@phdthesis{Sain2022, author = {Sain, Chetan Kumar}, title = {Concepts development of variable fan nozzle for future generation of aeroengines}, doi = {10.26127/BTUOpen-6515}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-65158}, school = {BTU Cottbus - Senftenberg}, year = {2022}, abstract = {The next generation of civil turbofan engines targets the by-pass ratios of up to 20:1, requiring an innovative fan design with a low fan pressure ratio, low specific thrust and a radically increased fan diameter. The aerodynamic stability of such a large slow rotating fan is very sensitive against the back-pressure variations in the by-pass duct, especially during the take-off operations. The back-pressure regulation can be achieved significantly through a Variable Area Fan Nozzle (VAFN). This work deals with the design development of VAFN concepts for ultra-high by-pass ratio engines which was researched in EU funded program ENOVAL and received funding under grant agreement number 604999. A system engineering approach was implemented for the VAFN development by following the requirements in conceptual, preliminary and detailed design phases. The design domains in the rear nacelle and under the core fairing were selected for the concept generation. Several qualitative and quantitative trade studies were conducted to down-select the best-fit solution during each design phase. These included the kinematic simulations of various types of VAFN modulations; analytical calculations to understand the thermodynamics of the selected VAFN kinematics; aerodynamic performance predictions using CFD simulations on a large number of preliminary designs; 3D CFD simulations for detailed performance assessments including the design optimization of individual features and distortions due to failed modulations; and FEM calculations for the topology generation and optimization of structural components. The overall weighted effect was determined for each output parameter and the results were presented in percentile changes relative to that with a fixed nozzle reference geometry. Two VAFN concepts were selected for the final detailed design phase, Flaps in rear nacelle domain and Variable Inner Fairing Structure (VIFS). Both concepts showed better outputs in terms of specific fuel consumption, noise emission and fan's safety margin during the take-off, with an over-area exhaust position than those with a fixed nozzle operation. During the climb phase, with an under-area VAFN position, both concepts resulted in drawbacks due to higher aerodynamic losses relative to the fixed nozzle. During MCR, both the VAFN concepts with stowed positions caused losses mainly due to leakages and higher structural weights relative to the fixed nozzle configuration. For each VAFN concept, a detailed system definition was developed and the function trees for each operation were explained. A discrete modulation type with two positions was described and recommended for both concepts. This included an over-area deployed position for the take-off phase and a stowed position for the rest of the flight, based on the beneficial performance of the VAFN concepts over the fixed clean nozzle configuration.}, subject = {Variable area fan nozzle; Ultra high bypass ratio turbofan engine; Performance analysis; Bypass duct; Fan nozzle structural analysis; Turbofan-Triebwerk; Variable Fan-D{\"u}se; Leistungsanalyse der D{\"u}se; D{\"u}senkonzept; Designentwicklung; Mantelstromtriebwerk; D{\"u}se; Thermodynamik; Design}, language = {en} } @article{AsliMhgoubKlaus2025, author = {Asli, Majid and Mhgoub, Mosaab and Klaus, H{\"o}schler}, 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}, address = {Amsterdam}, issn = {2666-2027}, doi = {10.1016/j.ijft.2025.101356}, year = {2025}, 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.}, subject = {Unsteady turbine; Entropy generation; Rotating detonation; Optimization; Computational fluid dynamic}, language = {en} } @article{KondaFranzkiSharmaetal.2024, author = {Konda, Karunakar Reddy and Franzki, Jonas and Sharma, Dikshant and K{\"o}nig, Paul and Mathiazhagan, Akilan and Henke, Markus and H{\"o}schler, Klaus}, title = {Quantitative assessment of cooling methods for electrical machines in aircraft drives}, series = {IEEE Access}, volume = {12}, journal = {IEEE Access}, publisher = {IEEE}, address = {New York}, issn = {2169-3536}, doi = {10.1109/ACCESS.2024.3517319}, pages = {192768 -- 192785}, year = {2024}, abstract = {Transformation of the aviation sector towards climate-neutral solutions such as electrification is urgent. Aviation electrification requires reasoned selection of suitable technologies which has to meet strict requirements and standards. Cooling of electrical components plays a vital role in the sizing and overall performance of the electrical drive system and must achieve high effectiveness and reliability at low weight. Three cooling methods - air