Investigation on the flow characteristics of a VNT turbine under pulsating flow conditions

2017 ◽  
Vol 233 (2) ◽  
pp. 396-412 ◽  
Author(s):  
Mingxu Qi ◽  
Xinguo Lei ◽  
Zhen Wang ◽  
Chaochen Ma
Keyword(s):  
Shock Wave ◽  
Rotor Blade ◽  
Strong Influence ◽  
Flow Characteristics ◽  
Turbine Rotor ◽  
Pulsating Flow ◽  
Flow Conditions ◽  
Turbine Performance ◽  
Turbine Inlet ◽  
Excitation Force

The turbines used in turbochargers naturally experience unsteadiness caused by inlet pulsating flow conditions and stator–rotor interaction. The unsteadiness has an influence on turbine performance. Meanwhile, under certain small-nozzle opening conditions, strong shock waves can be generated. The synergistic effect of turbine inlet pulsation and shock waves has a significant influence on the turbine performance, rotor blade loading as well as the excitation force exerted on the turbine rotor, which is responsible for turbine rotor high cycle fatigue. In order to understand the influence of pulsating flows on turbine performance and the shock wave characteristic at nozzle trailing edge as well as the incidence angle characteristic of the rotor blade, unsteady numerical simulations were performed to investigate the effect of pulsating flow conditions on the performance, flow characteristics in frequency domain and shock wave behavior in a variable nozzle turbine. The results indicate that the turbine inlet pressure pulsation has strong influence on the turbine performances. Meanwhile, the turbine inlet pulsation flow has a strong influence on the intensity of the shock wave and clearance leakage flow in the nozzle, which causes significant flow losses in the turbine. In addition, at the turbine rotor inlet, the unsteadiness caused by the turbine inlet pulsation varies significantly along the circumferential direction and spanwise. Up to two-thirds of the unsteadiness caused by the turbine inlet pulsation dissipates before entering the rotor due to the flow dissipation and mixing process along the nozzle streamwise. The excitation force exerted on the rotor blade leading edge caused by the turbine inlet pulsation is about the same level as that caused by the stator–rotor interaction.

Radial Turbine Rotor Response to Pulsating Inlet Flows

2013 ◽  
Vol 136 (7) ◽  
Author(s):  
Teng Cao ◽  
Liping Xu ◽  
Mingyang Yang ◽  
Ricardo F. Martinez-Botas
Keyword(s):  
Numerical Method ◽  
Time Lag ◽  
Turbine Rotor ◽  
Pulsating Flow ◽  
Navier Stokes ◽  
Transient Effects ◽  
Flow Conditions ◽  
Radial Turbine ◽  
Reduced Frequency ◽  
Integrated Performance

The performance of automotive turbocharger turbines has long been realized to be quite different under pulsating flow conditions compared to that under the equivalent steady and quasi-steady conditions on which the conventional design concept is based. However, the mechanisms of this phenomenon are still intensively investigated nowadays. This paper presents an investigation of the response of a stand-alone rotor to inlet pulsating flow conditions by using a validated unsteady Reynolds-averaged Navier–Stokes solver (URANS). The effects of the frequency, the amplitude, and the temporal gradient of pulse waves on the instantaneous and cycle integrated performance of a radial turbine rotor in isolation were studied, decoupled from the upstream turbine volute. A numerical method was used to help gain the physical understanding of these effects. A validation of the numerical method against the experiments on a full configuration of the turbine was performed prior to the numerical tool being used in the investigation. The rotor was then taken out to be studied in isolation. The results show that the turbine rotor alone can be treated as a quasi-steady device only in terms of cycle integrated performance; however, instantaneously, the rotor behaves unsteadily, which increasingly deviates from the quasi-steady performance as the local reduced frequency of the pulsating wave is increased. This deviation is dominated by the effect of quasi-steady time lag; at higher local reduced frequency, the transient effects also become significant. Based on this study, an interpretation and a model of estimating the quasi-steady time lag have been proposed; a criterion for unsteadiness based on the temporal local reduced frequency concept is developed, which reduces to the Λ criterion proposed in the published literature when cycle averaged. This in turn emphasizes the importance of the pressure wave gradient in time.

