Multiphase-flow simulation of a rotating rectangular profile within a cylinder in terms of hydraulic loss mechanisms

Abstract

In wet running screw compressors, liquid (oil or water) is injected into the machine. The advantage of liquid injection is cooling of the compressed fluid, sealing of clearances, lubrication of rotors and bearings, and reduced noise and vibration. The disadvantage of wet running machines is the loss in internal mechanical efficiency from the hydraulic loss caused by the liquid. In this paper, multiphase flow simulations are performed using the Volume of Fluid method to investigate hydraulic loss mechanisms. The 2D geometric model consists of a rectangular profile rotating in a cylinder with a clearance height that represents the screw machine housing clearance. In this investigation, the distribution and flow pattern of the liquid are examined with regard to hydraulic losses. Furthermore, the influence of the amount of liquid and the circumferential tip speed is determined through calculation of the torque on the rectangular contour. The hydraulic losses increase with increasing liquid mass in a working chamber and with increasing circumferential tip speed. For the simulations points examined, the tip speed has a greater impact on the hydraulic loss than does the amount of liquid.