Micro gas turbine combustion chamber CFD modelling

Abstract

The interest in micro gas turbines has been steadily increasing. As a result, the researchers’ attention has been focused on obtaining optimal configurations for micro gas turbines depending on the applications in which they are used. Micro gas turbines are suitable for both civil and military applications. Presently, they are often used in the development of Unmanned Air Vehicles (UAVs). Micro gas turbines have the following advantages: a wider range of options regarding the used fuel and a significant system weight reduction. This paper presents the CFD modelling results regarding an annular type combustion chamber. This combustion chamber is part of a 80 daN micro gas turbine, destined to equip a small scale multifunctional airplane. The combustion chamber is equipped with eight pressure-swirl injectors, using Jet-A as fuel. A 3D RANS numerical integration of the Navier-Stokes equations has been carried out, using an Eddy Dissipation combustion Model (EDM) and the k-ε turbulence model, implemented in a numerical simulation conducted using the commercial software ANSYS CFX. An unstructured computational grid, generated using ICEM CFD, has been used. The fuel is injected directly in the fire tube in the form of droplets. The initial fuel droplet’s diameter has been considered to be 50µm and the fuel spraying cone angle has been set at 90°. The fuel droplet break-up and evaporation processes have been simulated using numerical models available in ANSYS CFX library. A two steps reaction mechanism, which takes into consideration the formation of NO, has been used. The results thus obtained are encouraging. The flame developed in the central area of the fire tube, its walls thus not being subjected to high temperatures. Also, the maximum temperatures were obtained in the primary zone of the fire tube. The temperature then decreased in the fire tube’s secondary zone and dilution zone, until it reached an average value of 1200 K at the combustion chamber exit. Regarding the pressure, based on the numerical simulation results, a 5% pressure loss has been obtained. The numerical results will be validated by conducting combustion tests on a testing rig which will be developed inside the institute’s Combustion Chamber Laboratory.