@misc{XieMathiazhaganBarkowskietal., author = {Xie, Tianxiao and Mathiazhagan, Akilan and Barkowski, Daniel and Starick, Tommy and Berg, Heinz Peter and H{\"o}schler, Klaus}, title = {Comparison of convective heat transfer in metal foam-filled channels of three different cross-sections}, series = {Numerical Heat Transfer, Part A: Applications}, volume = {85}, journal = {Numerical Heat Transfer, Part A: Applications}, number = {2}, issn = {1521-0634}, doi = {10.1080/10407782.2023.2181892}, pages = {222 -- 236}, abstract = {This work introduces a new approach of analyzing convective heat transfer in porous medium by considering the foam structure as a type of fin. It provides the resulting heat transfer characteristics for the design of a longitudinally flowed tube bundle reformer used for the Micro Gas Turbine Solid Oxide Fuel Cell (MGT-SOFC) hybrid process. Owing to a limited experimental database available in literature for the above-mentioned situation, a physical model is initially introduced for a channel flow configuration between two large flat plates using a commercial PDE solver. This model is then validated with experimental results available in literature. A comparison with theoretical solutions is also conducted. Later, this model is modified/adapted for a pipe flow configuration. The physical model for a channel with representative cross-section shape of a longitudinally flowed tube bundle is more complex and is therefore built in a commercial CFD-Solver. A comparative study of the heat transfer behavior in channels of different cross-sections is performed based on a new dimensionless correlation, whose physical coherence with fin efficiency is explained and mathematically proved. The applicability of the heat transfer correlation from one cross-sectional shape to the other are discussed. The proposed new treatment of the porous medium as a fin structure considerably simplifies the heat transfer analysis in porous medium by the clear physical meaning behind fin efficiency and Biot number. This relationship contributes to a better understanding of the heat heat transfer characteristics in porous media in contrast to the correlation between Nusselt number and Reynolds number. Furthermore, this correlation enables a direct comparison between foam structures of different parameters because the fin efficiency is always between 0 and 1. The strong physical background of new correlations also enhances the reliability and plausibility at characterizing and designing the metal foam for heat transfer enhancement.}, language = {en} } @misc{AsliMhgoubHoeschler, author = {Asli, Majid and Mhgoub, Mosaab and H{\"o}schler, Klaus}, title = {Numerical investigation of a turbine working with a highly unsteady exhaust flow of a hydrogen-driven rotating detonation combustion}, series = {International journal of thermofluids}, volume = {29}, journal = {International journal of thermofluids}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {2666-2027}, doi = {10.1016/j.ijft.2025.101356}, pages = {1 -- 9}, abstract = {Traditionally, turbomachines are designed for steady-state operations around which they achieve optimal performance and efficiency. However, in novel applications, a turbomachine may be exposed to unsteady flow forcing the machine to operate under fluctuating off design conditions. Pressure Gain Combustion (PGC) through detonation can be an extreme example of unsteady flow which affects the turbine performance adversely. The efficient way of energy extraction from PGCs is still an open question which needs extensive turbine design optimizations for such unsteady flow. Any flow field optimization problem in such applications needs a multitude of simulations, which can be too computationally expensive to be utilized as it is realized as an unsteady 3D-CFD problem. In this regard, the current study aims at proposing and evaluating an approach for optimizing a turbine working under highly unsteady exhaust flow of a Rotating Detonation Combustion (RDC). A two stage turbine is placed downstream an RDC and the turbine inlet condition is calculated by a 2D-Euler simulation tool. A turbine optimization problem is defined and three optimization processes with an objective of minimizing entropy are performed using steady-state 3D-CFD simulation as the objective function evaluator. The turbine inlet boundary conditions in the three optimization efforts include peak, mean and trough values of the RDC outlet pulsating flow condition. Finally, detailed unsteady simulations are carried out for the three new geometries and compared with the baseline turbine. The results showed that the steady-state Reynolds Averaged Navier Stocks (RANS) simulations can be utilized using either mean or trough values of the pulsating boundary condition in iterating a design optimization problem, instead of full unsteady RANS simulations applying time and circumferential location dependent boundary conditions. Given the specific RDC boundary condition and the turbine geometry in this study, the optimized turbine exhibited up to 7.71\% less entropy generation and up to 7\% higher output power compared to the baseline counterpart in unsteady operation. This approach enables a more efficient design optimization process while accounting for the complex dynamics of the RDC exhaust flow. Overall, the approach presented in this paper is practical for optimizing highly unsteady turbomachines specifically for the case of RDCs during any early design optimization procedure, addressing the computational challenges associated with simulating unsteady flows while ensuring the turbine's effectiveness under real operating conditions.