scholarly journals Influence of Heat Transfer and Material Temperature on Combustion Instabilities in a Swirl Burner

2016 ◽  
Vol 139 (5) ◽  
Author(s):  
Christian Kraus ◽  
Laurent Selle ◽  
Thierry Poinsot ◽  
Christoph M. Arndt ◽  
Henning Bockhorn
Keyword(s):  
Heat Transfer ◽  
Combustion Chamber ◽  
Passive Control ◽  
Unstable Mode ◽  
Combustion Instabilities ◽  
Ambient Conditions ◽  
Swirl Burner ◽  
Helmholtz Resonators ◽  
Eddy Simulation ◽  
Limited Frequency

The current work focuses on the large eddy simulation (LES) of combustion instability in a laboratory-scale swirl burner. Air and fuel are injected at ambient conditions. Heat conduction from the combustion chamber to the plenums results in a preheating of the air and fuel flows above ambient conditions. The paper compares two computations: In the first computation, the temperature of the injected reactants is 300 K (equivalent to the experiment) and the combustor walls are treated as adiabatic. The frequency of the unstable mode (≈ 635 Hz) deviates significantly from the measured frequency (≈ 750 Hz). In the second computation, the preheating effect observed in the experiment and the heat losses at the combustion chamber walls are taken into account. The frequency (≈ 725 Hz) of the unstable mode agrees well with the experiment. These results illustrate the importance of accounting for heat transfer/losses when applying LES for the prediction of combustion instabilities. Uncertainties caused by unsuitable modeling strategies when using computational fluid dynamics for the prediction of combustion instabilities can lead to an improper design of passive control methods (such as Helmholtz resonators) as these are often only effective in a limited frequency range.

scholarly journals Influence of Heat Transfer and Material Temperature on Combustion Instabilities in a Swirl Burner

2016 ◽  
Author(s):  
Christian Kraus ◽  
Laurent Selle ◽  
Thierry Poinsot ◽  
Christoph M. Arndt ◽  
Henning Bockhorn
Keyword(s):  
Heat Transfer ◽  
Combustion Chamber ◽  
Passive Control ◽  
Unstable Mode ◽  
Combustion Instabilities ◽  
Ambient Conditions ◽  
Swirl Burner ◽  
Helmholtz Resonators ◽  
Eddy Simulation ◽  
Limited Frequency

The current work focuses on the Large Eddy Simulation of a combustion instability in a laboratory-scale swirl burner. Air and fuel are injected at ambient conditions. Heat conduction from the combustion chamber to the plenums results in a preheating of the air and fuel flows above ambient conditions. The paper compares two computations with different modeling strategies. In the first computation, the temperature of the injected reactantsis 300 K (equivalent to the experiment) and the combustor walls are treated as adiabatic. The frequency of the unstable mode (≈ 635 Hz) deviates significantly from the measured frequency (≈ 750 Hz). In the second computation, the preheating effect observed in the experiment and the heat losses at the combustion chamber walls are taken into account. The frequency (≈ 725 Hz) of the unstable mode agrees well with the experiment. These results illustrate the importance of accounting for heat transfer/ losses when applying LES for the prediction of combustion instabilities. Uncertainties caused by unsuitable modeling strategies when using CFD for the prediction of combustion instabilities can lead to an improper design of passive control methods (such as Helmholtz resonators), as these are often only effective in a limited frequency range.

scholarly journals Passive control of instabilities in combustion systems with heat exchanger

2017 ◽  
Vol 10 (4) ◽  
pp. 362-379 ◽  
Author(s):  
Aswathy Surendran ◽  
Maria A Heckl ◽  
Naseh Hosseini ◽  
Omke Jan Teerling
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Transfer Function ◽  
Heat Source ◽  
Passive Control ◽  
Time Lag ◽  
Acoustic Scattering ◽  
Resonant Mode ◽  
Combustion Instabilities ◽  
Wide Range

One of the major concerns in the operability of power generation systems is their susceptibility to combustion instabilities. In this work, we explore whether a heat exchanger, an integral component of a domestic boiler, can be made to act as a passive controller that suppresses combustion instabilities. The combustor is modelled as a quarter-wave resonator (1-D, open at one end, closed at the other) with a compact heat source inside, which is modelled by a time-lag law. The heat exchanger is modelled as an array of tubes with bias flow and is placed near the closed end of the resonator, causing it to behave like a cavity-backed slit plate: an effective acoustic absorber. For simplicity and ease of analysis, we treat the physical processes of heat transfer and acoustic scattering occurring at the heat exchanger as two individual processes separated by an infinitesimal distance. The aeroacoustic response of the tube array is modelled using a quasi-steady approach and the heat transfer across the heat exchanger is modelled by assuming it to be a heat sink. Unsteady numerical simulations were carried out to obtain the heat exchanger transfer function, which is the response of the heat transfer at heat exchanger to upstream velocity perturbations. Combining the aeroacoustic response and the heat exchanger transfer function, in the limit of the distance between these processes tending to zero, gives the net influence of the heat exchanger. Other parameters of interest are the heat source location and the cavity length (the distance between the tube array and the closed end). We then construct stability maps for the first resonant mode of the aforementioned combustor configuration, for various parameter combinations. Our model predicts that stability can be achieved for a wide range of parameters.

Aerothermal Prediction of an Aeronautical Combustion Chamber Based on the Coupling of Large Eddy Simulation, Solid Conduction and Radiation Solvers

2015 ◽  
Author(s):  
Sandrine Berger ◽  
Stéphane Richard ◽  
Gabriel Staffelbach ◽  
Florent Duchaine ◽  
Laurent Gicquel
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Combustion Chamber ◽  
Gas Turbines ◽  
Thermal Environment ◽  
Heat Fluxes ◽  
High Fidelity ◽  
Eddy Simulation ◽  
Precise Knowledge ◽  
Large Eddy

A precise knowledge of the thermal environment is essential for gas turbines design. Combustion chamber walls in particular are subject to strong thermal constraints. It is thus essential for designers to characterize accurately the local thermal state of such devices. Today, the determination of wall temperatures is performed experimentally by complex thermocolor tests. To limit such expensive experiments and integrate the knowledge of the thermal environment earlier in the design process, efforts are currently performed to provide high fidelity numerical tools able to predict the combustion chamber walls temperature. Many coupled physical phenomena are involved: turbulent combustion, convection and mixing of hot products and cold flows, conduction in the solid parts as well as gas to gas, gas to wall and wall to wall radiative transfers. The resolution of such a multiphysics problem jointly in the fluid and the solid domains can be done numerically through the use of several dedicated numerical and algorithmic approaches. In this paper, a partitioned coupling methodology is used to investigate the solid steady state wall temperature of a helicopter combustor in take-off conditions. The methodology relies on a high fidelity Large Eddy Simulation reacting flow solver coupled to conduction and radiative solvers. Different computations are presented in order to assess the role of each heat transfer process in the temperature field. A conjugate heat transfer simulation is first proposed and compared with experimental thermocolor tests. The effect of radiation is then investigated comparing relative importance of convective and radiative heat fluxes.

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