Análise numérica da influência da velocidade na combustão supersônica em um demonstrador Scramjet

Abstract

Supersonic combustion ramjet, or scramjet, is a hypersonic airbreathing propulsion system that utilizes flat oblique or conical shock waves to compress and decelerate hypersonic air flow in supersonic speeds. Recent flight tests have demonstrated that there’s viability in supersonic combustion concept, but such technology is not fully mastered yet. The objective of this Master’s Thesis is to study the effects of vehicle speed variation on the supersonic combustion for a hydrogen/atmospheric air mixture on the scramjet demonstrator combustor. Two methods of fuel transverse injection (single and double) and three situations of vehicle operation were evaluated: at design speed conditions (corresponding to the Mach number 6.8), at lower speed (corresponding to the Mach number 6.4) and at a higher than projected speed (corresponding to the Mach number 7.2) considering flight at the geometric altitude of 30 km. Different fuel injection methods have interactions of particular and distinct phenomena in relation to the flow, therefore, seeks to verify how vehicle's operating conditions variations may influence the flow behavior, in terms of the performance and the efficiency of the combustion process. Steady state flow was considered, air as calorically perfect gas and simplified chemical kinetic mechanism with 4 species and 1 chemical reaction using laminar finite-rate model and the turbulence modeled by the k-kl-ω transition model. Second order upwind schemes were used in the discretization. Variation curves of thermodynamic and species properties, shock trains visualization, flow contours and average properties at the isolator and combustor outputs are presented. It was revealed that there was an increase in the values of the thermodynamic properties (pressure, temperature, density, etc.) and intensification of shock trains in the isolator with the increase of the flight speed. In addition, there was a reduction in the amount of air admitted to the isolator due to non-operating speeds, as a result of the shock waves moving away from the cowl attack board. However, the flow remained supersonic in the combustion chamber. Spontaneous fuel burning was visualized for all conditions tested, whose average efficiencies with single and double injection obtained 10% and 22%, respectively.