Numerical simulation of separated boundary-layer flow

The numerical simulation of time-dependent, 2-D compressible boundary-layer flow containing a region of separation is studied. The separation is generated by the introduction of an adverse pressure gradient along the freestream boundary. In order to validate the numerical method, a low Mach-number laminar separation bubble flow is considered, which enables an extensive comparison with incompressible results. The generation of an adverse pressure gradient along the freestream boundary can be realized in various ways. An imposed decelerating flow boundary is compared with a suction technique. The effects of the strength of the pressure gradient and the presence of small upstream perturbations on the separation bubble are also investigated. The time-averaged characteristics of the flow are in good quantitative agreement with incompressible approximate theories predicting the condition for separation. The appearance of self-excited vortex shedding in unperturbed flows under a sufficiently strong adverse pressure gradient is consistent with incompressible flow simulations reported in the literature. The satisfactory result achieved in the calculation of the low-Mach-number flow encourages the application of the numerical method to flows with strong compressibility effects.