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Global burning velocities of methane-air-steam mixtures are measured on prismatic laminar Bunsen flames and lifted turbulent V-flames for various preheating temperatures, equivalence ratios and steam mixture fractions at atmospheric pressure. Experiments are conducted on a new rectangular slot-burner. Experimental burning velocities are compared to computed flame speeds of one dimensional adiabatic premixed flames using detailed mechanisms (Konnov 0.5 and GRI Mech 3.0). Mean profiles of radicals OH * are also extracted from these flames and compared to simulation results.

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A first‐order estimation of the prediction of combustion‐generated noise from turbulent premixed flames was explored. The method was based on Lighthill's acoustic analogy and used measurement data from high‐speed imaging of chemiluminescent emissions as input. To determine the noise‐generating source, that is, the overall heat release rate from the measured chemiluminescence signals, numerical simulations were performed for 1 D laminar and 3 D turbulent freely propagating flames by employing detailed transport models and reaction mechanisms, including the full reaction chain of the electronically excited hydroxyl radical (OH*). It was shown for both the 1 D and 3 D cases that the local generation of OH* correlated strongly with the heat released from the chemical reaction, especially in the fuel‐lean range. As the chemiluminescence measurements gathered light only along the viewing direction, the line‐of‐sight summed values of heat release rate and OH* concentration were evaluated from the 3 D simulation, and a quasilinear relationship was identified for these integral values. Hence, a proportionality relation was applied for computation of the integral heat release from measured chemiluminescence intensity. An analytical solution of Lighthill's wave equation served as a transfer function, which took fluctuations in the total heat release rate or light intensity as input to calculate the sound radiation in the far field. This approach was applied to a generic burner operated with premixed methane/air jet flames. Good quantitative agreement was obtained between the sound pressures derived from the chemiluminescence measurements and the microphone data, which highlights the potential of the method for applications to more complex flame configurations.

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The work aims to develop and to validate hybrid LES/CAA techniques for numerical computation of direct combustion noise exclusively using the unsteady heat release as main source for the CAA modeling. In order to calculate the unsteady heat release, compressible LES has been carried out for amoderately turbulent jet flame employing ac ombustion model, which is based on tabulation of chemical scalars to include reaction kinetics and modeling the turbulent flame speed to account for flame-turbulence interaction. As the heat release is not explicitly known due to the use of tabulated chemistry,an ew method has been introduced first to evaluate this parameter from turbulent combustion modeling. Forthe CAA simulation, arearranged Lighthill wave equation has been used, where the source term is essentially built up by the heat release rate and provided by the LES. The sound pressure levelderivedfrom the CAA computation showed areasonable good agreement with the measured microphone da ta. In addition, with help of the heat release calculated from LES, the analytical solution of the CAA equation has been explored in order to predict noise emissions without solving the corresponding acoustic equation. Applicability of this approach has provedtobepromising. PACS no. 43.28.Kt, 43.28.Ra 940 ©S.Hirzel Verlag · EAA Zhang et al.:P rediction of combustion noise ACTA ACUSTICA UNITED WITH ACUSTICA Vol. 99 (2013)

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