acceleration time is 1s. Then the broadband noise source model is used to investigate the dipole and quadrupole noise. Finally, the acoustic analogy method with Ffowcs Williams and Hawkings (FW–H) equation is adopted to study the far-field radiated noise features. Results reveal that during the acceleration process, vortex, vorticity and turbulent kinetic energy are generated at the leading edge of hydrofoil, and present corresponding shedding characteristics. Results also reveal that vortex, turbulence and noise are correlated at t = 2.4. For the distribution of vortex, turbulence and noise on the middle longitudinal section, there exists a strong correlation between turbulent kinetic energy (TKE) and Proudman Acoustic Power (AP). The relationship between vorticity and Proudman AP and TKE is complex, which is closely related to the generation, development and shedding of vorticity. Moreover, the distribution and development of Curle dipole noise sources on the suction surface are symmetrical. The directivity curve of the overall sound pressure level (OASPL) presents a butterfly-shaped symmetrical distribution. With the increase of accelerated time, the OASPL of most monitoring points gradually increases. Through the analysis on the spectral curves of vorticity, TKE, near-field and far-field characteristics, it is indicated that these quantities have a strong spectral correlation, which share the same peak frequency.

Cavitation flow and broadband noise source characteristics of NACA66 hydrofoil with a V groove on the suction surface

In the present work, a V groove on the suction surface is proposed to investigate the cavitation flow and noise sources of a NACA66 hydrofoil. The SST k-ω turbulence model and broadband noise source model is employed to analyze the flow pattern and noise distribution. Proper orthogonal decomposition (POD) is then used to investigate the coherent structure of cavitation flow around the hydrofoil. The results show that, under cloud cavitation conditions, the groove improves the energy characteristics of the hydrofoil and increases the lift-to-drag ratio by 2.95%. During the sheet cavitation growth phase, the groove can suppress the development of low-pressure, low-velocity regions on the hydrofoil surface, thus suppressing cavitation near the leading edge of the hydrofoil. During the cavitation collapse stage, the groove reduces the pressure impact of cavitation collapse on the hydrofoil. The groove extends a cavitation cycle and reduces the average cavitation volume during a cavitation cycle by 17.46%. Results indicate that during a cavitation cycle, the groove reduces the average dipole noise on the hydrofoil surface by 5.07% and the average quadrupole noise on the middle longitudinal section by 6.86%. POD results show that the first five orders of the modes capture more than 90% of the energy of the flow field. The primary frequency of the modal coefficients of Mode 1 and Mode 2 is the cavitation frequency, and the other frequencies are multiples of the cavitation frequency. The groove significantly affects Mode 2, which represents a change in velocity distribution in the flow field characteristics.

Large Eddy Simulation on the Cavitation Flow and Noise Characteristics of a NACA0009 Hydrofoil With Different Tip Clearance Sizes

Abstract All hydraulic machinery has a tip clearance, which not only produces tip-leakage vortexes (TLVs), but also reduces the energy performance of the machinery. In addition, tip clearance leads to cavitation and attendant vibration and noise. Therefore, investigating tip-leakage cavitating flow and noise characteristics is of great practical importance. In this paper, the energy performance and noise characteristics of NACA0009 hydrofoils with different tip clearance sizes are studied. A large eddy simulation model and Schnerr–Sauer cavitation model are employed to simulate tip-leakage cavitating flow. Additionally, a broadband noise source model and the Ffowcs Williams–Hawkings (FW–H) equation are used to calculate the noise source and far-field radiated noise characteristics, respectively. Results show that the numerical simulation of cavitation vortex and velocity field is in good agreement with the experimental data, illuminating the characteristics of energy performance, flow pattern, cavitation flow, broadband noise source, and near-field and far-field radiated noise. Compared with the original NACA0009 hydrofoil, the tip clearance reduces the noise of the Curle dipole on the hydrofoil surface and Proudman noise around the hydrofoil. Moreover, study of the far-field noise shows that the directivity curve of the overall sound pressure level (SPL) is distributed in a butterfly shape, symmetrically. Evidently, the tip clearance size has a large impact on the energy performance of the hydrofoil, the intensity of the TLV, and the cavitation. This paper lays a solid foundation for further research on cavitation flow in large-scale hydraulic machinery.

