Noise Prediction Method Research Articles

Prediction of Rotorcraft Broadband Trailing-Edge Noise and Parameter Sensitivity Study

This paper investigates the effects of rotorcraft design and operating parameters on trailing-edge noise. A rotor trailing-edge noise prediction method is first developed where the aerodynamics and the turbulence wall pressure spectrum near the trailing edge on airfoils are predicted by a combination of the standard blade element momentum theory , a viscous boundary-layer panel method, and a recently developed empirical wall pressure spectrum model. The coordinate transformations are combined with the Amiet model to predict far-field noise. Compared to experimental data, the validation of this method demonstrates its advantages and validity for airfoil and rotorcraft broadband noise predictions. Then, this method is used to study the effects of rotorcraft design and operating parameters on rotor trailing-edge noise. It is found that helicopter broadband noise scales with the 4.5th to 5.0th power of the tip Mach number in which the range is determined by the typical helicopter collective pitch angle in operation. Detailed trend analyses of noise levels as a function of frequency are presented in terms of the collective pitch angle, twist angle, rotor solidity, rotor radius, disk loading, and number of blades. It is found that the collective pitch angle, twist angle, and chord length make noticeable impacts on low- and midfrequency noise. Finally, a semianalytic model is presented to predict the directivity and geometric attenuation of rotor trailing-edge noise.

Modelling, simulation and evaluation of ground vibration caused by rail vehicles

ABSTRACTThere is a great need to develop rail networks over long distances and within cities as more sustainable transport options. However, noise and vibration are seen as a negative environmental consequence. Compared with airborne noise, the related problem of ground vibration is much more complex. The properties of the ground vary significantly from one location to another. There is no common assessment criterion or measurement quantity and no equivalent to the noise maps. Ground-borne vibration is transmitted into buildings and perceived either as feelable whole-body vibration or as low frequency noise; it can also affect sensitive equipment but it is generally at a level that is too low to cause structural or cosmetic damage to buildings. A review is given of evaluation criteria for both feelable vibration and ground-borne noise, empirical and numerical prediction methods, the main vehicle and track parameters that can affect the vibration levels and a range of possible mitigation methods.

Modulation Effect of Slotted Structure on Vibration Response in Electrical Machines

Analytical method for vibration and noise prediction in electrical machines is computationally efficient and widely used. In conventional analytical approaches, the slotted stator is simplified as a cylinder, and it is generally believed that the vibration is more sensitive to the air-gap forces with low spatial orders, hence, those high-order air-gap forces are usually neglected. In this paper, the force distribution on the slotted stator is analyzed using a force transformation model and a new phenomenon, i.e., the modulation effect, is found, which indicates that a high-order air-gap force could also induce a low-mode stator vibration with a large amplitude. As a result, the conventional analytical methods are not so accurate for machines with a strong modulation effect, such as fractional-slot concentrated-winding machines. The existence condition for the modulation effect is also discussed in this paper. Finite-element analysis and experiments have been done to verify the analysis results.

Performance Evaluation of Distance Measurement Methods for Construction Noise Prediction Using Case-Based Reasoning

Concerns over environmental issues have recently increased. Particularly, construction noise in highly populated areas is recognized as a serious stressor that not only negatively affects humans and their environment, but also construction firms through project delays and cost overruns. To deal with noise-related problems, noise levels need to be predicted during the preconstruction phase. Case-based reasoning (CBR) has recently been applied to noise prediction, but some challenges remain to be addressed. In particular, problems with the distance measurement method have been recognized as a recurring issue. In this research, the accuracy of the prediction results was examined for two distance measurement methods: The weighted Euclidean distance (WED) and a combination of the Jaccard and Euclidean distances (JED). The differences and absolute error rates confirmed that the JED provided slightly more accurate results than the WED with an error ratio of approximately 6%. The results showed that different methods, depending on the attribute types, need to be employed when computing similarity distances. This research not only contributes an approach to achieve reliable prediction with CBR, but also contributes to the literature on noise management to ensure a sustainable environment by elucidating the effects of distance measurement depending on the attribute types.

