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| 1 | Numerical and Experimental Modelling of Gas Flow and Heat Transfer in the Air Gap of an Electric Machine. Part II: Grooved Surfaces显示文摘The study deals with the cooling of a high-speed electric machine through an air gap with numerical and experimental methods. The rotation speed of the test machine is between 5000-4000 r/rain and the machine is cooled by a forced gas flow through the air gap. In the previous part of the research the friction coefficient was measured for smooth and grooved stator cases with a smooth rotor. The heat transfer coefficient was recently calculated by a numerical method and measured for a smooth stator-rotor combination. In this report the cases with axial groove slots at the stator and/or rotor surfaces are studied. Numerical flow simulations and measurements have been done for the test machine dimensions at a large velocity range. At constant mass flow rate the heat transfer coefficients by the numerical method attain bigger values with groove slots on the stator or rotor surfaces. The results by the numerical method have been confirmed with measurements. The RdF-sensor was glued to the stator and rotor surfaces to measure the heat flux through the surface, as well as the temperature. | Maunu KUOSA Petri SALLINEN Arttu REUNANEN Jari BACKMAN Jaakko LARJOLA Lasse KOSKELAINEN | 2005 | Journal of Thermal Science2005，14，1： | 4 |
| 2 | Fluid dynamic modeling of a free piston engine with labyrinth seals显示文摘Preliminary design and simulation of a free piston engine suitable for small-scale energy production in distributed energy systems is presented in this paper.The properties,particularly the properties of gas seals of the engine are simulated using a simulation program developed for this case,and the results are utilized in preliminary main design parameter selection.The engine simulation program was developed by combining and modifying the source codes of the simulation and calculation programs obtained from Helsinki University of Technology,Tampere University of Technology,and Lappeenranta University of Technology.Because of the contact-free labyrinth seal used in the piston,the efficiency of the motor is lower than the efficiency of a conventional motor with oil lubricated piston rings.On the other hand,the lack of bearing losses,and the lack of losses associated with a crankshaft system and a gearbox,as well as the lack of lubrication oil expenses,compensates this effect.As a net result,this new motor would perform slightly better than the conventional one.Being completely oil-free,it is very environmentally friendly,and its exhaust gases are completely free of oil residuals which are causing problems in normal gas motors. | Jaakko Larjola Juha Honkatukia Petri Sallinen Jari Backman | 2010 | Journal of Thermal Science2010，19，2： | 4 |
| 3 | Feasibility of Pulse Combustion in Micro Gas Turbines显示文摘In gas turbines, a fast decrease of efficiency appears when the output decreases; the efficiency of a large gas turbine (20…30 MW) is in the order of 40 %, the efficiency of a 30 kW gas turbine with a recuperator is in the order of 25 %, but the efficiency of a very small gas turbine (2…6 kW) in the order of 4…6 % (or 8…12 % with an optimal recuperator). This is mainly a result of the efficiency decrease in kinetic compressors, due to the Reynolds number effect. Losses in decelerating flow in a flow passage are sensitive to the Reynolds number effects. In contrary to the compression, the efficiency of expansion in turbines is not so sensitive to the Reynolds number; very small turbines are made with rather good efficiency because the flow acceleration stabilizes the boundary layer. This study presents a system where the kinetic compressor of a gas turbine is replaced with a pulse combustor. The combustor is filled with a combustible gas mixture, ignited, and the generated high pressure gas is expanded in the turbine. The process is repeated frequently, thus producing a pulsating flow to the turbine; or almost a uniform flow, if several parallel combustors are used and triggered alternately in a proper way. Almost all the compression work is made by the temperature increase from the combustion. This gas turbine type is investigated theoretically and its combustor also experimentally with the conclusion that in a 2 kW power size, the pulse flow gas turbine is not as attractive as expected due to the big size and weight of parallel combustors and due to the efficiency being in the order of 8 % to 10 %. However, in special applications having a very low power demand, below 1000 W, this solution has better properties when compared to the conventional gas turbine and it could be worth of a more detailed investigation. | Juha Honkatukia Esa Saari Timo Knuuttila Jaakko Larjola Jari Backman | 2012 | Journal of Thermal Science2012，21，5： | 2 |
