Investigation Into the Impact of Span-Wise Flow Distribution on the Performance of a Mixed Flow Turbine

Lee, Samuel P.; Barrans, Simon; Jupp, Martyn; Nickson, A.K.

doi:10.1115/gt2018-76992

Cited by 6 publications

(9 citation statements)

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“…Morrison et al 10 found that a flow cone angle of 95 resulted in a small efficiency improvement while an angle of 65 resulted in greater losses. Meanwhile Lee et al 11 found a performance benefit with a reduction in cone angle but a change in MFP meant the efficiency benefits were not directly comparable. Lee et al argued that the misalignment of the flow with the rotor nozzle-less area in the study by Morrison et al 10 could be responsible for the differing conclusions.…”

Section: Introductionmentioning

confidence: 99%

The impact of volute aspect ratio and tilt on the performance of a mixed flow turbine

Lee

Barrans

Nickson

2021

Proceedings of the Institution of Mechanical Engineers, Part A:

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Current trends in the automotive industry towards engine downsizing means turbocharging now plays a vital role in engine performance. The purpose of turbocharging is to increase the engine inlet air density by utilising, the otherwise wasted energy in the exhaust gas. This energy extraction is commonly accomplished through the use of a radial turbine. Although less commonly used, mixed flow turbines can offer aerodynamic advantages due to the manipulation of blade leading (LE) angles, improving performance at low velocity ratios. The current paper investigates the performance of a mixed flow turbine with four volute designs, two radial and two tilted volutes each with one variant with an aspect ratio (AR)=0.5 and one with AR = 2. To ensure constant mass flow parameter (MFP) for aerodynamic similarity, volute area to radius ratio (A/r) was manipulated between the design variants. The maximum variation of cycle averaged normalized efficiency measured between the designs was 2.87%. Purely in the rotor region, the variation in normalized cycle averaged efficiency was 3%. The smallest volute AR designs showed substantial secondary flow development. The introduction of volute tilt further complicated the secondary flow development with the introduction of asymmetry to the flows. It was established that both AR and tilt have a notable effect on secondary flows, rotor inlet conditions and over all mixed flow turbine performance.

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Section: Introductionmentioning

confidence: 99%

The impact of volute aspect ratio and tilt on the performance of a mixed flow turbine

Lee

Barrans

Nickson

2021

Proceedings of the Institution of Mechanical Engineers, Part A:

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“…It was determined that reducing the flow angle towards the hub side of the passage resulted in an efficiency improvement of 1% relative to a baseline case with a uniform distribution. A further study on the impact of inlet flow angle distributions on MFT rotor performance was conducted by Lee et al [13]. This study imposed five different spanwise flow velocity profiles at the inlet to a numerical model of a MFT rotor.…”

Section: Introductionmentioning

confidence: 99%

“…Morrison et al [12] and Lee et al [13] have demonstrated that MFT performance can potentially be improved by altering the flow conditions at rotor inlet. However, the results of these studies were obtained by imposing the desired flow angle distributions and total pressure and temperature conditions directly upstream of the rotor leading edge.…”

Section: Introductionmentioning

confidence: 99%

Evaluating the Use of Leaned Stator Vanes to Produce a Non-Uniform Flow Distribution Across the Inlet Span of a Mixed Flow Turbine Rotor

