Numerical Study of Incidence Angles and Gap Heights in Turbine Cascades and Rotors on Tip Clearance Losses

Abstract

The design and optimization of turbines demands the use of fast low-fidelity tools. To obtain adequate results, loss correlations simplifying the complex turbine throughflow are implemented. Accounting for modern turbine designs and flow conditions, revisions of profile and secondary loss correlations were primarily focused upon, while improvements of the tip clearance loss correlations are difficult to achieve. Realistic engine-like conditions concerning variations of the tip clearance, blade loading and solidity are time- and cost-intensive to investigate. This paper is focused on an extensive numerical study, intending to support experiments on tip clearance loss correlations. The losses of a high pressure axial turbine rotor are analyzed for different tip clearance gap heights and incidence angles at cruise condition. The results are contrasted with a cascade having comparable tip profile and gap heights. The cascade’s flow is comparable to the rotor, but with respect to experimental restrictions concerning inlet and outlet conditions. Steady 3D calculations in the stationary and rotating frame were performed applying DLR’s turbomachinery CFD code TRACE using Menter’s SST k – ω turbulence model. The tip clearance loss coefficients were extracted from the flow field by post-processing data of an outlet plane and as massflow averaged global values. The findings are discussed referencing previous publications about the leakage flow system and tip clearance loss. Finally, a comparison to results from tip clearance loss correlations of Ainley-Mathieson and Dunham-Came is presented.