The confirm many of the inferences reported in

The flow field in the mixed compression inlet and isolator of a Mach 4 dual mode scramjet has been investigated numerically. Favre averaged compressible Navier-Stokes equations have been solved along with the two equation SST k? turbulence model. Default values have been used for the constants in the turbulence model. The predictions have been extensively validated against experimental data for three cowl lengths and four or five convergence angles for each cowl length. Schlieren pictures of the flow field predicted by the numerical simulations convincingly confirm many of the inferences reported in the experiments (10) which were based on wall static pressure measurements. The calculations also reveal intricate details of the flow field including shock-boundary layer interaction. The compression achieved by the intake is seen to be higher for higher cowl lengths and cowl angles, although at the expense of stagnation pressure. For a given cowl length, the loss of stagnation pressure increases with an increase in the cowl convergence angle owing to the increase in mass flow rate and the attendant increase in the shock strength. The calculations are especially useful for assessing the distortion in the flow due to shocks and boundary layers. The flow distortion decreases with an increase in the cowl convergence angle with the 2.5 in. cowl producing the highest distortion. However, for the given Mach number, the 3.9 in. cowl operates optimally with low flow distortion and high pressure recovery. This is on account of the fact that, in this geometry, the shock is incident upon the expansion corner at the ramp shoulder and is thus cancelled. The calculations also reveal that the location of shock impingement (apart from shock strength) in relation to the ramp shoulder plays an important role in the distortion of the flow at entry into the isolator. Inlet unstart has also been successfully simulated in the present work for the 4.4 in. cowl at a cowl convergence angle of 11o. The strong shocks impinging on the ramp surface at this cowl angle cause a massive separation of the boundary layer resulting in a normal shock standing just ahead of the throat. The present work demonstrates that FANS calculatio