NUMERICAL INVESTIGATION OF THE INFLUENCE OF THE DEGREE OF REACTION IN AN AXIAL COMPRESSOR STAGE WITH TANDEM VANES

Many investigations have defined Smith-type diagrams to guide the preliminary designs of conventional axial compressor stages on the choice of loading, flow coefficient, and degree of reaction. The recent development of unconventional axial compressor stages with tandem vanes has not been accompanied by similar works aimed at tailoring existing correlations to the new type of vanes. While it is clear that axial compressor stages with tandem vanes operate in higher working ranges than conventional stages, it is less clear how the choice of reaction affects the aerodynamic behavior of such setups. Recent works have shown that higher work coefficients would require higher degrees of reaction thanks to the centrifugal effects' beneficial influence on the rotor's boundary layer. However, the interaction of tandem vanes with such phenomena is still not fully understood. For this purpose, this paper numerically investigates a low-speed axial compressor stage developed at the Technical University of Munich with different degrees of reaction for increasing loading levels. The metal angles of the unshrouded rotor and the shrouded stator are modified to ensure that the other design parameters of the stage, namely the work and flow coefficients, are kept constant and that the influence of the degree of reaction is isolated. The investigation starts with Q2D simulations of the reference midspan aerofoils, and it is then extended to a 3D configuration by maintaining the radial distribution of the aerofoil parameters together with the lean and bow distributions of the reference 3D vanes. New correlations are presented, aiming to show how the performance of the stage in terms of efficiency, total pressure losses, and loading coefficients of the vanes are influenced by the different degrees of reaction investigated. This paper therefore provides insight into the preliminary choices of parameters for the design of axial compressor stages with tandem vanes.