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.

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.

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

Experimental Investigation of the Performance of H-Darrieus Wind Turbines With Tubercle Leading Edge Blades

2020 ◽  
Author(s):  
Longhuan Du ◽  
Robert G. Dominy ◽  
Grant Ingram
Keyword(s):  
Wind Turbines ◽  
Leading Edge ◽  
Simulation Models ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Small Scale ◽  
Flow Conditions ◽  
Turbine Performance ◽  
Start Up ◽  
Blade Leading Edge

Abstract The most significant challenge associated with employing small-scale H-Darrieus wind turbines is to ensure that they self-start without compromising their efficiency at the design operating condition. One of the key and straightforward methods to improve the turbine performance is to choose an optimized blade profile. It has been shown that by creating rounded protuberances (tubercles) around the blade leading edge, not only do the blades demonstrate a more gradual stall characteristic but also that the tubercles significantly increase the blade lift performance in the post-stall regime at the expense of slightly degraded lift performance in the pre-stall regime. This effect might be beneficial for the H-Darrieus turbine application where the blades experience extreme incidence range during the turbine start-up period. Therefore, in this study the performance of standard NACA0021 blades is compared experimentally to a modified set of blades which have a sinusoidal tubercle configuration along the original NACA0021 blade leading edge (0 ≤ x ≤ 0.3c). Time-accurate, self-starting data were recorded from wind tunnel tests under different flow conditions and the power coefficient (Cp) versus tip speed ratio (λ) curve was calculated. It is demonstrated conclusively that blades with an appropriate configuration of tubercle leading edges can considerably improve turbine self-starting capability. To the best of the authors’ knowledge, this study provides the first experimental data of H-Darrieus wind turbine performance with tubercle leading edge blades and the data are valuable for future designs and for the validation of simulation models.

Effects of Pulsating Flow Conditions on Mixed Flow Turbine Performance

2011 ◽  
Author(s):  
Li Chen ◽  
Weilin Zhuge ◽  
Yangjun Zhang ◽  
Lei Xie ◽  
Shuyong Zhang
Keyword(s):  
Combustion Engine ◽  
Flow Fields ◽  
Pulsating Flow ◽  
Phase Lag ◽  
Pulsation Frequency ◽  
Flow Conditions ◽  
Operating Characteristics ◽  
Mixed Flow ◽  
Turbine Performance ◽  
Steady Performance

Turbines work under actual pulsating flow conditions due to the operating characteristics of a reciprocating internal combustion engine. The pulsating flow conditions affect the flow fields in a turbine, and lead to obvious difference between actual and steady performance. A three-dimensional numerical investigation into mixed flow turbine under different kinds of pulsating flow conditions was conducted, in order to get an inner sight of the unsteady impact. The effects of the pulsation frequency and amplitude on the turbine performance were analyzed. The results show that the period average performance of the turbine under pulsating conditions is lower than the steady performance under the mean pulsating conditions. The actual power output varies little with the pulsation frequency changing, while the phase lag increases as the pulsation frequency increases. The unsteady characteristics become more obvious when the pulsation amplitude increases. Under the pulsating flow conditions, of which amplitude is 0.8, the period average efficiency is 4.11 percent lower than the steady efficiency. The flow fields fluctuate seriously under this high pulsating flow conditions. The occurrence and vanishing of the votex are dynamic procedures, and hysteresis effect is observed in the unsteady flow.

A Critical Analysis on Low-Order Simulation Models for Darrieus VAWTs: How Much Do They Pertain to the Real Flow?

2018 ◽  
Author(s):  
Alessandro Bianchini ◽  
Francesco Balduzzi ◽  
Giovanni Ferrara ◽  
Giacomo Persico ◽  
Vincenzo Dossena ◽  
...  
Keyword(s):  
Flow Field ◽  
Incidence Angle ◽  
Computational Cost ◽  
Simulation Models ◽  
Small Scale ◽  
Critical Issues ◽  
Overall Performance ◽  
Lift And Drag ◽  
Real Flow ◽  
Low Order

To improve the efficiency of Darrieus wind turbines, which still lacks from that of horizontal-axis rotors, Computational Fluid Dynamics (CFD) techniques are now extensively applied, since they only provide a detailed and comprehensive flow representation. Their computational cost makes them, however, still prohibitive for routine application in the industrial context, which still makes large use of low-order simulation models like the Blade Element Momentum (BEM) theory. These models have been shown to provide relatively accurate estimations of the overall turbine performance; conversely, the description of the flow field suffers from the strong approximations introduced in the modelling of the flow physics. In the present study, the effectiveness of the simplified BEM approach was critically benchmarked against a comprehensive description of the flow field past the rotating blades coming from the combination of a two-dimensional unsteady CFD model and experimental wind tunnel tests; for both data sets, the overall performance and the wake characteristics on the mid plane of a small-scale H-shaped Darrieus turbine were available. Upon examination of the flow field, the validity of the ubiquitous use of induction factors is discussed, together with the resulting velocity profiles upstream and downstream the rotor. Particular attention is paid on the actual flow conditions (i.e. incidence angle and relative speed) experienced by the airfoils in motion at different azimuthal angles, for which a new procedure for the post-processing of CFD data is here proposed. Based on this model, the actual lift and drag coefficients produced by the airfoils in motion are analyzed and discussed, with particular focus on dynamic stall. The analysis highlights the main critical issues and flaws of the low-order BEM approach, but also sheds new light on the physical reasons why the overall performance prediction of these models is often acceptable for a first-design analysis.