cooling, direct slot cooling and cooling jacket - are sized for a 300 kW commuter aircraft (CS23) all-electric propulsion system. They are further evaluated quantitatively for weight, drag, reliability and effectiveness in a conservative assessment. A lumped parameter thermal network (LPTN) approach is utilized to assess and evaluate the thermal performance of the cooling systems. The LPTN model served as the basis to determine the temperature limits and capabilities of the cooling system which are then utilized to size the auxiliary components. Reliability is assessed via fault tree analysis, drag via scoop inlet characteristics and effectiveness via the heat load dissipated per weight of the system and the required cooling power per mechanical power. Cooling jacket achieves the highest effectiveness closely followed by slot cooling. Air cooling proves to be most reliable and lightest.}, subject = {Cooling systems; Electric aircrafts; Motor drives; Sizing; Thermal management}, language = {en} } @phdthesis{Konstantinidis2022, author = {Konstantinidis, Aris}, title = {Konzeptfindung und strukturmechanische Optimierung von Anbindungsstrukturen f{\"u}r Planetengetriebe in Flugtriebwerken}, doi = {10.26127/BTUOpen-6014}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-60141}, school = {BTU Cottbus - Senftenberg}, year = {2022}, abstract = {Kernziel der Arbeit ist es, einen Beitrag zur Konzeptfindung und zur strukturmechanischen Optimierung von Anbindungsstrukturen f{\"u}r Planetengetriebe in Flugtriebwerken zu leisten. Hierzu wurde ein auf CAD-Geometrien basierender Optimierungsprozess geschaffen und auf verschiedene Problemstellungen angewendet. Die Arbeit gliedert sich in sechs Kapitel, in denen ein Verst{\"a}ndnis f{\"u}r die Notwendigkeit und die Problemstellung vermittelt werden soll. Die Einleitung beschreibt Entwicklungstendenzen f{\"u}r Triebwerke in der zivilen Luftfahrt und die Gr{\"u}nde f{\"u}r den Einsatz von Planetengetrieben. Da die hier entwickelten Methoden die Konzeptfindung und somit die Produktentwicklung unterst{\"u}tzen sollen, wird skizziert, an welcher Stelle des Produktentwicklungsprozesses die Methoden am besten einzusetzen sind. Das zweite und dritte Kapitel sind der Strukturoptimierung gewidmet. Zun{\"a}chst werden die Grundlagen Optimierung und wichtige Ans{\"a}tze erl{\"a}utert. Anschließend werden die {\"u}blichen Verfahren zur Strukturoptimierung mithilfe von finiten Elemente-Netzen vorgestellt. Folgend werden zwei Sonderf{\"a}lle betrachtet, die Optimierung von flexiblen Bauteilen und von mehreren Bauteilen im Verbund. Beides stellt eine besondere Herausforderung dar und wird in den sp{\"a}teren Fallstudien aufgegriffen. Im dritten Kapitel wird der alternative, auf CAD-Geometrien basierende Ansatz zur Strukturoptimierung vorgestellt. Abschließend werden die Methoden anhand von akademischen Beispielen validiert. Das vierte Kapitel befasst sich mit Antwortfl{\"a}chenverfahren. Sie sind ein g{\"a}ngiges Mittel, um Optimierungsprozesse zu beschleunigen. Hierzu werden zun{\"a}chst die wichtigsten Grundlagen zur n{\"o}tigen Versuchsplanung erl{\"a}utert und die drei g{\"a}ngigsten Ans{\"a}tze diskutiert. Auf der Grundlage eines Vergleichs dieser Verfahren wird ein geeigneter Ansatz ausgew{\"a}hlt. Im f{\"u}nften Kapitel werden f{\"u}nf Fallstudien aufgef{\"u}hrt. Jede davon greift eine praxisnahe Problemstellung auf und demonstriert die Herangehensweise und die M{\"o}glichkeiten und Grenzen eines auf CAD-Geometrien basierten Ansatzes zur Strukturoptimierung. Das erste, zweite und f{\"u}nfte Fallbeispiel beziehen sich auf die im zweiten Kapitel genannten Sonderf{\"a}lle. Im dritten Fallbeispiel wird eine Optimierung der Systemeigenfrequenz durchgef{\"u}hrt, die es n{\"o}tig macht, eine Br{\"u}cke von der Einzelkomponente zu einem aus reduzierten Matrizen bestehenden Systemmodell zu schlagen. Im vierten Fallbeispiel werden die im vierten Kapitel beschriebenen Antwortfl{\"a}chenverfahren eingesetzt, um die reduzierte Matrix einer Einzelkomponente f{\"u}r ein Systemmodell auf der Basis der Geometrieparameter vorherzusagen. Abschließend fasst das sechste Kapitel die Ergebnisse zusammen. Die gezeigten Ans{\"a}tze sind sehr gut geeignet, um flexible Strukturen zu finden. Die Systemoptimierung und Prozessbeschleunigung konnten erfolgreich durchgef{\"u}hrt werden und haben zu signifikanten Verbesserungen gef{\"u}hrt. Abschließend wird das Vorgehen im Vergleich zu anderen L{\"o}sungsm{\"o}glichkeiten bewertet.