@article{FrankRoedderNeefetal.2021, author = {Frank, Lena and R{\"o}dder, Maximilian and Neef, Matthias and Adam, Mario}, title = {Heating, Ventilation, Domestic Appliances - an Energy Integrated System Concept for the Household of the Future}, series = {Energy}, volume = {234}, journal = {Energy}, publisher = {Elsevier}, issn = {0360-5442}, doi = {10.1016/j.energy.2021.121303}, year = {2021}, language = {en} } @inproceedings{DubberkePriebeVrabecetal.2015, author = {Dubberke, Frithjof H. and Priebe, Klaus-Peter and Vrabec, Jadran and Neef, Matthias and R{\"o}dder, Maximilian}, title = {Thermodynamic simulation and experimental validation of a cascaded two-stage organic Rankine cycle}, series = {ASME ORC 2015, Brussels}, booktitle = {ASME ORC 2015, Brussels}, address = {Brussels}, year = {2015}, language = {en} } @inproceedings{RoedderNeefLauxetal.2015, author = {R{\"o}dder, Maximilian and Neef, Matthias and Laux, Christoph and Priebe, Klaus-P.}, title = {Systematic Fluid Selection for Organic Rankine Cycles (ORC) and Performance Analysis for a Combined High and Low Temperature Cycle}, series = {Volume 3: Coal, Biomass and Alternative Fuels; Cycle Innovations; Electric Power; Industrial and Cogeneration}, booktitle = {Volume 3: Coal, Biomass and Alternative Fuels; Cycle Innovations; Electric Power; Industrial and Cogeneration}, publisher = {American Society of Mechanical Engineers}, organization = {International Gas Turbine Institute}, isbn = {978-0-7918-5667-3}, doi = {10.1115/GT2015-42432}, year = {2015}, abstract = {The organic Rankine cycle (ORC) is an established thermodynamic process that converts waste heat to electric energy. Due to the wide range of organic working fluids available the fluid selection adds an additional degree of freedom to the early design phase of an ORC process. Despite thermodynamic aspects such as the temperature level of the heat source, other technical, economic and safety aspects have to be considered. For the fluid selection process in this paper, 22 criteria were identified in six main categories while distinguishing between elimination and tolerance criteria. For an ORC design, the suggested method follows a practical engineering approach and can be used as a structured way to limit the number of interesting working fluids before starting a detailed performance analysis of the most promising candidates. For the first time the selection process is applied to a two-stage reference cycle which uses the waste heat of a large reciprocating engine for cogeneration power plants. It consists of a high temperature and a low temperature cycle in which the condensation heat of the high temperature (HT) cycle provides the heat input of the low temperature (LT) cycle. After the fluid selection process the detailed thermodynamic cycle design is carried out with a thermodynamic design tool that also includes a database for organic working fluids. The investigated ORC cycle shows a net thermal efficiency of about 17,4\% in the high temperature cycle with Toluene as the working fluid and 6,2\% in low temperature cycle with iso-Butane as the working fluid. The electric efficiency of the cogeneration plant increases from 40,4\% to 46,97\% with the both stages of the two-stage ORC in operation.}, language = {en} } @inproceedings{HelmSpliethoffNeef2007, author = {Helm, Peter and Spliethoff, Hartmut and Neef, Matthias}, title = {Closing the Gap: Measuring Bristle Blow Down of Brush Seals}, series = {19 th International Conference on Fluid Sealing, Poitiers}, booktitle = {19 th International Conference on Fluid Sealing, Poitiers}, address = {Poitiers}, year = {2007}, language = {en} } @inproceedings{NeefHepermannSuerkenetal.2007, author = {Neef, Matthias and Hepermann, Florian and S{\"u}rken, Norbert and Schettel, Joachim}, title = {Brush Seal Porosity Modeling: Applicability and Limitations}, series = {ETC7 - 7th Conference on Turbomachinery, Athens}, booktitle = {ETC7 - 7th Conference on Turbomachinery, Athens}, address = {Athens}, year = {2007}, language = {en} } @inproceedings{NeefHummel2000, author = {Neef, Matthias and Hummel, Dietrich}, title = {Euler solutions for a