Multi-objective design optimization of a high efficiency and low noise blower unit of a car air-conditioner

Car air-conditioners consist of a blower unit and a heater unit. A blower unit sends wind to a heater unit, and a heater unit adjusts the temperature inside the vehicle. Blower units of car air-conditioners are required to be smaller, lighter, noiseless, and power-saving. However, it is difficult and expensive to predict the noise directly by computational fluid dynamics simulation. Hereupon, this study employs an indirect noise prediction method based on a noise prediction theory to evaluate noise for blower units inexpensively. This method is investigated through a comparison with actual sound pressure level measurement. Then, using this method, this study moves to design optimization of a blower unit of car air-conditioners. The optimization aims to improve total pressure efficiency and sound pressure level from the current design that has been employed for a real commercial vehicle. This study employs a genetic algorithm to explore global optima in a two-objective problem. The present genetic algorithm is assisted by the Kriging surrogate model to reduce computational cost required for evaluating objective functions. The optimization results indicate that the optimized blower unit involves a multi-blade fan with the high chord-pitch ratio to decrease the loss of total pressure efficiency, which is often induced by the flow separation on the blade and the swirling flow on the meridional plane. In addition, the sound pressure level of blower unit can be reduced by decreasing the local flow velocity on the meridian plane due to a blockage factor. A blower unit, which has a scroll with a large tongue angle, shows high total pressure efficiency because the increase in eddy loss is suppressed at the tongue. They suggest the importance of the matching of multi-blade fan and scroll to achieve the good overall performance of a blower unit.

A Pass-By Noise Prediction Method Based on Source-Path-Receiver Approach Combining Simulation and Test Data

<div class="section abstract"><div class="htmlview paragraph">Optimizing noise control treatments in the early design phase is crucial to meet new strict regulations for exterior vehicle noise. Contribution analysis of the different sources to the exterior acoustic performance plays an important role in prioritizing design changes. A method to predict Pass-by noise performance of a car, based on source-path-receiver approach, combining data coming from simulation and experimental campaigns, is presented along with its validation. With this method the effect of trim and sound package on exterior noise can be predicted and optimized.</div></div>

Development of an inland waterway traffic noise prediction model considering water surface adsorption and embankment shielding influences

This paper proposed an improved prediction method of inland waterway vessel noise considering the effects of water surface adsorption and embankment shielding. The method was established on the basis of the UK Calculation of Road Traffic Noise (CoRTN) method, and the effects of water surface adsorption and embankment shielding were integrated into the governing equations. The developed method was validated using the data measured at the 40 monitoring points along Da Yunhe Channel in China. The results showed that the improved method had a higher accuracy and precision than that of the unmodified CoRTN method. The predicted noise exposure level by the unmodified CoRTN method correlated with the measured values with an R2 of 0.74569, which was enhanced to 0.86457 by the improved method. The current research is the prime to forecast river vessel noise level on the basis of the CoRTN method considering water surface adsorption and embankment shielding influences in China. It is expected that the modified method could be a new tool for estimating vessel noise effect on the inhabitant around the urban inland waterways.

Selection of a leading edge noise prediction method for PNoise

Wind energy expansion is worldwide followed by various limitations, i.e. land availability, the NIMBY (not in my backyard) attitude, interference on birds migration routes and so on. This undeniable expansion is pushing wind farms near populated areas throughout the years, where noise regulation is more stringent. That demands solutions for the wind turbine (WT) industry, in order to produce quieter WT units. Focusing in the subject of airfoil noise prediction, it can help the assessment and design of quieter wind turbine blades. Considering the airfoil noise as a composition of many sound sources, and in light of the fact that the main noise production mechanisms are the airfoil self-noise and the turbulent inflow (TI) noise, this work is concentrated on the latter. TI noise is classified as an interaction noise, produced by the turbulent inflow, incident on the airfoil leading edge (LE). Theoretical and semi-empirical methods for the TI noise prediction are already available, based on Amiet’s broadband noise theory. Analysis of many TI noise prediction methods is provided by this work in the literature review, as well as the turbulence energy spectrum modeling. This is then followed by comparison of the most reliable TI noise methodologies, qualitatively and quantitatively, with the error estimation, compared to the Ffowcs Williams-Hawkings solution for computational aeroacoustics. Basis for integration of airfoil inflow noise prediction into a wind turbine noise prediction code is the final goal of this work.

