Application of Numerical Aerothermal Models on Jet Engine Combustors

Doktorsavhandling, 1994

The use of numerical simulations with combustion for predicting the flow field in a gas turbine combustor or afterburner may reduce the required time in the development process. To investigate the performance of numerical simulation codes some different combustor geometries was studied. By combining water tunnel tests, engine rig data and numerical simulations, conclusions were made regarding the cause for pressure oscillations in a studied afterburner. The numerical predicted flow field characteristics was verified by water tunnel testing and the measured thrust effective efficiency characteristics versus afterburn equivalence ratio was qualitatively predicted in the numerical simulations. To get a detailed evaluation of computer codes with combustion a specially designed test rig was built at Volvo Flygmotor AB. In this rig different types of bluff body flameholders were tested and several non-intrusive, as well as conventional measurement techniques, were applied on the premixed system. Two different numerical methods, a standard stationary flow solver with a k-.epsilon. model, and an inhouse developed large eddy simulation (LES) technique were applied. The calculation results were compared with gas analysis, LDA-data and for the LES also with temperature pdf's. The simulations with the k-.epsilon. model showed an underprediction of the generated turbulent kinetic energy behind the flameholder leading to an underprediction of the mixing process. Corresponding results using the LES code improved the results and demonstrated that the large eddy simulation technique captured most of the significant features of the studied turbulent premixed flame. A vaporisation liquid droplet model has also been implemented into the LES code and applied on an airblast atomizer. Parcels representing varying number of physical droplets of specified initial sizes are injected and followed in time while exchanging momentum, energy and mass with the surrounding gas.