A Detailed Comparison on the Influence of Flow Unsteadiness Between the Vaned and Vaneless Mixed-Flow Turbocharger Turbine

2017 ◽  
Vol 140 (4) ◽  
Author(s):  
M. H. Padzillah ◽  
S. Rajoo ◽  
R. F. Martinez-Botas
Keyword(s):  
Flow Field ◽  
Combustion Engine ◽  
Incidence Angle ◽  
Detailed Comparison ◽  
Pressure Profile ◽  
Operating Conditions ◽  
Pulsating Flow ◽  
Mixed Flow ◽  
Field Level ◽  
Pulse Cycle

A turbocharger is a key enabler for lowering CO2 emission of an internal combustion engine (ICE) through the reutilization of the exhaust gas energy that would otherwise have been released to the ambient. In its actual operating conditions, a turbocharger turbine operates under highly pulsating flow due to the reciprocating nature of the ICE. Despite this, the turbocharger turbines are still designed using the standard steady-state approach due to the lack of understanding of the complex unsteady pressure and mass propagation within the stage. The application of guide vanes in a turbocharger turbine stage has increased the complexity of flow interactions regardless of whether the vanes are fixed or variable. Although it is enticing to assume that the performance of the vaned turbine is better than the one without (vaneless), there are currently no tangible evidences to support this claim, particularly during the actual pulsating flow operations. Therefore, this research looks into comparing the differences between the two turbine arrangements in terms of their performance at flow field level. For this purpose, a three-dimensional (3D) “full-stage” unsteady turbine computational fluid dynamics (CFD) models for both volutes are constructed and validated against the experimental data. These models are subject to identical instantaneous inlet pressure profile of 60 Hz, which is equivalent to an actual three-cylinder four-stroke engine rotating at 2400 rpm. A similar 95.14 mm diameter mixed-flow turbine rotor rotating at 48,000 rpm is used for both models to enable direct comparison. The complete validation exercises for both steady and unsteady flow conditions are also presented. Results have indicated that neither vaned nor vaneless turbine is capable of maintaining constant efficiency throughout the pulse cycle. Despite that, the vaneless turbine indicated better performance during peak power instances. This work also showed that the pulsating pressure at the turbine inlet affected the vaned and vaneless turbines differently at the flow field level. Furthermore, results also indicated that both the turbines matched its optimum incidence angle for only a fraction of pulse cycle, which is unfavorable.

An Investigation of Compressor Map Width Enhancement and the Inducer Flow Field Using Various Configurations of Shroud Bleed Slot

2010 ◽  
Author(s):  
Subenuka Sivagnanasundaram ◽  
Stephen Spence ◽  
Juliana Early ◽  
Bahram Nikpour
Keyword(s):  
Flow Field ◽  
Incidence Angle ◽  
Leading Edge ◽  
Detailed Comparison ◽  
Operating Conditions ◽  
Tip Vortex ◽  
Performance Measurements ◽  
Impeller Blade ◽  
Choked Flow ◽  
The Impact

This paper describes an investigation of various shroud bleed slot configurations of a centrifugal compressor using CFD with a manual multi-block structured grid generation method. The compressor under investigation is used in a turbocharger application for a heavy duty diesel engine of approximately 400hp. The baseline numerical model has been developed and validated against experimental performance measurements. The influence of the bleed slot flow field on a range of operating conditions between surge and choke has been analysed in detail. The impact of the returning bleed flow on the incidence at the impeller blade leading edge due to its mixing with the main through-flow has also been studied. From the baseline geometry, a number of modifications to the bleed slot width have been proposed, and a detailed comparison of the flow characteristics performed. The impact of slot variations on the inlet incidence angle has been investigated, highlighting the improvement in surge and choked flow capability. Along with this, the influence of the bleed slot on stabilizing the blade passage flow by the suction of the tip and over-tip vortex flow by the slot has been considered near surge.

Impact of the Expansion Ratio on the Unsteady Aerodynamics and Performance of a HP Axial Turbine

2016 ◽  
Author(s):  
P. Gaetani ◽  
G. Persico ◽  
A. Spinelli ◽  
A. Mora
Keyword(s):  
Flow Field ◽  
Incidence Angle ◽  
Flow Direction ◽  
Axial Flow ◽  
Unsteady Aerodynamics ◽  
Fast Response ◽  
Expansion Ratio ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
And Performance

