Numerical Analysis of Hypersonic Intakes for Airbreathing Propulsion Systems

Ramjet and scramjet engines represent a key technology for high-speed airbreathing propulsion due to their ability to operate efficiently at supersonic and hypersonic speeds without requiring rotating parts. A crucial component of these engines is the air intake, which is responsible for compressing the incoming airflow through shock waves before combustion. The design of an efficient intake significantly affects the overall performance of the propulsion system. This thesis focuses on the design, analysis, and optimization of hypersonic intakes, with particular attention to the Busemann intake, which is known for its high efficiency in the inviscid flow regime. The initial phase of this research involves the numerical generation of intake geometries using a MATLAB-based design algorithm. The intake configuration is defined by key parameters, including the freestream Mach number, the post-shock Mach number M_3, and the intake exit cross-sectional radius r. To evaluate the aerodynamic performance of the designed intakes, Computational Fluid Dynamics (CFD) simulations are performed in Ansys Fluent, solving the Navier-Stokes equations for an initial two-dimensional model, where geometric variations are analyzed to evaluate their impact on performance, flow uniformity, and startability. Given that real-world applications deviate from the ideal inviscid model, additional viscous corrections are applied to account for boundary layer effects. These corrections address the increased pressure ratios relative to the ideal case and the reduction in intake efficiency caused by boundary layer-induced flow distortion. The correction methodology involves computing the boundary layer displacement thickness using Reynolds-Averaged Navier-Stokes (RANS) simulations and integrating it into the ideal inviscid design. Moreover, truncated intake designs are explored to mitigate the excessive length of the classical Busemann intake while maintaining optimal aerodynamic performance. Following the optimization of the two-dimensional intake contour, a three-dimensional counterpart is generated using the Wavecatching technique, which traces streamlines to adapt the intake to an elliptical cross-section. A mesh convergence study is carried out for both 2D and 3D cases to ensure the reliability of numerical results. Finally, the off-design performance of the 3D intake is analyzed to evaluate the system’s response to varying operating conditions. This analysis helps identify configurations that exhibit greater robustness against unstart phenomena and offer improved efficiency across a wider range of Mach numbers. The results confirm the feasibility of the developed design methodology, demonstrating that the proposed intake geometries maintain high efficiency while addressing real-world constraints such as viscosity, manufacturability, and operational robustness.