Aerodynamic Noise Prediction Research Articles

Modeling and Prediction of Cutting Noise in the Face-Milling Process

A cutting noise prediction model is developed to relate the cutter-workpiece vibrations to the sound pressure field around the cutter in the high-speed face-milling process. The cutter-workpiece vibration data are obtained from a dynamic mechanistic face-milling force simulation model. The total noise predicted, based on both cutting noise and aerodynamic noise prediction, compares well to the noise observed experimentally in the face-milling process. Using the model, the effects of various machining and cutter geometry parameters are studied. It is shown that cutter geometry, machine dynamics, and cutting speed all play important roles in determining overall noise in face milling.

Use of Finite Element Methods in Frequency Domain Aeroacoustics

The linearized Euler equations are used widely in many aerodynamic noise prediction schemes. The linearized Euler equations also support instability waves, which can obscure the acoustic solution. An approach to suppress the instability waves is to solve the linearized Euler equations in the frequency domain. Also, the frequency domain approach is far less expensive compared to the time domain approach in terms of the computational time though only a single frequency can be computed at one time. The application and comparison of two unstructured grid methods for the solution of aeroacoustic problems in the frequency domain are presented. Algorithms are developed using the discontinuous Galerkin and the streamline upwind Petrov-Galerkin finite element methods in two spatial dimensions on conforming triangular meshes using nodal polynomial basis sets. Unlike other existing frequency domain solvers, no assumption is made regarding the nature of the mean flow. The application of the two methods to a two-dimensional benchmark problem involving the suppression of instability waves is presented. The two methods are compared in terms of the computational cost. It is concluded that the discontinuous Galerkin method is prohibitively more expensive compared to the streamline upwind Petrov-Galerkin method for aeroacoustic applications in the frequency domain using conforming meshes and nodal polynomials.

Numerical prediction of aerodynamic noise radiated from a cross-flow fan

The surface pressure fluctuations of blades, vortex wall, and the rear wall of a cross-flow fan are commonly considered as the aerodynamic noise sources of an air conditioning unit. In order to predict the noise, these pressure fluctuations were at first obtained by solving the 2D unsteady Reynolds-averaged Navier-Stokes (RANS) equations using a computational fluid dynamics software. It was validated by the fan performance experiments that the prediction of static pressure in the channel agreed well with the test data. It means the results of the pressure fluctuations obtained from the numerical simulation are correct. Then, the Ffowcs Williams-Hawkings (FW-H) equation was used to predict the far-field noise caused by these sources. The errors of the prediction of the sound-pressure levels of the blade passing frequency (BPF) and total noise are within 4 and 3 dB, respectively, comparing with the corresponding measured data. It is shown from the numerical prediction that only the surface pressure fluctuations of the rear wall and the vortex wall are main sources, and that the method of numerical prediction of aerodynamic noise radiated from a cross-flow fan is successful.

4124 騒音予測モデルを用いた貫流ファンの低騒音化(G05-11 翼・翼列,G05 流体工学)

4124 騒音予測モデルを用いた貫流ファンの低騒音化(G05-11 翼・翼列,G05 流体工学)

쓰로틀 밸브의 빠른 열림 동작에 의한 내부공력소음

For many industrial problems originating from aerodynamic noise, noise prediction techniques, reliable and easy to apply, would be of great value to engineers and manufacturers. General algorithm is presented for the prediction of internal flow-induced noise from quick opening throttle valve in an automotive engine. This algorithm is based on the integral formula derived by using the General Green Function, Lighthill's acoustic analogy and Curle's extension of Lighthill's. Novel approach of this algorithm is that the integral formula is so arranged as to predict frequency-domain acoustic signal at any location in a duct by using unsteady flow data in space and time, which can be provided by the Computational Fluid Dynamics Techniques. This semi-analytic model is applied to the prediction of internal aerodynamic noise from a throttle valve in an automotive engine. The predicted noise levels from the throttle valve show good agreement with actual measurements. The results show that the dipole noise is dominant in this phenomena and the origin of noise sources is attributed to the anti-vortex lines formed in the down-stream from a throttle valve. This illustrative computation shows that the current method permits generalized predictions of flow noise generated by bluff bodies and turbulence in flow ducts.

Prediction of Aerodynamic Noise Level of Cross-Flow Fans for Air Conditioners (2nd Report, Development of Cross-Flow Fans by means of Aerodynamic Noise Prediction Model)

A model for predicting the noise level of cross flow fans has been developed. This model uses the relative air-flow velocities on the outside of the fan's impeller. And it is based on two assumptions : (i) noise levels are in proportion to the relative velocities at the edge of the blade raised to the sixth power and (ii) the velocities on the outside of the fan's impeller have an especially close relation to the noise level. Computational fluid dynamics is used to obtain the necessary velocity field data for this model. It was found that the noise levels calculated by this model agree well with the measured noise levels of a test impeller. This agreement confirms that noise level of a conventional cross-flow fan can be predicted by this simple model, since relative velocity data is readily available from frequently executed computational analyses. Accordingly, the predicted noise level was then applied in the design of a new cross-flow fan. This new cross flow fan has a velocity field that produces a quiet flow. As a result, it has a lower noise level and higher performance.