In the frame of the European research project RECORD, the flow field within a HP axial-flow turbine model was investigated experimentally for several operating conditions. A number of studies on stator-rotor interaction in HP turbines for subsonic as well as transonic/supersonic conditions were proposed in the last decades, but none of them compared different conditions for the same geometry. In this paper, the transonic condition is investigated and compared to three subsonic ones, in the frame of an entirely new experimental campaign. The research was performed at the Laboratorio di Fluidodinamica delle Macchine of the Politecnico di Milano (Italy), where a cold-flow, closed-loop test rig is available for detailed studies on turbines and compressors. The boundary conditions resulted in keeping constant both the turbine inlet temperature and the stage outlet absolute flow direction; so far, while the expansion ratio was varied, the rotational speed was also modified accordingly. The analysis was performed by means of a conventional five hole probe in the stator – rotor axial gap and by a fast response aerodynamic probe downstream of the rotor. The local time-averaged and phase-resolved flow field was then derived and used to analyze the stage aerodynamics and performance. Results show that the stage expansion ratio has a dramatic impact on both the rotor aerodynamics and stage performance. In particular, Mach number effects are recognized in the stator cascade that passes from transonic to low subsonic conditions. On the rotor cascade the reduction of expansion ratio reduces significantly the Mach and Reynolds numbers and increases the incidence angle as well; the rotor loss mechanics as well as the vane-rotor interaction are greatly amplified. Correspondingly a significant variation of stage overall efficiency is recorded.

An Impact of Various Shroud Bleed Slot Configurations and Cavity Vanes on Compressor Map Width and the Inducer Flow Field

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Subenuka Sivagnanasundaram ◽  
Stephen Spence ◽  
Juliana Early ◽  
Bahram Nikpour
Keyword(s):  
Flow Field ◽  
Incidence Angle ◽  
Pressure Ratio ◽  
Leading Edge ◽  
Operating Conditions ◽  
Choked Flow ◽  
Recirculating Flow ◽  
Heavy Duty Diesel ◽  
Compressor Map ◽  
The Impact

This paper describes an investigation of map width enhancement and a detailed analysis of the inducer flow field due to various bleed slot configurations and vanes in the annular cavity of a turbocharger centrifugal compressor. The compressor under investigation is used in a turbocharger application for a heavy duty diesel engine of approximately 400 hp. This investigation has been undertaken using a computational fluid dynamics (CFD) model of the full compressor stage, which includes a manual multiblock-structured grid generation method. The influence of the bleed slot flow on the inducer flow field at a range of operating conditions has been analyzed, highlighting the improvement in surge and choked flow capability. The impact of the bleed slot geometry variations and the inclusion of cavity vanes on the inlet incidence angle have been studied in detail by considering the swirl component introduced at the leading edge by the recirculating flow through the slot. Further, the overall stage efficiency and the nonuniform flow field at the inducer inlet have been also analyzed. The analysis revealed that increasing the slot width has increased the map width by about 17%. However, it has a small impact on the efficiency, due to the frictional and mixing losses. Moreover, adding vanes in the cavity improved the pressure ratio and compressor performance noticeably. A detail analysis of the compressor with cavity vanes has also been presented.

Laser Velocimeter Measurements in the Pump of an Automotive Torque Converter: Part II—Unsteady Measurements

1996 ◽  
Vol 118 (3) ◽  
pp. 570-577 ◽  
Author(s):  
K. Brun ◽  
R. D. Flack ◽  
J. K. Gruver
Keyword(s):  
Velocity Field ◽  
Flow Field ◽  
Incidence Angle ◽  
Angular Position ◽  
Three Dimensional ◽  
Torque Converter ◽  
Operating Conditions ◽  
Plane Flow ◽  
Periodic Fluctuations ◽  
Pump Inlet

The unsteady velocity field found in the pump of an automotive torque converter was measured using laser velocimetry. Velocities in the inlet, mid-, and exit planes of the pump were investigated at two significantly different operating conditions: turbine/pump rotational speed ratios of 0.065 and 0.800. A data organization method was developed to visualize the three-dimensional, periodic unsteady velocity field in the rotating frame. For this method, the acquired data are assumed to be periodic at synchronous and blade interaction frequencies. Two shaft encoders were employed to obtain the instantaneous angular position of the torque converter pump and turbine at the instant of laser velocimeter data acquisition. By proper “registration” of the data, visualizing the transient interaction effects between the stator and the pump, and between the pump and the turbine, was possible. Results showed strong cyclic velocity fluctuations in the pump inlet plane as a function of the relative stator-pump position. Typical percent periodic fluctuations in the through flow velocity were 70 percent of the average throughflow velocity. The upstream propagation influence of the turbine on the pump exit plane flow field was seen to be smaller. Percent periodic fluctuations of the throughflow velocity were typically 30 percent. The effect of the stator and turbine on the midplane flow field was seen to be negligible. The incidence angle at the pump inlet fluctuated by 27 and 14 deg for the 0.065 and 0.800 speed ratios, respectively. Typical slip factors at the exit were 0.965 and fluctuated by less than 1 percent.

