Strut or guide vane secondary flows and their effect on turbomachinery noise

Abstract

Results of an investigation in which the turbomachinery rotor sound spectra were correlated with aerodynamic measurements of upstream strut secondary flow are reported. The aerodynamic measurements, carried out in an aeroacoustic turbomachinery facility, included mean-velocity and turbulence-intensity profiles across the wake and the secondary flow regions at the strut exit or rotor inlet. The measurements were carried out at incidence angles of 0, 4, 12, and -12 deg to the strut. The far-field acoustic measurements were carried out for all these operating conditions. The strut span was kept small to eliminate the wake interaction effects. The acoustic results correlated with the aerodynamic measurements indicate that secondary flow could be a significant noise source in cases where secondary flow/vortex strength is large.x,6,r Nomenclature = blade passing frequency = nondimensional radius = r/r i[p = sound pressure level = mean axial velocity at r/r tip = 0.75 = blade tip speed = local mean tangential and axial velocity, respectively = fluctuating turbulent velocity in the axial, tangential, and radial directions, respectively = axial, tangential, and radial directions, respectively = tangential probe distance nondimensionalized with respect to local rotor blade spacing = distance between hot wire and strut trailing edge for aerodynamic measurements and distance between rotor blade leading edge and strut trailing edge for acoustic measurements, nondimensionalized with respect to strut chord = flow incidence angle to the strut = tangential probe location, rad = axial velocity defect normalized by freestream velocity = strength of vortex = flow coefficient =U c /U t = tip = components in axial, tangential, and radial directions, respectively

An Experimental and Numerical Study on Wake Vortex Noise of a Low Speed Propeller Fan

“…In a study on the aerodynamic noise of the propeller fan, the authors verified experimentally the mechanism of the discrete frequency noise of a propeller fan generated because of the pseudo rotor-stator interaction [4]. In such previous studies, there are not a few study cases about the mechanism of the discrete frequency noise synchronizing with the blade passing frequency of the high specific speed fan [5]. On the other hand, in a study on the turbulent noise of a low pressure axial fan, Fukano et al suggested that the broadband noise was mainly generated because of the vortex shedding to the wake if the turbulence of the incoming flow to the fan is weak [6].…”

“…In such previous studies, there are not a few study cases about the mechanism of the discrete frequency noise synchronizing with the blade passing frequency of the high specific speed fan [5]. On the other hand, in a study on the turbulent noise of a low pressure axial fan, Fukano et al suggested that the broadband noise was mainly generated because of the vortex shedding to the wake if the turbulence of the incoming flow to the fan is weak [6]. Whereas the relationship between the tip vortex and noise has been discussed in a study of the aerodynamic noise from the propeller fan [7], there are several reports stating that the affect of the tip vortex on the fan noise is small in the vicinity of the design point [8].…”

Experimental and numerical investigations on the flow characteristics of rotary machineries

“…However, the interactions between rotor and stator may induce unnecessary aeroacoustic noise if the guide vanes are poorly designed. The mechanism of rotor-stator interaction noise was investigated by Lakshminarayana et al (1982). He suggested that the main source of this noise was caused by flow irregularities in the tip leakage flow and the secondary flow around the tip and hub regions.…”