Scanning paths for estimating sound power of noise sources by sound intensity scanning method

A mathematical model of deterndulng sound power by using the scanning method is developed. It is assumed that the scanning speed is constant and the noise source is stationary The accuracy of estimating sound power along some simple paths on the surfaces such as rectangle, disc and hemisphere is analyzed. It is argued that the accuracy of estimating sound power is strongly depended on a suitable selection of scan path. The accurate estdriation of sound power can be made by scanning along some simple paths.

Prediction of propeller non-cavitation noise by superimposing shifted sound signal from an isolated blade

The time-cost of the propeller non-cavitation noise prediction can be greatly re- duced by the isolated blade method, which is validated via hybrid URANS and acoustic analogy, followed by the acoustic characteristics of propeller in time domain are analyzed. Firstly, we predicted the sound of the E779A propeller operating in uniform inflow and found a typical periodic characteristic of the sound pressure distribution on propeller blade as well as the sound signal of the receiver, and the result by the superimposing shifted sound signal from an isolated blade （isolated blade method） agreed well with the result by the integration on total blades, which validated the credibility of the isolated blade method in uniform inflow. Finally, we pre- dicted the sound of a propeller running in the wake of submarine by the isolated blade method, and the result also agreed well with the result by the integration on total blades, which further indicated that the isolated blade method was also applicable for the non-cavitation noise prediction of the propeller running in non-uniform inflow. The noise prediction of the counter-rotating propeller, the pump-jet can also benefit from this method.

Correlation Research between Turbulent Pressure Pulsation and Internal Sound Field Characteristics of Centrifugal Pump

In order to study the correlation between the internal flow noise of the centrifugal pump and the turbulent pressure pulsation,a single-stage single-suction centrifugal pump was used as the research object by the combination of numerical calculation and experiment.Based on the RNG k-?model and the N-S equation,the model pump was simulated numerically by CFD.A dipole sound source was extracted by the turbulent pulse action of the volute wall surface according to the FW-H equation.The acoustic field of the model pump was solved on the basis of the boundary element method,and the sound pressure distribution of the internal flow field under the action of the dipole sound source of the volute wall and the frequency response of the inlet and outlet fields were obtained.The results show that the distribution of hydrodynamic noise inside the centrifugal pump is related to the pressure pulsation,presenting obvious dipole distribution and disturbance at the tongue.The sound pressure value of the field is mainly concentrated in the blade passing frequency and double frequency,in which the blade passing frequency is the strongest,and the sound pressure value decreases obviously under other double frequency.The main frequency of hydrodynamic noise is the blade passing frequency.