Effects of various geometric parameters on the computed swirl numbers and flow topology in a bidirectional vortex chamber

Abstract

A finite-volume solver is used to compute the cyclonic motion in a vortex chamber assuming steady, incompressible, and inviscid flow conditions. A parametric campaign enables us to characterize the computed swirl number over a wide range of properties. These include the tangential injection speed, number of injectors, injector port diameter, axial injection plane, and outlet fraction. In addition to the traditional swirl number, both geometric and modified swirl numbers are evaluated. In this process, the characteristic values of all three swirl numbers are determined over a wide range of design and inflow parameters. Overall, the geometric and modified swirl numbers are seen to follow similar trends, being different by a constant multiplier, with the former ranging between 0.9 and 410. We also find that increasing the injection speed has no bearing on the swirl numbers. In contrast, adding more injectors leads to a linear decrease in the swirl number, except for the case of a single injector. Although expanding the injector diameter initially results in larger swirl numbers, these begin to diminish after reaching an optimal diameter. Moreover, as the injection plane is displaced toward the headwall, the swirl number is reduced while remaining positive as long as a coherent cyclonic motion is present. As the injection plane is raised above the chamber midsection plane, the traditional swirl number turns negative. Varying the normalized outlet radius β is also found to affect the pressure and velocity distributions, with a central recirculation zone emerging beyond β = 0.707 and leading to vortex breakdown past β = 0.866.