Session: 04-26: Novel Combustors II

Paper Number: 103459

103459 - Reacting Flow Prediction of the Low-Swirl Lifted Flame in an Aeronautical Combustor With Angular Air Supply 

The development of lean-burn combustion systems is of major importance for reducing the pollutant emissions of future aero engine generations. In the present study, an innovative gas turbine combustor concept called Short Helical Combustor (SHC) is investigated. By tilting the burners of an annular combustor in circumferential direction relative to the rotational axis of the engine, increased combustion stability may be achieved due to flame piloting by the interaction of adjacent burners. Aiming at the implementation of a lean-burn configuration, a low-swirl lifted flame is adopted in this annular combustor concept. The objective is to reach low NOx emissions by complete evaporation and extensive premixing of fuel and air upstream of the reaction zone.

In this paper, numerical predictions of the reactive flow field featuring the low-swirl lifted flame of the SHC concept are presented. Large Eddy Simulation (LES) employing the finite-rate chemistry approach is used to capture the dynamic characteristics of the flame. At first, a validation study investigating the lifted methane-air flame in an enclosed single burner configuration is carried out. It is demonstrated that the Partially Stirred Reactor (PaSR) combustion model accounting for turbulence-chemistry interaction is capable of reproducing the lift-off height and the shape of the low-swirl flame adequately. Moreover, a skeletal reaction mechanism for methane oxidation is extended by a sub-mechanism which includes the chemiluminescent species OH* allowing the comparison with optical experimental measurements. To establish the particular low-swirl flow field inside the combustor, dedicated mean velocity profiles are used at the inlet patch of the computational domain, and turbulent velocity fluctuations are superimposed by a synthetic inflow turbulence generator.

In case of predicting the lean lifted flame in the tilted burner arrangement of the SHC, the focus is on the interaction of adjacent swirling flows. It was shown in a previous study by the authors that for the isothermal flow the asymmetrically confined swirling jet is strongly deflected towards the sidewall of the staggered SHC dome leading to an increased outflow angle at the combustor exit. The deflection of the flow is associated with an asymmetric pressure field in the vicinity of the burner which is a phenomenon generally known as the Coandă effect. Comparing the reactive to the isothermal flow field, it can be concluded that the deflection is reduced due to the thermal expansion of the flow which may be advantageous for the design of the turbine nozzle guide vanes (NGV) requiring lower turning angles. For the stabilization of this specific type of flame, outer recirculation zones are of primary significance due to an upstream transport of hot combustion products which constantly ignite the incoming fresh mixture. Hence, the interaction of the low-swirl flame and the SHC sidewall is investigated with regard to these recirculation effects. The present work emphasizes the potential of the proposed lean-burn combustor concept for future aero engine applications.

Presenting Author: Sven Hoffmann Institute of Thermal Turbomachinery, Karlsruhe Institute of Technology

Presenting Author Biography: 2011 – 2014
Bachelor of Science in Mechanical Engineering at Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
Major Field: Dimensioning and Validation of Mechanical Constructions

2014 – 2018
Master of Science in Mechanical Engineering at Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
Major Fields: Fluid Mechanics and Thermal Turbomachines

2019 – today
Research assistant at Institute of Thermal Turbomachinery, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany

Authors:

Sven Hoffmann Institute of Thermal Turbomachinery, Karlsruhe Institute of Technology
Rainer Koch Institute of Thermal Turbomachinery, Karlsruhe Institute of Technology
Hans-Jörg Bauer Institute of Thermal Turbomachinery, Karlsruhe Institute of Technology