Morrison

Spence

Kim

et al. 2020

Journal of Turbomachinery

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Current trends in the automotive industry have placed an increased emphasis on downsized turbocharged engines for passenger vehicles. The turbocharger is increasingly relied upon to improve power output across a wide range of engine operating conditions, placing a greater emphasis on turbocharger off-design performance. An off-design condition of significant importance is performance at low turbine velocity ratios, since it is relevant to engine transient response and also to efficient energy extraction from pressure pulses in the unsteady exhaust flow. An increased focus has been placed on equipping turbochargers with mixed flow turbine rotors instead of conventional radial flow turbine rotors to improve off-design performance and to reduce rotor inertia. A recognized feature of a mixed flow turbine is the spanwise variation of flow conditions across the blade leading edge. This is a consequence of the reduction in leading edge radius from shroud to hub, coupled with the increasing tangential velocity of the flow due to conserved angular momentum as the radius decreases. The result is increasingly positive incidence toward the hub side of the leading edge. The resulting region of highly positive incidence at the hub produces separation from the suction surface and generates significant loss within the rotor passage. The aim of this study was to determine if the losses in a mixed flow turbine (MFT) could be reduced by the use of leaned stator vanes, which deliberately created a significant spanwise variation of flow angle between hub and shroud at rotor inlet, to reduce the positive incidence at the hub. The turbine performance with a series of leaned vanes was compared against that of a straight vane using a validated computational fluid dynamics (CFD) model. It was found that increasing vane lean improved turbine performance at all operating points considered. An increase of 3.2 percentage points in stage total-to-static efficiency was achieved at a key off-design operating point. Experimental testing of a set of leaned vanes and the baseline vanes confirmed the advantage of the leaned vanes at all operating points, with an increase in measured efficiency of 2.6 percentage points at the key off-design condition. Unsteady CFD models confirmed the same level of improvement at this operating point. The CFD and experimental results confirmed that the losses in an MFT can be reduced by the use of leaned stator vanes to shape the flow at rotor inlet.

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“…It was found the tilted volute could increase both the steady-state performance [10] and the cycle-averaged performance under pulsating working conditions [11]. A follow-up study investigated the effect of inlet spanwise flow distributions on the aerodynamic performance by implementing different distributions on a radial and a tilted stator layouts [12]. However, a direct comparison of those two stator layouts was not achievable due to the lack of aerodynamic similarity [12].…”

Section: Introductionmentioning

confidence: 99%

“…A follow-up study investigated the effect of inlet spanwise flow distributions on the aerodynamic performance by implementing different distributions on a radial and a tilted stator layouts [12]. However, a direct comparison of those two stator layouts was not achievable due to the lack of aerodynamic similarity [12]. Morrison et al [13] investigated the effect of inlet flow cone angle on the performance of an MFT, as an indirect way to investigate the stator endwall tilting designs.…”

Section: Introductionmentioning

confidence: 99%

Numerical Investigation of the Performance Impact of Stator Tilting Endwall Designs on a Mixed Flow Turbine

Fridh

Morrison

Ren

et al. 2021

IJTPP

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This paper numerically investigates stator endwall designs for a mixed flow turbine. One key design parameter studied is the tilting angle of the stator endwall. By examining stator designs with different tilting angles, the aim of this paper is to improve the efficiency of the studied mixed flow turbine at low velocity ratio working conditions. The performance curve at the design speed was chosen for the comparison between the baseline design and the tilted endwall designs. First, the numerical predictions for the baseline design were validated with experimental data. Then, to understand the mechanism of the performance variation between the different designs, the internal flow field was analyzed in detail. It was found that the tilting stator endwall could form a geometric “kink” in the endwall profiles. On the shroud side, certain designs with such kink caused local flow separations upstream the rotor leading edge. This separation could have the effect of reducing the intensity of the tip leakage vortex and the exit kinetic energy losses at the rotor outlet and may also improve the performance of the exhaust diffuser. As a result, the peak of the efficiency curve shifted toward lower velocity ratio. If the turbine stage incorporated a downstream exhaust diffuser, the optimal design in this study showed a shift of the velocity ratio of the peak efficiency point from 0.62 to 0.60 compared with the baseline. The maximum efficiency improvement was 1.3% points, which occurred at low velocity ratio. Meanwhile, the peak efficiency was 0.2% points higher than the baseline. If the exhaust diffuser was removed, a similar shift of the efficiency curve was observed but less efficiency gain was achieved at the low velocity ratio condition. A preliminary unsteady simulation was also conducted for the optimal design in this study.

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Investigation Into the Impact of Span-Wise Flow Distribution on the Performance of a Mixed Flow Turbine

Cited by 6 publications

References 0 publications

The impact of volute aspect ratio and tilt on the performance of a mixed flow turbine

The impact of volute aspect ratio and tilt on the performance of a mixed flow turbine

Evaluating the Use of Leaned Stator Vanes to Produce a Non-Uniform Flow Distribution Across the Inlet Span of a Mixed Flow Turbine Rotor

Numerical Investigation of the Performance Impact of Stator Tilting Endwall Designs on a Mixed Flow Turbine

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