Simulation of discharge pressure pulsation within twin screw compressors

Abstract

Even in the absence of self-acting valves, flow through the discharge port of a twin screw compressor is oscillatory in nature. This unsteady but periodic flow variation at the discharge port excites the pressure pulsation, which is the main source of noise and vibration. In this paper, a mathematic model based on the one-dimensional unsteady gas flow equations is established to describe the discharge pressure pulsation, which considers the effects of friction and heat transfer between the gas and the pipe. The boundary conditions of the discharge pressure pulsation model are given in detail. The two-step Lax—Wendroff scheme is applied to solve the one-dimensional unsteady gas flow equations. In order to verify the theoretical analysis, the discharge pressure pulsations under various working conditions are measured and compared. It is shown that the model established in this paper is a useful tool to obtain a better understanding of the behaviour of the pressure pulsation in discharge pipe. It is found that the most important factor that affects the discharge pressure pulsation is the pressure difference between the pressure upstream of the discharge port in the compression chamber and the pressure in the discharge line some way downstream. The minimum fluctuation occurs when the discharge pressure is equal to the pressure corresponding to the built-in volume ratio. For a constant discharge pressure, the pressure pulsation amplitude increases with the rotational speed.