The effect of four part gap geometry configurations for variable stator vanes in a compressor cascade
Marcel Gottschall, Ronald Mailach, Konrad Vogeler
abstract:
The article describes investigations on the influence of four different endwall clear- ance topologies for variable stator vanes to secondary flow field development and the performance of high pressure compressors. The aim of this work is to quantify the characteristics like flow turning and pressure losses of different clearance configura- tions depending on the penny-axis position and the penny diameter for a representa- tive operating range. These results of an aerodynamically optimized principle of the vane mounting can be considered in further investigations to improve future design processes.
All clearance configurations were implemented to a linear cascade of modern stator profiles. The analysis was introduced using a relative clearance size of 1.3 % chord at three stagger angles and two characteristic Reynolds numbers to comprise the operating range on aircraft engines. Measurements were conducted with a 5-hole-probe in several planes up- and downstream the cascade as well as pressure tappings on the airfoil and the endwall. Additional 3D numerical calculations were carried out to gain information about the flow field inside the cascade.
The results indicate that small gaps in the rear part of the vane have a beneficial effect on the flow field. Significant enhanced performance was determined near the endwall especially with a higher stagger angle. The mixing losses of the interaction of clearance flow and passage flow were reduced by smaller gradients of flow directions. Also an improved and smoothened axial pressure distribution was found around the vane and results in a higher averaged flow turning even compared to a configuration without a clearance.
In contrast, a clearance in the higher loaded front part of the vane always resulted in increased losses due to the amplified corner separation. This drawback is reduced when adding a rear clearance with the penny only in the middle chordposition. Especially the blade turning near the wall with higher stagger angle increases for such configurations to almost the magnitudes of the no clearance configuration.
reference:
Marcel Gottschall, Ronald Mailach, Konrad Vogeler
"The effect of four part gap geometry configurations for variable stator vanes in a compressor cascade"
Paper No. GT2012-69757, ASME Turbo Expo, Copenhagen, Denmark, 2012