finite-span flapping wing}, series = {"Fixed, flapping and rotary wing vehicles at very low Reynolds numbers, Notre Dame, Indiana, USA}, booktitle = {"Fixed, flapping and rotary wing vehicles at very low Reynolds numbers, Notre Dame, Indiana, USA}, year = {2000}, language = {en} } @article{BaierNeef2019, author = {Baier, Andr{\´e} and Neef, Matthias}, title = {Studierende lehren und lernen sozial-{\"o}kologische Verantwortung}, series = {Die Neue Hochschule}, volume = {60}, journal = {Die Neue Hochschule}, number = {5}, organization = {Hochschullehrerbund - Bundesvereinigung - e.V. (hlb)}, pages = {8 -- 11}, year = {2019}, language = {de} } @inproceedings{NeefFusseneckerNiemannetal.2018, author = {Neef, Matthias and Fussenecker, Claudia and Niemann, J{\"o}rg and Zielke, Thomas}, title = {Publish your undergraduate research! A mandatory course for master students in engineering}, series = {Creativity, innovation and entrepreneurship for engineering education excellence : proceedings of the 46th SEFI Annual Conference 2018, Copenhagen, Denmark}, booktitle = {Creativity, innovation and entrepreneurship for engineering education excellence : proceedings of the 46th SEFI Annual Conference 2018, Copenhagen, Denmark}, editor = {Clark, Robin and Munkebo Hussmann, Peter and J{\"a}rvinen, Hannu-Matti}, publisher = {SEFI - Soci{\´e}t{\´e} Europ{\´e}enne pour la Formation des Ing{\´e}nieurs}, address = {Brussels}, organization = {European Society for Engineering Education SEFI}, isbn = {978-2-87352-016-8}, year = {2018}, abstract = {Undergraduate students in engineering often have little exposure to the world of scientific publishing and the culture of sharing research work. While the beneficial exchange between research and teaching is well promoted, while the benefits of conference participation for students have already been surveyed and while courses on scientific writing are readily available, the concept of mini-conferences as part of the curriculum combines all three aspects into one. Therefore, the course "Engineering Conferences" was developed and installed as a mandatory part of a master program for engineering students. The idea is to go beyond simply teaching the standards of academic writing and skills for using scientific publications. By using a learner-centered approach, the students are engaged in typical activities around an active attendance of a real conference. Based on their bachelor thesis, they write a paper complying with common academic standards, submit the paper and review submissions of their fellow students. They also produce a poster and defend their work in a poster session held publicly on campus. This contribution is based on the experience from the first four terms teaching the course. It explains the didactic rationale behind the concept and individual teaching modules, it comprises the collection of useful resources for teaching and organizing scientific publishing and it includes the consequences drawn from course evaluation results.}, language = {en} } @inproceedings{Neef2013, author = {Neef, Matthias}, title = {Innerst{\"a}dtische Nutzung von Kleinwindkraftanlagen: Potentiale und H{\"u}rden}, series = {M{\"u}lheimer Initiative f{\"u}r Klimaschutz, 06.05.2013}, booktitle = {M{\"u}lheimer Initiative f{\"u}r Klimaschutz, 06.05.2013}, address = {M{\"u}lheim an der Ruhr}, organization = {M{\"u}lheimer Initiative f{\"u}r Klimaschutz e.V.}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:due62-opus-21017}, year = {2013}, language = {de} } @phdthesis{Neef2002, author = {Neef, Matthias}, title = {Analyse des Schlagfluges durch numerische Str{\"o}mungsberechnung}, volume = {ZLR-Forschungsbericht, 2}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:084-14501}, pages = {245}, year = {2002}, abstract = {Mit Hilfe eines Finite-Volumen-Verfahrens wird die dreidimensionale reibungsbehaftete Stroemung um einen schlagenden Fluegel berechnet. Die Bewegungsparamter sind dabei vergleichbar mit den Bedingungen im Reiseflug grosser Voegel. Das numerische Verfahren wird fuer den gezeigten Anwendungsfall, indem eine Methode zur Realisierung von beliebigen periodischen Bewegungen