Through rneasuring & analysing the noise of five hammer mills the authorsproved that the dominant noise source of hammer mill under rated loas&no load condi-tions was aerodynamic noise,and could be subclassified as rotation noise.
The author analyzed the results of noise measurement and identified the noise sources of the FFC-23A disk mill made in Jimo agricultural machinery works of Shandong Province in this paper. Also, the noise spectrum of three other model disk mills was analyzed. The primary noise source of disk mill falls un-der the aerodynamic noise and mainly the rotation noise.
In order to obtain the equivalent sound source center of a propeller rotating noise for noise control,the investigation is concerned with the theory based on a cross-spectrum method and the experiment based on time average and space average.
As an example,the measurement of the equivalent sound source center of the propeller rotating noise on the light aircraft AD-200 has been carried out and the results of the measurement are satisfactory.
A simple semi-empirical noise predicting equations are presented in this paper, which could be used respectively to predict rotating noise, wide-band Noise and total sound power level. A axial fan (T-40-No. 3 1/2) is experimentally messured and predicted by these equations the results are agreeable.
Based on Farassat Formulation 1A for subsonic time domain, a method which is valid for arbitrary observer position and all linear flight conditions is developed in this paper to predict the rotor rotational noise.
The theories and methods presented in the paper can be used to predict the rotary noise level of acentrifugal fan and the effect of the structural and flow feild parameters of the fan on the rotary noiselevel so that those provide theoretical basis and method for optimizing design of the centrifugal fan inair dynamic acoustics.
A new non-isometric impeller is gotten by analyzing the sound pressure level spectra of non-isometric impellers, and the new non-isometric impeller can reduce the rotary noise of the cross-flow fan of air-conditioner effectively.