Optimizing pressure recovery in mixed compression inlets for high-speed ramjet applications

The flow entering the combustion chamber of a ramjet engine should be converted from supersonic flow to a subsonic uniform flow where a high total pressure recovery is to be maintained for efficient combustion and optimum operations. The inlet of a ramjet engine is designed to decelerate the incoming supersonic flow to a Mach number less than 0.4 approximately. To ensure this, the design phase of supersonic engines is critical, which leads to an enhanced performance. Analytical Prandtl–Meyer function calculations and computational fluid dynamics (CFD) simulations using MATLAB and ANSYS Fluent were employed to assess ramp performance. The study was performed at a design Mach number of 3, to optimally select the ramp configuration. The work carried out on the optimization of the inlet focuses on improving or maximizing the total pressure recovery and attaining an ideal exit Mach number, by minimizing the cowl lip drag. An off-design Mach number ranging from 1.8 to 3.3 was chosen to perform the CFD simulations, where the pressure recovery and exit Mach numbers are calculated at the convergence of simulations. The optimal configurations for the inlet design obtained through the numerical calculations are a total turning angle of 23° where β1 = 26.48, β2 = 35.24, and β3 = 51.26. The Mach number deviation from the Oswatitsch condition for the first two waves is 0.0075, whereas for the third oblique shock it is 0.99. There was clear concordance between the numerical data and analytical solutions obtained; the pressure recovery showed a 4.37% error between the datasets obtained, which is within the accepted range.