Advances in endwall contouring using continuous diffusion method and its application to a three-stage high pressure turbine
Blades of high pressure turbines have a relatively small aspect ratio that produce major secondary flow regions close to the hub and tip. The secondary flows caused by a system of hub and tip vortices induce drag forces resulting in an increase of secondary flow losses and, thus, a reduction of stage efficiency. Given the high level of technological maturity and the current state of turbine aerodynamic efficiency, major efficiency improvement, if any, can be achieved only by significant R&D effort. In contrast, a moderate increase in aerodynamic efficiency is attainable by reducing the effect of parasitic vortices such as those mentioned above. Introducing an appropriate non-axisymmetric endwall contouring reduces the secondary flow effect caused by the pressure difference between pressure and suction surfaces. Likewise, attaching leading edge fillets reduces the strength of horseshoe vortices. While an appropriate endwall contouring design requires special care, the design of the leading edge fillet is straight forward. In this paper, we present a physics based method which enables researchers and engineers to design endwall contours for any arbitrary blade type regardless of the blade loading, degree of reaction, stage load and flow coefficients. A thorough, step-by-step design instruction is followed by its application to the second rotor of the three-stage research turbine of Turbomchinery Performance and Flow Research Laboratory of Texas A&M University. Comprehensive numerical calculations of the flow field, including the secondary flow, show the positive impact of an appropriately designed endwall contouring on the efficiency. The results also show how an inappropriately designed contour can be detrimental to turbine efficiency. The numerical result of the efficiency calculations is compared with the experimentally obtained efficiency for the reference non-contoured turbine.
author list (cited authors)
Schobeiri, M. T., & Lu, K.