An optimal design program of an axial-flow compressor stage has been developed by applying the gradient projection method to a simulation program. Total pressure losses required to calculate the total-to-total efficiency are estimated by integrating empirical loss coefficients of six loss mechanisms along the radial direction of three-dimensional blade. The weight of a stage is estimated by considering stress distribution and the material of stage components. Example optimization problems for maximum-efficiency, minimum-weight and balanced optimum between efficiency and weight are given and sensitivities in the whole feasible range of design variables are analysed.
In case of a shock-in-rotor compressor, the flow passage must be configured in such a way to deflect the meanline of the flow radially outward in a meridional plane to obtain high efficiency. Under a limited tip radius, the stage weight is decreased mainly by reducing the cascade solidity and the blade height. Minimization of the stage weight penalizes the attainable efficiency. The optimum stage pressure ratio can be obtained by treating the stage pressure ratio as an additional design variable. The global optimum pressure ratio corresponds to the stall-beginning point. The equivalent diffusion factor is an active constraint for all optimization problems.
The present design optimization program is useful to obtain an optimum configuration of an axial-flow compressor stage under simultaneous consideration of efficiency and weight. It can be applied to a multi-stage compressor in conjunction with a stage- stacking technique, since the simulation equations include the effects of Mach number and Rehnolds number.
