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Journal of Thermal Science 2005年第1期14卷 1-8页

作者： Arttu REUNANEN jaakko larjola Department of Energy and Environmental Technology Lappeenranta University of Technology LappeenrantaFinlandDepartment of Energy and Environmental Technology Lappeenranta University of TechnologyLappeenrantaFinland

The volute of a centrifugal compressor causes a non-uniform pressure distribution which leads to a radial force on the impeller. This force was measured using magnetic bearings. In addition, the radial force was estimated using the static pressure distribution measured at the impeller outlet. The impeller force was found to be the highest at choke, the lowest at the design flow and moderate at stall. The radial force determined from the pressure measurements was only slightly different from the force obtained from the bearing measurements. The rotational speed was seen to affect the force to some extent.

关键词： centrifugal compressor aerodynamic force radial force volute.

Unsteady Pressure Field in a Vaneless Diffuser of a Centrifugal Compressor: An Experimental and Computational Analysis

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Journal of Thermal Science 2004年第4期13卷 302-309页

作者： Teemu TURUNEN-SAARESTI jaakko larjola Lappeenranta University of Technology Laboratory of Fluid Dynamics P.O. Box 20 53851 Lappeenranta FinlandLappeenranta University of Technology Laboratory of Fluid Dynamics P.O. Box 20 53851 Lappeenranta Finland

Unsteady static pressure was measured and time-accurate numerical simulations were conducted in order to analyze unsteady behaviour of the centrifugal compressor diffuser. The unsteady static pressure was measured at the diffuser inlet and outlet at three different circumferential positions. Operation points near the surge, the design operation point and operation point near the choke were used in measurements. The time-accurate simulations were conducted at the design operation point and operation point near the choke. The whole compressor was modelled and the low Reynolds number k-εturbulence model was utilized in numerical simulations. The gathered numerical and experimental unsteady pressures were compared with each other.

关键词： centrifugal compressor vaneless diffuser unsteady pressure.

Numerical and Experimental Modelling of Gas Flow and Heat Transfer in the Air Gap of an Electric Machine

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Journal of Thermal Science 2004年第3期13卷 264-278页

作者： Maunu KUOSA Petri SALLINEN jaakko larjola Lappeenranta University of Technology (LUT) Department of Energy and Environmental Technology P.O. Box 20 53851 Lappeenranta FinlandLappeenranta University of Technology (LUT) Department of Energy and Environmental Technology P.O. Box 20 53851 Lappeenranta FinlandLappeenranta University of Technology (LUT) Department of Energy and Environmental Technology P.O. Box 20 53851 Lappeenranta Finland

This work deals with the cooling of high-speed electric machines, such as motors and generators, through an air gap. It consists of numerical and experimental modeling of gas flow and heat transfer in an annular channel. Velocity and temperature profiles are modeled in the air gap of a high-speed test machine. Friction and heat transfer coefficients are presented in a large velocity range. The goals are reached acceptably using numerical and experimental research. The velocity field by the numerical method does not match in every respect the estimated flow mode. The absence of secondary Taylor vortices is evident when using time averaged numerical simulation.

关键词： heat transfer electric machine air gap friction coefficient CFD.

Fluid dynamic modeling of a free piston engine with labyrinth seals

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Journal of Thermal Science 2010年第2期19卷 141-147页

作者： jaakko larjola Juha Honkatukia Petri Sallinen Jari Backman Lappeenranta University of Technology P.O.Box 2053851 Lappeenranta

Preliminary design and simulation of a free piston engine suitable for small-scale energy production in distributed energy systems is presented in this *** 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 *** 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 *** 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 *** 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 *** a net result,this new motor would perform slightly better than the conventional *** 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.

关键词： free piston engine distributed energy systems simulation labyrinth seal

Optimization of the Mean Radius Flow Path of a Multi-Stage Steam Turbine with Evolution Algorithms

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Journal of Thermal Science 2011年第4期20卷 318-323页

作者： Jukka Huttunen jaakko larjola Teemu Turunen-Saaresti Jari Backman Savonia Power ljytie 678710 VarkausFinlandjukka Lappeenranta University of Technology P.O.Box 2053851 LappeenrantaFinland

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 opti- mization too much. The rest of the problems were due to the novelty of the application and problems with pre- ciseness when handling the areas of qualification of the functions. Although the accuracy of the optimization re- suits 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 ε cost-benefit per turbine in the form of additional electricity capacity.

关键词： steam turbine evolution algorithm optimization mean radius flow path semi-empirical loss correlations

Feasibility of Pulse Combustion in Micro Gas Turbines

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Journal of Thermal Science 2012年第5期21卷 466-473页

作者： Juha Honkatukia Esa Saari Timo Knuuttila jaakko larjola Jari Backman Lappeenranta University of Technology P.O. Box 2053851 Lappeenranta Finland T-Turbine Oy Rakentajainkuja 4 B02330 Espoo Finland

In gas turbines, a fast decrease of efficiency appears when the output decreases; the efficiency of a large gas tur-bine （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 op- timal 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 con- trary 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 uni- form flow, if several parallel combustors are used and triggered a/ternately in a proper way. Almost all the com- pression 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 ef- ficiency 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.

关键词： Gas turbine pulse combustion micro size low Reynolds number

Numerical and Experimental Modelling of Gas Flow and Heat Transfer in the Air Gap of an Electric Machine. Part II: Grooved Surfaces

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Journal of Thermal Science 2005年第1期14卷 48-55页

作者： Maunu KUOSA Petri SALLINEN Arttu REUNANEN Jari BACKMAN jaakko larjola Lasse KOSKELAINEN Lappeenranta University of Technology Department of Energy and Environmental Technology P.O.Box 2053851 LappeenrantaFinland

The study deals with the cooling of a high-speed electric machine through an air gap with numerical and experimental *** 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 *** the previous part of the research the friction coefficient was measured for smooth and grooved stator cases with a smooth *** heat transfer coefficient was recently calculated by a numerical method and measured for a smooth stator-rotor *** this report the cases with axial groove slots at the stator and/or rotor surfaces are *** flow simulations and measurements have been done for the test machine dimensions at a large velocity *** constant mass flow rate the heat transfer coefficients by the numerical method attain bigger values with groove slots on the stator or rotor *** results by the numerical method have been confirmed with *** RdF-sensor was glued to the stator and rotor surfaces to measure the heat flux through the surface,as well as the temperature.

关键词： electric machine air gap groove slot heat transfer computational fluid dynamics experimental modelling high-speed technology.

Computational and Experimental Study of an Industrial Centrifugal Compressor Volute

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Journal of Thermal Science 2000年第1期9卷 77-84页

作者： Harri Pitkanen Haunu Esa Arttu Reunanen Petri Sallinen jaakko larjola Department of Energy Technology Lappeenranta University of TechnologyFinland

A centrifugal compressor with a vaneless diffuser was studied experimentally and numerically. The main target of the study was to analyze the volute flow. Two different volute geometries was studied. The numerical solution was done by using a steady-state RANS code at both design and off-design conditions. Both calculated and measured pressure and velocity distributions are presented.

关键词： centrifugal compressor volute CFD.