Discharge coefficients for flow through holes normal to a rotating shaft

A possible design for a more compact gas turbine engine uses contra-rotatin g high pressure (HP) and intermediate pressure (IP) turbine discs. Cooling air for the IP turbine stages is taken from the compressor and transferred to the turbine stage via holes in the drive shaft. The aim of this work was to investigate the discharge coefficient characteristics of the holes in t his rotating shaft, and, in particular, to ascertain whether the sense of r otation of the shaft with respect to the discs affected these significantly . This paper reports mostly on experimental measurements of the discharge c oefficients. Some CFD modelling of this flow was carried out and this has h elped to explain the experimental work. The experimental results show the e ffects on the discharge coefficient of rotational speed, flow rate, and co- and contra-rotations of the shaft relative to the discs. The measured valu es of the discharge coefficient are compared with established experimental data for non-rotating holes in the presence of a cross-flow. For stationary shaft and discs, co-rotation of the shaft and discs and differential rotat ion with the disc speed less than the shaft tin the same rotational directi on), the discharge coefficients are in reasonable agreement with these data . For differential rotation (including contra-rotation) with the disc speed greater than the shaft, there is a significant decrease in discharge coeff icient. (C) 2000 Elsevier Science Inc. All rights reserved.