Identification of Tip-Leakage Vortex Wandering in Large-Eddy Simulation of ECL5/CATANA Transonic Fan Stage
Résumé
The tip-leakage flow in fan stages affects aerodynamic efficiency, stability and contributes to broadband noise. Its behavior is difficult to predict, especially in transonic configurations. This study focuses on the ECL5 fan/OGV stage, an open test case from École Centrale de Lyon. At nominal speed, the flow is transonic, with a relative Mach number at the inlet slightly above unity near the tip. A large-eddy simulation (LES) is performed on a periodic angular sector to simulate the unsteady flow phenomena. A first comparison with experimental measurements focuses on the validation of the LES. The analysis of the pressure fluctuation spectra reveals an unexpected low-frequency peak upstream of the rotor blades. A dynamic mode decomposition at the corresponding frequency shows an unsteadiness in the tip-leakage flow. Tracking the tip-leakage flow dynamically using conventional vortex identification methods such as Galilean invariants can be challenging, especially in complex flow conditions. A purely kinetic vortex tracking algorithm is developed and validated to determine the trajectory and size evolution of the tip-leakage vortex. In the mean flow, the vortex is detected up to two rotor chords downstream of the leading edge of the rotor blade. By using frequencyfiltered fields from the unsteady simulation, vortex wandering is investigated. The interaction with the surrounding flow features is outlined.
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