Noise Prediction Method Research Articles

Research on prediction and control method of car exterior noise

In order to predict and control exterior noise, a new car exterior noise prediction method is presented based on Statistical Energy Analysis (SEA) principle and point sound source radiation formula. The Sound Pressure Level (SPL) of the car exterior structure-borne noise is predicted by using a SEA model. The exhaust noise and tyre noise are also considered. The prediction result was validated. The sound package schemes of the engine cabin for controlling car exterior noise are designed and analysed. A control measure of the exterior noise is chosen and put into practice for controlling car exterior noise.

GA-BP Neural Network Based Tire Noise Prediction

According to the complexity and the highly nonlinear characteristics of the tire sound, various parameters affecting tire noise were analyzed. By employing neural network a new method of tire noise prediction was proposed. Combining BP neural networks with genetic algorithms the noise prediction model was set up. In order to effectively predict tire noise, the neural network structure was designed and the input and output parameters of the network were determined. The genetic algorithm was added to the BP network in order to optimize initial weights and search out the optimal solution of the network. Applying laboratory drum method large amounts of tire noise test samples were obtained to train the BP network. Trained neural network can accurately predict tire noise in range of typical frequency bands. The results show that precision of this method is sufficient and the prediction effect is better.

Landing Gear Aerodynamic Noise Prediction Using Building-Cube Method

Landing gear noise prediction method is developed using Building-Cube Method (BCM). The BCM is a multiblock-structured Cartesian mesh flow solver, which aims to enable practical large-scale computation. The computational domain is composed of assemblage of various sizes of building blocks where small blocks are used to capture flow features in detail. Because of Cartesian-based mesh, easy and fast mesh generation for complicated geometries is achieved. The airframe noise is predicted through the coupling of incompressible Navier-Stokes flow solver and the aeroacoustic analogy-based Curle’s equation. In this paper, Curle’s equation in noncompact form is introduced to predict the acoustic sound from an object in flow. This approach is applied to JAXA Landing gear Evaluation Geometry model to investigate the influence of the detail components to flows and aerodynamic noises. The position of torque link and the wheel cap geometry are changed to discuss the influence. The present method showed good agreement with the preceding experimental result and proved that difference of the complicated components to far field noise was estimated. The result also shows that the torque link position highly affects the flow acceleration at the axle region between two wheels, which causes the change in SPL at observation point.

Semi-Empirical Modeling of Turbulent Anisotropy for Airfoil Self-Noise Predictions

In the present paper an approach to derive anisotropic turbulence properties from standard Reynolds-averaged Navier-Stokes simulations is proposed. The theory includes models for anisotropic velocity spectra and scaling functions that can be used to derive other turbulence parameters required for the turbulent boundary-layer trailing-edge interaction noise prediction. This type of noise is supposed to be affected by the inhomogeneous and anisotropic flow character near the trailing edge of an airfoil or wing. For this purpose, two-point turbulent velocity correlation measurements in the near wake of two airfoils (NACA 0012 and NACA 64 3 -418) at high Reynolds numbers (Re = 1.5 x 10 6 and 2.5 x 10 6 ) were conducted in the Laminar Wind Tunnel of the University of Stuttgart. A detailed postprocessing along with assessment of the experimental data has been performed for the modeling of different isotropic and anisotropic velocity spectra and related length scales. For this modeling, an anisotropy amplitude scaling method and Kolmogorov local-isotropy hypothesis have been applied. Furthermore, two different semi-empirical functions have been correlated to the resultant anisotropy scaling factors to model the effects of turbulence anisotropy in numerically predicted Reynolds-averaged Navier-Stokes data. The proposed spectrum modeling allows an accurate evaluation of the turbulence mean dissipation rate. The new models were validated and applied to a turbulent boundary-layer trailing-edge interaction noise prediction method (Rnoise) to analyze the impact of anisotropy on the total predicted noise spectra.

Automotive Interior Noise Prediction Based on Single Sound Cavity Using Statistical Energy Analysis Method

In order to predict car interior noises at the car design and development stage, the statistical energy analysis (SEA) method was used. All the input parameters – modal density (MD), damping loss factor (DLF) and coupling loss factor (CLF) were calculated with SEA principle. Meanwhile, the sound excitation was calculated with sound power experiment data of internal combustion engine given by the engine manufacturer and sound source radiation formula. Engine mount excitation was also computed through the acceleration at initiative side of the engine mount and the transmissibility. A car virtual prototype was built to calculate a car body suspension receiving excitation from road roughness. A computational fluid dynamics (CFD) model was also built up to analyze the wind excitation on the outside surfaces. The car interior noises were predicted by the SEA model with all of the parameters and excitations. A good agreement was indicated by comparing predicted results with measured ones. The maximum relative error between prediction and measurement results is less than 3%, and the maximum absolute error is less than 2.5 dB (A). The above predicted results satisfy engineering precision requirements and as well as showing that using SEA method to predict car internal noises is feasible. The acoustic sensitivity analysis was made at the end. The car internal noise prediction method presented in the paper can be used at car design and development stage.

