Effect of phase variation on total acoustic power of axial-flow turbomachine noise.

Abstract

This paper deals with the effect of linear phase variation on total acoustic power generated from an axial-flow turbomachinery. In a previous paper (J. Acoust. Soc. Jpn.(E) 2, 203-211), the authors derived a simple expression on the power when all the fluctuating forces on rotor (or stator) blades are in phase. The expression is extended to the case where the phase of the fluctuations varies linearly with the circumferential distance. This is a model for turbomachines with differentn umber of stator and rotor blades. It is shown that the Fourier components of the fluctuation contributing to the power are related to the phase variation and that the dependence of some parameters on the power has the same form as that where the fluctuationsa re in phase. Furthermore, it is suggested that the noise with discrete frequencies is emitted mainly from rotor blades not from stator ones. To obtain a further understanding an estimation of the fluctuationa re made using a lineart heory and important effectos f blade geometry and flow configuration are pointed out.