Project
Unsteady Combustor-Turbine-Interaction
Figure 1: Instantaneous normalized temperature at the inlet of the high pressure turbine stage 
Figure 2: Film cooling effectiveness on vane surfaces for a variation of inlet boundary conditions and simulation types (van de Wouw, J. Aerothermal Impact of Time-Resolved Inlet Boundary Conditions in High-Pressure Turbine Simulations, Darmstadt 2024, PhD, https://doi.org/10.26083/tuprints-00028652) 
Figure 3: Radial temperature distribution under variation of inlet boundary condition at multiple relative streamwise locations (van de Wouw, J. Aerothermal Impact of Time-Resolved Inlet Boundary Conditions in High-Pressure Turbine Simulations, Darmstadt 2024, PhD, https://doi.org/10.26083/tuprints-00028652) Climate change presents us with challenges in terms of increasing efficiency and reducing emissions such as CO2, NOX and soot. Even though aviation is a pioneer in the development of lower-emission and more efficient technologies, the emissions of aircraft propulsion systems must be further reduced. To optimise the efficiency of the engine, it is no longer sufficient to consider the engine components separately. The interaction between the combustion chamber and turbine is particularly important. In addition to the fundamentally different physical properties of the flow in the combustion chamber and turbine (combustion, flow velocities), the number of elements required for a coupled simulation of the combustion chamber and turbine also makes joint analysis difficult. In order to consider the unsteady effects of the combustion chamber in the simulation of turbines, an unsteady 1-way coupling was realised using the PODFS method. This allows the influence of combustion chamber instability on the aerothermal load of the turbine blades to be analysed. In this project, the development of turbulent characteristics across the turbine was investigated using scale-resolving simulations and compared with stationary RANS simulations, which are still an established method in the industry.
Project Details
Project term
May 1, 2024–April 30, 2025
Affiliations
TU Darmstadt
Institute
Institute of Gas Turbines and Aerospace Propulsion
Project Manager
Jonathan van de Wouw (nee Gründler)
Nico Rademacher
Principal Investigator
Methods
The methods used in this project were the numerical simulation of an engine-realistic high pressure turbine by means of Computational Fluid Dynamics (CFD) and an unsteady 1- way coupling method for the coupling of stand-alone combustion chamber and turbine simulations. The code used for the coupling method was developed at the Institute of Gas Turbines and Aerospace Propulsion at TU Darmstadt. For the CFD simulations the commercial CFD solver ANSYS CFX was used.
In this project an unsteady 1-way coupling method was developed to transfer time- and spatial resolved data from a combustion chamber CFD simulation to a stand-alone turbine CFD simulation. With this a consideration of unsteady flow characteristics of a combustor flow were applicable on turbine simulation without running a coupled simulation of both components. The method was first validated on a simplified test geometry before applying in on a turbine simulation.
The test channel was a simple rectangular channel with a turbulence generator. At a location downstream of the turbulence generator, time- and spatial resolved data were extracted and used to create a boundary condition with the unsteady 1-way coupling method. This boundary condition was then used to simulate a truncated version of the test channel. Various parameters of the coupling method such as spatial and temporal resolution of the boundary condition as well as amount of data for creation of the unsteady boundary condition were tested. Turbulent characteristics and the overall flow behaviour and prediction of aerothermal behaviour in the channel were analysed.
Results
The effects of combustor unsteadiness on the aerothermal load of turbine stator vanes were investigated in this project. It was shown that due to the unsteadiness of the combustor flow, the mixing of hot gas and cold gas in the turbine intensifies which leads to a more homogeneous temperature distribution within the turbine. This means, that the temperature close to the walls is higher than simulations with constant inlet boundary conditions would predict and the flow in the middle of the channel height seems to be colder than predicted by commonly used methods. Furthermore, it was shown that the predicted film cooling effectiveness is much lower than a simulation with steady boundary condition would predict. And it was shown that scale-resolving simulations are necessary to have accurate predictions of film-cooling effectiveness and the correct prediction of mixing processes in general.
Discussion
The consideration of combustor unsteadiness in transient turbine simulations has a major influence on the prediction of aerothermal load of the turbine blades and therefore their lifetime expectancy. Hence, combustor unsteadiness has to be considered in future design processes. Additionally, this implies different loss mechanisms and therefore not only effects lifetime but also performance and therefore efficiency of the turbine. Therefore, the consideration of unsteady boundary conditions using the unsteady 1-way coupling method has a huge impact on the cooling design of future turbines. The results show that the coupling method is suited very well to transfer the unsteady data from one simulation to another. Additionally, it was shown that scale-resolving simulations of the first turbine stage need unsteady boundary conditions to map the mixing processes adequately. Therefore, the unsteady 1-way coupling method offers the opportunity to run scale-resolving simulations of turbines which are relevant for more accurate predictions of film-cooling effectiveness and with that for the cooling design of the turbine. Since the simulations were only carried out using the stator of the turbine, an expansion of the domain by a rotor is definitely necessary to investigate if the combustor unsteadiness also influences the aerothermal behaviour of the rotor and maybe further downstream components. In first studies it was already shown that the homogenisation of the temperature profile effects the interaction with cooling and sealing flows in the rotor and therefore has a major impact on the wall temperature of the rotor blades.
Additional Project Information
DFG classification: 404-03 Fluid Mechanics
Software: ANSYS
Cluster: Lichtenberg
Publications
van de Wouw, J. Aerothermal Impact of Time-Resolved Inlet Boundary Conditions in High-Pressure Turbine Simulations, Darmstadt 2024, PhD, https://doi.org/10.26083/tuprints-00028652