implemetiert wird. Eine Verifizierung erfolgt durch den Vergleich mit analytischen, numerischen und experimentellen Ergebnissen aus der Literatur. Mit dem verifizierten Verfahren werden die instationaeren Groessen wie Druck und Geschwindigkeiten in der Umgebung des bewegten Fluegels berechnet. Daraus ergeben sich ferner die zeitlich gemittelten Groessen wie Schub und Wirkungsgrad des Schlagfluges. Ausserdem wird die Interaktion von Laengs- und Querwirbeln im Nachlauf des schlagenden Fluegels untersucht. Es zeigt sich ein dominanter Einfluss der pulsierenden Randwirbel aufgrund der endlichen Spannweite, waehrend die Anfahr- und Stoppwirbel, verursacht durch die Fluegelbewegung, im Reiseflug grosser Voegel nahezu vernachlaessigbar erscheinen.}, language = {de} } @inproceedings{HelmPugachevNeef2008, author = {Helm, Peter and Pugachev, Alexander and Neef, Matthias}, title = {Breaking the Swirl With Brush Seals: Numerical Modeling and Experimental Evidence}, series = {Proceedings of the ASME Turbo Expo 2008 : presented at the 2008 ASME Turbo Expo, June 9 - 13, 2008, Berlin, Germany}, volume = {4}, booktitle = {Proceedings of the ASME Turbo Expo 2008 : presented at the 2008 ASME Turbo Expo, June 9 - 13, 2008, Berlin, Germany}, publisher = {ASME}, address = {New York}, organization = {American Society of Mechanical Engineers Corporation; International Gas Turbine Institute Corporation}, isbn = {978-0-7918-4314-7}, doi = {10.1115/GT2008-50257}, pages = {1387 -- 1396}, year = {2008}, abstract = {Striving for smaller losses in turbomachinery has led to many advancements in the design of seals. Modern sealing concepts such as brush seals hold a great potential to increase the efficiency of both flight engines and stationary turbines. At the same time, in order to maintain stable operating conditions of the rotor, swirl-induced forces must be kept at a minimum in the sealing channels. Therefore, the influence of the permeable and flexible bristle pack of brush seals on the flow around the rotor surface must be known. In this paper the swirl flow in the cavities of two different seal geometries is studied experimentally and numerically. A conventional three-tooth labyrinth serves as a reference. A second seal arrangement with a bristle pack upstream of two teeth is compared with the reference labyrinth. The swirl is evaluated experimentally from total and static pressure measurements in various axial and circumferential positions. Additionally, the axial swirl distribution is calculated using computational fluid dynamics (CFD). Here, the numerical model of the brush seal is based on the porous medium approach and is calibrated using the experimental values of the leakage and the bristle clearance by adjusting the thickness of the bristle pack. The calibrated CFD model is then used to study the impact of the brush seal on the swirl component of the sealing flow. The observed significant decrease of the swirl by the brush seal shows good agreement with the experimental data. The impact of changes in bristle pack clearance on the swirl is also investigated and compared with experimental evidence. The aim is to show that the brush seals have a natural tendency to interrupt seal swirl. They can therefore be used for swirl control in order to create a beneficial impact on the dynamic stability of turbomachines.}, language = {en} } @inproceedings{NeefSuldaSuerkenetal.2006, author = {Neef, Matthias and Sulda, Erik and S{\"u}rken, Norbert and Walkenhorst, Jan}, title = {Design Features and Performance Details of Brush Seals for Turbine Applications}, series = {Proceedings of the ASME Turbo Expo 2006 : presented at the 2006 ASME Turbo Expo, May 6 - 11, 2006, Barcelona, Spain}, volume = {3}, booktitle = {Proceedings of the ASME Turbo Expo 2006 : presented at the 2006 ASME Turbo Expo, May 6 - 11, 2006, Barcelona, Spain}, publisher = {ASME}, address = {New York}, organization = {American Society of Mechanical Engineers Corporation; International Gas Turbine Institute Corporation}, isbn = {0-7918-4238-X}, doi = {10.1115/GT2006-90404}, pages = {1385 -- 1392}, year = {2006}, abstract = {Adaptive and contacting seals such as