Transient Numerical Analysis of a Tandem Compressor Stage

Minimizing the number of axial flow compressor stages for a specific work output, and thereby lowering the engine size and weight has always been the designer’s goal. A major limitation on the pressure rise in a subsonic axial-flow compressor stage is boundary layer separation on the blade suction surface. One method of mitigating the suction surface separation is to employ tandem airfoil blades. Tandem blading is a method of increasing the flow deflection by delaying the separation in diffusing cascade arrangements. The basic concept is that a new boundary layer forms on the second (aft) airfoil, allowing for high overall loading without the large flow separations that would be seen with a single airfoil. The unsteady 3D flow fields in a single-stage compressor with tandem blades under designed conditions are simulated numerically to investigate the stage performance and the aerodynamic interaction between the blade rows. In this work, the Time Transformation method (TT) to stage modeling has been employed to predicting stage compressor performance. In the compressor, three main aerodynamic structures are responsible for the unsteadiness of the flow: the wakes, the corner stalls and the tip-clearance flows. The study of the aerodynamic structures is the subject of this paper.