LES Investigation of Wake Development in a Transonic Fan Stage for Aeroacoustic Analysis

摘要

The development of the fan wake in a transonic fan stage (NASA R4 fan stage) was investigated in detail with the Unsteady Reynolds-averaged Navier-Stokes (URANS) approach and a Large Eddy Simulation (LES). The primary focus is to compare simulation results from the two approaches with the available experimental data so that some guidance can be developed for future applications to aeroacoustic studies of the fan flow field. Many previous studies on fan noise have indicated that the generation of noise in the fan stage changes with the fan RPM, fan tip clearance, fan loading, and the configuration of the fan stage geometry. Also, it has been reported that the development of the fan wake is significantly different among different designs under similar operating conditions. Therefore, an accurate measurement and/or numerical simulation of the fan stage flow field are required to understand the generation of noise in a particular fan stage. For numerical simulation, URANS has been applied for many previous studies. Although some studies of fan noise generation based on URANS flow simulations have shown promising results, higher fidelity CFD tools, such as LES, are pursued for a reliable physics-based assessment of fan noise generation. The present study indicates that the major difference in the simulated flow fields from URANS and LES is how the small eddies are calculated in the fan stage. When the small eddies play an important role in the generation of fan noise, a higher-fidelity CFD tool, like LES, gives a much more accurate and realistic flow field for noise generation assessment.