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.

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.

Analysis of a Tilted Turbine Housing Volute Design Under Pulsating Inlet Conditions

2017 ◽  
Author(s):  
Samuel P. Lee ◽  
Martyn L. Jupp ◽  
Ambrose K. Nickson ◽  
John M. Allport
Keyword(s):  
Steady State ◽  
Incidence Angle ◽  
Leading Edge ◽  
Pulsating Flow ◽  
Flow Conditions ◽  
Low Velocity ◽  
Mixed Flow ◽  
Turbine Wheel ◽  
Housing Design ◽  
Inlet Conditions

Radial inflow turbines are widely used in the automotive turbocharger industry due to the greater amount of work that can be extracted per stage and their ease of manufacture compared with equivalent axial designs [1]. The current industry trend towards downsized engines for lower emissions has driven research to focus on improving turbine technologies for greater aero-thermal efficiency. Consequently, mixed flow turbines have recently received significant interest due to a number of potential performance benefits over their radial counterparts, including reduced inertia and improved performance at low velocity ratios. This paper investigates the performance of a tilted volute design compared with that of a radial design, under steady state and pulsating flow conditions. The tilted volute design was introduced in an attempt to improve inlet flow conditions of a mixed flow turbine wheel and hence improve performance. The investigation is entirely computational and the approach used was carefully validated against gas stand test results. The results of the study show that under steady state conditions the tilted volute design resulted in stage efficiency improvements of up to 1.64%. Under pulsating flow conditions, the tilted housing design resulted in a reduction in incidence angle and a maximum cycle averaged rotor efficiency improvement of 1.49% while the stage efficiencies resulted in a 1.23% increase. To assess the loss mechanisms within the rotor, the entropy flux generation through the blade passage was calculated. The tilted housing design resulted in reductions in leading edge suction and shroud surface separation resulting in the improved efficiency as observed.

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.

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.

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

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.

Sign in / Sign up

Export Citation Format

Share Document