Upstream interaction within a dual-mode scramjet engine is investigated numerically. The upstream interaction is investigated by increasing the freestream-to-injector pressure ratio. The constant area duct and sudden expansion geometries are used to achieve these results. Analysis using the symmetry boundary condition is compared to the full boundary condition for the constant area duct. Numerical analysis of the Mach 3.5 freestream is conducted using normal sonic injection of nitrogen gas to create the upstream interaction. Comparisons, where applicable, are made to experimental results. Due to the high speed of the flowfield, oblique shockwaves are present causing numerical convergence difficult to achieve. The flowfield symmetry assumptions break down due to the high shear stresses present in the boundary layer separation region. As the freestream-to-injector pressure ratio is increased this separation region begins to move upstream within the isolator region. This study proves that the upstream interaction is not related to reacting flows, but rather to the high turbulent shear stresses that are present in the boundary layer separation regions
