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Analysis of diffuser and ejector performance in a high altitude test facility
Date Issued
01-01-2008
Author(s)
Manikanda Kumaran, R.
Vivekanand, P. K.
Sundararajan, T.
Balasubramanian, S.
Raja Manohar, D.
Rajarathnam, S. M.
Abstract
This paper describes the influence of back pressure on the performance of a second throat ejector-diffuser system. Second throat ejector-diffuser (STED) is a subsystem in the high altitude test facility of large area ratio rocket motors. STED is employed to create the low pressure environment (of the order of a few thousand Pascals) corresponding to the high altitude flight situation, in a ground testing installation. During full flow condition (steady state operation) of the rocket motor, often the self pumping action of the rocket exhaust plume may itself be sufficient to maintain the low vacuum level required for the motor testing. However, during the initial startup and shut down phases of the rocket motor, an external ejector system is necessary for avoiding back flow of the motor exhaust into the vacuum test chamber. Therefore, in the present study, a numerical investigation has been conducted to analyze the performance of a second throat supersonic diffuser at various diffuser exit pressures. Simulations have been carried out for an adiabatic diffuser (without wall cooling) by varying the back pressure from 50,000 Pa to 150,000 Pa. Diffuser heat transfer analysis (with wall cooling) has been simulated only for a back pressure of 93,000 Pa. The flow pattern, shock location, shock structure, pressure gradients and temperature distributions in the diffuser system are investigated in detail. A decoupled ejector analysis has also been carried out to study the variation of suction pressure with mass flow rate of driving fluid (nitrogen) used in the ejector system. The analysis has been carried out by solving axi-symmetric Navier-Stokes equations using finite volume discretisation technique. The numerical findings agree well with the available in-house experimental data. Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.