Flow measurements in the discharge port of a screw compressor

Abstract

The angle-resolved mean velocity and turbulence characteristics of axial air flow within the rotors and discharge chambers of a screw compressor have been measured, using a laser Doppler velocimeter with high spatial and temporal resolution. The measurements were made through special transparent windows fixed in the compressor casing and in the pipe immediately above the discharge port. Results were obtained at a speed of 1000 r/min, a discharge pressure 1 bar, and a temperature of 57 °C. The flow interaction between the rotors and the discharge chamber was established as well as the spatial variation of the axial mean velocity and turbulence velocity fluctuation. It was shown that the discharge flow was complex, strongly time-dependent, and controlled by several mechanisms. In general, the axial velocity, on entering the working chamber downstream of the discharge port exit was higher than that immediately upstream with large variation in mean and root mean square velocities immediately after the opening of the discharge port, then flow becomes more uniform. The high velocity values and large fluctuation are mainly controlled by the pressure gradient across the port at the very beginning of the discharge process, after that, as the port opens wider, uniform flow is influenced mainly by the rotor action. These measurements will be used as input data for more reliable optimization of compressor design and to validate a computational fluid dynamics model of fluid flow within twin screw compressors, already developed in-house.