Unsteady Performance of a Double Entry Turbocharger Turbine With a Comparison to Steady Flow Conditions

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Colin D. Copeland ◽  
Ricardo Martinez-Botas ◽  
Martin Seiler
Keyword(s):  
Steady Flow ◽  
Flow Behavior ◽  
Turbine Rotor ◽  
Flow Conditions ◽  
Turbine Performance ◽  
Pulsed Flow ◽  
Performance Map ◽  
Engine Operating Condition ◽  
Double Entry ◽  
The Impact

Circumferentially divided, double entry turbocharger turbines are designed with a dividing wall parallel to the machine axis such that each entry feeds a separate 180 deg section of the nozzle circumference prior to entry into the rotor. This allows the exhaust pulses originating from the internal combustion exhaust to be preserved. Since the turbine is fed by two separate unsteady flows, the phase difference between the exhaust pulses entering the turbine rotor will produce a momentary imbalance in the flow conditions around the periphery of the turbine rotor. This research seeks to provide new insight into the impact of unsteadiness on turbine performance. The discrepancy between the pulsed flow behavior and that predicted by a typical steady flow performance map is a central issue considered in this work. In order to assess the performance deficit attributable to unequal admission, the steady flow conditions introduced in one inlet were varied with respect to the other. The results from these tests were then compared with unsteady, in-phase and out-of-phase pulsed flows most representative of the actual engine operating condition.

Unsteady Performance of a Double Entry Turbocharger Turbine With a Comparison to Steady Flow Conditions

2008 ◽  
Author(s):  
Colin D. Copeland ◽  
Ricardo Martinez-Botas ◽  
Martin Seiler
Keyword(s):  
Steady Flow ◽  
Turbine Rotor ◽  
Flow Conditions ◽  
Turbine Performance ◽  
Pulsed Flow ◽  
Performance Map ◽  
Unsteady Performance ◽  
Engine Operating Condition ◽  
Double Entry ◽  
The Impact

Circumferentially divided, double-entry turbocharger turbines are designed with a dividing wall parallel to the machine axis such that each entry feeds a separate 180° section of the nozzle circumference prior to entry into the rotor. This allows the exhaust pulses originating from the internal combustion exhaust to be preserved. Since the turbine is fed by two separate unsteady flows, the phase difference between the exhaust pulses entering the turbine rotor will produce a momentary imbalance in the flow conditions around the periphery of the turbine rotor. This research seeks to provide new insight into the impact of unsteadiness on turbine performance. The discrepancy between the pulsed flow behaviour and that predicted by a typical steady flow performance map is a central issue considered in this work. In order to assess the performance deficit attributable to unequal admission, the steady flow conditions introduced in one inlet were varied with respect to the other. The results from these tests were then compared to unsteady, in-phase and out-of-phase pulsed flow most representative of the actual engine operating condition.

The Effect of Leading Edge Curvature on a Mixed Flow Turbine Performance Under Pulsating Flow Conditions

2009 ◽  
Author(s):  
Li Chen ◽  
Weilin Zhuge ◽  
Yangjun Zhang ◽  
Shuyong Zhang
Keyword(s):  
Incidence Angle ◽  
Leading Edge ◽  
Simulation Models ◽  
Pulsating Flow ◽  
Flow Conditions ◽  
Mixed Flow ◽  
Turbine Performance ◽  
Unsteady Simulation ◽  
Overall Performance ◽  
Inlet Angle

Turbines used in turbochargers matched to reciprocating engines are under natural pulsating flow conditions, and the turbine which has a good performance under steady design condition normally cannot get the same performance in the whole engine actual working circle. Under the pulsating conditions, the incidence angle will change tremendously, thus leads to undesirable flowfield in the turbine. It is shown in some published literature that varying turbine blade inlet angle can achieve better performance characteristics. In this paper, leading edge curvature is introduced to an original mixed flow turbine, while steady and unsteady simulation models of the mixed flow turbine are built to investigate the aerodynamic performance of the original and modified turbine. Flowfield analysis shows that the leading edge curvature can make the flow less sensitive to the incidence change, and average instantaneous efficiency under pulsating flow conditions is improved, while a better overall performance of the turbine is achieved.

