Analysis of the Sound Field Emitted by a Doubly Salient Switched Reluctance Motor using Acoustic Intensity Measurement

Abstract

we propose in this article to apply the technique of acoustic intensity measurement for the analysis of the sound field emitted by the doubly salient switched reluctance motor (DSSRM).The measurements got here try to make profitable the power of this technique by using a Matlab code in order to obtain a visualization of the sound images for given frequencies, of the principal sources of vibrations present in this motor. This technique allowed calculating the sound power of the acoustic noise radiated by each face of the motor, which is calculated by using the discrete points method. It can be an original and a complementary experimental method to traditional used up to now for this kind of motor. Keywords-switched reluctance motor, sound intensity measurement, sound power and acoustic noise I INTRODUCTIONThe switched reluctance motors always showed an acoustic noise particularly higher than all the other types of variable speed motors. The techniques of investigation of noise and vibrations in the motors do not miss frequency domain analysis, time domain analysis and analysis of the acoustic and vibration behavior by the finite element method, etc. But, these techniques remain limited when the study of the field distribution around the motor is wanted. Concerning the intensity measurement, its principal interest is the possibility of quantifying the sound energy radiated by a source, as a space complex magnitude, i.e. active and reactive. It brings a significant immunity to the background noise, especially if it is a random noise. The applications which result from this are the determination of the sound power and the localization of noise sources, more delicate to realize. This paper, presents an analysis of the sound field distribution of the DSSRM, by the technique of the intensity measurement. Discrete measurements of the sound intensity for bands of frequencies of one tierce d'octave, for the five faces of the motor were done. Based on the discrete points method, the measurement of the sound power will be consequently a continuity of the first method. In fact, a part of the data being used for obtaining the visualization of the sound images, are used for the calculation of the sound power of the five faces. II THEORETICAL ASPECTSAcoustic intensity is a magnitude that corresponds to an energy flux density per unit time. It is expressed in W/m2 and is determined from the product of acoustic pressure and particle velocity In specified direction the acoustic intensity I is the average value of the instantaneous acoustic power of a surface W:pressure at a point in space [Pa] ( ) r v t : particle acoustic velocity in a considered point [m/s] As the particle velocity in the acoustic field is not measured directly, the relationship defined by Euler may be employed that states equivalence between the velocity and the pressure gradient under linear and steady state conditions: 1 r p v d t r ∂ = − ρ ∂ ∫ Where r v : Component of v defined in direction and sense by a vector r. ∂p/∂r: Gradient of p in the direction r.