Influence of Degree of Reaction on Turbine Performance for Pulsating Flow Conditions

Roclawski, Harald; Gugau, Marc; Langecker, Florian; Böhle, Martin

doi:10.1115/gt2014-25829

Cited by 11 publications

(12 citation statements)

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“…The rotor region uses a structured hexahedral mesh completed in ANSYS TurboGrid [15]. All CFD simulations were completed in ANSYS CFX 17 [15] using the frozen rotor approach to account for the turbine rotation as used by a number of authors [16][17][18]. Yang et al [19] used the same computational approach to study the performance of a vaneless mixed flow turbine and showed good agreement with experimental results under both steady state and pulsating flows.…”

Section: Computational Approachmentioning

confidence: 99%

“…As the variation between the two approaches was small and the frozen rotor method was found to be capable of predicting the volute exit flow conditions, the frozen rotor approach was used throughout this study. The Shear Stress Transport (SST) model is commonly used in radial and mixed flow turbine studies [8,16,17]. While the model has been validated by a number of authors and its accuracy proven over a number of years, the true turbulence is not modelled in the Unsteady Reynold Averaged Navier-Stoke (URANS) approach.…”

Section: Computational Approachmentioning

confidence: 99%

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The Impact of Volute Aspect Ratio on the Performance of a Mixed Flow Turbine

et al. 2017

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Current trends in the automotive industry towards engine downsizing mean turbocharging now plays a vital role in engine performance. A turbocharger increases charge air density using a turbine to extract waste energy from the exhaust gas to drive a compressor. Most turbocharger applications employ a radial inflow turbine. However, mixed flow turbines can offer non-zero blade angles, reducing leading edge (LE) separation at low velocity ratios. The current paper investigates the performance of a mixed flow turbine with three different volute aspect ratio (AR) designs (AR = 0.5, 1 and 2). With constant A/r (ratio of volute area to centroid radius), the AR = 0.5 volute design produced a 4.3% increase in cycle averaged mass flow parameter (MFP) compared to the AR = 2 design. For the purpose of performance comparison, it was necessary to manipulate the volute A/r's to ensure constant MFP for aerodynamic similarity. With the volute A/r's manipulated to ensure constant MFP for aerodynamic similarity, the maximum variation of cycle averaged normalized efficiency measured between the designs was 1.47%. Purely in the rotor region, the variation in normalized cycle averaged efficiency was 1%. The smallest tested volute aspect ratio showed a significant increase in volute loss while the ARs of 1 and 2 showed similar levels of loss. The smallest AR volute showed significant secondary flow development in the volute. The resulting variation in LE incidence was found to vary as a result.

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Section: Computational Approachmentioning

confidence: 99%

Section: Computational Approachmentioning

confidence: 99%

The Impact of Volute Aspect Ratio on the Performance of a Mixed Flow Turbine

et al. 2017

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“…Greater mass accumulation within the system results in further deviation from quasi-steady performance. Conversely, the relatively small volume of the rotor region has been shown by a number of authors to behave in a quasi-steady manor [2,13]. Figure 6 shows the mass accumulation within the turbine volute for the four pulse shapes tested.…”

Section: Resultsmentioning

confidence: 97%

“…The inlet wave forms implemented include sinusoidal, triangular and square wave forms, as well as a pulse shape that was determined by a one dimensional engine model using a similar approach to Roclawski et al [13] and Hellstrom and Fuchs [14], and is considered to be a 'realistic' wave form.…”

Section: Boundary Conditionsmentioning

confidence: 99%

“…al stated that as the inlet pressure pulse can be decomposed into a sum of sinusoidal wave forms (as demonstrated by Costall and Martinez-Botas [12]), therefore the turbine behavior under a sinusoidal pulse is of particular importance. Alternately, Roclawski et al [13] and Hellstrom and Fuchs [14] simulated turbine operation using inlet pulses generated from one dimensional engine simulation tools. Yang et al [15] and Padzillah et al [8] used the pulse form generated from experimental test facilities using a chopper plate and therefore had extensive experimental validation for the computational method used.…”

Section: Introductionmentioning

confidence: 99%

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The Influence of Pulse Shape on the Performance of a Mixed Flow Turbine for Turbocharger Applications

Lee¹,

Rezk²,

Jupp³

et al. 2016

IJMERR

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Engine downsizing allows automotive manufactures to achieve improved efficiency and reduce emissions. Turbocharging can increase the power density of the engine, and therefore plays a vital role in downsizing. Due to the nature of the reciprocating engine, a turbocharger turbine operates in a highly unsteady environment. This paper presents a computational investigation looking at the impact of pulse shape on the performance of a mixed flow turbine for turbocharger applications. While the impact of pulse frequency and amplitude on turbine unsteady performance has received significant attention in the past, little work has been done on the impact of the pulse shape. In the current study, four inlet pulse shapes have been investigated and shown to have a significant impact on turbine instantaneous performance, where efficiency and mass flow hysteresis varied significantly between test cases. This result shows for in-depth analyses of turbine flow physics and loss mechanisms, accurately modelling the inlet pulse shape is vital. The square pulse showed the most distinct impact with normalized cycle average efficiency decreasing by 1.37% and a 2.23% reduction in normalized stage MFP when compared to the sinusoidal wave. The variation in normalized cycle averaged stage efficiency was found to be less than 0.25% for the remaining three wave forms and the variation in normalized cycle averaged MFP less than 0.5%. This finding suggests that a simple sinusoidal wave form can be used for the majority of cycle-averaged performance comparisons.

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Computational Fluid Dynamics Analysis of a Radial Turbine During Load Step Operation of an Automotive Turbocharger

Roclawski

Gugau

Böhle

2017

Journal of Fluids Engineering

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A method for evaluating the transient performance of a turbocharger (TC) is so-called load step tests. In these tests, the load of the engine is increased at constant engine speed and the time measured from the start to the end of the load step is measured. Usually, these tests can be run relatively late in the development process, since hardware needs to be already available. In order to judge the transient TC performance at an earlier stage, engine process simulations are run using maps of compressor and turbine. For the turbine, these maps usually need to be extrapolated, since only a certain range of each speed line can be measured on a standard gas stand. Furthermore, because of the exhaust gas pulsation of the engine, it is known that the turbine performance differs from the steady-state case which the maps rely on. This has to be respected by additional models. Using computational fluid dynamics (CFD) simulations, the transient performance of the turbine can be analyzed independent from steady-state maps. So far, these investigations have been usually performed with a constant turbine speed. In this paper, a method is presented which includes the speed fluctuations of the TC caused by the exhaust pulsations as well as the change in mean speed during the load step by including compressor and engine in the CFD analysis with User-Fortran models. Results for a load step from 21,000 rpm to 196,400 rpm are discussed.

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Influence of Degree of Reaction on Turbine Performance for Pulsating Flow Conditions

Cited by 11 publications

References 0 publications

The Impact of Volute Aspect Ratio on the Performance of a Mixed Flow Turbine

The Impact of Volute Aspect Ratio on the Performance of a Mixed Flow Turbine

The Influence of Pulse Shape on the Performance of a Mixed Flow Turbine for Turbocharger Applications

Computational Fluid Dynamics Analysis of a Radial Turbine During Load Step Operation of an Automotive Turbocharger

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