Abstract
Combustion instabilities in a small MMH/NTO liquid rocket engine used for satellite attitude and course control are numerically investigated. A three-dimensional Navier-Stokes code is developed to simulate two-phase spray combustion for cases with five different droplet Sauter Mean Diameters. As the droplet size increases from 30 microns to 80 microns, pressure oscillations are stronger with larger amplitudes. But an increase of the droplet size in the range of 80 microns to 140 microns indicates a reduction in the amplitudes of pressure oscillations. This trend is the same as the Hewitt criterion. The first tangential (1T) mode and the first longitudinal (1L) mode self-excited combustion instabilities are captured in the 60-micron and 80-micron cases. Abrupt spikes occur in the mass fraction of MMH and coincide with abrupt spikes in the mass fraction of NTO at the downstream regions just adjacent to the impinging points. Thus, local combustible high-dense mixtures are formed, which result in quasiconstant volume combustion and abrupt pressure spikes. The propagation and reflection of pressure waves in the chamber stimulate the combustion instability. When the droplet size is too small or too large, it is difficult to form local high-dense premixtures and combustion is stable in the chamber.
Highlights
A small MMH/NTO liquid rocket engine (LRE) is developed for the purpose of attitude control and course corrections for tactical missiles and artificial satellites
The first ring is located at r = 10:3 mm, while the second ring is located at r = 19:4 mm. 20 like-doublet injectors are uniformly distributed in the first ring every 18 degrees in the circumference direction, while 40 like-doublet injectors are uniformly distributed in the second ring every 9 degrees
A three-dimensional two-phase reaction turbulent flow is predicted by the Eulerian-Lagrangian method, in which the Unsteady ReynoldsAveraged Navier-Stokes (URANS) equations are for the gas-phase flow and the DDM are for the trajectories of droplets
Summary
A small MMH/NTO liquid rocket engine (LRE) is developed for the purpose of attitude control and course corrections for tactical missiles and artificial satellites. High-frequency combustion instability has plagued the development of LRE since the 1940s, in which organized oscillations with high amplitude greater than 10% of mean chamber pressure would be induced [1, 2]. Such oscillations may result in poor performance, unacceptable vibrations, or even catastrophic events. Because of the complexity of this problem and limited computational power to capture all the physical processes in the numerical simulations, combustion instability is still a challenge to the development of a rocket engine. Computational Fluid Dynamics (CFD) method is regarded as an effective way to investigate combustion instability, which can provide insight into more detailed physical processes. For two-phase turbulent reactive flow, Unsteady ReynoldsAveraged Navier-Stokes (URANS) is always employed
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