}, subject = {Strukturoptimierung; Geometriebasierte Optimierung; Konzeptfindung; Planetengetriebe; Flugtriebwerke; Structural optimization; Geometry-based optimization; Concept development; Planetary gear box; Aero engines; Flugtriebwerk; Planetengetriebe; Strukturoptimierung}, language = {de} } @phdthesis{Spiess2023, author = {Spieß, Benjamin}, title = {The artificial engineer : a smart holistic framework for the automated transfer of geometry to analysis models}, doi = {10.26127/BTUOpen-6530}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-65308}, school = {BTU Cottbus - Senftenberg}, year = {2023}, abstract = {The creation of adequate simulation models for complex assemblies is an extensive process that requires a lot of experience, and on the other hand involves a multitude of manual, tedious tasks. These are significant obstacles for improving the process performance and capabilities. The objective of this research is to develop methods which digitally imitate the way of thoughts of the engineer in the design process towards a digital system understanding and which support the automation of the involved manual workflow. This thesis presents a strategy to translate engineering reasoning and actions to an equivalent in the computer domain. A cardinal step is to gain understanding of system arrangements, boundary conditions and its components. Based on this evaluation, the identification of assembly parts is forming the foundation for optimized process chains for the transfer to the analysis environment. Model complexity relates to computational effort, which in turn affects model capabilities and manageability. To achieve a satisfactory compromise of model quality and complexity, this transfer process is strongly dependent on the visual analysis, reasoning and manual implementation of skilled engineers. The principle of translating engineering logics is pursued from the assembly system to its smallest parts. Component segmentation methods allow subdividing regions of interest into substructures which are assigned with a feature vector. This vector comprises metrics describing the substructures with regard to specific aspects and is the key decision point for subsequent steps as idealization, suitable Finite-Element modeling and ultimately building an analysis model. The created system database is continuously maintained and supports these process chains as well as the final setup of the assembly simulation model. An automated workflow like this implies advantages for efficiency, but also creates opportunities for further use cases. This workflow has been exploited for generating a training data set from the different simulation variants as a basis to a knowledge representation imitating engineering experience. An algorithm from the graph neural network field is applied to this data set as a conceptual approach. The intention pursued in this concept is to model the learning progress about estimating the influence of modelling decisions on simulation results and quality. This research proposes a holistic strategy and describes methods to achieve the objectives of decreasing manual effort, introducing an automated and geometry-based process and digitally replicating engineering experience by introducing a knowledge database.}, subject = {Engineering; Automation; Artificial intelligence; Design; Machine learning; Automatisierung; Simulation; K{\"u}nstliche Intelligenz; CAD; FEM; Automatisierung; CAD; Finite-Elemente-Methode; K{\"u}nstliche Intelligenz; Simulation}, language = {en} } @article{KoenigSharmaKondaetal.2023, author = {K{\"o}nig, Paul and Sharma, Dikshant and Konda, Karunakar Reddy and Xie, Tianxiao and H{\"o}schler, Klaus}, title = {Comprehensive review on cooling of permanent magnet synchronous motors and their qualitative assessment for aerospace applications}, doi = {10.3390/en16227524}, year = {2023}, abstract = {The permanent magnet synchronous motor (PMSM) can be a suitable candidate for electrified propulsion in aviation. Despite the very high efficiency, heat dissipation during operation leads to performance limitations. Elevated temperatures in the electrical insulations and the magnets pose a potential safety risk that must be reduced by selective cooling. A comprehensive review is conducted to capture current research interests in cooling methods in PMSM. Cooling methods are described according to their heat transfer mechanism, grouped, and assigned to the components within the motor. Key findings of the literature reviewed are described in the context of PMSM cooling. Information on cooling media and potential combinations of cooling methods in components is gathered. Assessment parameters such as safety, weight, effectiveness, integrability, complexity and cost are defined to enable a subsequent qualitative analysis for six selected cooling methods. A point-weighted evaluation approach, according to VDI 2225, was applied to identify the most promising cooling approach for successful implementation in aviation.