@misc{NeubauerGensslerRadmannetal., author = {Neubauer, Moritz and Genßler, Julia and Radmann, Vincent and Kohlenberg, Fleming and Pohl, Michael and B{\"o}hme, Kurt and Knobloch, Karsten and Sarradj, Ennes and H{\"o}schler, Klaus and Modler, Niels and Enghardt, Lars}, title = {Experimental and Numerical Investigation of Novel Acoustic Liners and Their Design for Aero-Engine Applications}, series = {Aerospace}, volume = {10}, journal = {Aerospace}, number = {1}, issn = {2226-4310}, doi = {10.3390/aerospace10010005}, abstract = {This paper presents a combined experimental and numerical investigation on a novel liner concept for enhanced low-frequency and broadband acoustic attenuation. In particular, two different realizations, derived from conventional Helmholtz resonators (HR) and plate resonators (PR) are investigated, which both deploy flexible materials with material inherent damping. In this context, a comprehensive experimental investigation was carried out focusing the identification and evaluation of various geometric parameters and material properties on the acoustics dissipation and related properties of various materials in a simplified setup of a single Helmholtz resonator with flexible walls (FHR concept). Furthermore, a parameter study based on analytical models was performed for both liner concepts, taking into account material as well as geometric parameters and their effects on transmission loss. In addition, design concepts that enable cylindrical or otherwise curved liner structures and the corresponding manufacturing technologies are presented, while considering essential structural features such as drainage. With respect to the potential application in jet engines, a structural-mechanical analysis considering the relevant load cases to compare and discuss the mechanical performance of a classical HR and the FHR concept liner is presented. Finally, both concepts are evaluated and possible challenges and potentials for further implementation are described.}, language = {en} } @misc{NeubauerPohlKucheretal., author = {Neubauer, Moritz and Pohl, Michael and Kucher, Michael and B{\"o}hm, Robert and H{\"o}schler, Klaus and Modler, Niels}, title = {DMA of TPU Films and the Modelling of Their Viscoelastic Properties for Noise Reduction in Jet Engines}, series = {Polymers}, volume = {14}, journal = {Polymers}, number = {23}, issn = {2073-4360}, doi = {10.3390/polym14235285}, abstract = {Due to current developments in jet engine design, the acoustic performance of conventional acoustic liners needs to be improved with respect to lower frequency spectrums and broadband absorption. In this context, the present study aimed to determine the viscoelastic material properties of a thermoplastic polyurethane (TPU) film for targeted application in novel acoustic liners with integrated film material for enhanced noise reduction. Therefore, a dynamic mechanical analysis (DMA) was performed to determine these viscoelastic material properties. Based on the acquired data, the time-temperature shift (TTS) was applied to obtain the material's temperature- and frequency-dependent mechanical properties. In this regard, the William-Landel-Ferry (WLF) method and an alternative polynomial approach determining the shift factors were investigated and compared. Furthermore, a generalized Maxwell model—so-called Prony-series—with and without pre-smoothing utilizing of a fractional rheological model was applied to approximate the measured storage and loss modulus and to provide a material model that can be used in finite element analyses. Finally, the results were discussed concerning the application of the films in acoustic liners under the conditions of a standard flight cycle and the applied loads. The present investigations thus provide a method for characterizing polymer materials, approximating their mechanical behavior for vibration applications at different ambient temperatures and enabling the identification of their operational limits during the application in acoustic liners.}, language = {en} } @misc{KoenigMuellerHoeschler, author = {K{\"o}nig, Paul and M{\"u}ller, Phillip and H{\"o}schler, Klaus}, title = {Assessment of (hybrid)-electric drive-train architectures for future aircraft applications}, series = {Journal of Physics: Conference Series}, volume = {2526}, journal = {Journal of Physics: Conference Series}, issn = {1742-6596}, doi = {10.1088/1742-6596/2526/1/012023}, abstract = {Future regional aircraft and propulsion systems will have to address both a growing market and stricter environmental constraints. Besides the increase of component efficiencies, the technological transformation from conventional to (hybrid)-electric propulsion systems represents a paradigm shift with great potential for the aviation industry. In this context, economic, market-relevant as well as technological boundary conditions for the electrical and mechanical components are developed in this paper for a reference regional aircraft and are based on current research results from different institutions. The propulsion performance analysis of a conventional turboprop is compared and evaluated with a serial-hybrid and a fully-electric configuration (both battery-electric), status today as well as status ~2035, as an example, whereby the presented process can also be applied to other hybrid configurations too. An energy-optimised propulsion and operating concept is derived with regard to minimum resulting system weight. The results of this analysis help to define necessary boundary conditions for future subsystem investigations and identify key research items, especially in the field of the battery.