Numerical Investigation of Flow Structure and Pressure Drop Prediction for Radial Inflow Between Corotating Disks With Negative Effective Inlet Swirl Ratio

Abstract

This paper presents a numerical simulation of the flow structure of radial inflow between corotating disks with a negative ceff (effective inlet swirl ratio), which may occur in a vortex reducer equipped with deswirl nozzles. When the value of ceff approaches zero, asymmetric flow structure is observed in the cavity. Besides this, the flow structure inside the disk cavity at ceff < 0 can be divided into a source region, a sink region, an interior core region, and two Ekman layers, which is identical to the situation when 0 < ceff < 1. However, there exist two distinct patterns: the stagnation point on the disk and on the peripheral. According to a theoretical analysis, ceff = −1/8 is used to distinguish between these two patterns. Based on flow structure partitioning, a theoretical model for predicting the swirl ratio radial distribution and pressure drop in a disk cavity with ceff < 0 was established. The model employs the turbulent boundary layer integral method, and von Karman's assumption of velocity profile and wall shear stress for a free disk. The calculation results of the swirl ratio in the cavity are in good agreement with the computational fluid dynamics results except when the negative ceff approaches zero because of the deviation of the radial velocity profile from the “1/7” power law. Furthermore, pressure drop prediction across the cavity by the model has been verified through comparison with public experimental results.