Calculation Of Sound Pressure Level Research Articles

Numerical investigation on the use of various blade tips for the helicopter's main rotor blade in forward flight regarding aerodynamic performance and HSI noise considerations

The goal of this research is to investigate aerodynamic performance and high-speed impulsive (HSI) noise of various blade tips for the helicopter's main rotor in forward flight. For this purpose, three-dimensional compressible flow field around the rotor blades is numerically simulated by the solution of the unsteady Reynolds averaged Navier-Stokes (URANS) equations with the "SST k-ω" turbulence model. Solution is quantified by the calculation of torque, drag, and thrust coefficients of CQ, CD, CT, and L/D ratio. HSI noise on the rotor plane is assessed by the calculation of sound pressure level at certain points of the flow field using the Ffowcs Williams-Hawking (FW-H) equation. Blade tips are eleven and include anhedral, dihedral, Eagle and combinations of them, and also Blue Edge and rectangular. The combinations are inspired by the tip configurations of the fixed wings. In this regard effects of the tip geometry parameters including curvature and height of its parts have been considered as well. All of the tips are examined for two flight conditions of Caradonna and Tung two-blade rotor with fixed pitch angle and time-varying pitch angles. Based on the present results, it is found that blade tips of dihedral family do not improve the aerodynamic performance of the helicopter blade. Also, addition of anhedral part to the blade tip improves the L/D ratio. According to the present acoustic analysis, it was seen that after the Blue Edge, the Eagle tip stands in order of priority. For the condition of Caradonna and Tung two-blade rotor with tip Mach number of 0.8 and advance ratio of 0.2, HSI noise of the Eagle-tip blade decreases by 2.39 % compared to that of the two-blade rotor with rectangular tip. However, the aerodynamics performance of the Eagle tip is much better than that of the Blue Edge.

Ensuring safe working conditions during manual abrasive processing of welded joints of frame elements of transport vehicles

One of the essential problems of current mechanical engineering is the re-duction of noise and vibration of technological processes. Excessive noise not only leads to the developing of operator illnesses, but is also an indicator of the poor quality of the final product. The article deals with the problem of reducing hazardous and harmful production factors during manual processing of welded joints of vehicle body elements. An obligatory stage after welding is the mechanical abrasive treatment of welded joints to remove stress concentrators and straighten the profile. The existing technology uses a hand-held grinder, which creates a lot of noise and vibration and reduces the accuracy of welding seams. It is shown that with the existing technology, the noise levels are exceeded in the frequency range of 250…8000 Hz and reach 20 dB. To reduce the noise level, theoretical results were obtained for the dependences of the vibrational velocities of the abrasive tool and the results of experimental studies of the noise and vibration spectra during manual abrasive processing of welded seams of body structures. Obtained mathematical models enable the calculation of sound pressure level for abrasive processing. A scheme of a device is proposed that makes it possible to reduce the level of sound pressure during manual abrasive processing of welded seams of frame structures and its advantage over vibration damping coatings is presented. The combination of an integrated approach and protective equipment can decrease the sound pressure level by as much as 30 dB.

Selected Approaches to the Assessment of Environmental Noise from Railways in Urban Areas.

Rail transport is the second most important way of transporting people and freights by land in the European Union. Rail noise affects around 12 million people in the European Union during the day and around 9 million at night. There are two possible ways to assess environmental noise: noise measurement in situ and prediction using mathematical models. The aim of the work is based on the performed measurements and selected noise predictions to evaluate the accuracy of the prediction models and assess their sensitivity to various aspects. Two measuring points in the Banská Bystrica Self-Governing Region, within Slovakia, were selected for measurement, which is characterized by increased mobility of the population. For prediction, the two methodologies were selected (Schall 03 and Methodical instructions for the calculation of sound pressure level from transport). The results show that the Schall 03 method is sensitive to the measurement location (the value reaches half of the significance level) and to the location–period interaction. The second prediction method is sensitive to systematic error (absolute term) and, such as Schall 03, to the location–period interaction. This method systematically overestimates the results. Results showed greater accuracy of both prediction models compared to the measured noise values than the results of the authors in other countries and conditions.

