Research Topic

Numerical Investigations of Altitude Relight Phenomena

Introduction and Motivation

Ignition processes can be subdivided into autoignition and forced ignition. Autoignition is a spontaneous self ignition because of ambient conditions while forced ignition is characterized by an external energy source which triggers the transition from unburnt to burnt.

The transition process e.g. in an aircraft engine consists of multiple physical processes, starting with the injection of a liquid spray into the combustion chamber. The jet breaks into droplets which evaporate. Due to mixing a flammable region develops which is ignited by a spark. Next, a flame kernel develops which is convected and grows and finally lights the whole combustion chamber. This complex transition is not jet fully understood. Therefore, the Computational Fluid Dynamics (CFD) technique can help to gain a better understanding of the complex phenomena.

Method and Theory

Instantaneous temperature plot of the Flame D configuration.

The present work focuses on the flame kernel propagation and the development to the point of a fully accomplished flame. Since this is a transient physical phenomena the Large Eddy Simulation (LES) technique is used which has proven its ability to predict turbulent, unsteady phenomena. The idea of the method is to adopt a spatial filter to the flow field which allows to simulate the large, energy containing eddies while modeling the small structures.

The combustion is simulated by using the Flamelet-Generated Manifold (FGM) approach which allows to reduce the combustion process to three dimensions: mixture fraction, reaction progress and mixture fraction variance, respectively. Second, the Artificially Thickened Flame (ATF) model will be implemented to calculate premixed combustion.

Proceeding

Within the present work the isothermal as well as the reacting LES should be verified and validated. Verification test cases like the density wave or the laminar premixed flame calculation will be taken out. As validation test cases serve the TECFLAM swirl burner as well as the Flame D configuration.

Key Research Area

Multi-Physics; Numerical Combustion Modeling, Non Premixed Combustion, Premixed Combustion, Ignition

Contact

Kai Aschmoneit
Dipl.-Ing.

Address:

Petersenstra├če/30

D-64287 Darmstadt

Germany

Phone:

+49 6151 16 - 24401 or 24402

Fax:

+49 6151 16-6555

Office:

L1|01 291

Email:

aschmoneit (at) gsc.tu...

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