| 1. |
- Axelsson, Lars-Uno, 1979, et al.
(författare)
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Experimental investigation of the time-averaged flow in an intermediate turbine duct
- 2008
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Ingår i: GT2008-50829. Proceedings of ASME Turbo Expo 2008: Power for Land, Sea and Air, June 9-13, 2008, Berlin, Germany. - 9780791843161 ; 6:PART B
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Konferensbidrag (refereegranskat)abstract
- Intermediate turbine ducts are used in modern multi-spool jet engines to connect the high pressure turbine with the lowpressure turbine. The trend towards turbofan engines with larger by-pass ratios requires the radial off-set between the high-pressure and low-pressure turbines to increase with a corresponding increase in radial off-set for the intermediate turbine ducts. Other improvements of the ducts is to make them shorter and more diffusing but this strive towards more aggressive design increases the risk for separation. This paper deals with an experimental investigation of the time-averaged mean flow field and turbulence development in an aggressive intermediate turbine duct (downstream a rotating turbine stage) using a 5-hole probe and 2-component hot-wire anemometry. In addition the duct endwall static pressure distribution is discussed. The investigation revealed the complex flow structure development within the duct, where corotating vortices emanating from the break-up of the tip gap shear-layer dominates the flow pattern.
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| 2. |
- Hellström, Fredrik, et al.
(författare)
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Effects of inlet conditions on the turbine performance of a radial turbine
- 2008
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Ingår i: PROCEEDINGS OF THE ASME TURBO EXPO 2008. - New York : AMER SOC MECHANICAL ENGINEERS. - 9780791843161 ; , s. 1985-2001
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Konferensbidrag (refereegranskat)abstract
- For a turbocharger working under internal combustion engine operating conditions, the flow will be highly pulsatile and the efficiency of the radial turbine will vary during the engine cycle. In addition to effects of the inflow unsteadiness, there is also always a substantial unsteady secondary flow component at the inlet to the turbine depending on the geometry upstream. These secondary motions may consist of swirl, Dean vortices and other cross-sectional velocity components formed in the exhaust manifold. The strength and the direction of the vortices vary in time depending on the unsteady flow in the engine exhaust manifold, the engine speed and the geometry of the manifold itself. The turbulence intensity may also vary during the engine cycle leading to a partially developed turbulent flow field. The effect of the different perturbations on the performance of a radial nozzle-less turbine is assessed and quantified by using Large Eddy Simulations. The turbine wheel is handled using a sliding mesh technique, whereby the turbine wheel, with its grid is rotating, while the turbine house and its grid are kept stationary. The turbine performance has been compared for several inflow conditions. The results show that an inflow-condition without any perturbations gives the highest shaft power output, while a turbulent flow with a strongly swirling motion at the inlet results in the lowest power output. An unexpected result is that a turbulent inflow yields a lower shaft power than a turbulent inflow with a secondary flow formed by a pair of Dean vortices. The flow field for the different cases is investigated to give a better insight into the unsteady flow field and the effects from the different inlet conditions.
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| 3. |
- Zheng, Xinqian, et al.
(författare)
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Design of a centrifugal compressor with low specific speed for automotive fuel cell
- 2008
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Ingår i: 2008 ASME Turbo Expo; Berlin; Germany; 9 June 2008 through 13 June 2008. - 9780791843161 ; 6:PART B
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Konferensbidrag (refereegranskat)abstract
- Centrifugal compressors driven by electric motor are the promising type for fuel cell pressurization system. A low specific speed centrifugal compressor powered by an ordinary high-speed (about 25,000rpm) electric motor has been designed at Tsinghua University for automotive fuel cell engines. The experimental results indicate that the designed low specific speed centrifugal compressor has comparatively high efficiency and wide operating range. In the condition of designed speed (24,000rpm), the highest efficiency and pressure ratio of the centrifugal compressor is up to 70% and 1.6, respectively. The designed low specific speed centrifugal compressor can meet the requirement of air systems of automotive fuel cell engines preliminarily. Moreover, the low specific speed centrifugal compressor avoids difficulties of usage of ultra-high-speed electric motors (about 60,000rpm) in high specific speed compressor. Based on the preliminary results of this centrifugal compressor, a new low specific speed centrifugal compressor with higher performances is being developed.
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