Applications of Computational Fluid Dynamics in the E-Cigarettes Industry

An advanced pod E-cigarette, launched by Shenzhen Woody Vapes Technology Co., Ltd., was researched and analysed in this paper with the help of computational fluid dynamics (CFD) simulation. The standard k-ε turbulent model was introduced to simulate the flow of air, the Broadband Noise Source model adapted to measure the noise and the Discrete Phase Model (DPM) used to calculate the trajectories of the aerosols. The pressure, velocity and noise fields, the trajectories of the aerosols, obtained by Reynolds-Averaged Navier-Stokes (RANS) simulation, were analysed to optimize the structure design of this pod system. Several related experiments were performed and significant improvement was also confirmed.

Influence of water injection on broadband noise and hydrodynamic performance for a NACA66 (MOD) hydrofoil under cloud cavitation condition

Cavitation and its induced noise have negative effects on the hydrodynamic performance of underwater devices such as marine propellers. In this paper, a new flow control method of water injection is proposed to investigate its influence on the flow field around NACA66 (MOD) hydrofoil under the condition of cloud cavitation (Cavitation number σ = 0.83, Reynolds number Re = 5.1 × 105). The density corrected turbulence model (DCM) combined with Zwart-Gerber-Belamri cavitation model (ZGB) is used to simulate the hydrodynamic performance and the pressure fluctuation, while the dipole noise and quadrupole noise are calculated by Broadband noise source models. The numerical results are in good agreement with our previous experimental observations. The results are all compared with those for the original hydrofoil without water injection and show that the injected water noticeably weakens the severe pressure fluctuation on the hydrofoil suction surface and reduce the volume of cavitation by 72.89%. The water injection also performs well on drag reduction, which reduces the drag coefficient by 17.9%. The dipole noise on the hydrofoil surface is effectively suppressed, and the Curle Acoustic Power (AP) for over 50 dB is decreased by 28.99%. It is also found that the water injection significantly reduces the region of over 45 dB for Proudman AP by 46.21%. The water injection improves the stability of the flow field by means of providing extra energy, blocking the re-entrant jet, hindering the evolution process of turbulence and weakening the impact of the fluid on the hydrofoil wall.

Analysis of noise sources in the acoustic field of a combine harvester’s rotating thresher drum

The main goal of the current research is to analyze the acoustic field of the threshing unit of a combine harvester. This research implements a numerical simulation of gas flow based on the Navier-Stokes equations with discretization of equations by the finite volume method. The finite element mesh used in the idealized model allows one to adequately analyze noise sources up to a frequency of 2500 Hz based on the broadband noise source models of Curl and Proudman. In this paper, the analysis of the flow around the threshing unit at two rotation speeds of 500 rpm and 980 rpm was performed in order to point out elements contributing the most to the noise environment of a combine harvester in operation. As a result of the analysis, the spectra of maximum acoustic pressure and intensity were obtained. Based on this data, there were obtained design refinement areas and areas of increased technological control of a typical thresher drum for the practical implementation in the noise reduction strategies.

Influence of C groove on energy performance and noise source of a NACA0009 hydrofoil with tip clearance

Abstract In present work, the SST k-ω turbulence model and broadband noise source models are adopted to analyze the effect of the C groove on the energy performance and sources generated by dipoles and quadrupoles around a NACA0009 hydrofoil. Then the correlation mechanism between tip leakage flow (TLF) characteristics and its induced noise is investigated. Results show that the C groove significantly reduces both the area of the primary tip leakage vortex (PTLV) and the turbulent kinetic energy. It can be deduced that the closer the C groove is to the leading edge, the smaller the area of high decibel value of the dipole noise on the surface near the leading edge, but the area of the high decibel value of the dipole noise emitted from the blade tip becomes larger. Furthermore, compared with the original hydrofoil, the C groove reduces the area of quadrupole noise with maximum decrease of 29% for 50 dB. The turbulent kinetic energy in the flow region has a great influence on the quadrupole noise.