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.

scholarly journals Detailed Flow Measurements at the Exit of a Mixed Flow Turbine Under Steady Flow Conditions

1999 ◽  
Author(s):  
N. Karamanis ◽  
R. F. Martinez-Botas ◽  
C. C. Su
Keyword(s):  
Laser Doppler Velocimetry ◽  
Incidence Angle ◽  
Performance Tests ◽  
Doppler Velocimetry ◽  
Flow Conditions ◽  
Blade Angle ◽  
Mixed Flow ◽  
Flow Measurements ◽  
Flow Investigation ◽  
Improved Performance

A detailed flow investigation downstream of two mixed-flow turbocharger turbines has been carried out at 50% and 70% design speeds, equivalent to 29,400 and 41,300 rpm respectively. The measurement technique used was laser Doppler velocimetry (LDV). The measurements were performed at a plane 9.5 mm behind the rotor trailing edge, they were resolved in a blade-to-blade sense to fully examine the nature of the flow. The results confirmed the performance tests and indicated the improved performance of the rotor with a constant inlet blade angle relative to the rotor with a nominally constant incidence angle.

INVESTIGATION OF TORQUE GENERATION CAPABILITY OF MIXED FLOW TURBINE UNDER STEADY STATE CONDITIONS

2017 ◽  
Vol 79 (7-3) ◽  
Author(s):  
M. A. S. Izaiddin ◽  
A. F. Mustaffa ◽  
M. H. Padzillah
Keyword(s):  
Mass Flow ◽  
Leading Edge ◽  
Maximum Efficiency ◽  
Blade Surface ◽  
Mixed Flow ◽  
Factors Affecting ◽  
Turbine Performance ◽  
Radial Turbine ◽  
Torque Generation ◽  
Edge Surface

A mixed flow turbine is a type of turbine that is used mostly in turbocharger engine for vehicle. The ability of this turbine in obtain maximum efficiency on a wider operating range makes it more favorable compared to axial turbine and radial turbine. In this project, one of the factors affecting turbine performance which is torque has been studied using simulation. The simulation is then being run by varying the mass flow supply to the turbine. In this simulation, torque generation has been identified and plot on the entire blade surface. This torque generation capability is then been compared between 0.25 kg/s, 0.45 kg/s and 0.65 kg/s mass flow. From the simulation, the torque generated is founded to fluctuate along the turbine blade surface. Besides, the torque generated at the leading edge and trailing edge surface are negative. The magnitude of torque generated increases, as the mass flow increased. At the mid span of the blade, torque generated at 0.25 kg/s, 0.45 kg/s and 0.65 kg/s is -3.73 X 10-3Nm, 4.33 X 10-3Nm, and 11.8 X 10-3Nm respectively.

Investigation of a Novel Turbine Housing to Produce a Non-Uniform Spanwise Flow Field at the Inlet to a Mixed Flow Turbine and Provide Variable Geometry Capabilities

2021 ◽  
Author(s):  
Richard Morrison ◽  
Charles Stuart ◽  
Sung In Kim ◽  
Stephen Spence ◽  
Andre Starke ◽  
...  
Keyword(s):  
Flow Separation ◽  
Incidence Angle ◽  
Operating Conditions ◽  
Variable Geometry ◽  
The Novel ◽  
Mixed Flow ◽  
Engine Operation ◽  
Turbine Performance ◽  
The Impact ◽  
Spanwise Flow

Abstract Automotive engine downsizing has placed an increased focus on the ability of the turbocharger to provide adequate boost levels across the full engine operating rage. To achieve the desired levels of turbocharger performance the turbine must be capable of operating effectively at the intended design point and also at off-design conditions. Mixed flow turbines (MFTs) provide a potential method to improve performance at off-design conditions and during transient engine operation. A unique feature of a MFT is the spanwise variation of incidence angle at the rotor leading edge. This results in additional flow separation from the blade suction surface near the hub under a wide range of operating conditions. The flow separation generates additional loss and has a detrimental impact on turbine performance. A novel design of turbine volute similar to a conventional twin-entry turbine volute was examined. The novel turbine volutes were designed to produce a spanwise variation in flow conditions at the rotor inlet. The primary objective was to reduce the incidence angle and increase the mass flow rate at the hub side of the passage relative to the shroud side, as it has previously been identified that this can be beneficial for MFT performance. A number of different volute geometries were examined by numerical analysis to determine the impact of key parameters on turbine performance. The results indicated that generating a suitable spanwise flow distribution could produce a moderate improvement in turbine efficiency at off-design operating conditions. The novel volute design also provided a means of achieving a degree of variable geometry operation to further improve off-design performance. Turbine performance was examined under the variable geometry operation and an improvement in turbine power output at low speed, off-design conditions was achieved. This was analogous to operating with a conventional pivoting vane variable geometry system and had the potential to benefit performance during transient engine 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.

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