Session: 15-01 Impingement Cooling I

Paper Number: 122465

122465 - Investigating the Unsteady Dynamics of a Multi-Jet Impingement Cooling Flow Using Large Eddy Simulation 

Since a high turbine inlet temperature correlates with high thermodynamic efficiency, high-pressure turbine blades in modern jet engines and gas turbines face the challenge of enduring temperatures that can exceed their material's melting point. Therefore, they require active cooling systems, which utilize air at lower temperature extracted from the compressor. However, the air allocated for cooling is no longer available for combustion, resulting in a decrease in engine efficiency. Consequently, a comprehensive understanding of the flow physics governing cooling systems is pivotal for optimizing cooling efficiency. One crucial element of turbine blade cooling systems is impingement cooling, employed within the blade's internal cooling channels. This cooling method commonly involves arrays of jets directing cooling air onto the blade's inner surfaces. The effectiveness of impingement cooling directly influences the overall performance and durability of high-pressure turbine blades.

We investigate a generic configuration of nine cooling jets with a separation of five jet diameters in a square channel. The cooling jets with an average Reynolds number based on jet diameter of 10000 impinge on a heated plate at a distance of five jet diameters with a constant wall heat flux. Notably, the channel with a length of roughly 60 jet diameters remains closed to one side, exposing the jets to a self-generated developing crossflow. The configuration is not only realised numerically but has also been set up with good optical access for particle image velocimetry (PIV) measurements, which limited the jet bulk Mach number to 0.045. It was initially introduced by Tabassum et al. (Assessment of Computational Fluid Dynamic Modeling of Multi-Jet Impingement Cooling and Validation With the Experiments, J. Turbomach. Jul 2023, 145(7): 071005, https://doi.org/10.1115/1.4056715) with a focus on Reynolds-averaged Navier-Stokes (RANS) approaches compared to temporally averaged PIV and a baseline large eddy simulation (LES) with a wall heat flux of 5000 W/m$^2$.

In the current study, we extend the presentation and discussion of our LES setup with a more detailed examination of the baseline case, along with a sensitivity study related to the inflow boundary conditions. Therefore, an additional LES is considered, where resolved turbulence is introduced at the previously laminar inflow boundaries. We will investigate the effect of these modified boundary conditions on the development of the cooling jets and their heat transfer characteristics. The primary aspect of this study is our focus on the unsteady behavior of the interacting jets. This will be validated with available PIV data, which are currently limited to measurement windows spanning a maximum of three jets. We will analyse our LES datasets to investigate the potential coupling between adjacent jets and those further apart using modal decomposition techniques. We seek to provide valuable insights necessary for the design of advanced cooling channel geometries targeted at improved efficiency of the cooling system.

Presenting Author: Christian Morsbach German Aerospace Center (DLR) - Institute of Propulsion Technology

Presenting Author Biography: After finishing his studies of physics at RWTH Aachen and Imperial College London in 2009, Christian started to work at DLR's Institute of Propulsion Technology in the department of numerical methods as a developer of DLR's turbomachinery flow solver TRACE. In 2016, he obtained his PhD (Dr. rer. nat.) from the Technical University of Darmstadt with a thesis on Reynolds stress turbulence modeling for turbomachinery flows. Since 2017 he has been leading a team within the same department whose focus is on scale-resolving simulations as well as turbulence and transition modelling.

Authors:

Christian Morsbach German Aerospace Center (DLR) - Institute of Propulsion Technology
Marcel Matha German Aerospace Center (DLR) - Institute of Propulsion Technology
Robin G. Brakmann German Aerospace Center (DLR) - Institute of Propulsion Technology
Sadiya Tabassum German Aerospace Center (DLR) - Institute of Test and Simulation for Gas Turbines
Michael Bergmann German Aerospace Center (DLR) - Institute of Propulsion Technology
Michael Schroll German Aerospace Center (DLR) - Institute of Propulsion Technology
Christian Willert German Aerospace Center (DLR) - Institute of Propulsion Technology
Edmund Kügeler German Aerospace Center (DLR) - Institute of Propulsion Technology