Session: 35-04 Fan, Compressor and Engine Noise 1

Paper Number: 120948

120948 - Effects of Radially Variable Sweep Vanes on Rotor-Stator Interaction Noise 

Rotor-stator interaction noise has been a major source for aero-engine and aircraft noise, especially for modern high by-pass ration turbofan engines. Much effort has been taken to suppress such noise either by attenuating it during its propagation using a duct liner or directly weakening the source strength through structural design of the fan-stage, among which a sweep stator vane design has been proved to be an effective way to reduce both the broadband and tonal components of rotor-stator interaction noise. Nevertheless, with the application of three-dimensional aerodynamic designs, the stator vanes in modern engines’ fan stage have more complicated variable sweep layouts rather than a simple constant swept angle structure. Therefore, in this paper we extend our previously established three-dimensional cascade model to include the influences of arbitrarily variable vane sweep and chord length along the radial direction. In other words, both the leading edge and the trailing edge of the stator vanes can be radially varied without restrictions. The effect of leaned vanes is temporarily neglected, since a small lean angle has little effect on the noise reduction and a large-lean-angle design is very unlikely to be applied in a practical aero-engine due to structural strength and weight limitations. The tonal rotor-stator interaction noise is then theoretically studied with different radially varied swept-vane layouts under different working conditions at the first three blade passing frequencies (BPFs). The unsteady pressure loading on vanes is further investigated to reveal the characteristic of the dipole source of the rotor-stator interaction noise. It was observed that when the rotor tip Mach number is mildly above unity such that the tonal noise at 1 BPF has only one cut-on mode, rotor-stator interaction noise is more sensitive to the variation in swept angles. But for tonal noise at other BPFs or at working conditions where tonal interaction noise at 1 BPF is fully cut-off, there exist multiple cut-on modes and the interaction noise is less sensitive to the variation in sweep. In such cases, the propagating noise may tend to monotonically decrease with the increase in the swept angle and the radial variation in the phase angle of the incident wake velocity. Also, when only one mode is cut-on, the effect of sweep near the stator tip region seems to be more profound. This should be attributed to the radial distribution of Tyler-Sofrin’s rotating acoustic modes in annular ducts showing that an acoustic mode with higher circumferential mode order is more concentrated near the tip region. Therefore, the phase variation of the unsteady pressure loading in this area induced by the sweep design can cause more interference to the propagating duct mode and leads to more reduction in tonal noise compared to a non-swept situation.

Presenting Author: Zihan Shen Beihang University

Presenting Author Biography: I am Shen, Zihan and I'm now working on my Doctoral degree in Fluid and Acoustic Engineering Laboratory (FAEL) of Beihang University under the supervision of Professor Sun, Xiaofeng. My current study interest is in aeroacoustics and its related unsteady phenomenon in turbomachinery, especially in aero-engines.

Authors:

Zihan Shen Beihang University
Xiaoyu Wang Beihang University
Guangyu Zhang Beihang University
Xiaofeng Sun Beihang University