A novel traffic-noise prediction method for non-straight roads

In view of the well-recognized need for the availability of simple traffic noise–prediction methods for non-straight roads, such as interchanges and flyovers, an approximate traffic noise–prediction model, suitable for non-straight roads, was developed following the modeling process of the Federal Highway Administration’s (FHWA) traffic-noise model. The approximate model is simpler than the FHWA model when the non-straight road is divided into several road sections, their traffic-noise levels calculated individually, and all the sound levels superimposed to obtain the total traffic-noise level of the entire non-straight road. The rational length of the small road section was investigated. The traffic-noise levels predicted using the approximate and the FHWA models were compared through an example and were shown to differ only very marginally. The approximate model is thus suitable for traffic-noise prediction for non-straight roads.

Study on Reasonable Fastener Stiffness of Ballastless Turnout's Vibration Decrease and Noise Reduction of 350 km/h Passenger Dedicated Line

With the large-scale construction of passenger dedicated line, more and more ballastless turnouts were laid as the important infrastructure of passenger dedicated line, and the fastener stiffness of it influenced the vibration and noise of the track. Using the vehicle-turnout coupling dynamic analysis created the method for determining the reasonable fastener stiffness of ballastless track turnout to analyse mutative fastener stiffness's impact on the vibration and noise. Then from three parts of the excitation of wheel-rail roughness, the sound radiation efficiency and the calculation of wheel-rail radiated noise, the noise prediction method for ballastless turnout was stated. Using the above methods, The reasonable fastener stiffness of ballastless turnout can be obtained. The results showed that the stiffness of 25 kN/mm to the fastener of ballastless turnout was reasonable for vibration decrease and noise reduction.

Prediction Method of Tunnel Blasting Work Vibration, Noise and infrasound

Prediction Method of Tunnel Blasting Work Vibration, Noise and infrasound

Computational aero-acoustics for fan duct propagation and radiation. Current status and application to turbofan liner optimisation

Novel techniques are presented to reduce noise from turbofan aircraft engines by optimising the acoustic treatment in engine ducts. The application of Computational Aero-Acoustics (CAA) to predict acoustic propagation and absorption in turbofan ducts is reviewed and a critical assessment of performance indicates that validated and accurate techniques are now available for realistic engine predictions. A procedure for integrating CAA methods with state of the art optimisation techniques is proposed in the remainder of the article. This is achieved by embedding advanced computational methods for noise prediction within automated and semi-automated optimisation schemes. Two different strategies are described and applied to realistic nacelle geometries and fan sources to demonstrate the feasibility of this approach for industry scale problems.

Broadband trailing edge noise from a sharp-edged strut

This paper presents experimental data concerning the flow and noise generated by a sharp-edged flat plate at low-to-moderate Reynolds number (Reynolds number based on chord of 2.0 × 10(5) to 5.0 × 10(5)). The data are used to evaluate a variety of semi-empirical trailing edge noise prediction methods. All were found to under-predict noise at lower frequencies. Examination of the velocity spectra in the near wake reveals that there are energetic velocity fluctuations at low frequency about the trailing edge. A semi-empirical model of the surface pressure spectrum is derived for predicting the trailing edge noise at low-to-moderate Reynolds number.

Application of frequency-domain linearized Euler solutions to the prediction of aft fan tones and comparison with experimental measurements on model scale turbofan exhaust nozzles

