3-Dimensional Detached Eddy Simulations of a Novel Variable Geometry Radial Ejector

Rae, Lachlan (2024) 3-Dimensional Detached Eddy Simulations of a Novel Variable Geometry Radial Ejector. [USQ Project]

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Abstract

Ejectors are often described as compressors with no moving parts, a low maintenance and reliable device capable of being powered by sustainable energy. Their greatest downfall, however, is their low efficiency which is often attributed to their performance being a function of both operating conditions and geometry. For fixed geometry ejectors great care needs to be taken to keep the flow pressures at a constant value. As an alternative to this much work has been done to provide solutions based on variable geometries. The traditional axial ejector configuration makes this process difficult without impeding of the flow through the ejector. Instead a novel solution has been developed in the form of the variable geometry radial ejector (VGRE).

From its initial inception to the present, the VGRE has shown promising results compared to axial ejectors in both numerical and experimental investigations. The purpose of the present work is to develop a 3-dimensional (3D) detached eddy simulation (DES) model to assist in further development of the device in a cost effective manner. The intended application for the VGRE is for use in solar-powered ejector refrigeration systems. The development of this device will increase the capability and efficiency of the sustainable cooling technology. The ability to reliably assess the VGRE by numerical methods is paramount to its development, this is the reasoning behind the present work.

A full review of the improved VGRE’s development to date was conducted to gain a full understanding of the device and the requirements needed for a suitable simulation model. Additional research was conducted into the literature regarding ejector refrigeration systems, ejector performance metrics, and ejector geometry. During this process relevant data was obtained for creating geometries and performing computational fluid dynamic (CFD) analyses. Previously documented experimental data was also collected for the purpose of validating the CFD model.

Previous studies had conducted 2D axisymmetric simulations and determined the optimal DES turbulence model for the improved VGRE to be the DES Realizable k-ϵ model. Replication of the2Dsimulations was performed as a means to familiarise the author with the CFD analysis methods and program, ANSYS Fluent. Nine geometries and meshes were reproduced to represent different configurations of the adjustable VGRE. Several simulations were performed resulting in very poorly agreeing solutions. Difficulties identifying the issue lead to a sample simulation being acquired from a previous study for comparison. Other than minor geometry and mesh variances there were no issues identified. A number of subsequent simulations were conducted in an attempt to determine the problem, but to no avail. Project time constraints required the 2D simulations be concluded and work continued with the 3D simulations.

The acquired 2D geometry was adapted into a 3D model and several meshing methods were tested. The meshing process was hindered by insufficient hardware resulting in long mesh processing times. Eventually, a relatively simple mesh was utilised to simulate the improved VGRE. Unfortunately the simulation provided very poor agreement to the experimental data. Although, a certain level of agreement was noticed between the 3D and 2D simulations conducted in the present work.

The cause of the poor simulations could not be ascertained and as such the project was deemed a failed process. Upon preparing this dissertation, however, a previously unknown parameter was identified relating to pressure settings. By default, this setting had introduced a gross error into the simulations causing the poor simulations. By this point, however, there was insufficient time to perform any more simulations.

This dissertation discusses the efforts undertaken, albeit unsuccessful, to develop a reliable 3DDESmodel for the simulating the improved VGRE.

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Item Type:	USQ Project
Item Status:	Live Archive
Faculty/School / Institute/Centre:	Current – Faculty of Health, Engineering and Sciences - School of Engineering (1 Jan 2022 -)
Supervisors:	Saleh, Khalid
Qualification:	Bachelor of Engineering (Honours) (Mechanical)
Date Deposited:	17 Mar 2026 04:55
Last Modified:	17 Mar 2026 04:55
Uncontrolled Keywords:	ejectors; variable geometry radial ejector (VGRE); 3DDESmodel
URI:	https://sear.unisq.edu.au/id/eprint/53151

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