Development of an automated non-axisymmetric endwall contour design system for the rotor of a 1-stage research turbine – Part 2 computed and experimental results

In this paper, we present the computed flow results for those endwall designs produced using the automated non-axisymmetric endwall design procedure and target objective functions detailed in Part 1 of this paper, and where available, compare these with experimental measurements made using the CSIR low-speed research turbine used as the test case for the designs. Experimental measurements were taken immediately aft (X3) as well as downstream (X4) of the rotor row using a drilled 5-hole elbow probe, and both the computed as well as physical results were processed identically to ensure as high a degree of comparability between the computed and physical datasets. For the two initial cases (the η_tt- and C_ske-based designs), the results of the experiments confirmed the predictions of the simulations, although unexpected flow separations which were not predicted by the computational fluid dynamics (CFD) resulted in poorer agreement for the two remaining contoured cases. In general, the results of the CFD, as confirmed by the experiment, showed that the best metric for the design of the endwall contours for this rig was that based on the rotor total–total efficiency although importantly, the well-known coefficient of secondary kinetic energy (C_ske), even when formulated using a reasonably simple approach, was able to produce closely competitive results to the efficiency-based metric. These findings are significant firstly because, to date, the use of efficiency is not widespread for the design of non-axisymmetric endwall contours, and secondly, because in cases where the efficiency might be difficult to measure and/or predict, the C_ske may form a robust if only slightly less effective alternative.