Although it is widely accepted that aircraft noise needs to be further reduced, there is an equally important, on-going requirement to accurately predict the strengths of all the different aircraft noise sources, not only to ensure that a new aircraft is certifiable and can meet the ever more stringent local airport noise rules but also to prioritize and apply appropriate noise source reduction technologies at the design stage. As the bypass ratio of aircraft engines is increased – in order to reduce fuel consumption, emissions and jet mixing noise – the fan noise that radiates from the bypass exhaust nozzle is becoming one of the loudest engine sources, despite the large areas of acoustically absorptive treatment in the bypass duct. This paper addresses this ‘aft fan’ noise source, in particular the prediction of the propagation of fan noise through the bypass exhaust nozzle/jet exhaust flow and radiation out to the far-field observer. The proposed prediction method is equally applicable to fan tone and fan broadband noise (and also turbine and core noise) but here the method is validated with measured test data using simulated fan tones. The measured data had been previously acquired on two model scale turbofan engine exhausts with bypass and heated core flows typical of those found in a modern high bypass engine, but under static conditions (i.e. no flight simulation). The prediction method is based on frequency-domain solutions of the linearized Euler equations in conjunction with perfectly matched layer equations at the inlet and far-field boundaries using high-order finite differences. The discrete system of equations is inverted by the parallel sparse solver MUMPS. Far-field predictions are carried out by integrating Kirchhoff's formula in frequency domain. In addition to the acoustic modes excited and radiated, some non-acoustic waves within the cold stream-ambient shear layer are also captured by the computations at some flow and excitation frequencies. By extracting phase speed information from the near-field pressure solution, these non-acoustic waves are shown to be convective Kelvin–Helmholtz instability waves. Strouhal numbers computed along the shear layer, based on the local momentum thickness also confirm this in accordance with Michalke's instability criterion for incompressible round jets with a similar shear layer profile. Comparisons of the computed far-field results with the measured acoustic data reveal that, in general, the solver predicts the peak sound levels well when the farfield is dominated by the in-duct target mode (the target mode being the one specified to the in-duct mode generator). Calculations also show that the agreement can be considerably improved when the non-target modes are also included, despite their low in-duct levels. This is due to the fact that each duct mode has its own distinct directionality and a non-target low level mode may become dominant at angles where the higher-level target mode is directionally weak. The overall agreement between the computations and experiment strongly suggests that, at least for the range of mean flows and acoustic conditions considered, the physical aeroacoustic radiation processes are fully captured through the frequency-domain solutions to the linearized Euler equations and hence this could form the basis of a reliable aircraft noise prediction method.

New approach to railway noise modeling employing Genetic Algorithms

Main goal of this paper was to describe an innovative method of noise prediction based on Genetic Algorithms. First part of the paper addresses the problem of growing noise, mainly in the context of a unified method for measuring noise. Further, Genetic Algorithms are described with regards to their fundamental features. Further a description is provided as to how Genetic Algorithms were used in the area of noise modeling. Next chapter shows results achieved with prototype software created for the purpose of research experiments. Finally, a practical technical application of this method is presented.

A Method for Prediction of Structure-borne Noise Radiated from Concrete Railway Viaducts

Prediction of structure-borne noise has been a significant issue for railway viaducts, since it causes an excessive degree of noise attributable to structural member vibration. A new method of flexural vibration analysis expanded to cover whole structure for the prediction of structure-borne noise has therefore been developed. After calculation and measurement of noise in the vicinity of a floor slab of a concrete viaduct constructed on a Shinkansen line, it was revealed that the proposed method can be used as a practical means for predicting structure-borne noise.

Estimation of the effect of shadow zone boundary for noise calculation on large wind turbines

The prediction methods of wind turbine noise in common use are valid for weather conditions that correspond to moderate down-wind. In this study the up-wind propagation is examined for a point source (turbine hub) and plane source (turbine blades with the hub). Since the wind turbine noise limits are related either to an average�or the highest noise imission at the receiver, the up-wind propagation is considered for the wind speed of 10 m/s at 10 m above the ground surface (wind class W5). It is shown that the up-wind refraction results in the change of the effective sound power level of the wind turbine. It explains some up-wind measurement data

One, no one and one hundred thousand methods for low-speed fan noise prediction

One, no one and one hundred thousand methods for low-speed fan noise prediction

Experimental and numerical studies on the discrete noise about the cross-flow fan with block-shifted impellers

The experimental and numerical studies have been carried out to investigate the blade passage frequency (BPF) noise of a cross-flow fan (CFF) with the block-shifted impeller. Firstly, the aeroacoustic and aerodynamic features about the five different block-shifted impellers have been obtained experimentally. Secondly, the dynamic pressure sensors were put in the noise generating surfaces to investigate the pressure fluctuations generated by the shifted blocks in the near-field through the cross-correlation analysis. Thirdly, the two-dimensional (2D) unsteady flow field has been simulated by commercial CFD software and the vortex flow patterns and the unsteady force of the blade have been analyzed to detect the noise source about the CFF. Finally, the noise properties about the CFF were predicted by a hybrid method through the Farassat’s equation and the surface pressure fluctuations were provided by the CFD simulations. A simplified theory model has also been built up at the same time. The comparisons are made between the results of hybrid method and the theory model to validate the correctness of the noise prediction methods. The accuracy of these results was also evaluated by the corresponding experimental ones. The results indicate that the impellers with different block-shifted angles are the same in aerodynamic performance but different in the BPF noise. The relations between the shifted angles and the BPF noise levels have been predicted and discussed for the noise reduction.