Numerical simulation of heavy truck’s aerodynamic noise

A 3D numerical simulation is built on heavy truck including cab, frame, and tires. And vehicle exterior flow field in steady state is computed by computational fluid dynamics software. In the computation process, the distribution of sound power levels on the surface of vehicle body as well as the connection between sound power level and vehicle speed are obtained from aerodynamic noise source, which is using broadband noise source models. Taking the steady flow field results as original values, the exterior flow field computations in transient state are performed by large eddy simulation. Based on the transient fluid field, the near field aerodynamic noise from cab accessories is predicted using FW-H model, and the comparison of the simulation results and the test results is carried out. The results show that the aerodynamic noise sources are from the upwind side with a great pressure gradient. Attentions should be paid more on rearview mirror, diversion trench and sun visor for Aerodynamic noise optimization of heavy truck. The maximum sound power level of aerodynamic noise in vehicle body accessories is quadratic to vehicle speed. And the aerodynamic noise of heavy trucks is analysed by numerical simulation, in which noise distribution law is consistent with the test. Therefore, the numerical simulation can be adopted to provide the guidance for the design of vehicle body with low noise.

Multi-objective optimization for the aerodynamic noise of the high-speed train in the near and far field based on the improved NSGA-II algorithm

With the increased running speed of trains, the aerodynamic noise of trains becomes increasingly obvious. Reducing aerodynamic noises has become one of keys to controlling the noise of high-speed trains. This paper conducted a numerical simulation on the aerodynamic noise of head of the high-speed train. Firstly, this paper established a mathematical-physical model for the three-dimensional turbulent flow field of a high-speed train, adopted standard k-ε equation turbulent model and broadband noise source model to compute the aerodynamic noise sources of the high-speed train and applied three-dimensional transient large eddy simulation (LES) to compute the external unsteady flow field of the high-speed train after obtaining noise sources. Based on the unsteady flow field, then this paper applied FW-H equations to compute the far-field aerodynamic noise of the high-speed train. After obtaining the unsteady fluctuation pressure on the surface of the train, this paper computed the radiation characteristics of aerodynamic noises around the high-speed train based on the boundary element method (BEM). Researched results showed: The main aerodynamic noise sources of the high-speed train were at the nose tip of head train; fluid separation and recombination were main reasons for the aerodynamic noise of the high-speed train; vortexes in the position of head train were striped and horseshoe-shaped or hairpin vortexes were mainly in the area of tail train; in addition, vortexes were symmetrically distributed along the longitudinal symmetry plane of train; dipole noises were mainly distributed in the area of head train, whose main energy was decreased with the increased frequency; the quadrupole noise of aerodynamic noises of the high-speed train was mainly distributed in the wake flow area of tail train; when the high-speed train ran at the speed of 300 km/h, the maximum sound pressure level of far-field observation points was 76.8 dB; additionally, aerodynamic noises in the far field were mainly a broadband noise, whose main energy was within the frequency range of 1250 Hz to 3150 Hz. Finally, the improved NSGA-II algorithm was used to conduct a multi-objective optimization for the head shape. The aerodynamic drag of the high-speed train could be most reduced by 6.74 %, and the dipole aerodynamic noise source could be most reduced by 8.34 dB. The improved NSGA-II algorithm has an obvious effect on the multi-objective optimization of the head shape.

Research on Aerodynamic Noise Reduction for High-Speed Trains

A broadband noise source model based on Lighthill’s acoustic theory was used to perform numerical simulations of the aerodynamic noise sources for a high-speed train. The near-field unsteady flow around a high-speed train was analysed based on a delayed detached-eddy simulation (DDES) using the finite volume method with high-order difference schemes. The far-field aerodynamic noise from a high-speed train was predicted using a computational fluid dynamics (CFD)/Ffowcs Williams-Hawkings (FW-H) acoustic analogy. An analysis of noise reduction methods based on the main noise sources was performed. An aerodynamic noise model for a full-scale high-speed train, including three coaches with six bogies, two inter-coach spacings, two windscreen wipers, and two pantographs, was established. Several low-noise design improvements for the high-speed train were identified, based primarily on the main noise sources; these improvements included the choice of the knuckle-downstream or knuckle-upstream pantograph orientation as well as different pantograph fairing structures, pantograph fairing installation positions, pantograph lifting configurations, inter-coach spacings, and bogie skirt boards. Based on the analysis, we designed a low-noise structure for a full-scale high-speed train with an average sound pressure level (SPL) 3.2 dB(A) lower than that of the original train. Thus, the noise reduction design goal was achieved. In addition, the accuracy of the aerodynamic noise calculation method was demonstrated via experimental wind tunnel tests.