Measurement and Prediction of Railway Noise Case Study from Slovakia.

The paper deals with comparing the measurement of noise from the railroads in the residential zone of the town of Zvolen with the results calculated using the prediction methods “Schall 03“ (Deutsche Bundesbahn, 1990) and “Methodical instructions for the calculation of sound pressure level from transport” (MPVHD). The first is used in the Slovakia and second in the Czech Republic. The measurement results and the results obtained from the prediction methods for both measurement locations were evaluated graphically and statistically. The evaluation of the conformity of the measurement with the prediction showed that the results obtained using the method “Schall 03” are in better agreement with the measurement.

Wind turbine low frequency and infrasound propagation and sound pressure level calculations at dwellings.

This study was developed to estimate wind turbine low frequency and infrasound levels at 1238 dwellings in Health Canada's Community Noise and Health Study. In field measurements, spectral peaks were identifiable for distances up to 10 km away from wind turbines at frequencies from 0.5 to 70 Hz. These measurements, combined with onsite meteorology, were in agreement with calculations using Parabolic Equation (PE) and Fast Field Program (FFP). Since onsite meteorology was not available for the Health Canada study, PE and FFP calculations used Harmonoise weather classes and field measurements of wind turbine infrasound to estimate yearly averaged sound pressure levels. For comparison, infrasound propagation was also estimated using ISO 9613-2 (1996) calculations for 63 Hz. In the Health Canada study, to a distance of 4.5 km, long term average FFP calculations were highly correlated with the ISO based calculations. This suggests that ISO 9613-2 (1996) could be an effective screening method. Both measurements and FFP calculations showed that beyond 1 km, ISO based calculations could underestimate sound pressure levels. FFP calculations would be recommended for large distances, when there are large numbers of wind turbines, or when investigating specific meteorological classes.

Calculation of sound pressure level of marine propeller in low frequency

The research performed in this paper is carried out to calculate the sound pressure level of the marine propeller by Reynolds-Averaged Navier–Stokes solver in low frequencies band. Noise is generated by the induced trailing vortex wake and induced pressure pulses. The two-step Fflowcs Williams and Hawkings equations are used to calculate hydrodynamic pressure and its performance as well as sound pressure level at various points around the propeller. The directivity patterns of this propeller and accurate explanation of component propeller noise are discussed. Comparison of the numerical results shows good agreement with the experimental data.

The fuzzy two-load method for measurement of ducted one-port source characteristics

Knowledge of source characteristics is important for the calculation of sound pressure level and insertion loss of a silencer in sourced ducts. Measurement is usually the only feasible approach for the determination of source characteristics. The present paper is concerned with the measurement methods based on the Helmholtz-Thévenin equivalent of ducted one-port plane wave sources. Existing methods are classified as crisp and over-determined methods. In the crisp methods, the measured data are just sufficient for unique characterization of the source. This calls for two loads if their phase relative to the source is known, otherwise three loads are required. Over-determined methods use more number of loads than the crisp methods and are motivated for possible minimization of variations due to measurement errors. The point estimates for the source parameters are, however, still subject to some uncertainty, but estimation of confidence intervals is not feasible because the loads do not constitute a probability sample. The present paper proposes an approach which can yield the source characteristics in intervals from auto-power spectral density measurements with only two loads. The method is based on a novel Apollonian circle formulation. It is called the fuzzy two-load method, because uncertainty inherent to measurements is modelled by fuzzification of a characteristic parameter of the Apollonian circle of two loads. Fuzzy number transformations leading to the source pressure strength, sound pressure level and insertion loss interval predictions are discussed in depth. The paper includes an application showing the working features of the fuzzy two-load method.

Wind turbine sound pressure level calculations at dwellings.

