METHOD FOR THE PREDICTION OF SUPERSONIC COMPRESSOR BLADE PERFORMANCE

A simple model is used to calculate the flow in compressor blades with supersonic relative inlet flow. The method addresses the common irreversible deceleration and compression that takes place when a shock stands ahead of the blade leading edge: it does not attempt to describe the process when inverse camber in the forward part is used to decelerate the flow before the shock. The one-dimensional model utilizes the conservation of stagnation enthalpy, mass flow, and momentum in the inlet region. The momentum equation is applied in the direction parallel to the blade surface at inlet, and one of the fundamental simplifications adopted is that the projected area of the blades gives such a small force in this direction that a very simple approximation for it suffices. The model is able to predict the loss creation in the inlet region. The levels of calculated loss agree well with measured values when the Mach numbers are sufficiently high for the inlet loss to dominate. Furthermore, the correct trends of loss with incidence and blade speed are predicted. The method predicts other trends usually seen in measurements: the narrowing of the useful operating range between choke and flow instability (surge) as blade speed is increased and a steepening of the surge line at the higher speeds.