brush seals have been successfully applied to turbomachinery for several years. In large steam turbine applications, however, various challenges still persist. Special focus is directed at the long-term performance and longevity of brushes on conventional spring-backed seal segments in steam turbines. This issue is particularly related to wear during startup conditions. This paper discusses the results of wear tests, derived from simulated transient turbine behavior, where the resultant seal leakage under steady state conditions is monitored. It is shown that the brush seal is significantly capable of adapting to varying operating conditions, but exhibits a degree of performance degradation during the initial startups. Together with previously reported mid-term wear data and an experience based long-term phenomenological approach a general model for brush seal performance degradation is developed. This model can be used for performance prediction and exerts influence on brush seal design.}, language = {en} } @inproceedings{HurdTruckenmuellerThammetal.2005, author = {Hurd, Paul and Truckenmueller, Frank and Thamm, Norbert and Pollak, Helmut and Neef, Matthias and Deckers, Mathias}, title = {Modern Reaction HP/IP Turbine Technology Advances and Experiences}, series = {Proceedings of the ASME Power Conference - 2005 : includes papers from the 2005 International Conference on Power Engineering (ICOPE) ; presented at the 2005 ASME Power Conference, April 5 - 7, 2005, Chicago, Illinois, USA}, booktitle = {Proceedings of the ASME Power Conference - 2005 : includes papers from the 2005 International Conference on Power Engineering (ICOPE) ; presented at the 2005 ASME Power Conference, April 5 - 7, 2005, Chicago, Illinois, USA}, publisher = {ASME}, address = {New York}, isbn = {0-7918-4182-0}, doi = {10.1115/PWR2005-50085}, pages = {425 -- 435}, year = {2005}, language = {en} } @inproceedings{VoelkerCaseyNeefetal.2005, author = {V{\"o}lker, Lutz and Casey, Michael and Neef, Matthias and St{\"u}er, Heinrich}, title = {The Flow Field and Performance of a Model Low Pressure Steam Turbine}, series = {6th European Conference on Turbomachinery - Fluid Dynamics and Thermodynamics : conference proceedings; 7-11 March 2005, Lille, France}, booktitle = {6th European Conference on Turbomachinery - Fluid Dynamics and Thermodynamics : conference proceedings; 7-11 March 2005, Lille, France}, address = {Lille}, organization = {{\´E}cole Nationale Sup{\´e}rieure d'Arts et M{\´e}tiers}, year = {2005}, abstract = {A 3-stage model of a low pressure steam turbine has been equipped with extensive instrumentation to assess aerodynamic performance and for validation of numerical methods. Emphasis was placed on detailed measurements at the inlet and exit of the last stage guide vane. Two configurations were examined - the first used a guide vane with lean in the last stage and a the second used a guide vane combining both lean and sweep. The experimental results from the two configurations have been compared with data from various design methods, ranging from through-flow to 3D multistage viscous simulations with mixing planes. Despite the challenges in modelling complex rotating blades in a wet steam environment, good agreement between the numerical and experimental results was obtained, and the new stator vane combining lean and sweep achieved the desired increase in reaction at the hub section.}, language = {en} } @inproceedings{WindteRadespielNeef2005, author = {Windte, Jan and Radespiel, Rolf and Neef, Matthias}, title = {Aerodynamic Analysis of Flapping Airfoil Propulsion at Low Reynolds Numbers}, series = {MEGAFLOW - Numerical Flow Simulation for Aircraft Design}, volume = {NNFM, 89}, booktitle = {MEGAFLOW - Numerical Flow Simulation for Aircraft Design}, editor = {Kroll, Norbert and Fassbender, Jens K.}, publisher = {Springer-Verlag}, address = {Berlin, Heidelberg}, isbn = {978-3-540-24383-0}, doi = {10.1007/3-540-32382-1_21}, pages = {299 -- 313}, year = {2005}, language = {en} } @incollection{NeefHummel2002, author = {Neef, Matthias and Hummel, D.