An advanced joint time-frequency analysis procedure to study cavitation-induced noise by using standard series propeller data

Underwater noise has attracted significant amount of interest in the last decade because of its potential impact on marine fauna. Commercial shipping is one of the major contributors. Amongst various sources on-board, cavitation dominates the overall radiated noise levels beyond its inception. Besides its significance, the mechanisms driving cavitation related noise and frequency regions that certain cavitation dynamics contribute into are not studied sufficiently. To address this gap in the literature, a study has been conducted to provide means of a plausible propeller cavitation noise prediction method and to provide enhanced insight to the noise creating mechanisms of cavitation by applying appropriate signal processing methods.Within this framework this study presents an advanced joint time-frequency analysis procedure to study cavitation-induced noise by using standard series propeller data. Systematic cavitation tunnel test are conducted with 6 members of the Meridian Standard propeller series that are carefully chosen to study the influence of major propeller design parameters such as Blade Area Ratio (BAR), Pitch to Diameter (P/D) ratio and blade number. Moreover, these propellers are tested behind systematically varied wake inflows reproduced by wake screens in addition to the open water conditions. Synchronized pressure pulse and noise measurements in combination with high-speed cavitation observations are then utilized to develop an advanced cavitation dynamics analysis tool to provide better insight into cavitation-induced noise. The analysis of the measurements has shown the significance of the cavitation on radiated noise levels and the impact of different cavitation dynamics in certain frequency regions.

A six-category heavy vehicle noise emission model in free-flowing condition

Annoyance and sleep disturbance caused by transportation noise are frequently associated with heavy vehicles. The ability to accurately predict heavy vehicle noise impact using conventional road traffic noise prediction methods has reduced over the years as the variety of heavy vehicles have increased progressively and the predominant long haul freight vehicle is trending towards larger trucks with a greater number of axles. In this paper, a six-category heavy vehicle source emission model in free-flowing condition has been developed based on the state-wide road setting in New South Wales, Australia. The six-category model allows traffic noise across the road network, carrying a diverse fleet of heavy vehicles, to be predicted with notably higher accuracy and precision in comparison to conventional models that aggregate heavy vehicles into one, or at most, two distinct categories. A comparative analysis is carried out to examine the source emission from various traffic mix scenarios in urban areas and along major freight routes. Current findings also highlight the importance of distinguishing regional characteristics in a harmonised road traffic noise prediction model.

Numerical and experimental study on noise reduction of concrete LRT bridges

Rolling noise and structure-borne noise radiating from the bridge are two major sources of noise in light rapid transit (LRT) bridges. To control the noise radiation from LRT bridges, an efficient numerical method for noise prediction is needed. In this study, a combined three-dimensional dynamic model and 2.5-dimensional acoustic model were used to investigate noise reduction in a rail and in a U-shaped girder bridge. The effects of three noise mitigation measures on noise control were then compared: installation of a noise barrier, use of a rail pad with a lower stiffness, and use of a floating ladder track. The corresponding noise reduction was investigated using the numerical method. A field test was conducted to validate the noise reduction effects. It was found that the noise barrier was more effective in reducing the rail noise, and the soft rail pad is more effective to control the bridge noise. The floating ladder track can significantly reduce bridge vibration, but the excessive vibration of the ladder track itself became another major noise source. The findings should guide the selection of appropriate mitigation measures for noise reduction in LRT bridges.

Progress in prediction of jet noise and quantification of aircraft/engine noise components

