An Inviscid-Viscous Method to Model Leading Edge Separation Bubbles

Separation bubbles are likely to occur near the leading edges of sharp-edged blade sections in axial compressors and turbines, particularly when the sections are operated at positive incidence. Typically the flow reattaches a short distance from the leading edge as a turbulent boundary layer, the thickness of which depends on the details of the separation bubble. The overall performance of the blade section can be significantly affected by the thickness of this initial boundary layer — in some cases blade stall is mainly associated with the change in thickness of the layer as blade incidence is increased. A recent experimental study at the Whittle Laboratory, Cambridge demonstrated the importance of the blade leading edge shape on the separation bubble. In the present work, an inviscid-viscous method has been set up to model the experimental data and to provide a way of predicting the performance of this critical region for different leading edge shapes.