This paper provides calculations of outdoor sound pressure levels (SPLs) at dwellings for 10 wind turbine models, to support Health Canada's Community Noise and Health Study. Manufacturer supplied and measured wind turbine sound power levels were used to calculate outdoor SPL at 1238 dwellings using ISO [(1996). ISO 9613-2-Acoustics] and a Swedish noise propagation method. Both methods yielded statistically equivalent results. The A- and C-weighted results were highly correlated over the 1238 dwellings (Pearson's linear correlation coefficient r > 0.8). Calculated wind turbine SPLs were compared to ambient SPLs from other sources, estimated using guidance documents from the United States and Alberta, Canada.

Effect of Planform Aspect Ratio on Flow Oscillations in Rectangular Cavities

An experimental investigation was undertaken to examine the effect of cavity lateral width on the flow oscillations that occur in an open cavity placed within a turbulent subsonic boundary layer. A rectangular cavity with a length to depth ratio L/D=1 and planform aspect ratio L/W=0.115 was placed within a thick turbulent boundary layer with a corresponding Reθ=10.5×103. Pressure time histories were acquired at six separate cavity widths (or L/W values) using microphone-type pressure transducers. The spectral character of these signals was analyzed and the pressure levels and dominant frequencies determined. This study indicates that large changes in the pressure level occur as L/W varies from 0.115 to 0.682. A state of fluid dynamic resonance was observed at L/W=0.137 and fluid–acoustic resonance at L/W=0.682, the smallest cavity width. Relative sound pressure level calculations indicate that the energy within the cavity compared with that of the boundary layer, was observed to increase by approximately 40 percent at L/W=0.137. [S0098-2202(00)00601-5]

Pressure Oscillations in a Subsonic Cavity at Yaw

An experimental investigation was undertaken to examine the effect of yaw angle on flow oscillations that occur in an open cavity placed within a subsonic boundary layer. A rectangular cavity with a length-to-depth ratio of unity and a planform aspect ratio of 8.7 was placed within a thick turbulent boundary layer with a corresponding Reynolds number based on the momentum thickness of 10.5 × 10 3 . Pressure time histories were acquired at 15 separate yaw angles using microphone-type pressure transducers. The spectral character of these signals was analyzed, and the pressure levels and dominant frequencies were determined. This study indicates that large changes in the pressure level occur as the yaw angle is changed from 0 to 70 deg. A state of resonance was observed at an angle of 60 deg. Relative sound pressure level calculations indicate that the energy within the cavity increased more than seven times at this orientation. Evidence suggesting a critical angle of approximately 60 deg, as well as mode switching from a fluid dynamic mode to a fluid acoustic mode, is also presented.

Low-frequency sound propagation modeling over a locally reacting boundary with the parabolic approximation

There is substantial interest in the analytical and numerical modeling of low-frequency, long-range atmospheric acoustic propagation. Ray-based models, because of their frequency limitations, do not always give an adequate prediction of quantities such as sound-pressure or intensity levels. However, the parabolic approximation method, widely used in ocean acoustics and often more accurate than ray models for frequencies of interest, can be applied to this type of acoustic propagation in the atmosphere. Modifications of an existing implicit finite-difference implementation for computing solutions to the parabolic approximation are discussed. A locally reacting ground surface is used with one- and two-parameter impedance models, while a nonreflecting boundary condition is used to handle the upper boundary. Relative sound-pressure level calculations are performed for a number of flow resistivity values in both homogeneous and nonhomogeneous atmospheres. Comparisons to experimental data are made which suggest this modeling approach can be useful in the study of these types of propagation problems.

