Axial Flow Contra-Rotating Turbines

Abstract

Two types of contra-rotating stages are considered; the first uses guide vanes and the second is vaneless. The wheels of the first type use bladings which are mirror images of each other and they operate with inlet and outlet swirl. The second type uses dissimilar bladings in each of the two wheels with axial inlet velocity to the first wheel and axial outlet velocity for the second wheel. An analysis of their performance indicates that both types can reach stage loading coefficients comparable or larger than conventional turbines with the same number of wheels. A comparison of the contra-rotating stages with conventional ones indicate a significant stage efficiency advantage of the contra-rotating over the conventional single rotation stages due mainly to the elimination of stationary vanes. The off-design performance indicates that relative wheel speed must be controlled. The attributes of contra-rotating turbines suggest their potential use in high performance aircraft engines, in dynamic space power systems and in low speed industrial gas turbines.