Attempt to correlate simulations and measurements of turbine performance under pulsating flows for automotive turbochargers

2017 ◽  
Vol 233 (2) ◽  
pp. 174-187 ◽  
Author(s):  
Calogero Avola ◽  
Colin Copeland ◽  
Alessandro Romagnoli ◽  
Richard Burke ◽  
Pavlos Dimitriou
Keyword(s):  
Mass Flow ◽  
Turbine Rotor ◽  
Inlet Temperature ◽  
Inlet Section ◽  
Flow Measurements ◽  
Virtual Sensors ◽  
Turbine Performance ◽  
Turbine Inlet ◽  
1D Model ◽  
Turbine Model

The paper attempts to correlate simulations and measurements of turbine performance under pulsating flows for automotive turbochargers. Under real automotive powertrain conditions, turbochargers are subjected to pulsating flows, due to the motion of the engine’s valves. Experiments on a purpose-built 2.2 L diesel engine gas-stand have allowed the quantification of unsteady pulsating turbine performance. Temperature, pressure and mass flow measurements are fundamental for the characterisation of turbine performance. An adequate sampling frequency of the instruments and acquisition rates are highly important for the quantification of unsteady turbomachine performance. In the absence of fast, responsive sensors for monitoring mass flow and temperature, however, appropriate considerations would have to be taken into account when making estimates of turbine performance under pulsating flows. A 1D model of the engine gas-stand has been developed and validated against experimental data. A hybrid unsteady/quasi-steady turbine model has been adopted to identify unsteadiness at the turbine inlet and outlet. To evaluate isentropic turbine efficiency and reduce the influence of external heat transfer upon measurements, the turbine inlet temperature has been measured experimentally in the vicinity of the turbine rotor in the inlet section, upstream of the turbine tongue. The hybrid unsteady/quasi-steady turbine model considers the presence of unsteady flows in the turbine inlet and outlet, leaving the rest of the turbine to react quasi-steadily. Virtual sensors and thermocouples have been implemented in a 1D model to correlate experimental time-averaged temperature measurements.

Investigation of the mixed flow turbine performance under inlet pulsating flow conditions

2012 ◽  
Vol 340 (3) ◽  
pp. 165-176 ◽  
Author(s):  
Mohammed Hamel ◽  
Miloud Abidat ◽  
Sid Ali Litim
Keyword(s):  
Pulsating Flow ◽  
Flow Conditions ◽  
Mixed Flow ◽  
Turbine Performance

Comparison Between Steady and Unsteady Double-Entry Turbine Performance Using the Quasi-Steady Assumption

2010 ◽  
Vol 133 (3) ◽  
Author(s):  
Colin D. Copeland ◽  
Ricardo Martinez-Botas ◽  
Martin Seiler
Keyword(s):  
Steady State ◽  
Pulsating Flow ◽  
Flow Conditions ◽  
Experimental Performance ◽  
State Data ◽  
Turbine Performance ◽  
Partial Admission ◽  
Unsteady Operation ◽  
Unsteady Performance ◽  
Double Entry

The experimental performance evaluation of a circumferentially divided, double-entry turbocharger turbine is presented in this paper with the aim of understanding the influence of pulsating flow. By maintaining a constant speed but varying the frequency of the pulses, the influence of frequency was shown to play an important role in the performance of the turbine. A trend of decreasing cycle-averaged efficiency at lower frequencies was measured. One of the principal objectives was to assess the degree to which the unsteady performance differs from the quasi-steady assumption. In order to make the steady-unsteady comparison for a multiple entry turbine, a wide set of steady equal and unequal admission flow conditions were tested. The steady-state data was then interpolated as a function of three, nondimensional parameters in order to allow a point-by-point comparison with the instantaneous unsteady operation. As an average, the quasi-steady assumption generally underpredicted the mass flow and efficiency loss through the turbine, albeit the differences were reduced as the frequency increased. Out-of-phase pulsations produced unsteady operating orbits that corresponded to a significant steady-state, partial admission loss, and this was reflected as a drop in the quasi-steady efficiency. However, these differences between quasi-steady in-phase and out-of-phase predictions were not replicated in the measured results, suggesting that the unequal admission loss is not as significant in pulsating flow as it is in steady flow.

