scholarly journals Vortex Patterns Investigation and Enstrophy Analysis in a Small Scale S-CO2 Axial Turbine

Energies ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 6112
Author(s):  
Qiyu Ying ◽  
Weilin Zhuge ◽  
Yangjun Zhang ◽  
Can Ma ◽  
Jinlan Gou ◽  
...  
Keyword(s):  
Energy Loss ◽  
Vortex Flow ◽  
Flow Patterns ◽  
Small Scale ◽  
Vortex Interaction ◽  
Tip Leakage Vortex ◽  
Axial Turbine ◽  
Aerodynamic Loss ◽  
Tip Leakage ◽  
Passage Vortex

Supercritical carbon dioxide (S-CO2) Brayton cycle system is a promising closed-loop energy conversion system frequently mentioned in the automotive and power generation field in recent years. To develop a suitable design methodology for S-CO2 turbines with better performance, an understanding of the vortex flow patterns and associated aerodynamic loss inside a S-CO2 turbine is essential. In this paper, a hundred-kilowatt level S-CO2 axial turbine is designed and investigated using a three-dimensional transient viscous flow simulation. The NIST Span and Wagner equation of state model that considers the real gas effects is utilized to estimate the thermodynamic properties of the supercritical fluid. The numerical methods are experimentally validated. The results indicates that the aspect ratio and tip-to-hub ratio are different in the S-CO2 turbine from that in the gas turbine, and the vortex flow patterns are influenced notably by these geometrical parameters. Both the vortex structure and moving tracks of passage vortices are changed as a result of large centrifugal force. An interaction between tip leakage vortex and hub passage vortex is observed in the impeller passage and its formation and development mechanism are revealed. To further explore the aerodynamic loss mechanism caused by vortex interaction, the energy loss in the impeller passage is analyzed with the enstrophy dissipation method, which can not only accurately calculate the energy loss but also estimate how the vortical motions occur. It is found that the enstrophy and energy loss can be effectively reduced by vortex interaction between tip leakage vortex and hub passage vortex. The results in this study would increase the knowledge of vortex flow patterns in S-CO2 turbine and the proposed enstrophy production method can be used intuitively to provide a reference for flow vortical motion study in turbines.

Flow Field Unsteadiness in the Tip Region of a Transonic Compressor Rotor

1997 ◽  
Vol 119 (1) ◽  
pp. 122-128 ◽  
Author(s):  
S. L. Puterbaugh ◽  
W. W. Copenhaver
Keyword(s):  
Flow Field ◽  
High Performance ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Vortex Interaction ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Operating Points

An experimental investigation concerning tip flow field unsteadiness was performed for a high-performance, state-of-the-art transonic compressor rotor. Casing-mounted high frequency response pressure transducers were used to indicate both the ensemble averaged and time varying flow structure present in the tip region of the rotor at four different operating points at design speed. The ensemble averaged information revealed the shock structure as it evolved from a dual shock system at open throttle to an attached shock at peak efficiency to a detached orientation at near stall. Steady three-dimensional Navier Stokes analysis reveals the dominant flow structures in the tip region in support of the ensemble averaged measurements. A tip leakage vortex is evident at all operating points as regions of low static pressure and appears in the same location as the vortex found in the numerical solution. An unsteadiness parameter was calculated to quantify the unsteadiness in the tip cascade plane. In general, regions of peak unsteadiness appear near shocks and in the area interpreted as the shock-tip leakage vortex interaction. Local peaks of unsteadiness appear in mid-passage downstream of the shock-vortex interaction. Flow field features not evident in the ensemble averaged data are examined via a Navier-Stokes solution obtained at the near stall operating point.

scholarly journals Investigation of the groove effect on the tip leakage vortex flow

2021 ◽  
Vol 627 ◽  
pp. 012004
Author(s):  
Zhaodan Fei ◽  
Rui Zhang ◽  
Hui Xu ◽  
Tong Mu
Keyword(s):  
Vortex Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage

Effects of Tip Gap Size on the Aerodynamic Performance of a Cavity-Winglet Tip in a Turbine Cascade