The bypass ratio of newer turbofan engines has been increasing steadily and has reached ∼10; even higher bypass ratios are being considered for improving aircraft fuel efficiency. An accurate method for the prediction of jet noise over a wide range of bypass ratio, from ∼5 to ultra-high bypass ratios (∼20), is required to address current and future needs. The main objective of the current study is the development of a procedure for real-world application that would permit the accurate prediction of jet noise, which in turn would enable the quantification of the non-jet noise component. A new empirical method for prediction of noise from realistic dual-stream jets is developed and validated against an extensive database acquired at model scale; the range of validity covers a velocity ratio ( Vs/Vp) ≥ ∼0.6, as this is the range of interest in real turbofan engines. Accurate absolute spectral predictions at all angles and all cycle conditions are first demonstrated at model scale. The same method is then extended to full-scale predictions, both from static engine tests and airplane flyover tests. The range of Strouhal number of interest in full-scale tests spans ∼0.1 to ∼100. Nearfield effects on the jet noise from dual-stream jets have been quantified and a simple and improved procedure for incorporating spectral effects has been developed. Accurate spectral predictions are obtained for noise from static engine tests and flyover tests, over a wide range of engine operating conditions and bypass ratio. Therefore, the good quality and accuracy of the new prediction method have been confirmed at both model scale and full scale, with and without forward flight. An absolute prediction takes ∼1 s on a workstation, as only a single scaling equation is utilized. The application of the new prediction method in gaining better quantification and understanding of the non-jet noise components, and their reduction, is described.

Emission surfaces and noise prediction from rotating sources

An accurate and efficient prediction method for noise emanating from rotating sources such as helicopter rotors and aircraft propellers, is presented. Combining bifurcation analysis of the retarded time equation with different emission surface topologies, a new Emission Porous Surface (EPS) algorithm has been developed. The algorithm can be used in the framework of hybrid methods that combine Computational Fluid Dynamics, for noise generation, and integral formulations for noise propagation. A panel-by-panel reconstruction of the supersonic emission surface is also proposed, which allows to manage an unstructured mesh. The noise prediction method is applied to the analysis of the UH1H rotor in strong shock delocalization conditions, a well known and extensively studied case of High Speed Impulsive (HSI) noise. The present results are compared with experimental and numerical data available in literature.

Rotor Airload and Acoustics Prediction Based on CFD/CSD Coupling Method

An advanced airload and noise prediction method based on computational fluid dynamics/computational structural dynamics (CFD/CSD) coupling for helicopter rotor has been developed in this paper. In the present method, Navier-Stokes equation is applied as the governing equation, and a moving overset grid system is generated in order to account for the blade motions in rotation, flapping and pitching. The blade structural analysis is based on 14-DOF Euler beam model, and the finite element discretization is conducted on Hamilton's variational principle and moderate deflection theory. Aerodynamic noise is calculated by Farassat 1A formula derived from FW-H equation. Using the developed method, numerical example of UH-60A is performed for aeroelastic loads calculation in a low-speed forward flight, and the calculated results are compared with both those from isolated CFD method and available experimental data. Then, rotor noise is emphatically calculated by CFD/CSD coupling method and compared with the isolated CFD method. The results show that the aerodynamic loads calculated from CFD/CSD method are more satisfactory than those from isolated CFD method, and the exclusion of blade structural deformation in rotor noise calculation may cause inaccurate results in low-speed forward flight state.

A Semi-Empirical Prediction Method for Broadband Hull-Pressure Fluctuations and Underwater Radiated Noise by Propeller Tip Vortex Cavitation †

A semi-empirical method is presented that predicts broadband hull-pressure fluctuations and underwater radiated noise due to propeller tip vortex cavitation. The method uses a hump-shaped pattern for the spectrum and predicts the centre frequency and level of this hump. The principal parameter is the vortex cavity size, which is predicted by a combination of a boundary element method and a semi-empirical vortex model. It is shown that such a model is capable of representing the variation of cavity size with cavitation number well. Using a database of model- and full-scale measured hull-pressure data, an empirical formulation for the maximum level and centre frequency has been developed that is a function of, among other parameters, the cavity size. Acceptable results are obtained when comparing predicted and measured hull-pressure and radiated noise spectra for various cases. The comparison also shows differences that require adjustments of parameters that need to be further investigated.

High-speed switched reluctance machine: natural frequency calculation and acoustic noise prediction

In this study, an analytical model is proposed for natural frequency calculation and acoustic noise prediction for high speed switched reluctance machines. The developed natural frequency model results are compared with the mechanical finite element analysis results in terms of 6 different mode shapes that cause the majority of the acoustic noise in switched reluctance machines. The results show that the analytical results are consistent with the numerical method results with minimum 90% matching. Based on the natural frequency calculation model, a new acoustic noise prediction method is developed that only needs a radial force waveform as an input emerging on stator pole surfaces. The comparison of the developed and the numerical results clearly indicates that the acoustic noise level of the switched reluctance machine can be effectively found during the design process without using time-consuming numerical methods.

