Modelling of Sound Generation by Turbulent Reacting Flows

Abstract

The two components of combustion noise, namely the direct noise induced by heat release fluctuations in the flow and the indirect noise caused by acceleration of entropy perturbations through mean flow gradients resulting in acoustic radiation, are examined by considering different types of inhomogeneous wave equations deduced from the balance equations of fluid dynamics. This is accomplished by adapting acoustic analogies initially derived by Lighthill (1952), Phillips (1960) and Lilley (1972) for non-reactive flows to the reacting case. This reformulation is based on a standard set of assumptions borrowed from combustion. It is shown that a consistent formulation of a wave operator and its associated source terms is required.

Two-time correlation of heat release rate and spectrum of combustion noise from turbulent premixed flames

“…The sound field radiated from a turbulent reacting flow has been derived previously [4,33] which includes a variety of source terms associated with flow noise, viscous dissipation, heat and molecular transports, direct and indirect combustion noise. At low Mach number condition as in open flames, the direct noise from unsteady heat input is the dominant source [34,35], and therefore the governing linear wave equation can be expressed in a reduced form as…”

Reliable reduced-order models for time-dependent linearized Euler equations

“…For instance, LEEs associated with appropriate source terms are often used as an extension to Lighthill's analogy in computational aeroacoustics [5] and as an efficient simplified aerodynamic model for aeroelastic predictions [16]. The LEEs are succinctly presented in this section.…”

“…In this paper, the mean flow will be first supposed uniform to introduce model reduction concepts. The treatment of nonuniform or even unstable base flows remains much more complex theoretically and numerically [1,5] due to possible growing energy at finite time. It can be shown that this potential growing is only induced by the reaction matrix at least for isothermal and incompressible base flows.…”

On Prediction of Combustion Generated Noise with the Turbulent Heat Release Rate

“…Therefore, af ully or apartially non-reflecting treatment accounting for this effect remains mandatory for the direct methods [4]. As a wayout, the indirect or hybrid CFD (Computational Fluid Dynamics)/CAA (Computational Aero-Acoustics)m ethods are often used [5,6]. In these techniques, the noisegenerating sources (e.g.…”

“…Due to its simplicity,L ighthill'sa nalogy as well as its modifications are widely used for combustion noise problem in the last decade [3,9,10,11,12,13]. Recently,o ther more sophisticated methods, such as the Phillips' analogy [14], the Linearized Euler-Equations (LEE) [ 5] and the APE (Acoustic Perturbation Equations)system [15], have been successfully applied for the prediction of combustion noise [16,17,18], which are derivedf rom the governing equations for afl owing fluid as well. The Phillips' analogy is represented by awaveequation for the logarithmic pressure.…”