Overshoot of the Rankine Vortex Formed in the Flow Field Behind the Inlet Guide Vane of Centrifugal Compressors

Abstract

This paper is aimed to analyze the experimental results obtained by Kassens and Rautenberg (1998) and Kassens (1997) concerning the overshoot of the rotating velocity field behind the IGV. Since the IGV used in the present investigation has the form of a disc in the closed condition of the blades, the vorticity field of the rotating flow behind the outlet edge of the IGV can be determined by means of the streamline deflection in this IGV, whose function as an actuator disc does not need to be used. The potential-vortex field generated by these streamlines out of the IGV is calculated with good accuracy compared with the experimental results. The further development of the vorticity field mentioned into the distribution of the tangential velocities can be derived from the diffusion of the vorticity, but with an inaccuracy caused by the overshoot of the Rankine vortex. This overshoot originates from the potential vortex field and travels towards the vortex core, which acts as a rigid body rotation. The overshoot degenerates downstream from the outlet of the IGV due to strong damping incorporated in its unusual velocity field. Its disappearance introduces the formation of the orderly Lamb-Oseen vortices, whose theoretical property coincides well with the experimental result. Thus, the overshoot plays an active role for the loss in the total pressure in the central region of the rotating flow generated by the IGV.