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Fangpan Zhong ◽  
Chao Zhou
Keyword(s):  
Suction Side ◽  
Aerodynamic Performance ◽  
Gap Size ◽  
Turbine Cascade ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Baseline Case ◽  
Passage Vortex ◽  
Aerodynamic Performances ◽  
Blade Tip

The aerodynamic performance of a cavity-winglet tip is investigated in a high-pressure turbine cascade by experimental and numerical methods. The winglet tip has geometric features of a cavity and a suction side fore-part winglet. A cavity tip is studied as the baseline case. The aerodynamic performances of the two tips are investigated at three tip gaps of 0.8%, 1.7%, and 2.7% chord. At tip gaps of 1.7% and 2.7% chord, the loss near the blade tip is dominated by the tip leakage vortex (TLV) for both tips, and the winglet tip mainly reduces the loss generated by the tip leakage vortex. In the past, it was concerned that at a small tip gap, the winglet tip could introduce extra secondary loss and show little aerodynamic benefits. The winglet tip used in the current study is also found to be able to effectively reduce the loss at the smallest tip gap size of 0.8% chord. This is because at this small tip gap, the tip leakage vortex and the passage vortex (PV) appear simultaneously for the cavity tip. The winglet tip is able to reduce the pitchwise pressure gradient in the blade passage, which tends to suppress the formation of the passage vortex. The effects of the winglet tip on the flow physics and the loss mechanisms are explained in detail.

Tip Clearance Effects in a Turbine Rotor: Part I — Pressure Field and Loss

2000 ◽  
Author(s):  
Xinwen Xiao ◽  
Andrew A. McCarter ◽  
Budugur Lakshminarayana
Keyword(s):  
Total Pressure ◽  
Pressure Field ◽  
Turbine Blades ◽  
Turbine Rotor ◽  
Tip Clearance ◽  
Laser Doppler Velocimeter ◽  
Tip Leakage Vortex ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Passage Vortex

This paper presents an experimental investigation of the effects of the tip clearance flow in an axial turbine rotor. The effects investigated include the distribution and the development of the pressure, the loss, the velocity, and the turbulence fields. These flow fields were measured using the techniques of static pressure taps, rapid response pressure probes, rotating five-hole probes, and Laser Doppler Velocimeter. Part I of this paper covers the loss development through the passage, and the pressure distribution within the passage, on the blade surfaces, on the blade tip, and on the casing wall. Regions with both the lowest pressure and the highest loss indicate the inception and the trace of the tip leakage vortex. The suction effect of the vortex slightly increases the blade loading near the tip clearance region. The relative motion between the turbine blades and the casing wall results in a complicated pressure field in the tip region. The fluid near the casing wall experiences a considerable pressure difference across the tip. The highest total pressure drop and the highest total pressure loss were both observed in the region of the tip leakage vortex, where the loss is nearly twice as high as that near the passage vortex region. However, the passage vortex produces more losses than the tip leakage vortex in total. The development of the loss in turbine rotor is similar to that observed in cascades. Part II of this paper covers the velocity and the turbulence fields.

Aeromechanical Optimization of a Winglet-Squealer Tip for an Axial Turbine

2014 ◽  
Vol 136 (7) ◽  
Author(s):  
Zbigniew Schabowski ◽  
Howard Hodson ◽  
Davide Giacche ◽  
Bronwyn Power ◽  
Mark R. Stokes
Keyword(s):  
Mechanical Performance ◽  
Turbine Blades ◽  
Careful Consideration ◽  
Rate Of Change ◽  
Leakage Loss ◽  
Simple Method ◽  
Axial Turbine ◽  
Low Speed ◽  
Aerodynamic Loss ◽  
Tip Leakage