| 4 | Numerical Modelling of a Supersonic Axial Turbine Stator显示文摘In order to improve the turbocharging process,a supersonic axial turbine stator was modelled numerically with a pulsatile inlet mass flow.The main objectives of the study were to find out how pulsation affects the flow field and the performance of the stator.At the beginning of the study,a supersonic turbine stator was modelled using three different techniques:quasi-steady,time-accurate with constant boundary conditions and time-accurate with a pulsatile inlet mass flow.The time-averaged and quasi-steady flow fields and performance were compared,and the flow field and stator performance with a pulsatile inlet mass flow was studied in detail at different time-steps.A hysteresis-like behaviour was captured when the total-to-static pressure ratio and efficiency were plotted as a function of the inlet mass flow over one pulse period.The total-to-static pressure ratio and efficiency followed the sinusoidal shape of the inlet flow as a function of time.It was also concluded that the stator efficiency decreases downstream from the stator trailing edge and the amplitude of the pulsating mass flow is decreased at the stator throat. | Aki Grnman Teemu Turunen-Saaresti Ahti Jaatinen Jari Backman | 2010 | Journal of Thermal Science2010，19，3： | 0 |
| 5 | Optimization of the Mean Radius Flow Path of a Multi-Stage Steam Turbine with Evolution Algorithms显示文摘A prototype model of the mean radius flow path of a four-stage,high speed 1 MWe axial steam turbine was optimized by using evolution algorithms,DE(differential evolution) algorithm in this case.Also the cost-benefits of the optimization were inspected.The optimization was successfully performed but the accuracy of the optimization was slightly less than hoped when compared to the control modeling executed with the CFD(computational fluid dynamics).The mentioned inaccuracy could have been hardly avoided because of problems with an initial presumption involving semi-empiric calculations and of the uncertainty concerning the absolute areas of qualification of the functions.This kind of algebraic modeling was essential for the success of the optimization because e.g.CFD-calculation could not have been done on each step of the optimization.During the optimization some problems occurred with the adequacy of the computer capacity and with finding a suitable solution that would keep the algorithms within mathematically allowable boundaries but would not restrict the progress of the optimization too much.The rest of the problems were due to the novelty of the application and problems with preciseness when handling the areas of qualification of the functions.Although the accuracy of the optimization results was not exactly in accordance with the objective,they did have a favorable effect on the designing of the turbine.The optimization executed with the help of the DE-algorithm got at least about 3.5 % more power out of the turbine which means about 150 000 € cost-benefit per turbine in the form of additional electricity capacity. | Jukka Huttunen Jaakko Larjola Teemu Turunen-Saaresti Jari Backman | 2011 | Journal of Thermal Science2011，20，4： | 0 |
| 6 | Effect of high negative incidence on the performance of a centrifugal compressor stage with conventional vaned diffusers显示文摘Three vaned diffusers, designed to have high negative incidence (-8°) at the design operating point, are studied experimentally. The overall performance (efficiency and pressure ratio) are measured at three rotational speeds, and flow angles before and after the diffuser are measured at the design rotational speed and with three mass flow rates. The results are compared to corresponding results of the original vaneless diffuser design. Attention is paid to the performance at lower mass flows than the design mass flow. The results show that it is possible to improve the performance at mass flows lower than the design mass flow with a vaned diffuser designed with high negative incidence. However, with the vaned diffusers, the compressor still stalls at higher mass flow rates than with the vaneless one. The flow angle distributions after the diffuser are more uniform with the vaned diffusers. | Ahti Jaatinen Aki Grnman Teemu Turunen-Saaresti Jari Backman | 2011 | Journal of Thermal Science2011，20，2： | 0 |
| 7 | Robust Analyzing Tools for Wind Turbine Blades Coupled with Multiobiective Optimization显示文摘 | Daniil Perfiliev Jari Haimailaiinen Jari Backman | 2013 | Journal of Energy and Power Engineering2013，7，10： | 0 |
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