An Impact of Various Shroud Bleed Slot Configurations and Cavity Vanes on Compressor Map Width and the Inducer Flow Field

2011 ◽  
Author(s):  
Subenuka Sivagnanasundaram ◽  
Stephen Spence ◽  
Juliana Early ◽  
Bahram Nikpour
Keyword(s):  
Flow Field ◽  
Incidence Angle ◽  
Pressure Ratio ◽  
Leading Edge ◽  
Operating Conditions ◽  
Choked Flow ◽  
Recirculating Flow ◽  
Heavy Duty Diesel ◽  
Compressor Map ◽  
The Impact

This paper describes an investigation of map width enhancement and a detailed analysis of the inducer flow field due to various bleed slot configurations and vanes in the annular cavity of a turbocharger centrifugal compressor. The compressor under investigation is used in a turbocharger application for a heavy duty diesel engine of approximately 400hp. This investigation has been undertaken using a CFD model of the full compressor stage which includes a manual multi-block structured grid generation method. The influence of the bleed slot flow on the inducer flow field at a range of operating conditions has been analysed, highlighting the improvement in surge and choked flow capability. The impact of the bleed slot geometry variations and the inclusion of cavity vanes on the inlet incidence angle have been studied in detail by considering the swirl component introduced at the leading edge by the recirculating flow through the slot. Further, the overall stage efficiency and the non-uniform flow field at the inducer inlet have been also analysed. The analysis revealed that increasing the slot width has increased the map width by about 17%. However, it has a small impact on the efficiency due to the frictional and mixing losses. Moreover, adding vanes in the cavity improved the pressure ratio and compressor performance noticeably. A detail analysis of the compressor with cavity vanes has also been presented.

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.

scholarly journals COMPARISON OF FLOW FIELD BETWEEN STEADY AND UNSTEADY FLOW OF AN AUTOMOTIVE MIXED FLOW TURBOCHARGER TURBINE

2016 ◽  
Vol 78 (8-4) ◽  
Author(s):  
M.H. Padzillah ◽  
S. Rajoo ◽  
R.F. Martinez-Botas
Keyword(s):  
Flow Field ◽  
Weight Ratio ◽  
Pulsating Flow ◽  
Transportation Industry ◽  
Mixed Flow ◽  
Irregular Pattern ◽  
Pressure Increment ◽  
Integral Element ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Blockage

Global decarbonizing efforts in transportation industry have forced the automotive manufacturers to opt for highly downsized high power-to-weight ratio engines. Since its invention, turbocharger remains as integral element in order to achieve this target. However, although it has been proven that a turbocharger turbine works in highly pulsatile environment, it is still designed under steady state assumption. This is due to the lack of understanding on the nature of pulsating flow field within the turbocharger turbine stage. This paper presents an effort to visualize the pulsating flow feature using experimentally validated Computational Fluid Dynamics (CFD) simulations. For this purpose, a lean-vaned mixed-flow turbine with rotational speed of 30000 rpm at 20 Hz flow frequency, which represent turbine operation for 3-cylinder 4-stroke engine operating at 800 rpm has been used. Results indicated that the introduction of pulsating flow has resulted in more irregular pattern of flow field as compared to steady flow operation. It has also been indicated that the flow behaves very differently between pressure increment and decrement instances. During the pressure decrement instance, flow blockage in terms of low pressure region occupies most of the turbine passage as the flow exit the turbine. 

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.

The Influence of Real Gas Effects on ICE-ORC Turbine Flow Fields

2014 ◽  
Author(s):  
Lei Zhang ◽  
Weilin Zhuge ◽  
Yangjun Zhang ◽  
Jie Peng
Keyword(s):  
Thermodynamic Parameters ◽  
Gas Flow ◽  
Combustion Engine ◽  
Incidence Angle ◽  
Flow Fields ◽  
Operating Conditions ◽  
Specific Power ◽  
Working Fluid ◽  
Perfect Gas ◽  
Real Gas

This paper presents a quantitative comparison of the flow fields of a radial turbine between real gas and perfect gas models for the internal combustion engine (ICE) organic Rankine Cycle (ORC) application. Three-dimensional turbulent Navier-Stokes simulations are carried out using CFD code NUMECA FINE™/TURBO, which is linked to an accurate thermodynamic model for organic working fluid R123 in the form of thermodynamic tables. Four turbine operating conditions including the design point and three part-load points, the inlet compressibility factors of which are 0.82–0.89, are analyzed to discuss the differences of flow fields. Obvious derivations of thermodynamic parameters are investigated in the turbine flow fields. The derivations of speed of sound and density at the nozzle inlet are about 15–20%. There exist about 10m/s value differences in the nozzle outlet velocity evaluation, and furthermore a difference of 10 degrees in the rotor inlet incidence angle comparison. The derivations of relative Mach number are about 20–35% in the rotor outlet near the shroud surface. More than 30% differences are shown in the comparison of turbine total temperature drops. Other thermodynamic parameters show much smaller derivations. The differences of thermodynamic parameters lead to a 1–3% larger in mas flow rate, 1–2% larger in isentropic efficiency and 6–8% smaller in specific power comparison. However, there do not exist obvious differences on thermodynamic parameters distributions in the flow fields. The similar flow fields provide a suggestion that perfect gas model may be an acceptable model for turbine preliminary design and one-dimensional analysis in this gas thermodynamic region, and also the real gas flow fields simulated can be used as a start point to refine the turbine design.

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.

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