}, subject = {Electrical machines; Electric aviation; Motor cooling; PMSM; Thermal management; Elektrische Luftfahrt; Elektrische Maschinen; Motork{\"u}hlung; W{\"a}rmemanagement; Luftfahrt; Raumfahrt; Elektroantrieb; Dauermagneterregter Synchronmotor; K{\"u}hlung}, language = {en} } @article{MathiazhaganKimVeginietal.2025, author = {Mathiazhagan, Akilan and Kim, Dongsuk and Vegini, George and Montemurro, Marco and Baltag, Serghei and Asli, Majid and H{\"o}schler, Klaus}, title = {Design strategies for enhancement of mechanical behaviour of hybrid cellular structures based on schwarz primitive geometry}, series = {Materials \& Design}, volume = {240}, journal = {Materials \& Design}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0264-1275}, doi = {10.1016/j.matdes.2025.115161}, year = {2025}, abstract = {Hybrid cellular structures are gaining attention for their multi-functionality in load-bearing, heat-transfer, and energy-absorption applications. Schwarz Primitive (SCP)-based geometries, a subclass of Triply Periodic Minimal Surfaces (TPMS), with their high surface area, tunable properties, and continuous topology, provide strong potential for such applications. To further enhance mechanical performance and stability, this work conducts a thorough investigation of hybrid designs that integrate SCP TPMS with Kelvin truss-based geometries, combining the high connectivity of TPMS with the reinforcement and directional stiffness benefits of struts. A theoretical strain-based homogenization framework was implemented over a design matrix that independently varies the relative densities of the SCP and the truss geometries, quantifying how each constituent proportion influences the overall mechanical response of the hybrid. These predictions were corroborated by finite element analyses in ANSYS 2023 and by mechanical testing of 3D-printed polylactic acid samples, providing independent validation of homogenization trends across orientations. The resulting formulation enables rapid property mapping, sensitivity analysis, and optimization of SCP-Kelvin hybrids, thereby reducing the prototyping effort while guiding application-based design selection and customization.}, subject = {Lightweight design; Anisotropy control; Homogenization; Triply periodic minimal surfaces; Periodic open cellular structures}, language = {en} } @article{AsliKimHoeschler2023, author = {Asli, Majid and Kim, Dongsuk and H{\"o}schler, Klaus}, title = {On the potentials of the integration of pressure gain combustion with a hybrid electric propulsion system}, doi = {10.3390/aerospace10080710}, year = {2023}, abstract = {As the issue of pollutant emissions from aviation propulsion escalates, research into alternative powertrains is gaining momentum. Two promising technologies are the Hybrid Electric Propulsion System (HEPS) and Pressure Gain Combustion (PGC). HEPS is expected to reduce pollutant emissions by decreasing fuel consumption, whereas PGC uses detonation in the combustor to increase the thermal efficiency of engines by elevating the total pressure during combustion. This study extensively explores the integration of these two emerging technologies, thoroughly assessing the advantages that arise from their combination. First, the renowned turboprop engine PW127 is benchmarked and modeled using Gasturb software. The model is integrated into Simulink using the T-MATS tool, with HEPS and pressure gain components added to analyze the thermodynamics of various configurations under different pressure gain values and HEPS parameters. The analysis, conducted up to the cruise phase of the baseline aircraft, reveals that applying pressure gain combustion through Rotating Detonation Combustion (RDC) results in a more significant increase in efficiency and decrease in fuel consumption compared to HEPS with conventional gas turbines. However, HEPS helps maintain a more uniform combustor inlet condition and reduces the Turbine Inlet Temperature (TIT) at the takeoff phase, where the highest TIT otherwise occurs. The results suggest that integrating HEPS with PGC can be beneficial in maintaining optimal combustor conditions and mitigating turbine efficiency degradation.}, subject = {Pressure gain combustion; Hybrid electric propulsion; Rotating detonation combustion; Druckverst{\"a}rkungsverbrennung; Rotierende Detonationsverbrennung; Hybrid-Elektroantrieb; Propeller-Turbinen-Luftstrahltriebwerk; Hybridantrieb; Verbrennung; Schadstoffemission; Emissionsverringerung}, language = {en} } @article{KimGerstbergerAslietal.2025, 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}, address = {Amsterdam}, issn = {2590-1230}, doi = {10.1016/j.rineng.2025.108864}, year = {2025}, 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.}, subject = {Crack detection; Semantic segmentation; Gas turbine blade; U-Net; Deep learning; Convolutional neural network}, language = {en} } @article{SharmaRadomskyMathiazhaganetal.2025, 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}, address = {Amsterdam}, issn = {2666-2027}, doi = {10.1016/j.ijft.2025.101465}, year = {2025}, 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.}, subject = {Electric propulsion; Electronics thermal management; Metal foam heatsink; Porous media; Forced convection}, language = {en} }