Effects of nozzle inlet size and curvature on the flow development in a bidirectional vortex chamber

Gaurav Sharma,Joseph Majdalani

doi:10.1063/5.0066121

Abstract

A finite-volume solver is used to describe the cyclonic motion in a cylindrical vortex chamber comprising eight tangential injectors and a variable nozzle size. The simulations are performed under steady, incompressible, and inviscid flow conditions with air as the working fluid. First, we apply a fine tetrahedral mesh to minimize cell skewness, particularly near injectors. Second, this mesh is converted into a polyhedral grid to improve convergence characteristics and precision. After achieving convergence, the velocity components are evaluated and compared to existing analytical solutions. We find that well-resolved numerical simulations can accurately predict the expected forced vortex behavior in the core region as well as the free vortex tail in the outer region. We also confirm that the swirl velocity remains axially invariant irrespective of the outlet radius. Similarly, we are able to ascertain that the axial and radial velocities embody the bidirectional nature of the motion. As for the computed pressure distribution, it is found to agree quite well with both theoretical formulations and experimental measurements of cyclone separators. Then using a parametric trade study, the effect of nozzle variations on the internal flow character, mantle structure, and recirculation zones is systematically investigated. Apart from the exit diameter, we find that the nozzle length and inlet curvature can substantially affect the internal flow development including the formation of backflow regions, recirculation zones, and mantle excursions. Finally, an empirical relation is constructed for the nozzle radius of curvature and shown to effectively suppress the emergence of recirculation and backflow regions.

Highlights

The characterization of wall-bounded cyclonic flows continues to receive attention in the propulsion and fluid dynamics communities, and this is largely due to the favorable attributes associated with the onset of rotating motion in vortex engines, cyclone separators, and other swirl-dominated chambers.[1]
Of the various computational studies that have undertaken the task of describing wall-bounded cyclonic flows, most have concentrated on industrial cyclone separators
The same can be said of the mantle location, which seems to adapt itself to the expanding outlet diameter, until it can no longer attach itself to the nozzle inlet circumference

Summary

Introduction

The characterization of wall-bounded cyclonic flows continues to receive attention in the propulsion and fluid dynamics communities, and this is largely due to the favorable attributes associated with the onset of rotating motion in vortex engines, cyclone separators, and other swirl-dominated chambers.[1] By translating the basic characteristics of unconfined tornadoes and hurricanes to propulsive, combusting, and flow separation devices,[2] one is able to exploit the high energy density, self-sustaining capability, self-cooling properties, prolonged residence time, flow separation efficiency, and effective mixing potential of cyclonic flows to optimize the design space, enhance the controllability, and improve the stability of numerous power production and thrust generation devices.[3].

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Results

Conclusion