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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.

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

Effect of high negative incidence on the performance of a centrifugal compressor stage with conventional vaned diffusers

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Journal of Thermal Science 2011年第2期20卷 97-105页

作者： Ahti Jaatinen Aki Grnman teemu turunen-saaresti Jari Backman Lappeenranta University of Technology

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.

关键词： centrifugal compressor vaned diffuser efficiency performance flow field

Numerical Modelling of a Supersonic Axial Turbine Stator

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Journal of Thermal Science 2010年第3期19卷 211-217页

作者： Aki Grnman teemu turunen-saaresti Ahti Jaatinen Jari Backman LUT Energy Lappeenranta University of TechnologyP.O.Box 20FI-53851 LappeenrantaFinland

In order to improve the turbocharging process,a supersonic axial turbine stator was modelled numerically with a pulsatile inlet mass *** main objectives of the study were to find out how pulsation affects the flow field and the performance of the *** 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 *** 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 *** total-to-static pressure ratio and efficiency followed the sinusoidal shape of the inlet flow as a function of *** 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.

关键词： CFD Supersonic Turbine Stator Turbocharging

Computational and Experimental Study of Pinch on the Performance of a Vaneless Diffuser in a Centrifugal Compressor

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Journal of Thermal Science 2006年第4期15卷 306-313页

作者： T.turunen-saaresti A.Reunanen J.Larjola Lappeenranta University of Technology Department of Energy and Environmental TechnologyLappeenrantaFinland teemu

This study focuses on the vaneless diffuser of a centrifugal compressor. The examined stage consists of an unshrouded impeller, a parallel wall vaneless diffuser and a volute. The walls of the diffuser were movable allowing different pinch configurations to be investigated. The baseline geometry had no pinch i.e. the height of the diffuser was equal to the height of the impeller flow channel plus the axial running clearance. The work consists of both numerical and experimental parts. Quasi-steady, turbulent, fully 3D numerical simulations were conducted. The inlet cone, rotor and diffuser were modelled. Six different configurations were studied. The height of the pinch was altered and the pinch made to different walls was tested. Two of the numerically studied cases were also experimentally investigated. The overall performance of the compressor, the circumferential static and total pressure and the spanwise total pressure distribution before and after the diffuser were measured. The numerical and experimental studies showed that the pinch improved the efficiency of the compressor.

关键词： Centrifugal compressor vaneless diffuser pinch