Proceedings of The 11th International Conference on Research in Engineering, Science & Technology
Sensitivity of Geometric Variables on Performance of an Axial Flow Turbine
Aji M. Abraham and S. Anil Lal
A variance based analysis to identify sensitivity of geometric variables on power and efficiency of a two stage axial flow turbine is presented. Six geometric variables identified for sensitive analysis are axial gap, tip clearance and stagger angle for four blade profiles; nozzle, first rotor, stator and second rotor. ANSYS-CFD model validated based on turbine test for design configuration is used for generation of computationally intensive data for sensitivity analysis. Flow in turbine blade flow passage is characterized by flow separation, jet-wake flow and tip clearance vortices. Study identified nozzle stagger angle, axial gap and tip clearance as the sensitive variables. Nozzle stagger angle and axial gap determines flow separation and jet-wake flow. Flow separation reduces effective flow area in rotors and increases flow velocity. Increased flow velocity produces higher specific work and power but reduces the efficiency due to higher losses. Tip clearance vortices influence flow pattern in tip clearance region. An optimum sized vortex reduces tip clearance leakage from pressure side to suction side. Tip clearance more than size of tip clearance vortex generates additional leak path and reduces efficiency. Power and efficiency of gas turbines can be fine-tuned by controlling the formation of flow structures through proper selection of the sensitive geometric variables.
Keywords: sensitivity analysis, stagger angle, axial gap, tip clearance, CFD.