Steady and Unsteady Numerical Characterisation of the Secondary Flow Structures of a Highly-Loaded Low-Pressure Compressor Stage

Authors

Riccardo Toracchio  - von Karman Institute for Fluid Dynamics, Belgium
Koen Hillewaert - University of Liège, Belgium
Fabrizio Fontaneto - von Karman Institute for Fluid Dynamics, Belgium

Abstract

This paper presents a numerical characterisation of a highly-loaded low-pressure compressor by means of 3D unsteady RANS simulations in view of identifying and quantifying changes in large scale structures arising especially close to the stability limit of the machine. The focus is on the unsteady evolution of these critical structures and their role with respect to the other flow features. In a first step, a mesh refinement study and a turbulence model sensitivity analysis are presented to support the reliability of the provided results. For the latter, rotor inlet parameters are analysed to assess their impact on the evolution of the end-wall flow and of the hub corner separation. The computed pressure ratio and efficiency are then characterised to assess the capability of the URANS simulation to reach the experimental global performance. To support this validation, comparisons with experimental data are provided in terms of spanwise distributions, rotor outlet maps and amplitudes of the pressure fluctuations. Finally, a full description of the unsteady features of the machine is provided, with a focus on the two regions where the most critical features, such as tip leakage flow and hub corner separation, are expected: the casing and the rotor hub wall. Retrieved frequencies and their link with the observed phenomena are also investigated. In the present paper results will be analysed at design and near-stall operating conditions, with a focus on the behaviour of the machine close to its stability limit at 100% speed.