Impact of the wastegate opening on radial turbine performance under steady and pulsating flow conditions

2019 ◽  
Vol 234 (2-3) ◽  
pp. 652-668 ◽  
Author(s):  
Ahmed Ketata ◽  
Zied Driss ◽  
Mohamed Salah Abid
Keyword(s):  
Mass Flow ◽  
Large Deviation ◽  
Pulse Frequency ◽  
Pulsating Flow ◽  
Flow Conditions ◽  
One Dimensional ◽  
Loop Area ◽  
Modeling Methodology ◽  
Turbine Performance ◽  
The One

The present article attempts to describe the behavior of wastegated turbines under various steady and pulsating flow conditions. For this, meanline and one-dimensional numerical codes including appropriate modeling approaches for wastegated turbines have been developed with the FORTRAN language. These codes were validated against experiments with an established test rig at the National School of Engineers of Sfax. The discharge coefficient map of the wastegate was determined with a developed correlation built from experiments, and it was served as an input to the developed codes for interpolations during computation. This correlation is based on a two-dimensional non-linear dose-response fitting relationship instead of classical polynomial function which is one novelty of the article in addition to the one-dimensional modeling methodology. The normalized root mean square error (NRMSE) of both cycle-averaged efficiency and mass flow parameter (MFP) remains below 2% which confirms the validity of the proposed calculation approach. The results indicated a large deviation in the turbine performance under pulsating flow conditions compared to the steady state ones. The shape of the hysteresis loop of the turbine efficiency remains unchanged toward the variation of the wastegate valve angle at the same pulse frequency. The mass flow hystereses loop area is decreased by around 50% as the pulse frequency increases from 33 up to 133.33 Hz. An increase of less than 1% of the cycle-averaged efficiency has been reported when the bypass flow through the wastegate increases. The fluctuation of the efficiency is decreased by 1.5% when the wastegate valve becomes fully opened under the whole range of the pulse frequency.

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

2014 ◽  
Author(s):  
Harald Roclawski ◽  
Marc Gugau ◽  
Florian Langecker ◽  
Martin Böhle
Keyword(s):  
Steady State ◽  
Hysteresis Loop ◽  
Pulsating Flow ◽  
Flow Conditions ◽  
Load Step ◽  
Turbine Wheel ◽  
Engine Load ◽  
Flow Capacity ◽  
Turbine Performance ◽  
Degree Of Reaction

This paper presents a study on the influence of the degree of reaction (DoR) on turbine performance under highly pulsating inflow. A reference test turbine wheel is designed and scaled to three different wheel diameters while an identical flow capacity of all three turbines is provided by adjusting the volute size. Hence, the three turbines differ by their DoR, inertia and efficiency characteristic. The investigation is done completely numerically using highly validated models. Naturally, the pulsating flow character of a 4-cylinder gasoline engine requires unsteady CFD. In addition steady-state turbine maps were calculated beforehand as a reference base. The results of the steady state calculation show that for the combination of the bigger turbine wheel with the smaller turbine volute the peak efficiency is smaller but is shifted towards higher pressure ratios respectively to lower blade speed ratios. This is fundamentally beneficial for turbines in automotive turbochargers for gasoline engines characterized by highly pulsating flow conditions, in particular at lower engine speeds. For the transient flow calculations with pulsating turbine inflow, the hysteresis loop and the turbine power generation was investigated. It is shown that the smallest volute compared to the biggest one causes a more contracted hysteresis loop combined with increased power output within one pulse cycle. In order to include the influence of moment of inertia, the turbines with varying DoR but same flow capacity were analytically compared with a 1D code simulating engine load step operation. Thus, the paper shows the effect of turbine DoR on both, steady-state turbine performance under pulsating inflow and the capability for optimum engine load step operation.

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