Bruit des avions légers : réduction du rayonnement acoustique d'une hélice

This paper deals with an acoustic and aerodynamic parametrical study of a light airplane propeller. The aim of this study is to obtain a decrease of noise level with checking the performances. Flyover sound generation is analysed through an analytical formulation which is a sum of blade passing frequency harmonics. D. B. Hanson's formulation used for sound pressure level calculations is coupled with aerodynamic investigations which are carried out with a model based on lifting line theory. In the first part, the accuracy of the acoustic method is achieved with experimental measurement comparison. Next, propeller geometry parametrical study shows the influence of number of blades and scale blade factor modifications. The most suitable solution to provide the same performances with a reduction of noise is obtained by performing the best compromise between acoustics and aerodynamics

Sound-pressure level calculations using the RRA algorithm for depth-dependent speeds of sound valid at turning points and focal points

Sound-pressure level (SPL) calculations are made along individual ray paths for arbitrary, one-dimensional, depth-dependent speeds of sound using an enhanced version of the RRA (recursive ray acoustics) algorithm. The SPL calculations are valid (i.e., finite) at turning points and focal points and do not require the use of Airy functions. The SPL calculations include the effects of frequency-dependent volume attenuation and frequency-dependent attenuation due to surface and bottom reflections. The ocean surface and bottom are treated as boundaries between viscous fluid media. Although the ocean surface is modeled as a planar boundary, the bathymetry is an arbitrary function of horizontal range. Sound speed versus depth and bathymetric data are represented by orthogonal function expansions. Computer simulation results from preliminary test cases are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Sound-pressure level calculations using the RRA algorithm for depth-dependent speeds of sound valid at turning points and focal points

Sound-pressure level (SPL) calculations are made along individual ray paths for one-dimensional, depth-dependent, speeds of sound using an enhanced version of the recursive ray acoustics (RRA) algorithm. The SPL calculations are valid (i.e., finite) at turning points and focal points and do not require the use of Airy functions. The SPL calculations include the effects of frequency-dependent volume attenuation and frequency-dependent attenuation due to surface and bottom reflections. The ocean surface and bottom are treated as boundaries between viscous fluid media. Although the ocean surface is modeled as a planar boundary, the bathymetry is an arbitrary function of horizontal range. Sound speed versus depth and bathymetric data are represented by orthogonal function expansions. Computer simulation results from preliminary test cases are presented. [Work supported by NAVSEA.]

Diesel engine-radiated noise as function of engine type, intake and exhaust restriction, and operating load-speed schedule

The diesel engine itself is an important source of diesel-powered vehicle noise, and becomes dominant after proper treatment of intake/exhaust and cooling system noise at vehicle speeds below 50 miles per hour. An investigation was conducted to quantify the effects of intake and exhaust restrictions, and load-speed scheduling on the radiated noise from four diesel engines, i.e., four-cycle naturally aspirated, four-cycle turbocharged w/wo precombustion chamber, and two-cycle blower scavenged. All engines were inline six-cylinder and rated approximately 250 hp at 2100 rpm. Each engine was asymmetrically positioned in a reverberant chamber, and sound pressure measurements were obtained 3 ft from the engine. The noise associated with intake, exhaust, cooling, and their respective ducting systems was appropriately abated to permit quantification of engine-radiated noise. Dampers were placed in the intake and exhaust ducting systems for pressure regulation, and engine loads were applied with an electric dynamometer. Exhaust emission data including temperature were also monitored. The engine-radiated noise was not significantly affected by intake pressure restrictions up to 60 in H2O or exhaust restrictions up to 90 in. H2O, except with naturally aspirated engines. The precombustion chambered engine exhibited low sound output with respect to the mechanical power available under various load-speed conditions. The engine noise efficiency, defined as engine-radiated sound power/engine brake horsepower, has a minimum value for air-to-fuel ratios in the range 15:1 to 19:1, and its dependence on engine speed is most pronounced for turbocharged engines. The latter finding suggests the presence of noncombustion or mechanical-combustion related noise sources in turbocharged engines. Engine sound pressure level calculations, projected to 50 ft, were made from the engine noise data with the resulting A-weighted noise levels ranging from 74 to 85 dBA at rated engine speed.