Tip flow evolution in a turbofan rotor for broadband noise diagnostic

摘要

A tip flow evolution in a realistic turbofan rotor is studied numerically for subsonic (approach) and transonic (cutback) operating conditions. Large Eddy Simulations are performed for Source Diagnostic Test benchmark rotor blade. Single-blade computations are performed for the two operating conditions. The mean-flow results and the wall-pressure statistics are analyzed in the tip flow region of the rotor. The mean trajectory of the tip leakage vortex is traced in both cases. The mean results reveal the presence of a strong tip blockage at approach. For cutback, the flow in the upper part of the blade produces a shock-boundary layer interaction with a lambda-shock. At approach conditions, the unsteady results show an early break-up of the tip leakage vortex and an impingement of the tip vortices with the leading-edge and the tip region of the blade. At cutback the tip leakage vortex is stronger and interacts with the leading edge of the adjacent blade. The blade wall-pressure spectra reflect the impact of the tip vortices on the blade leading-edge. The far-field noise is computed upstream with Ffowcs Williams and Hawkings' analogy using porous surface formulations. Downstream, the projection on acoustic duct modes is made to remove hydrodynamics spurious sources. Both methods showed a good comparison with experiments for the middle frequency range.