The possibility of reducing the over tip leakage loss of unshrouded axial turbine rotors has been investigated in an experiment using a linear cascade of turbine blades and by using CFD. A numerical optimization of a winglet-squealer geometry was performed. The optimization involved the structural analysis alongside the CFD. Significant effects of the tip design on the tip gap flow pattern, loss generation and mechanical deformation under centrifugal loads were found. The results of the optimization process were verified by low speed cascade testing. The measurements showed that the optimized winglet-squealer design had a lower loss than the flat tip at all of the tested tip gaps. At the same time, it offered a 37% reduction in the rate of change of the aerodynamic loss with the tip gap size. The optimized tip geometry was used to experimentally assess the effects of the opening of the tip cavity in the leading edge part of the blade and the inclination of the pressure side squealer from the radial direction. The opening of the cavity had a negligible effect on the aerodynamic performance of the cascade. The squealer lean resulted in a small reduction of the aerodynamic loss at all the tested tip gaps. It was shown that a careful consideration of the mechanical aspects of the winglet is required during the design process. Mechanically unconstrained designs could result in unacceptable deformation of the winglet due to centrifugal loads. An example winglet geometry is presented that produced a similar aerodynamic loss to that of the optimized tip but had a much worse mechanical performance. The mechanisms leading to the reduction of the tip leakage loss were identified. Using this knowledge, a simple method for designing the tip geometry of a shroudless turbine rotor is proposed. Numerical calculations indicated that the optimized low-speed winglet-squealer geometry maintained its aerodynamic superiority over the flat tip blade with the exit Mach number increased from 0.1 to 0.8.

Effect of Tip Configurations on Aerodynamic Performance of Variable Geometry Linear Turbine Cascade

2019 ◽  
Vol 36 (4) ◽  
pp. 457-470
Author(s):  
Guoqiang Yue ◽  
Hongfei Lin ◽  
Yuting Jiang ◽  
Qun Zheng ◽  
Ping Dong
Keyword(s):  
Passive Control ◽  
Pressure Coefficient ◽  
Aerodynamic Performance ◽  
Radial Clearance ◽  
Leakage Flow ◽  
Variable Geometry ◽  
Turbine Cascade ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Passage Vortex

Abstract The variable geometry turbine (VGT) has been widely used in different fields due to its higher efficiency and lower fuel consumption at part-load. However, the flow field in a VGT is characterized by the leakage flow through the radial clearance of rotational vane compared with a general fixed vane turbine. Numerical simulations are conducted on a linear turbine cascade to reduce the leakage flow based on passive control method. The aerodynamic performances and flow fields are compared for four kinds of tip configuration firstly. Then, the effect of variable geometry on the linear turbine cascade aerodynamic performance is investigated for five installation angles ranging from –5 to 5 deg. In addition, the development patterns and trends of the tip leakage vortex and the passage vortex are analyzed. The results show that the squealer tip and the rotating axis have a significant impact on suppressing leakage flow. The leakage flow rate has a tendency to decrease, and the total pressure coefficient is gradually increased when installation angle ranges from –5 to 5 deg. The interactions between tip leakage vortex and passage vortex leads to the different trends on leakage flow at various installation angles and axial sections.

Experiments With a New Ribbed Blade Tip and Endwall Geometry on a High Pressure Turbine Blade

2015 ◽  
Author(s):  
Ralph J. Volino
Keyword(s):  
Total Pressure ◽  
Flow Direction ◽  
Pressure Change ◽  
Flow Area ◽  
Tip Leakage Vortex ◽  
Pressure Drops ◽  
Tip Leakage ◽  
Image Velocimetry ◽  
Passage Vortex ◽  
Blade Tip

A new blade tip and endwall geometry were studied experimentally. The blade tips and endwall included ribs directed in the pitchwise direction. The blade tip ribs fit between the endwall ribs, with a gap of 1.5% of axial chord between the top of each rib and the surface which it faced. Hence, a tip gap was maintained, but the tip flow area was divided into pitchwise directed channels. Experiments were conducted in a linear turbine cascade with wakes generated by moving upstream rods. Cases were documented both with and without wakes. The total pressure drop coefficient, ψ, through the cascade was measured in the endwall region. Velocity fields were acquired in two planes normal to the flow direction using particle image velocimetry (PIV). The rib geometry eliminated the strong tip leakage vortex present in comparison cases with flat and squealer tipped blades. The passage vortex was strengthened and moved farther from the endwall. In spite of the elimination of the tip leakage vortex, total pressure drops were higher with the ribs than with a squealer tip and the same tip gap. Additional experiments showed that dividing the leakage flow area into channels did not reduce the total pressure change, and the endwall ribs acted as roughness and increased ψ. Although the increase in ψ was a negative outcome for the cascade experiment, the elimination of the tip leakage vortex could have some benefit if its detrimental effect were reduced in downstream stages.

