The effect of multiple conical shock waves at the engine intake on the performance of a single-mode ramjet

Abstract

Supersonic single-mode ramjet performance was analyzed using a prescribed two-dimensional conical shock wave in axisymmetric supersonic flow. The ramjet under consideration for the analysis consists of a mixed compression intake, a cylindrical combustion chamber and a supersonic constant convergent–divergent nozzle. A computer program was developed to carry out the analysis based on the formation of multiple conical shock waves at the engine intake at different flight Mach numbers and different altitudes in the range of 1.5–4 Mach and 9000–18,000 m, respectively. Accordingly, a supersonic convergent–divergent nozzle was designed and consequently, the area ratios along the ramjet were calculated to find the correct dimensions for the thrust required. The analysis of the multi-shock system showed that for a given number of conical shocks and Mach numbers, the thrust decreases as the altitude increases. Also, the thrust increases at higher Mach numbers and higher number of conical shocks regardless of the altitude. Furthermore, for $M>2.5$ , and at number of conical shocks greater than 2, thrust stays constant. The flow rate and the pressure after combustion showed similar trends as the thrust. The multi-shock system of the intake system proposed showed that a limit of a three conical shocks were sufficient for a reasonable pressure recovery for a $M>2$ , while for a $M<2$ , a single normal shock wave could be sufficient for different altitudes. Also, pressure recovery is unaffected by the altitude for the same Mach number and increases with lower Mach numbers. Moreover, the increase of number of conical shocks is limited to 3 where no further increase in pressure recovery could be indicated.