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.

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

2009 ◽  
Author(s):  
Colin D. Copeland ◽  
Ricardo Martinez-Botas ◽  
Martin Seiler
Keyword(s):  
Steady State ◽  
Pulsating Flow ◽  
Flow Conditions ◽  
Experimental Performance ◽  
Turbine Performance ◽  
Partial Admission ◽  
Dimensional Parameters ◽  
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, non-dimensional parameters in order to allow a point-by-point comparison with the instantaneous unsteady operation. As an average, the quasi-steady assumption generally under-predicted 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.

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.

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.

The Effect of Stator-Rotor Hub Sealing Flow on the Mainstream Aerodynamics of a Turbine

2006 ◽  
Author(s):  
Kevin Reid ◽  
John Denton ◽  
Graham Pullan ◽  
Eric Curtis ◽  
John Longley
Keyword(s):  
Steady State ◽  
Entropy Generation ◽  
Flow Rate ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Flow Conditions ◽  
Turbine Efficiency ◽  
Turbine Performance ◽  
Mainstream Flow ◽  
Flow Interactions

An investigation into the effect of stator-rotor hub gap sealing flow on turbine performance is presented. Efficiency measurements and rotor exit area traverse data from a low speed research turbine are reported. Tests carried out over a range of sealing flow conditions show that the turbine efficiency decreases with increasing sealant flow rate but that this penalty is reduced by swirling the sealant flow. Results from time-accurate and steady-state simulations using a three-dimensional multi-block RANS solver are presented with particular emphasis paid to the mechanisms of loss production. The contributions toward entropy generation of the mixing of the sealant fluid with the mainstream flow and of the perturbed rotor secondary flows are assessed. The importance of unsteady stator wake/sealant flow interactions is also highlighted.

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.

A Method of Map Extrapolation for Unequal and Partial Admission in a Double Entry Turbine

2013 ◽  
Author(s):  
Peter Newton ◽  
Alessandro Romagnoli ◽  
Ricardo Martinez-Botas ◽  
Colin Copeland ◽  
Martin Seiler
Keyword(s):  
Velocity Ratio ◽  
Test Stand ◽  
Turbine Wheel ◽  
Turbine Performance ◽  
Admission Data ◽  
Partial Admission ◽  
Single Entry ◽  
Data Points ◽  
Double Entry ◽  
The Impact

This paper presents a method for prediction of the unequal admission performance of a double entry turbine based on the full admission turbine maps and a minimal number of unequal admission points. The double entry turbine has two separate inlet ports which feed a single turbine wheel: this arrangement can be beneficial in a turbocharger application; however the additional entry does add complexity in producing a complete turbine map which includes unequal admission behaviour. When a double entry turbine is operated under full admission conditions, with both entries feeding the turbine equally, this will act effectively as a single entry device and the turbine performance can be represented by a standard turbine map. In reality a multiple entry turbine will spend the majority of time operating under varying degrees of unequal admission, with each entry feeding the turbine different amounts; the extent of this inequality can have a considerable impact on turbine performance. In order to produce a full map which extends from full admission through to the partial admission case (where one inlet has no flow) a large number of unequal admission data points are required. The paper starts by discussing previous attempts to describe the partial and unequal admission performance of a double entry turbine. The full unequal admission performance is then presented for a nozzled, double entry turbine. The impact of unequal admission on turbine performance is demonstrated. Under some conditions of operation, the turbine efficiency may be less than half that of the equivalent full admission case based on the average turbine velocity ratio. A method of using the steady, equal admission maps, with a limited number of unequal admission data points, to predict the full unequal admission behaviour is presented. A good agreement is found when the map extension method is validated against the full unequal admission turbine performance measured on a test stand. In the prediction of efficiency a mean error of approximately 0.39% is found between the test stand data and the proposed extrapolation method, with a standard deviation of 2.79%. A better agreement is generally found at conditions of higher power.

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.

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.

Optimization of a Radial Turbine for Pulsating Flows

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Zheng Liu ◽  
Colin Copeland
Keyword(s):  
Steady State ◽  
Cone Angle ◽  
Exhaust System ◽  
Maximum Energy ◽  
Pulsating Flow ◽  
Energy Output ◽  
Small Scale ◽  
Maximum Deviation ◽  
Flow Conditions ◽  
Blade Shape

Abstract A turbocharger turbine is exposed to pulsating flow conditions when it is connected to an engine exhaust system due to the opening and closing of the exhaust valves. However, many radial turbines are designed and tested under steady-state conditions without taking into account these unsteady exhaust flows. In order to seek the optimal aerodynamic design of a radial flow turbine (RFT) under pulsating flow conditions, the present research utilizes a numerical simulation approach to optimize the blade shape of a small-scale mixed flow turbine (MFT) under 50 Hz pulses. This corresponds to a four-stroke, three-cylinder engine rotating at 2000 rpm. In order to understand how a less computationally intensive, steady-state optimization compares, the blade shape was also optimized using the peak power point of the pulse. Three turbine features were modified during the optimization process, including blade cone angle, blade axial location, and blade camber angles. The optimization was carried out using a computational fluid dynamics (CFD)–genetic algorithm (GA) coupled approach, targeting at maximizing both energy-weighted efficiency and energy output during a predefined pulse period. To ensure that the new design maintains a similar matching to the engine, the maximum deviation of turbine swallowing capacity is controlled to within ±5% of the baseline for all new blade designs. The design that achieves the maximum pulse cycle-averaged efficiency was produced from unsteady optimization, with a performance benefit of 0.66%. The unsteady optimization also produced a blade shape that delivers the maximum energy output, with an improvement of 5.42%.

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
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