Session: 34-05 Flow Control

Paper Number: 82834

82834 - Numerical Investigations on the Rotating Stall in an Axial Compressor and Its Control by Flow Injection at Casing 

The stable operating range of compressors used in aeronautical engines is limited by the choke line, at high flow rate, and surge line, at low flow rate. Surge and rotating stall occurring at low flow rate must be avoided for safety reasons as they can lead to the engine failure. Thus, engine manufacturers design compressors using a safety margin, called surge margin, in order to ensure a stable operating conditions at all flight conditions.

This study is based on the experimental compressor CME2 tested at the Lille Laboratory of Fluid Mechanics (LMFL). This is a low-subsonic axial compressor dedicated to the investigation of rotating stall as this phenomenon can be easily observed and reproduced without any compressor damage. This compressor is tip-critical as the rotor tip is responsible for the rotating stall.

Active flow control improves compressor performances and extends the stable operating range. In the present configuration, flow injection is performed at the casing. Twenty pairs of actuators are added to the CME2 compressor. The geometry of the injector exit outlet on the Coanda effect so that the added flow stays close to the blade tip and can modify the tip flow and delays the rotating stall onset.

The present study aims at predicting numerically the rotating stall of this compressor. This investigation is performed with a full-annulus mesh of the compressor and unsteady RANS simulations. The rotating stall onset flow rate is well captured by CFD, compared to experiment, around 4 kg/s. Before the rotating stall limit, the flow remains periodic. Numerical convergence is obtained for operating points at lower flow rate and the results show that separation occurs at the rotor tip, close to the leading edge, causing the emergence of rotating stall cells. As each cell covers a different azimuthal extend and their rotating velocities differ, after ten revolutions, all cells are merged and only one cell remains, as in experiment. The baseline configuration is relative to the facility without active flow control.

The insertion of the actuators in the computational domain is carried out through hybrid meshes. Due to the complex geometry, an unstructured mesh is used for each actuator. The structured mesh of the blade passages is kept, except the area were the unstructured actuator meshes are added to the computational domain. The combination of structured and unstructured meshes is called an hybrid mesh. Although the flow is still not periodic below the rotating stall onset of baseline configuration, stalled cells are not numerically predicted. Thus, the rotating stall is delayed at lower flow rate, as expected by the use of active flow control and this is experimentally observed.

Presenting Author: Julien Marty DAAA, ONERA, Université Paris Saclay

Presenting Author Biography: Julien Marty awarded a Ph.D thesis in 2010 at ONERA dealing with impact of turbulence, laminar-turbulent transition and leakage flows on numerical stability limit of HP compressor. He received a Ph.D award of the ISAE-SUPAERO Foundation in December 2011 for this work. Hired by ONERA in 2009 as a research engineer, his main research interests are the turbulence modeling of separated or vortical flows in compressors and turbines, especially Large-Eddy Simulation and Zonal Detached-Eddy Simulation and transition modelling, mainly for turbine applications.

Authors:

Julien Marty DAAA, ONERA, Université Paris Saclay
Lionel Castillon DAAA, ONERA, Université Paris Saclay
Pierric Joseph Univ. Lille, CNRS, ONERA, Arts et Metiers Institute of Technology, Centrale Lille Institut, UMR 9014-LMFL, Laboratoire de Mécanique des Fluides de Lille - Kampé de Fériet