Session: 40-03: Compressor Secondary Flows and Interactions

Paper Number: 151156

Investigation of Shear Layer Induced Pressure Fluctuations in a Linear Compressor Cascade 

In axial compressor stages so called rotating instabilities can be detected at aerodynamically highly loaded operating conditions. Multiple explanations have been proposed on the origin of these pressure fluctuations, among others, that rotating instabilities are caused by rotating source mechanisms, periodic vortex structures, periodic changes in the vortices or the bursting of the tip clearance vortex, there is also the idea that they are caused by shear layer instabilities.

For this purpose, a segment of the rotor of an axial compressor was transferred into a linear cascade in which the Reynolds number is the same and the Mach number also remains below 0.3. In order to achieve the selective effects of tip clearance and incidence variation, the blade tip section of the axial compressor was selected as a reference profile.

In preliminary investigations, a configuration without tip clearance was also found to have spectral patterns similar to rotating instabilities, which supported the hypothesis of shear layer instabilities. To investigate the assumption, a Coanda nozzle was integrated into the sidewall upstream of a compressor cascade to induce pressure fluctuations. The injected air creates a defined shear layer with the inlet main air flow. In the first step, a parameter study is carried out in which the position, injection velocity and inflow angle of the Coanda nozzle are varied. Subsequently, selected combinations are applied to different linear cascade configurations. Tip clearance and incidence of the cascade are varied. The main focus of the paper is the comparison between measurements with and without injection through the Coanda nozzle. It is analysed whether the injection can induce, suppress or intensify pressure fluctuations. By analysing the time-resolved flow in the outlet plane, as well as the use of transient casing pressure measurements in the passage, the identification and occurrence of local development and propagation of vortex systems and pressure fluctuations within the passage will be investigated

Presenting Author: Christoph Jasmund Chair of Turbomachinery and Flight Propulsion, Technische Universität Dresden

Presenting Author Biography: Master's Degree in Aeronautics and Astronautics, Technische Universität Berlin
since 03/2020: Research Associate at the Chair of Turbomachinery and Flight Propulsion, TU Dresden
Research project: Rotating instabilities in axial compressors

Authors:

Christoph Jasmund Chair of Turbomachinery and Flight Propulsion, Technische Universität Dresden
Martin Lange Chair of Turbomachinery and Flight Propulsion, Technische Universität Dresden
Ronald Mailach Chair of Turbomachinery and Flight Propulsion, Technische Universität Dresden