Prediction of Pressure Oscillations in a Premixed Swirl Combustor Flow and Comparison to Measurements

Abstract

The most common and reliable technique used for flame stabilization of industrial combustors with high thermal loads is the application of strongly swirling flows. In addition to stabilization, swirl flames offer the possibility to influence emission characteristics by simply changing the swirl intensity or the type of swirl generation. Despite of these major advantages, swirling flows tend to evolve flow instabilities, that considerably constitute a significant source of noise. In general, noise generation is substantially enhanced, when such a swirling flow is employed for flames. Thus, the minimization of the resulting noise emissions under conservation of the benefit of high ignition stability is one major design challenge for the development of modern swirl stabilized combustion devices. The present investigation makes an attempt to determine mechanisms and processes to influence the noise generation of flames with underlying swirling flows. Therefore, a new burner has been designed, that offers the possibility to vary geometrical parameters as well as the type of swirl generation, typically applied in industrial devices. Experimental data has been acquired for the isothermal flow as well as swirl flames by means of 3-D-LDV-diagnostics comprising the components of long-time averaged mean and rmsvelocities as well as spectrally resolved velocity fluctuations for all components. The noise emission data was acquired with microphone probes resulting in sound pressure levels outside the zone of the perceptible fluid flow. Along to the experiments, numerical simulations using RANS and LES have been carried out for isothermal cases with different burner outlet geometries. The results of the measurements show a distinct rise of the sound pressure level, obtained by changing both the test setup from the isothermal into the flame configuration as well as the geometrical parameters. This is also resembled by the LES simulation results. Furthermore, a physical model has been developed from experiments and verified by the LES simulation, that

Numerical Investigations of the Noise Sources Generated in a Swirl Stabilized Flame

“…This combustion model has been implemented in the commercial CFD code CFX which uses an unstructured finite volume method (FVM) to solve the compressible Navier Stokes equations and is capable to run LES. Habisreuther et al [1] performed an isothermal LES with CFX for the strongly swirled burner used in this paper and achieved very good agreement with respect to the measured mean flow values and the Reynolds stresses.…”

Experimental Flame Front Characterisation in a Lean Premix Burner Operating with Syngas Simplified Model Fuel

“…For larger radii, such a component increases to a maximum equal to 1.1 u bulk located at r/R out = 0.92, from which it decreases with a rapid decay to an outer zone, characterized by values close to 0.1 u bulk . Hence, the axial component profile indicated the presence of an inner recirculation zone (IRZ), typical in swirl-stabilized injectors [29][30][31][32][33][34], having, in the selected axial position, a radial extension corresponding to 29% of the burner outlet diameter. Similarly, the flow leaving the burner was concentrated in an annular jet, which showed a centrifugal behaviour, as suggested by the u r profile characterized by continuously positive values (the maximum value is equal to 0.36 u bulk at r/R out = 0.92).…”

Non-Linear Response to Periodic Forcing of Methane-Air Global and Detailed Kinetics in Continuous Stirred Tank Reactors Close to Extinction Conditions

“…For instance, CFD (Computational Fluid Dynamics) simulations of combustion instabilities help to isolate the possible causes for the occurrence of the instabilities [23][24][25][26][27][28][29]. 3D CFD simulations, able to describe the unsteady structure of the flow (Large Eddy Simulation), give clear insights on the phenomenon [30,31].…”