An advanced time approach for acoustic analogy predictions

This paper deals with a new interpretation of the retarded time approach that is widely used in the prediction of acoustic fields from moving sources. A hierarchical inversion between the emission time and the reception time leads to advanced time approach. This consists in projecting the current status of a source in the observer time domain where the received signal is progressively built. The practical relevance of this methodology lies on two statements: no retarded time equations must be solved; an aerodynamic noise prediction can be processed parallelly to the aerodynamic computation. Theoretically, the advanced time approach differs from the retarded time approach only in one aspect. A signal emitted at a given instant by a point source, moving at subsonic as well as supersonic velocity, is received only one time by an observer moving at subsonic velocity. Consequently, only one value of the advanced time corresponds to a value of the emission time. The advanced time approach is herein applied to a retarded time solution of the Ffowcs Williams and Hawkings equation proposed by Farassat. The noise radiated by elementary acoustic sources in complex motion is then computed and checked against analytical solutions.

Applications of CFD Analysis to Aerodynamic Noise Prediction for Propeller Fans

Applications of CFD Analysis to Aerodynamic Noise Prediction for Propeller Fans

Landing Gear Aerodynamic Noise Prediction Using Unstructured Grids

Aerodynamic noise from a landing gear in a uniform flow is computed using the Ffowcs Williams-Hawkings (FW-H) equation. The time accurate flow data on the integration surface is obtained using a finite volume low-order flow solver on an unstructured grid. The Ffowcs Williams-Hawkings equation is solved using surface integrals over the landing gear surface and over a permeable surface away from the landing gear. Two geometric configurations are tested in order to assess the impact of two lateral struts on the sound level and directivity in the far-field. Predictions from the Ffowcs Williams-Hawkings code are compared with direct calculations by the flow solver at several observer locations inside the computational domain. The permeable Ffowcs Williams-Hawkings surface predictions match those of the flow solver in the near-field. Far-field noise calculations coincide for both integration surfaces. The increase in drag observed between the two landing gear configurations is reflected in the sound pressure level and directivity mainly in the streamwise direction.

Prediction of Aerodynamic Noise of Fans.

The aerodynamic and the noise characteristics of a centrifugal fan were obtained experimentally. Typical velocity components-for example absolute velocity and relative velocity-were caluculated from the characteristics of aerodynamics and the theory of fans. Changes in the typical velocity components with changes in the flow coefficient were converted to the change in the noise level by using 6th dependency of the power to the velocity and compared with the characteristics of noise. The results showed that the noise and the aerodynamic characteristics were closely correlated and showed that the principal velocity determining the noise level was relative velocity. A model for predicting the noise level of a centrifugal fan was described and its predictions were in good agreement with the measured levels.

The Impact of IEC 534-8-3 on Control Valve Aerodynamic Noise Prediction

The Impact of IEC 534-8-3 on Control Valve Aerodynamic Noise Prediction

Prediction and Reduction of Aerodynamic Noise generated by Circular Cylinders

Prediction and Reduction of Aerodynamic Noise generated by Circular Cylinders

On Numerical Prediction of Aerodynamic Noise of Turbulent Flow

On Numerical Prediction of Aerodynamic Noise of Turbulent Flow

Aerodynamic noise radiation from a circular cutting tool. Prediction of aerodynamic noise with Karman vortex.

The prediction of aerodynamic noise radiation from a circular cutting tool with a columnar tooth model is made. The noise level is calculated by a theoretical expression with the Karman Vortex model. Particularly, the change in the noise level with tooth length and tooth diameter is calculated. In the change of tooth numbers and tooth diameter, experimental values agreed qualitatively with the theoretical results. In the change of tooth length lx, a noise contribution rate Λ is adopted to express the transformation rate of fluctuated vortex circulation around the tooth into the sound pressure. By applying Λ=1.26lx-0.25 to the theoretical equation, the calculated results agreed with experimental values of the noise level within 2 dB difference.

The effect of motion on acoustic dipole models for aerodynamic noise prediction

The effect of motion on acoustic dipole models for aerodynamic noise is shown to greatly alter their directivity patterns. When this effect is included in an analysis of airframe noise measurements, directivity patterns computed with acoustic surface dipoles are in better agreement with observations than those obtained with edge dipole sources.