}, title = {Euler and Navier-Stokes Solutions for Flapping Wing Propulsion}, series = {High Performance Computing in Science and Engineering '01}, volume = {30}, booktitle = {High Performance Computing in Science and Engineering '01}, editor = {Krause, Egon and J{\"a}ger, Willi}, publisher = {Springer}, address = {Berlin}, isbn = {978-3-642-62719-4}, doi = {10.1007/978-3-642-56034-7_37}, pages = {386 -- 395}, year = {2002}, language = {en} } @incollection{NeefHummel2001, author = {Neef, Matthias and Hummel, Dietrich}, title = {Euler Solutions for a Finite-Span Flapping Wing}, series = {Fixed and Flapping Wing Aerodynamics for Micro Air Vehicle Applications}, volume = {16}, booktitle = {Fixed and Flapping Wing Aerodynamics for Micro Air Vehicle Applications}, editor = {Mueller, Thomas J.}, publisher = {American Institute of Aeronautics and Astronautics}, address = {Reston, VA}, isbn = {978-1-56347-517-7}, doi = {10.2514/5.9781600866654.0429.0451}, pages = {429 -- 451}, year = {2001}, language = {en} } @article{NeefFritzenSchumacher2003, author = {Neef, Matthias and Fritzen, J. P. and Schumacher, G.}, title = {Evaluation of mount loads in dynamic testing of a jet engine}, series = {Mechanical Systems and Signal Processing}, volume = {17}, journal = {Mechanical Systems and Signal Processing}, number = {3}, publisher = {Elsevier}, doi = {10.1006/mssp.2001.1405}, pages = {665 -- 681}, year = {2003}, abstract = {In the dynamic testing of jet engines the evaluation of loads on the mount structure is vital for comparison with finite element calculations of such testing. Measuring these loads with the help of strain gauges applied to the structure becomes difficult if the mount is overdetermined and thus not every strain gauge can be assigned to a single load direction. In this study, the overdetermined mount structure of the BR715 engine was examined at one of the three mounting points between the Boeing 717 airframe and the engine, where loads in five directions were reacted. Firstly, the dependence of five measured strains upon known static load conditions at the mounting point had to be determined. For this purpose a static calibration test was carried out where defined forces and moments in known directions were applied to the structure while the output from five strain gauges was measured accordingly. The result was the desired relationship between loads and strains in terms of a matrix, which yields the corresponding load condition of the examined mounting point if multiplied with a set of strains. The same calibration procedure was carried out with a finite element model of the mount, where direct comparison to dynamic load results from the model itself was possible. With this model the validity of the above method was shown as well as possible errors which may occur while evaluating dynamic test results. The method was found to give satisfactory results even for dynamic loading, although some inertia forces disturb the signals in dynamic testing. Finally, the results from an actual dynamic engine test were processed into loads and then compared to the simulated loads from a finite element model of the engine. Good agreement was found and the indication of any remaining discrepancies was used to update the model for an even better representation of the dynamic test loads.}, language = {en} } @incollection{JonesCastroMahmoudetal.2002, author = {Jones, Kevin and Castro, Breno and Mahmoud, Osama and Pollard, S. and Platzer, Max and Neef, Matthias and Gonet, K. and Hummel, D.}, title = {A collaborative numerical and experimental investigation of flapping-wing propulsion}, series = {40th AIAA Aerospace Sciences Meeting \& Exhibit}, booktitle = {40th AIAA Aerospace Sciences Meeting \& Exhibit}, publisher = {American Institute of Aeronautics and Astronautics}, address = {Reston, Virigina}, doi = {10.2514/6.2002-706}, pages = {36}, year = {2002}, abstract = {An international, collaborative investigation is undertaken to evaluate the relative merits and limitations of various numerical methods and experimental measurement techniques, specifically for the analysis of flapping-wing propulsion. A finite aspect-ratio configuration is extensively investigated, both quantitatively