A hybrid algorithm for far-field noise minimization

A general unsteady adjoint formulation is applied to a hybrid acoustic prediction algorithm to provide an efficient far-field noise minimization algorithm. Two-dimensional unsteady Navier–Stokes (NS) computations for calculating the properties of acoustic sources are combined with the Ffowcs Williams and Hawkings (FW–H) wave propagation formulation to calculate the resulting far-field noise. Two different time-marching methods, namely an implicit multi-stage and an implicit multi-step method, are used for time discretization. The hybrid NS/FW–H solver is verified by comparison to an analytical solution and a Navier–Stokes solution. A discrete-adjoint Newton–Krylov algorithm is used to enable gradient-based shape optimization to minimize far-field noise computed using the hybrid solver. Objective functions considered include remote inverse shape designs for verification as well as the far-field pressure fluctuations for a blunt trailing edge airfoil in an unsteady turbulent flow environment. The examples presented demonstrate that the combination of a discrete-adjoint Newton–Krylov algorithm with a hybrid NS/FW–H far-field noise prediction method can be an efficient design tool for reducing aerodynamically generated noise.

NMPB-Routes-2008: The Revision of the French Method for Road Traffic Noise Prediction

The revision of the French method for road traffic noise prediction (NMPB-Routes-2008) is now published. The major principles of NMPB-Routes-2008 are outlined. The most important modifications regarding the source are the reduction of its height and the introduction of two different spectra. In this complete revision, the main change is the replacement of the ISO 9613-2-based ground attenuation formula in downward-refraction conditions by the formula for ground attenuation in homogeneous conditions of NMPB-Routes-1996 with corrected heights in order to take into account the mean curvature of rays (refraction) and its scattering (turbulence). NMPB-Routes-2008 adds an attenuation term for an occasional cutting embankment. Regarding diffraction the dif formula is now more suitable for low height barriers. The validation of NMPB-Routes-2008 with respect to experiment is presented. It is based on measurement campaigns on 6 sites with complex geometries and shows that the predicted noise levels obtained from NMPB-Routes-2008 are significantly closer to experimental results than in the case of the original method. S. Hirzel Verlag.

Computational-Fluid-Dynamics-Based Clean-Wing Aerodynamic Noise Model for Design

A new noise metric is developed for clean-wing aerodynamic noise modeling that may be used in aircraft or wind turbine design studies involving aerodynamic noise. The method uses Reynolds-averaged Navier-Stokes calculations with a two-equation turbulence model to include the effects of the lift coefficient, flow three-dimensionality, and wing design parameters on the trailing-edge noise. These effects are not considered in the existing, relatively less expensive, semi-empirical noise prediction methods. The proposed noise metric is not the exact value of the noise intensity, but it is a relative noise measure suitable for design studies. The new noise metric is less expensive to compute compared to the full-noise calculations done with computational aeroacoustics methods, and it can be easily implemented using the solutions of Reynolds-averaged Navier-Stokes simulations that may have already been performed as part of the aerodynamic design and analysis. Parametric studies were performed to investigate the effect of the wing geometry and the lift coefficient on the noise metric. Two-dimensional studies were done using two subsonic (NACA 0012 and 0009) and two supercritical [SC(2)-0710 and -0714] airfoils. The energy-efficient transport wing (a generic conventional transport wing) was used for the three-dimensional study. Both two-and three-dimensional studies show that the trailing-edge noise increases significantly at high lift coefficients. The three-dimensional effects observed in the parametric wing study indicate the importance of calculating the noise metric with a characteristic velocity and length scale that vary along the span.

A hybrid prediction method for low-subsonic turbulent flow noise

A hybrid method is proposed for prediction of low-subsonic, turbulent flow noise. In this method, the noise sources in the near wall turbulences or in the wake are computed by the incompressible large eddy simulation (LES), while the generation and propagation of the acoustic waves are solved by the linearized perturbed compressible equations (LPCE), with acoustic sources represented by a material derivative of the hydrodynamic pressure, DP/Dt. The accuracy of the present method is critically assessed for two experiments conducted at the Ecole Centrale de Lyon and the University Erlangen, where aeroacoustic measurements were taken for (i) the flat plate self-noise at zero angle of attack (Rec=1.3×105,M=0.06) and (ii) the forward-facing step noise (Reh=8000,M=0.03), respectively. The noise sources are identified and analyzed further to determine their spectral-dependent, spanwise coherence functions, γij of the wall pressure fluctuations, in order to quantify the sizes of the noise sources. The far-field sound pressure level (SPL) spectra predicted by the present method are found in excellent agreement with the experimental measurements.