}, language = {en} } @misc{KazulaHoeschler, author = {Kazula, Stefan and H{\"o}schler, Klaus}, title = {Review of variable leading-edge patents for aircraft wings and engine inlets and their relevance for variable pitot inlets in future supersonic transport}, series = {CEAS Aeronautical Journal}, volume = {12}, journal = {CEAS Aeronautical Journal}, number = {3}, issn = {1869-5582}, doi = {10.1007/s13272-021-00520-y}, pages = {685 -- 700}, abstract = {The motivation for designing variable pitot inlets for future supersonic transport (SST) is explained. A comprehensive overview of existing technological solutions for variable leading edges of aircraft wings and engine inlets is given. The advantages and limitations of over 80 solutions, as well as their relevance for application on variable pitot inlets for SST are described. The challenges of existing solution options concerning design methodologies, level of detail, and experience with a technology are identified.}, language = {en} } @misc{KimAsliHoeschler, author = {Kim, Dogsuk and Asli, Majid and H{\"o}schler, Klaus}, title = {On the Potentials of the Integration of Pressure Gain Combustion with a Hybrid Electric Propulsion System}, series = {Aerospace}, volume = {10}, journal = {Aerospace}, number = {8}, issn = {2226-4310}, doi = {10.3390/aerospace10080710}, pages = {1 -- 17}, 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.}, language = {en} } @misc{KoenigSharmaKondaetal., 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}, series = {Energies}, volume = {16}, journal = {Energies}, number = {22}, issn = {1996-1073}, doi = {10.3390/en16227524}, 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.}, language = {en} } @misc{AsliKoenigSharmaetal., author = {Asli, Majid and K{\"o}nig, Paul and Sharma, Dikshant and Pontika, Evangelia and Huete, Jon and Konda, Karunakar Reddy and Mathiazhagan, Akilan and Xie, Tianxiao and H{\"o}schler, Klaus and Laskaridis, Panagiotis}, title = {Thermal management challenges in hybrid-electric propulsion aircraft}, series = {Progress in Aerospace Sciences}, volume = {144}, journal = {Progress in Aerospace Sciences}, issn = {1873-1724}, doi = {10.1016/j.paerosci.2023.100967}, pages = {1 -- 29}, abstract = {The utilization of hybrid electric propulsion concept in aviation offers a viable solution to address the limitations posed by the relatively low energy density of batteries in fully electric aviation. These hybrid systems enable the aircraft to achieve a significant range while simultaneously minimizing carbon emissions. While the individual components of a Hybrid Electric Propulsion (HEP) system, such as electric motors and batteries, are designed with high efficiency, their integration presents a significant challenge in the realm of thermal management. Designing an efficient system for managing the substantial waste heat generated by heat sources and effectively transferring it to heat sinks during various flight phases is a complex task. This challenge becomes even more critical as the design must adhere to system weight limits and prioritize aviation safety considerations. In this review article, we performed a systematic review of the challenges related to the key elements in a thermal management system. These elements encompass every component or subsystem that contributes to the thermal management of a generic hybrid-electric propulsion system. This includes electric motors and generators, batteries, heat exchangers, power transmission systems, power distribution systems, storages, fuel cells, cooling fluids and pipes, control system, pumps and fans. Following the identification of the challenges, the paper provides a comprehensive summary of the existing solutions that have been offered and pursued by the community to address the challenges. Furthermore, the paper also discusses emerging technologies related to each element, highlighting their potential in overcoming these challenges.}, language = {en} } @misc{AsliPatkarHoeschler, author = {Asli, Majid and Patkar, Siddharth and H{\"o}schler, Klaus}, title = {Investigation on the effects of blade leading-edge protuberances on the aerodynamic performance of an axial transonic compressor}, series = {15th European Conference on Turbomachinery Fluid dynamics \& Thermodynamics}, journal = {15th European Conference on Turbomachinery Fluid dynamics \& Thermodynamics}, doi = {10.29008/ETC2023-229}, abstract = {Leading-edge protuberances inspired by humpback whales have been proven to be effective in delaying dynamic stall and post-stall regime of two-dimensional airfoils while causing a performance penalty in the pre-stall regime. Basically, this leading-edge modification acts as a vortex generator to split the separation region over the blade into multiple smaller regions. In this work, different sinusoidal wavy leading shapes are applied to a transonic compressor rotor blade row to evaluate the technique's effectiveness from a compressor performance point of view. The compressor characteristic maps have been compared to the baseline case, which shows how the compressor pressure ratio and efficiency are affected by the leading-edge modifications. The compressor stability margin has also been studied, and a detailed discussion of the flow over the compressor blades is provided.}, language = {en} } @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} }