Influence of mean flow gradients on fan exhaust noise predictions

2008-12-01
Tester, Brian J.
Gabard, Gwénaël
Özyörük, Yusuf
Aft fan noise is becoming a more dominant source as engine bypass ratio is increased. In this paper an assessment of the effect of the mean flow gradients on fan exhaust noise propagation is carried out using both analytical models for simplified problems and numerical methods for realistic configurations. Fan exhaust noise can be significantly refracted by the mean flow gradients in the jet mixing layer, especially at high operating conditions (i.e. during take off). The refraction effect is predicted using either Lilley's equation or the linearized Euler equations. For parallel base flflows, an issue with these linear models is the presence of Kelvin-Helmholtz instabilities whose unlimited exponential growth is unphysical and problematic for computational methods. This problem is less critical for developing mixing layer for instance where the growth of the vorticity thickness reduces the growth of the instability waves [1]. Various techniques have been used for suppressing the instability; these include adding non-linear terms to saturate the growth of the instability [2], using frequency domain analysis [3], or removing the mean flow gradient terms [4]. It is the last approach, termed Gradient Term Suppression (GTS), which is investigated in the present work.

Suggestions

Numerical simulation of fore and aft sound fields of a turbofan
Özyörük, Yusuf (American Institute of Aeronautics and Astronautics (AIAA), 2004-10-01)
A framework for predicting fan related noise from high bypass ratio engines is presented. The methodology accounts for both fore and aft radiation and includes the effects of liner treatment on the engine walls. Solutions are obtained through a combination of Euler and linearized Euler solvers, coupled with a Kirchhoff formulation for far-field noise prediction. The nacelle region is solved using the Eider solver, whereas the linearized Euler solver is used for the fan exhaust stage. Switching to the linear...
Parallel optimization of flapping airfoils in a biplane configuration for maximum thrust
Tuncer, İsmail Hakkı (2004-05-27)
Flapping airfoils in a biplane configuration are optimized for a maximum thrust production. A parallel Navier-Stokes solver on overset grids and a gradient based parallel optimization method are employed. The periodic flapping motion of airfoils in a plane configuration is described in a combined pitch and plunge. The pitch and plunge amplitudes and the phase shift between them are optimized for a range of flapping frequencies. It is shown that at low flapping frequencies, flapping airfoils in a biplane con...
Simulation of Dynamic Operation in Salient Pole Synchronous Machines
Dordea, Toma; Munteanu, Radu; Campeanu, Aurel (2011-09-10)
The design of today's high performance synchronous motors must take into account not only the steady state but also practically inevitable dynamic regimes. In such conditions an accurate predetermination of the parameters and constructive solution by modeling and simulation of the given dynamic operation, becomes a mandatory step. In this aim, in the present paper a novel mathematical model of the high power salient pole synchronous machine (SPSM) is elaborated. We proposed to consider especially the effect...
Experimental investigation of the effects of tip-injection on the aerodynamic loads and wake characteristics of a model horizontal axis wind turbine rotor
Abdulrahim, Anas; Uzol, Oğuz; Department of Aerospace Engineering (2014)
In this study, tip injection is implemented on a model Horizontal Axis Wind Turbine (HAWT) rotor to investigate the power and thrust coefficient variations as well as the wake characteristics. The model wind turbine has a 0.95 m diameter 3-bladed rotor with non-linearly twisted and tapered blades that has NREL S826 profile. The nacelle, hub and the blades are specifically designed to allow pressurized air to pass through and get injected from the tips while the rotor is rotating. The experiments are perform...
Aerodynamic parameter estimation of a supersonic missile with rapid speed variation by using kalman filtering
Bayoğlu, Tuğba; Kutay, Ali Türker; Department of Aerospace Engineering (2016)
This study aims to develop an approach for the aerodynamic parameter estimation problem for supersonic air to air missile with rapid speed variation, as well as large variation of aerodynamic parameters with respect to Mach number. In literature, most of the estimation techniques require that estimator is time independent. Therefore, most of the aerodynamic parameter estimation methods are applied for air vehicles which have control over their speed or which can operate at relatively constant Mach number so...
Citation Formats
B. J. Tester, G. Gabard, and Y. Özyörük, “Influence of mean flow gradients on fan exhaust noise predictions,” Vancouver, Canada, 2008, Accessed: 00, 2021. [Online]. Available: https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=78249286214&origin=inward.