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Walkingshaw J.,Queens University of Belfast | Spence S.,Queens University of Belfast | Jan E.,IHI Charging Systems International | Thornhill D.,Queens University of Belfast
Proceedings of the ASME Turbo Expo | Year: 2010

Conventionally, radial turbines have almost exclusively used radially fibred blades. While issues of mechanical integrity are paramount, there may be opportunities for improving turbine efficiency through a 3D blade design without exceeding mechanical limits. Off-design performance and understanding of the secondary flow structures now plays a vital role in the design decisions made for automotive turbocharger turbines. Of particular interest is extracting more energy at high pressure ratios and lower rotational speeds. Operating in this region means the rotor will experience high values of positive incidence at the inlet. A CFD analysis has been carried out on a scaled automotive turbine utilizing a swing vane stator system. To date no open literature exists on the flow structures present in a standard VGT system. Investigations were carried out on a 90 mm diameter rotor with the stator vane at the maximum, minimum and 25% mass flow rate positions. In addition stator vane endwall clearance existed at the hub side. From investigation of the internal flow fields of the baseline rotor, a number of areas that could be optimized in the future with three dimensional blading were identified. The blade loading and tip leakage flow near inlet play a significant role in the flow development further downstream at all stator vane positions. It was found that tip leakage flow and flow separation at offdesign conditions could be reduced by employing back swept blading and redistributing the blade loading. This could potentially reduce the extent of the secondary flow structures found in the present study. © 2010 by ASME. Source


Walkingshaw J.,Queens University of Belfast | Spence S.,Queens University of Belfast | Ehrhard J.,IHI Charging Systems International | Thornhill D.,Queens University of Belfast
Proceedings of the ASME Turbo Expo | Year: 2011

Off-design performance now plays a vital role in the design decisions made for automotive turbocharger turbines. Of particular interest is extracting more energy at high pressure ratios and lower rotational speeds. In this region of operation the U/C value will be low and the rotor will experience high values of positive incidence at the inlet. The positive incidence causes flow to separate on the suction surface and produces high blade loading at inlet, which drives tip leakage. A CFD analysis has been carried out on a number of automotive turbines utilizing non-radial fibred blading. To help improve secondary flows yet meet stress requirements a number of designs have been investigated. The inlet blade angle has been modified in a number of ways. Firstly, the blading has been adjusted as to provide a constant back swept angle in the span wise direction. Using the results of the constant back swept blading studies, the back swept blade angle was then varied in the span wise direction. In addition to this, in an attempt to avoid an increase in stress, the effect of varying the leading edge profile of the blade was investigated. It has been seen that off-design performance is improved by implementing back swept blading at the inlet. Varying the inlet angle in the span wise direction provided more freedom for meeting stress requirements and reduces the negative impact on blade performance at the design point. The blade leading edge profile was seen to offer small improvements during off-design operation with minimal effects on stress within the rotor. However, due to the more pointed nature of the leading edge, the rotor was less tolerant to flow misalignment at the design point. Copyright © 2011 by ASME. Source


Walkingshaw J.,Queens University of Belfast | Spence S.,Queens University of Belfast | Ehrhard J.,IHI Charging Systems International | Thornhill D.,Queens University of Belfast
Proceedings of the ASME Turbo Expo | Year: 2012

