Understanding the Effect of Three-Dimensional Design in Tandem Blade

In order to maximize the pressure ratio and efficiency, compressor designers have tried several unconventional design approaches. Tandem blading is one such unconventional design that promises a higher pressure ratio per stage through a higher diffusion factor. The nozzle shape created between the forward and aft blades of a tandem configuration acts as a passive boundary layer control mechanism. The boundary layer growth over the aft rotor is therefore effectively controlled with the help of this gap-nozzle flow. The flow complexity is likely to increase in the case of a tandem rotor due to the twin leakage vortices, twin wake regions, and their interaction with the hub and casing boundary layers. Modern compressor blades are often designed with three-dimensional blade techniques such as sweep, lean, dihedral, end bent, etc., to reduce the various losses and achieve optimum performance. However, to the best of the author's knowledge, the effect of 3D blade designs on the performance of tandem rotors has not been fully explored so far. A comprehensive numerical investigation is undertaken to understand the effect of 3D designs on the performance of tandem blades. Axial sweep and dihedral failed to improve the performance of the tandem rotor. Significant improvement in the stall margin is observed for the forward chordwise-swept and negative lean tandem rotors and is largely attributed to lower tip incidence. The performance penalty of the forward-swept and negatively leaned cases can be reduced by integrating compound or variable lean and sweep into the design.