Axel Widenhorn

Experimental Investigations of Pressure Losses on the Performance of a Micro Gas Turbine System

Pressure losses between the compressor outlet and the turbine inlet are a major issue of overall efficiency and system stability for a solid oxide fuel cell/micro gas turbine (MGT) hybrid power plant system. The goal of this work is the detailed analysis of the effects of additional pressure losses on MGT performance in terms of steady-state and transient conditions. The experiments were performed using the micro gas turbine test rig at the German Aerospace Centre in Stuttgart using a butterfly control valve to apply additional pressure loss. This paper reports electric power and pressure characteristics at steady-state conditions as well as a new surge limit for this Turbec T100 micro gas turbine test rig. Furthermore, the effects of additional pressure loss on the compressor surge margin are quantified and a linear relation between the relative surge margin and additional pressure loss is shown. For transient variation of pressure loss at constant turbine speed, time delays are presented and an instability issue of the commercial gas turbine controller is discussed. Finally, bleed-air blow-off and reduction of the turbine outlet temperature are introduced as methods of increasing the surge margin. It is quantified that both methods have a substantial effect on the compressor surge margin. Furthermore, a comparison between both methods is given in terms of electric power output.

Thermodynamic Process Analyses of SOFC/GT Hybrid Cycles

This paper presents the description of a numerical design tool for the steady state thermodynamic process analysis of SOFC/GT hybrid systems. The tool includes models for all gas turbine components and for a SOFC stack, based on the tubular fuel cell design of Siemens. The modular structure of the code allows the simulation of all kinds of hybrid system configurations with gas turbines from different manufacturers and of varying performance ranges. Furthermore a selection of atmospheric and pressurized hybrid systems based on the Turbec T100 micro gas turbine and a tubular SOFC stack is discussed. Also parameter studies are shown which focus on the operating conditions of the chosen system configurations.

Numerical Investigation of a Laboratory Combustor Applying Hybrid RANS-LES Methods

In this paper the three-dimensional non-reacting turbulent flow field of a swirl-stabilized gas turbine model combustor is analysed with compressible CFD. For the flow analysis URANS and Hybrid RANS/LES (DES, SAS) turbulence models were applied. The governing equations and the numerical method are described. The simulations were performed using the commercial CFD software package ANSYS CFX-10.0. The numerically achieved velocity components show a good agreement with the experimental values obtained by Particle Image Velocimetry (PIV). Furthermore, a precessing vortex core (PVC) could be found in the combustion chamber.

Numerical Characterization of a Gas Turbine Model Combustor

In this contribution the three-dimensional reacting turbulent flow field of a swirl-stabilized gas turbine model combustor is analyzed numerically. The investigated partially premixed and lifted CH4/air flame has a thermal power load of P th =35kW and a global equivalence ratio of φ=0.65. To study the reacting flow field the Scale Adaptive Simulation (SAS) turbulence model in combination with the Eddy Dissipation/Finite Rate Chemistry combustion model was applied. The simulations were performed using the commercial CFD software package ANSYS CFX-11.0. The numerically achieved time-averaged values of the velocity components and their appropriate turbulent fluctuations (RMS) are in very good agreement with the experimental values (LDA). The same excellent results were found for other flow quantities like temperature and mixture fraction. Here, the corresponding time-averaged and the appropriate RMS profiles are compared to Raman measurements. Furthermore, instantaneous flow features are discussed. The simulations have been performed on the HP XC4000 system of the High Performance Computing Centre Karlsruhe.

Analysis of the Effects of Wall Boundary Conditions and Detailed Kinetics on the Simulation of a Gas Turbine Model Combustor Under Very Lean Conditions

The numerical study presents the simulation of the DLR gas turbine model combustor operated at very lean conditions, near the lean extinction limit. The results have been validated against numerical data: while the hybrid LES-RANS model adopted for the turbulence closure demonstrated to be very well suited for such complex simulations, the combustion revealed to be dependent on the chemical kinetic mechanism adopted for the finite rate chemistry module. The latter was used in combination with the eddy dissipation model and it was possible to show that the flame root zone is mainly controlled by chemical kinetic effects.