@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} } @article{BonkLauxRoedderetal.2017, author = {Bonk, Christian Dirk and Laux, Christoph and R{\"o}dder, Maximilian and Neef, Matthias}, title = {Design of a 1 KW Organic Rankine Cycle for Teaching and Research Issues}, series = {Energy Procedia}, volume = {129}, journal = {Energy Procedia}, publisher = {Elsevier}, doi = {10.1016/j.egypro.2017.09.117}, pages = {931 -- 938}, year = {2017}, abstract = {This paper deals with the design of a micro-scale ORC plant for teaching and research including the development of an automated control concept. The aim is to provide a safe and environmentally acceptable micro-scale heat engine, which can be developed, implemented and used in university labs for the education of students as well as for small research projects. The test rig allows the support of several learning outcomes on a multi-disciplinary level particularly for the implementation and simulation of small power systems. Special attention was given to the organic working fluid characteristics and its selection process. In addition to the above-mentioned performance goals, favourable safety properties and low global warming potential were decisive in the selection of the novel organic fluid called 3M™ Novec™ 649. The performance and the fluid behaviour of Novec 649 in a micro-scale power cycle are of major interest and the research goal for the test rig presented in this paper. Due to the expected power output of 1 kW, a scroll expander was chosen as the generator drive for the micro plant. In order to design the major parts of the ORC, the thermodynamic simulation software EBSILON®Professional was used. The supply temperature was set to 140 °C. As a result of the simulation, feasible expander inlet pressures spread from 5.5 bar to 8.5 bar. This leads to thermal efficiencies of the ORC in the order of 5 \%. Adding a recuperator to the cycle system decreases the operating pressure range but in the end, the thermal efficiency can be increased by 1.5 \%-points up to 6.2 \%. Finally, an automated control concept is introduced, where the pump is controlled via the fill level measurement system.}, language = {en} } @article{NeefZielkeFussenecker2017, author = {Neef, Matthias and Zielke, Thomas and Fussenecker, Claudia}, title = {„Engineering Conferences": Wissenschaftlich Kommunizieren im Master}, series = {Die Neue Hochschule}, volume = {58}, journal = {Die Neue Hochschule}, number = {3}, pages = {4}, year = {2017}, language = {de} } @article{RoedderNeefLauxetal.2016, author = {Roedder, Maximilian and Neef, Matthias and Laux, Christoph and Priebe, Klaus-P.}, title = {Systematic Fluid Selection for Organic Rankine Cycles and Performance Analysis for a Combined High and Low Temperature Cycle}, series = {Journal of Engineering for Gas Turbines and Power}, volume = {138}, journal = {Journal of Engineering for Gas Turbines and Power}, number = {031701}, publisher = {ASME}, doi = {10.1115/1.4031361}, pages = {168}, year = {2016}, 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 (EC) and tolerance criteria (TC). 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 (HT) and a low temperature (LT) cycle in which the condensation heat of the HT cycle provides the heat input of the 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 HT cycle with toluene as the working fluid and 6.2\% in LT cycle with isobutane 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} } @article{WolterZekornNeef2016, author = {Wolter, Nina and Zekorn, Thomas and Neef, Matthias}, title = {Station{\"a}re thermodynamische Prozesssimulationen am Beispiel eines Industriekraftwerks}, series = {BWK: das Energie-Fachmagazin}, volume = {68}, journal = {BWK: das Energie-Fachmagazin}, number = {6}, pages = {6 -- 10}, year = {2016}, abstract = {Um bauliche Ver{\"a}nderungen in bestehenden Kraftwerksprozessen auf ihre Wirkungsweise untersuchen und thermodynamisch beziehungsweise wirtschaftlich bewerten zu k{\"o}nnen, werden thermische Kraftwerksprozesse mit geeigneter Simulationssoftware abgebildet und in verschiedenen Detaillierungsstufen ausgelegt oder nachgerechnet. Im Folgenden wird ein Weg aufgezeigt, wie mit Hilfe einer station{\"a}ren Simulationssoftware die Gesamtjahresbilanz eines Kraftwerks vorausberechnet werden kann. Mit Hilfe von Prozessdaten aus Vorjahren wird nachgewiesen, dass das Berechnungsmodell das bestehende Kraftwerk mit einer Abweichung von weniger als drei Prozent bez{\"u}glich erzeugter elektrischer Leistung und Brennstoffeinsatz und bei bekannter Dampfproduktion abbilden kann. Das so verifizierte Modell kann zur Untersuchung von Zubaumaßnahmen oder Ver{\"a}nderungen im Kraftwerksprozess eingesetzt werden.}, language = {de} } @inproceedings{LauxGotterNeef2019, author = {Laux, Christoph and Gotter, Andreas and Neef, Matthias}, title = {Experimental investigation of a low pressure steam Rankine cycle for waste heat utilization of internal combustion engines}, series = {Proceedings of the 5th International Seminar on ORC Power Systems}, booktitle = {Proceedings of the 5th International Seminar on ORC Power Systems}, publisher = {The National Technical University of Athens (NTUA)}, address = {Athens}, isbn = {978-90-9032038-0}, year = {2019}, abstract = {High heat losses via exhaust gas and coolant in internal combustion engines (ICE) are the basis for numerous investigations regarding downstream processes for power generation. The most promising concepts are Organic Rankine Cycles (ORC) and Steam Rankine Cycles (SRC). In previous work of the Center of Innovative Energy Systems, D{\"u}sseldorf (Germany), the technical and economic feasibility of a low pressure SRC has been investigated and the advantages in comparison to organic Rankine cycles are highlighted. A distinctive feature of the cycle is the use of the ICE coolant heat for evaporation, which limits the cycles maximum steam pressure to values below atmospheric pressure. This work presents first results of a test rig with data reconciliation according to DIN 2048 to validate the simulation results and design calculations. As a basis for the experimental investigations, a gas fired CHP plant was selected. The design of the test rig is optimized for the operation in the laboratory, where the coolant heat is emulated by a tempering device and the exhaust heat of the CHP plant is emulated by a gas burner. With the designed test rig, it is possible to control the volume flow and the temperatures of the coolant and exhaust gas, so that different load conditions of the gas fired CHP plant can be investigated. For initial tests, the turbine in the SRC is replaced by a throttle to achieve the pressure drop of the turbine. The experimental results show, that the exhaust and coolant heat of a 36 kWel CHP plant can be emulated and the performance expectations of the cycle can be met in stable steady-state conditions. Based on the measurement results and the turbine design calculations an electric power output of the cycle of 3.8 kW will be possible, which results in a cycle efficiency of about 6.5 \% and an increase of the electrical power output of the CHP plant of about 10 \%. The results show that the plant concept is technically feasible and, with further optimization, also represents an alternative to ORC plants in terms of increasing the efficiency of a cogeneration plant.}, language = {en} }