Investigation of Fan-Wake/Outlet-Guide-Vane Interaction Broadband Noise

Abstract

Fan-wake/outlet-guide-vane interaction broadband noise in turbofan jet engines is studied. The mechanism and some issues are first discussed using a two-dimensional gust-prediction model. An oblique gust-prediction model is then developed. Quasi-three-dimensional unsteady lift is calculated using a two-dimensional equivalence method. It is coupled with annular duct modes to obtain the sound power spectrum density. Spanwise turbulence integral length scales and their impact on power spectrum density predictions are investigated. A spanwise integration limit suitable for the complete frequency range is proposed. The model is validated using the NASA Source Diagnostic Test data. Sound power scaling with vane count B is examined. If solidity is maintained, the cascade response does not converge on the single-airfoil response, even for low vane counts. The sound power varies inversely with B at low frequency; it scales with B at very high frequency. The power spectrum density trend with the fan tip Mach number M T is also identified. It scales with M 5 T if turbulence intensity in the fan wake scales "ideally" with M T. At offdesign conditions, fan wakes are not ideal; therefore, different speed trends apply. M 3.3 T scaling is found to best fit the Source Diagnostic Test data and the prediction.

Turbine Broadband Noise Predictions Using Linearised Frequency Domain Navier-Stokes Solvers

“…To keep a simpler formulation than in a previous publication [13], and as previously done by Ju et al [19], the vortical gusts, which are sub-critical, i.e., do not produce any cut-on response, are a priori filtered out. This is performed to avoid an over-prediction of the number of cut-on modes that would occur in a purely 2D case leading to large over-predictions of the resulting spectra.…”

Effects of Vane Sweep on Fan-Wake/Outlet-Guide-Vane Interaction Broadband Noise

“…The process to extract interaction BBN from the stage (rotor+stator) total noise and the fan self-noise was described in [6]. It turns out that the only data valid for the sweep study is at the approach condition.…”

“…Therefore the vorticity waves with maximum noise-generating energy are those with 0 3  k no matter it is on the radial OGV or the swept OGV. It has been shown in [6] that if the spanwise turbulence integral length scale is small, for lower order duct modes and away from the tip or hub, noise is mainly generated by 2D gusts ( 0 3  k ). Contributions from oblique gusts cancel each other.…”

“…The reduced order model is useful for preliminary designs. It is based on the semi-analytical method for oblique gust/cascade interaction in [5], and the broadband model for radial OGV in [6]. The NASA SDT data reported in [4] for low noise OGV is used to validate the method.…”

Tonal and Broadband Noise Control of an Axial Flow Fan with Metal Foams: Design and Experimental Validation

“…(1) Interactions of RBs with UMPs and OGVs. Although these interactions radiate both tonal and broadband noise [24][25][26], the tonal components are usually dominating. There are two mechanics responsible for these periodic interactions [24].…”