}, language = {en} } @misc{SharmaRadomskyMathiazhaganetal., author = {Sharma, Dikshant and Radomsky, Lukas and Mathiazhagan, Akilan and Asli, Majid and H{\"o}schler, Klaus and Mallwitz, Regine}, title = {Thermal analysis of metal foam integrated heatsink for electrified aircraft applications}, series = {International journal of thermofluids}, volume = {30}, journal = {International journal of thermofluids}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {2666-2027}, doi = {https://doi.org/10.1016/j.ijft.2025.101465}, pages = {1 -- 21}, abstract = {Metal foams facilitate large heat dissipation in high-power dense systems such as power electronics for electrified propulsion application. This work addresses the cooling of a power semiconductor device with aluminium and copper metal foam integrated hybrid heatsink and its comparative analysis to a conventional finned heatsink using 0D and 3D modelling approach. Two equation foam model in Fluent is utilized and the numerical approach is validated against experimental dataset. Inlet air velocity is varied such that the Darcy to turbulent regimes of the open-cellular foams are covered. Foam porosities from ∼ 0.85-0.95 with 10-20 PPI are investigated and the thermal performance of the heatsink is found to be independent of the foam material. High porosity (> 0.9), 20 PPI foams are found to aid forced-convection by improving the thermal resistance by more than 10\% against the 10 PPI counterparts. The hybrid heatsink outperforms the foam-based and conventional heatsink by 40\% and 15\% respectively when considering the reduction in junction temperatures, while the hydraulic resistance increases 10 times when compared to the conventional one. The 0D thermal resistance model is robust in predicting the junction temperatures for metal foam heatsinks with only a 5\%-6\% discrepancy for both the 50 W and 100 W heat load scenarios. The key and novel contribution of this study is the integration of detailed 3D simulations of a power electronics cooling environment with the development of a corresponding 0D thermal model. This approach not only eases the physical representation of the system but also enables the model to be extended to diverse heat load conditions.}, language = {en} } @misc{SharmaRadomskyMathiazhaganetal., author = {Sharma, Dikshant and Radomsky, Lukas and Mathiazhagan, Akilan and Konda, Karunakar Reddy and Hammami, Ghaieth and Asli, Majid and H{\"o}schler, Klaus and Mallwitz, Regine}, title = {Strut-based porous media heatsinks for high-performance power electronics thermal management in electrified aircrafts}, series = {ASME Turbo Expo 2025 : Turbomachinery Technical Conference and Exposition : Volume 4: Controls, Diagnostics \& Instrumentation; Cycle Innovations; Education; Electric Power : June 16-20, 2025, Memphis, Tennessee, USA}, volume = {4}, journal = {ASME Turbo Expo 2025 : Turbomachinery Technical Conference and Exposition : Volume 4: Controls, Diagnostics \& Instrumentation; Cycle Innovations; Education; Electric Power : June 16-20, 2025, Memphis, Tennessee, USA}, number = {V004T06A011}, publisher = {The American Society of Mechanical Engineers}, address = {New York, NY}, isbn = {978-0-7918-8880-3}, doi = {10.1115/GT2025-152670}, pages = {1 -- 11}, abstract = {Multi-level inverters are one promising solution for high-power applications, enabling higher efficiency and improved power quality over conventional inverters. The emergence of these converter topologies with a larger number of topological switches makes reliable, forced and even natural convection air cooling a feasible option for aircraft power electronics. The need for high heat dissipation rate, robust design and lightweight heatsinks has led to the development of strut-based porous media structures for forced air cooling. The current work focuses on investigating Kelvin, Body-Centered Cubic (BCC) and Simple Cubic (SC) periodic open cellular structured (POCS) lattice heatsink with a fixed porosity and a fixed unit cell size. 3D printed Kelvin and SC heatsinks using AlSi10Mg material are tested in an air duct experimental setup along with a conventional LAM aluminium heatsink. The Computational Fluid Dynamics (CFD) simulation model is validated with the experimental results and a 0D thermal model is developed using the CFD results. The CFD thermal results are in close accordance with the experimental results for the POCS heatsink within an error band of ±2\%. The 0D results using the thermal data from CFD simulations also show a close comparison for the calculated semiconductor junction temperatures. The Kelvin heatsink performs the best thermally from the CFD analysis and has the least error when comparing the 0D and 3D-CFD results.}, language = {en} } @misc{KimGerstbergerAslietal., author = {Kim, Dongsuk and Gerstberger, Ulf and Asli, Majid and H{\"o}schler, Klaus}, title = {U-Net driven semantic segmentation for detection and quantification of cracks on gas turbine blade tips}, series = {Results in engineering}, volume = {29}, journal = {Results in engineering}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {2590-1230}, doi = {10.1016/j.rineng.2025.108864}, pages = {1 -- 9}, abstract = {Crack detection and quantification on gas turbine blades is crucial for component validation during the development phase and for operational efficiency in service, as unexpected cracks can compromise blade integrity and lead to early engine removals. Gas turbine blades operate under extreme thermal and mechanical stresses, making them particularly susceptible to crack formation. At the same time deterministic predictions of crack formation are subject to high uncertainty in material data and actual loading conditions. Accurate detection and quantification of cracks, therefore, is essential for the validation and calibration of life predictions in order to prevent in-service failures, to extend component lifespan, and to reduce maintenance costs. This study introduces a U-Net based semantic segmentation model designed to automate crack detection on turbine blade tips. The model was trained on a dataset of 210 surface images with and without evidence of cracks, each divided into 128  ×  128 pixel patches. Data augmentation techniques were applied to address the class imbalance between cracked and non-cracked pixels. The U-Net architecture, optimized with a Dice loss function, achieved a validation IoU of 0.7557, along with approximately 85\% recall and precision in identifying cracked pixels. The pixel-based accuracy of the model primarily affects the quantification of cracks rather than their identification. A sliding window pipeline was implemented to extend the model's applicability, enabling segmentation of entire blade tip images for comprehensive crack localization. While the model may occasionally miss low-contrast cracks, it holds potential as a supplementary tool for manual inspection as part of the life prediction validation. By providing automated crack localization and quantification, the model can assist in analyzing crack characteristics relative to engine operating conditions.}, language = {en} }