Off-design performance is of key importance now in the design of automotive turbocharger turbines. Due to automotive drive cycles, a turbine which can extract more energy at high pressure ratios and lower rotational speeds is desirable. Typically a radial turbine provides peak efficiency at U/C values of 0.7, but at high pressure ratios and low rotational speeds the U/C value will be low and the rotor will experience high values of positive incidence at the inlet. The positive incidence causes high blade loading resulting in additional tip leakage flow in the rotor as well as flow separation on the suction surface of the blade. An experimental assessment has been performed on a scaled automotive VGS (Variable Geometry System). Three different stator vane positions have been analysed; minimum, 25% and maximum flow position. The first tests were to establish whether positioning the endwall clearance on the hub or shroud side of the stator vanes produced a different impact on turbine efficiency. Following this, a back swept rotor was tested to establish the potential gains to be achieved during off-design operation. A single passage CFD model of the test rig was developed and used to provide information on the flow features affecting performance in both the stator vanes and turbine. It was seen that off-design performance was improved by implementing clearance on the hub side of the stator vanes rather than on the shroud side. Through CFD analysis and tests it was seen that two leakage vortices form, one at the leading edge and one after the spindle of the stator vane. The vortices affect the flow angle at the inlet to the rotor, in the hub region. The flow angle is shifted to more negative values of incidence, which is beneficial at the off-design conditions but detrimental at the design point. The back swept rotor was tested with the hub side stator vane clearance configuration. The efficiency and MFR were increased at the minimum and 25% stator vane position. At the design point the efficiency and MFR were decreased. The CFD investigation showed that the incidence angle was improved at the off-design conditions, for the back swept rotor. This reduction in the positive incidence angle along with the improvement caused by the stator vane tip leakage flow, reduced flow separation on the suction surface of the rotor. At the design point both the tip leakage flow of the stator vanes and the back swept blade angle caused flow separation on the pressure surface of the rotor. This resulted in additional blockage at the throat of the rotor reducing MFR and efficiency. Copyright © 2012 by ASME. Source


Leonetti M.,Research Institute of Automotive Engineering and Vehicle Engines | Bargende M.,University of Stuttgart | Kreschel M.,IHI Charging Systems International | Meier C.,Mercedes Benz | Schulze H.,Mercedes Benz
SAE Technical Papers | Year: 2015

Due to the demands for today's passenger cars regarding fuel consumption and emissions, exhaust turbo charging has become a fundamental step in achieving these goals. Especially in upper and middle class vehicles it is also necessary to consider the noise comfort. Today, floating bushings are mainly used as radial bearings in turbochargers. In the conventional operating range of the turbocharger dynamic instability occurs in the lubrication films of the bearings. This instability is transferred by structure-borne noise into audible airborne sound and known as constant tone phenomenon. This phenomenon is not the major contributor of the engine noise but its tonal character is very unpleasant. In order to gain a more detailed understanding about the origin of this phenomenon, displacement sensors have been applied to the compressor- and the turbine-side of the rotor, to be able to determine the displacement path. Also, part of this investigation is the measurement of the rotational speed of the floating bearing bushings on turbine-and compressor-side of the turbocharger. The investigations are carried out on turbochargers from 1.6l and 2.0l four-cylinder gasoline engines. The turbocharger has been decoupled from the internal combustion engine to separate the turbocharger related effects from engine related sources. The constant tone can be identified in both the structure-borne and the airborne noise of the turbocharger. At the beginning of the constant tone, during a ramp-up of the rotor, the amplitude of the shaft-movement increases on turbine-and compressor-side. At the same time, a high, jump-like increase in the bearing bushing speed is ascertained. For a detailed analysis, the signals from the displacement sensors are separated into their components, consisting of 1st order of the rotor and the sub-synchronous oscillations. It is shown that the proportion of 1st order in amplitude remains unchanged and the proportion of sub-synchronous oscillation increases significantly. This oscillation is transmitted by the bearing system to the turbocharger housing and emitted from there to structure-borne and airborne noise. Considering now only the sub-synchronous portion of the movement on the turbine-and compressor-side, not only an increase in the amplitude can be seen, but also a change in motion of the rotor at the start of the constant tone, from a conical into a cylindrical motion. © 2015 SAE International. Source


Patent
Ihi Charging Systems International | Date: 2014-06-06

In a turbine for an exhaust gas turbocharger with a turbine casing having receiving chamber for accommodating a turbine wheel and at least one volute through which the exhaust gas is guided via a feed passage into the receiving chamber and wherein at least one guide element is provided in the turbine casing so as to project into the feed passage in a guide region for guiding the exhaust gas onto the turbine wheel, the guide element comprises a first length region in the axial direction of the turbine, in which the guide element is designed with respect to its aerodynamic properties differently from its aerodynamic design in a second length region adjoining the first length region.

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