Numerical Analysis of Aerodynamic Noise in a High Parameter Pressure Reducing Valve

The high parameter pressure reducing valve (PRV) is a key device for regulating gas pressure in industrial processes. For the large flow and the instability of the high pressure and high temperature steam, the noise of the working PRV is large and also its energy consumption. A numerical analysis of the flow field and acoustic field of the inner high parameter PRV was conducted, the main cause of the aerodynamic noise was analyzed. Basing on the RNG k-ε Model and the Broadband Noise Source Model, the flow and acoustic power are calculated. Comparing the distribution of acoustic power level with the distribution of the velocity and turbulent intensity, it is shown that the main reasons for noise in the PRV are forming and shedding alternately vortexes and shock waves of jet flow.

Diffuser perforation effects on the performance of a vent silencer

Numerical simulations are carried out for 3D steady compressible turbulent flowof air inside a vent silencer to investigate the effect of the diffuser perforation on the flow structure and acoustic performance of the silencer. The governing equations for the turbulent flow are solved using the finite volume method. The broadband noise source model is used in the simulations to predict the acoustic power level in the silencer. The inlet total absolute pressure ranges from 250 to 1000 kPa and the outlet absolute pressure is set to atmospheric. The results are presented in terms of the transmission loss of the silencer. The parameters considered in the present study are the diffuser holes diameters and the length of the perforated pipe in addition to the inflow conditions. In all the simulation cases, the inlet sound power level was in the range of the practical measurements of 120 to 150 dB. The results are presented to show the flow structure and the acoustic performance. The results show that increasing either the diffuser hole diameters or the length of the perforated pipe, the transmission loss of the silencer increases.

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.

A Simulation on Aerodynamic Noise of an Air-Conditioning Duck

The transient flow field is needed in order to predict the aerodynamic noise of an automotive HVAC duck by conventional methods. However, it is time-consuming when are several improved schemes .To solve the problem, schemes with large sound power can be discarded using Broadband Noise Source (BNS) model at first. Then, the best scheme can be found after the transient flow simulation .In this paper, an automotive HVAC duck is used as an example. Firstly BNS is used to predict which scheme is noisier, secondly the aerodynamic noise is computed using Fluent coupled with Sysnoise. At last they come to the same conclusion. The simulation results indicate BNS model can be used to find which scheme is the best without computing the transient flow field. So it can shorten the cycle of developing new products.

Prediction of the Aerodynamic Acoustic Power Contribution on Automobile’s Surface Based on Curle’s Integral in Broadband Noise Source Models

The Aerodynamic noise, which is generated by the moving vehicle at high speed, is a kind of broadband noise. This paper dwelled on the Ligthill’s Acoustic Analogy firstly, and applied the realizable k-ε turbulence model to simulate the external steady flow field of automobile, so as to get the distribution characters of statistical turbulence quantities based on the Reynolds-averaged Navier-Stokes (RANS) equation. Then the Curle’s Integral in Broadband Noise Source Models was utilized to predict the local aerodynamic acoustic power contribution on automobile’s surface, which is helpful to the farther research work in the vehicle body optimization design based on aerodynamic noise controlling. The results shows that: The aerodynamic acoustic power contribution regions on surface mainly distribute near the automobile’s head and tail; and the maximum SAPL (Surface Acoustic Power Level) value is up to 83.15 dB in the vicinity of the rear wheel hub when the vehicle speed is 120km/h; the higher the speed of automobile, the more scattered the distribution of main aerodynamic acoustic power on automobile’s surface.

Investigation of computational aeroacoustic tools for noise predictions of wind turbine aerofoils

In this work trailing edge noise levels of a research aerofoil have been computed and compared to aeroacoustic measurements using two different approaches.On the other hand, aerodynamic and aeroacoustic calculations were performed with the full Navier-Stokes CFD code Fluent [Fluent Inc 2005 Fluent 6.2 Users Guide, Lebanon, NH, USA] on the basis of a steady RANS simulation. Aerodynamic characteristics were computed by the aid of various turbulence models. By the combined usage of implemented broadband noise source models, it was tried to isolate and determine the trailing edge noise level. Throughout this work two methods of different computational cost have been tested and quantitative and qualitative results obtained.On the one hand, the semi-empirical noise prediction tool NAFNoise [Moriarty P 2005 NAFNoise User's Guide. Golden, Colorado, July. http://wind.nrel.gov/designcodes/ simulators/NAFNoise] was used to directly predict trailing edge noise by taking into consideration the nature of the experiments.