On combustion generated noise

Abstract

Tn order to estimate the scaling rules for combustion noise, a tu -rb lence autocorrelation function of the reaction rate must be estimated. This depends in part upon the active reaction volume in a turbulent flame. This volume may be measured by direct flame photography centering on the radiation of an active radical in the reaction zone. The paper describes experiments on fuel-lean propane, propylene, and ethylene-air turbulent open premixed flames with burners of 0.4" -0.96" diameter and velocities to 600 fps. The flame volume is measured from photographs of the flame centered on the CH emission. The volume is correlated to the flow velocity, burner diameter, laminar flame speed and fuel mass fraction in the form of a power law by a regression technique. The scaling rule obtained from experiments is shown to follow the law V cc UD 3 f 3 /s L . The scaling laws generated are compared with estimates previously drawn from Strahle's theory of combustion noise. Implications concerning the turbulence structure in the reaction zone are drawn from the correlations. Refraction, Convection and Diffusion Flame Effects in Combustion Generated Noise

Spatial Coherence of the Heat Release Fluctuations in Turbulent Jet and Swirl Flames

“…The simple model delivers a conversion efficiency of η total ≈ 5.3 × 10 −6 -9.2 × 10 −6 and overpredicts the literature data [4,5] as well as the microphone measurements of the authors, which also show total efficiencies of η total ≈ 0.5 × 10 −7 -1.5 × 10 −7 , by at least one order of magnitude.…”

“…While a literature study showed that the length scales were ranging from the laminar flame front thickness [5,19] to geometrical dimensions of the test rig [7], coherent length scales lying in between were found. Furthermore, the gap between theory and experiment mentioned by Strahle [5] of a factor of 100, could be allocated to non-stochastic, periodic effects.…”

“…A decade later, the first studies on combustion generated noise were published (e.g. [4][5][6]). Compared to fluiddynamic noise of non-reacting flows the generation of noise in combustion processes is still much less understood and precise prediction tools for combustion noise are not available.…”

Analysis of Unsteady Motion with Respect to Noise Sources in a Gas Turbine Combustor: Isothermal Flow Case

“…The scales determine the possible size and frequency of noise sources inside the combustor. Early publications related to aero-and thermo-acoustics relied heavily on these scales in order to provide order-of-magnitude analysis of the noise which are still helpful [30,31]. While the experimental measurements allow only for temporal analysis of the data, since one-point LDV measurements were performed, the LES delivers also spatial information.…”

Numerical analysis of the acoustic field of reacting flows via acoustic perturbation equations

“…In other words, the combustion process acts like a monopole. Strahle [3] published more theoretical studies. Based on Lighthill's procedure [4,5], he derived a wave equation using the conservation equation of multicomponent reacting flows.…”