and qualitatively, in a low-speed wind tunnel. Direct force measurements are made, as well as time-accurate and time-averaged laser Doppler velocimetry and unsteady flow visualization. The reduced frequency, mean angle of attack, aspect ratio and Reynolds number are varied in the experiments. The experiment is numerically simulated using flatplate theory, two and three-dimensional panel codes, and two and three-dimensional Euler and Navier- Stokes solvers. The ability of each of the methods to capture important aspects of the flow physics are evaluated through comparisons with each other and the experimental data. Additionally, the comparisons indicate areas where further research is needed. The collaborative effort provides a survey of available capabilities and provides a fixed set of flappingwing data for others to compare against.}, language = {en} } @article{FesekerKinellNeef2018, author = {Feseker, Daniel and Kinell, Mats and Neef, Matthias}, title = {Experimental Study on Pressure Losses in Circular Orifices With Inlet Cross Flow}, series = {Journal of Turbomachinery}, volume = {140}, journal = {Journal of Turbomachinery}, number = {7}, address = {ASME}, doi = {10.1115/1.4039842}, pages = {210}, year = {2018}, abstract = {The ability to understand and predict the pressure losses of orifices is important in order to improve the air flow within the secondary air system. This experimental study investigates the behavior of the discharge coefficient for circular orifices with inlet cross flow which is a common flow case in gas turbines. Examples of this are at the inlet of a film cooling hole or the feeding of air to a blade through an orifice in a rotor disk. Measurements were conducted for a total number of 38 orifices, covering a wide range of length-to-diameter ratios, including short and long orifices with varying inlet geometries. Up to five different chamfer-to-diameter and radius-to-diameter ratios were tested per orifice length. Furthermore, the static pressure ratio across the orifice was varied between 1.05 and 1.6 for all examined orifices. The results of this comprehensive investigation demonstrate the beneficial influence of rounded inlet geometries and the ability to decrease pressure losses, which is especially true for higher cross flow ratios where the reduction of the pressure loss in comparison to sharp-edged holes can be as high as 54\%. With some exceptions, the chamfered orifices show a similar behavior as the rounded ones but with generally lower discharge coefficients. Nevertheless, a chamfered inlet yields lower pressure losses than a sharp-edged inlet. The obtained experimental data were used to develop two correlations for the discharge coefficient as a function of geometrical as well as flow properties.}, language = {en} } @misc{FrankRoedderNeefetal.2018, author = {Frank, Lena and R{\"o}dder, Maximilian and Neef, Matthias and Adam, Mario}, title = {Heizung, L{\"u}ftung, Weiße Ware - Ein integriertes Systemkonzept f{\"u}r das Haus der Zukunft}, series = {KI K{\"a}lte Luft Klimatechnik}, volume = {54}, journal = {KI K{\"a}lte Luft Klimatechnik}, number = {11}, publisher = {H{\"u}thig}, issn = {1865-5432}, pages = {50 -- 56}, year = {2018}, abstract = {In energieeffizienten Geb{\"a}uden spielt der Bedarf an Energie f{\"u}r die Raumheizung gegen{\"u}ber der ben{\"o}tigten Energie f{\"u}r Warmwasser und zum Antrieb elektrischer Ger{\"a}te eine zusehends untergeordnete Rolle. Die thermische Energie f{\"u}r elektrische Haushalts­ger{\"a}te, wie Waschmaschine, K{\"u}hlschrank etc., wird f{\"u}r gew{\"o}hnlich dezentral im Ger{\"a}t erzeugt. Vor diesem Hintergrund ist das Ziel eines Forschungsprojekts der Bau und der Test eines Funktionsmusters zur funktionalen und energetischen Kopplung der Haushaltsger{\"a}te und der Heizungs- und L{\"u}ftungstechnik des Geb{\"a}udes. Grundgedanke dabei ist die Nutzung von Synergien bei Komponenten und W{\"a}rmestr{\"o}men, wie der W{\"a}rmepumpe als K{\"a}lteaggregat f{\"u}r den K{\"u}hlschrank, und die effiziente Nutzung von Abw{\"a}rme der Haushaltsger{\"a}te f{\"u}r die Warmwasserbereitung und Raumheizung.}, language = {de} }