Experiment study of the winglet-cavity tip on the aerodynamic performance in a turbine cascade

2017 ◽  
Vol 231 (7) ◽  
pp. 676-685 ◽  
Author(s):  
Shaowen Chen ◽  
Zhihua Zhou ◽  
Qinghe Meng ◽  
Songtao Wang ◽  
Xun Zhou
Keyword(s):  
Flow Field ◽  
Total Pressure ◽  
Static Pressure ◽  
Aerodynamic Performance ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Passage Vortex ◽  
Side Gap

The effects of a novel winglet-cavity tip on the flow field and aerodynamic performance of a turbine blade with tip clearance have been investigated in a low-speed wind tunnel. A calibrated five-hole probe is used for the measurement of three-dimensional flows downstream of the cascade. The method of oil-flow visualization is used to show the endwall flow field structure. The distribution of endwall static pressure is measured particularly by using the special moveable endwall. The downstream results show that, compared with the flat tip and cavity tip, the winglet-cavity tip reduces aerodynamic loss in the region of tip leakage vortex and passage vortex effectively and gives a 8.5% reduction of total pressure losses at a tip clearance of τ/ H = 1.0%. Meanwhile, a more uniform flow angle is obtained with the winglet-cavity tip. Thus, the winglet-cavity tip provides better aerodynamic performance. It was found that more endwall flow enters the cavity from the front of suction side gap, combines with the flow entering the tip from the pressure side, and then separates upon the cavity. This reduces the loss of passage vortex. The endwall static pressure indicates that the winglet-cavity tip reduces the driving pressure difference and weakens the tip leakage flow. With the tip clearance increasing, the leakage flow is significantly enhanced. This strengthens the interaction between the tip leakage vortex and the passage vortex. With respect to the flat tip and cavity tip, the winglet-cavity tip obtains the lowest total pressure loss at all tested tip clearances.

Aeromechanical Optimisation of a Winglet-Squealer Tip for an Axial Turbine

2010 ◽  
Author(s):  
Zbigniew Schabowski ◽  
Howard Hodson ◽  
Davide Giacche ◽  
Bronwyn Power ◽  
Mark R. Stokes
Keyword(s):  
Mechanical Performance ◽  
Turbine Blades ◽  
Careful Consideration ◽  
Rate Of Change ◽  
Leakage Loss ◽  
Simple Method ◽  
Axial Turbine ◽  
Low Speed ◽  
Aerodynamic Loss ◽  
Tip Leakage

The possibility of reducing the over tip leakage loss of unshrouded axial turbine rotors has been investigated in an experiment using a linear cascade of turbine blades and by using CFD. A numerical optimisation of a winglet-squealer geometry was performed. The optimisation involved the structural analysis alongside the CFD. Significant effects of the tip design on the tip gap flow pattern, loss generation and mechanical deformation under centrifugal loads were found. The results of the optimisation process were verified by low speed cascade testing. The measurements showed that the optimised winglet-squealer design had a lower loss than the flat tip at all of the tested tip gaps. At the same time, it offered a 37% reduction in the rate of change of the aerodynamic loss with the tip gap size. The optimised tip geometry was used to experimentally assess the effects of the opening of the tip cavity in the leading edge part of the blade and the inclination of the pressure side squealer from the radial direction. The opening of the cavity had a negligible effect on the aerodynamic performance of the cascade. The squealer lean resulted in a small reduction of the aerodynamic loss at all the tested tip gaps. It was shown that a careful consideration of the mechanical aspects of the winglet is required during the design process. Mechanically unconstrained designs could result in unacceptable deformation of the winglet due to centrifugal loads. An example winglet geometry is presented that produced a similar aerodynamic loss to that of the optimised tip but had a much worse mechanical performance. The mechanisms leading to the reduction of the tip leakage loss were identified. Using this knowledge, a simple method for designing the tip geometry of a shroudless turbine rotor is proposed. Numerical calculations indicated that the optimised low-speed winglet-squealer geometry maintained its aerodynamic superiority over the flat tip blade with the exit Mach number increased from 0.1 to 0.8.

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