Numerical Study of Supersonic Combustion Processes with Central Strut Injection

Abstract

The combustion chamber is shown in Fig. 1. It has a rectangular cross section with width w 40 mm and constant isolator height h 35:4 mm. Downstream distance, x, is measured from the Laval nozzle throat where x 0. Air enters the chamber from the left at a Mach number of M 2:1 at isolator entry. The combustor and diverging sections open at angles 1 1 and 2 2 , respectively. The outflow static pressure is p1 0:96 bar. The facility operates continuously at stagnation conditions T0;air 1400 K and p0;air 4 bar. For brevity, in the following, wall pressures in the symmetry plane are only shown for the upper wall. Our injector is shown in Fig. 1b. Chun et al. [1] provide further details about the facility and Gerlinger et al. [2,3] provide further details on the injector. Because of exploitation of symmetry, only half the channel width is modeled. H2 is injected through the horizontal slots (see Fig. 1b). At design conditions, the injection Mach number is MH2 2:6. However, in practice, this is probably not achieved, due to geometric deformation. As a conservative estimate we chose MH2 1:0. The validity of this choice is checked in Sec. V.E. Four combustion modes, i.e., blowoff, weak combustion, strong combustion, and thermal choking were observed. Because of flow overexpansion, all modes feature a shock train in proximity of the channel outflow. Another shock train develops in the isolator, due to injector displacement effects. In flight, strong combustion is desired. Here, the injector acts as the flame holder and heat release is high. For weak combustion the fuel–air mixture is ignited in the outflow shock train. The flame is detached from the injector and heat release is significantly lower. If, in these conditions, the exit pressure is lowered sufficiently, the outflow shock train disappears, and combustion ceases (blowoff). For excessive fuel injection, the flow becomes thermally choked. The combustion mode is determined by the geometry, stagnation conditions, ambient pressure, and the global equivalence ratio (see also Scheuermann et al. [4]).