Road traffic noise abatement scenarios in Gothenburg 2015 – 2035

Exposure to high levels of road traffic noise at the most exposed building facade is increasing, both due to urbanization and due to overall traffic increase. This study investigated how different noise reduction measures would influence the noise exposure on a city-wide scale in Gothenburg, a city in Sweden with approximately 550,000 inhabitants. Noise exposure was estimated under several different scenarios for the period 2015–2035, using the standardized Nordic noise prediction method together with traffic flow measurements and population statistics. The scenarios were based on reducing speed limits, reducing traffic flows, introducing more electrically powered vehicles and introducing low-noise tires and pavements. The most effective measures were introducing low-noise tires or pavements, which in comparison to business as usual produced between 13% and 29% reduction in the number of inhabitants exposed above 55 dB equivalent level.

Generalized flow-generated noise prediction method for multiple elements in air ducts

Unavoidable discontinuities due to in-duct elements in a ventilation ductwork system result in the generation of localized turbulence. Some of the turbulence energy is converted into noise. The flow-generated noise problem caused by in-duct elements is due to the complicated acoustic and turbulent interactions of multiple in-duct flow noise sources. Prediction of the flow-generated noise at the design stage is important in engineering, since it is almost impossible to solve the problem after the installation of a ventilation ductwork system. The measurement and computational fluid dynamics simulation can provide an accurate prediction but are expensive in terms of resources. There is an urgent need for developing a practical prediction method for the flow-generated noise in air ducts. Current design guides only provide a prediction method for aerodynamic sound produced by a single in-duct element in the ventilation system, which is usually not in accord with actual systems. An interaction factor βm is therefore proposed to take account of the interaction effects of multiple in-duct elements. Experimental measurements were conducted to verify the proposed prediction results. The predicted results show an acceptable agreement with the measurements. The proposed method provides engineers a practical generalized technique for predicting noise produced by multiple in-duct elements.

Aircraft Noise Assessment—From Single Components to Large Scenarios

The strategic European paper “Flightpath 2050” claims dramatic reductions of noise for aviation transport scenarios in 2050: “...The perceived noise emission of flying aircraft is reduced by 65%. These are relative to the capabilities of typical new aircraft in 2000...”. There is a consensus among experts that these far reaching objectives cannot be accomplished by application of noise reduction technologies at the level of aircraft components only. Comparably drastic claims simultaneously expressed in Flightpath 2050 for carbon dioxide and NOX reduction underline the need for step changes in aircraft technologies and aircraft configurations. New aircraft concepts with entirely different propulsion concepts will emerge, including unconventional power supplies from renewable energy sources, ranging from electric over hybrid to synthetic fuels. Given this foreseen revolution in aircraft technology the question arises, how the noise impact of these new aircraft may be assessed. Within the present contribution, a multi-level, multi-fidelity approach is proposed which enables aircraft noise assessment. It is composed by coupling noise prediction methods at three different levels of detail. On the first level, high fidelity methods for predicting the aeroacoustic behavior of aircraft components (and installations) are required since in the early stages of the development of innovative noise reduction technology test data is not available. The results are transferred to the second level, where radiation patterns of entire conventional and future aircraft concepts are assembled and noise emissions for single aircraft are computed. In the third level, large scale scenarios with many aircraft are considered to accurately predict the noise exposure for receivers on the ground. It is shown that reasonable predictions of the ground noise exposure level may be obtained. Furthermore, even though simplifications and omissions are introduced, it is shown that the method is capable of transferring all relevant physical aspects through the levels.

A time-domain method for prediction of noise radiated from supersonic rotating sources in a moving medium.

This paper presents a time-domain method for noise prediction of supersonic rotating sources in a moving medium. The proposed approach can be interpreted as an extensive time-domain solution for the convected permeable Ffowcs Williams and Hawkings equation, which is capable of avoiding the Doppler singularity. The solution requires special treatment for construction of the emission surface. The derived formula can explicitly and efficiently account for subsonic uniform constant flow effects on radiated noise. Implementation of the methodology is realized through the Isom thickness noise case and high-speed impulsive noise prediction from helicopter rotors.