Effect of penny gap geometry on performance and secondary flow field in a compressor cascade

Marcel Gottschall, Ronald Mailach, Konrad Vogeler

abstract:

The highly-loaded compressors of today's aircraft engines are equipped with adjustable sta- tor vanes to gain aerodynamic stability in a wider operation range. This leads to the problem of variable radial gaps between vane and casing responsible for increasing aerodynamic losses in the endwall regions. In the present work dierent penny gap geometries with a variation of penny size and position are evaluated with the aim to nd an optimized conguration for the entire operating range of modern axial compressors.
Experimental and numerical investigations on inuence of ve diverse endwall gap topologies and endwall designs in variable vanes of low pressure compressors were conducted in a linear cascade using modern stator proles. Parameters 'penny axis position' and 'penny diameter' are focussed in this paper. Analysis were performed with constant, characteristic low pressure stage clearance level of 1.3 % chord at three stagger angles and two characteristic Reynolds numbers which cover the adjusting range of modern aircraft engines. Data was extracted from measurements using a ve-hole probe in several planes up- and downstream the cascade, prole and endwall pressure distributions as well as 3D numerical calculations.
Results indicate extensive interactions between secondary ow and leakage ow through a penny gap depending on aerodynamic loading. It was found that complex casing and penny constructions with the aim of completely avoiding penny gaps are not required. A small gap in the trailing part of the vane has a benecial eect on the ow eld. Especially with higher loading by closing the stator (lowering the stagger angle) a strong impact of the leakage ow on the cascade ow was observed. The leakage vortex aects the channel vortex positively and as a result a signicant decrease in losses and increase in turning near the endwall was discovered. This tendency is observed in the entire adjusting range of cascade stagger angle. Hence there is an overall benet by approving a small rear gap. Otherwise it is shown, that a gap in the higher loaded front part of the vane resulted in strong leakage ow. The subsequent interaction of the separated leakage vortex and the channel vortex always leads to increasing losses.

reference:

Marcel Gottschall, Ronald Mailach, Konrad Vogeler
"Effect of penny gap geometry on performance and secondary flow field in a compressor cascade"
AIAA Journal of Propulsion and Power, 28(5):9. [DOI: 10.2514/1.B34536]