Semi-Analytical Method for Conceptual Design and Optimization of Scramjet Combustor Using Thermally Perfect Gas Model

Abstract A semi-analytical method is proposed to predict Mach number, static pressure, and temperature in a scramjet combustor for a calorically imperfect but thermally perfect gas. The method accounts for the simultaneous presence of variable area, friction, and heat addition. The results of the semi-analytical method were compared against the computational fluid dynamics (CFD) prediction for a hydrogen-fueled scramjet combustor operating at an inlet Mach number of 2, 4, and 6 for an equivalence ratio of 0.30. The comparison showed that the prediction from the semi-analytical method was within 3.1% of the CFD prediction for Mach number, pressure, and temperature. The results demonstrate that a thermally perfect gas model is required for accuracy at higher Mach numbers, as neglect of it can lead to an error of 14% in the Mach number and as much as 21% in the temperature predictions for an inlet Mach number of 6. The utility of the semi-analytical method was demonstrated by its application in optimizing the combustor exit height, resulting in a close to zero static pressure loss in the combustor. The semi-analytical method-driven optimization method is highly desirable during the preliminary stages of design as it enables rapid assessment and optimization of multiple design concepts as compared to the efforts required by a CFD simulation and/or physical tests.