Jesch,David

Motivation and objectives

The objective of this project is to develop an integrated model which is suitable for simulating systems such as afterburners, ram-jet or scram-jet combustors. These systems are the subjects of intensive research since they are strongly believed to play an essential role in the future of aviation. Reliable and accurate models with reasonable computation time are crucial for their further development. In order to improve the existing simulation methods, the influence of high Mach-number flows on combustion processes should be investigated since present models are only valid for cases with low Mach-number.

Introduction

The effects of compressibility has been handled in the CTI (combustor-turbine interaction) context (Details can be found in the thesis of Eva Verena Klapdor: Simulation of combustor-turbine interaction in a jet engine ). Due to compressibility effects the temperature is no longer a passive scalar but it is a function of the total enthalpy and the kinetic energy. The basic assumption is that the regions of reaction and compressibility can be separated due to the low Mach-number. The reactive flow within the combustor is assumed to be incompressible. The sensible enthalpy does not change due to reaction, but only due to mixing of fuel and oxidizer streams. However, in the compressible region (within the NGV) the enthalpy changes due to compressibility while the total enthalpy remains constant. In this region chemical reactions are almost negligible (Fig. 1.).

Fig. 1. : Source term of CO2 indicating the zone of reaction
Fig. 1. : Source term of CO2 indicating the zone of reaction

During the calculations the FGM method is used. Only one table is applied for the entire domain which is calculated for a given pressure value. Therefore the parameters read from the table have to be corrected. This is done in accordance with the observed enthalpy difference between the results calculated by the energy equation (which accounts for compressibility effects) and the ones stored in the table. Due to the low Mach-number, these corrections are small in the region of combustion. This assumption is not valid anymore when the Mach-number is high. Pressure needs to be added to the table as a control variable.