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.

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.

Aerodynamic Interaction Between Incoming Vortex and Tip Leakage Flow in a Turbine Cascade

2018 ◽  
Author(s):  
Kai Zhou ◽  
Chao Zhou
Keyword(s):  
Numerical Study ◽  
Aerodynamic Performance ◽  
Leakage Flow ◽  
Computational Domain ◽  
Turbine Cascade ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Swirl Generator ◽  
Swirling Vortex

In turbines, secondary vortices and tip leakage vortices develop and interact with each other. In order to understand the flow physics of vortices interaction, the effects of incoming vortex on the downstream tip leakage flow are investigated in terms of the aerodynamic performance in a turbine cascade. Experimental, numerical and analytical methods are used. In the experiment, a swirl generator was used upstream near the casing to generate the incoming vortex, which interacted with the tip leakage vortex in the turbine cascade. The swirl generator was located at ten different pitchwise locations to simulate the quasi-steady effects. In the numerical study, a Rankine-like vortex was defined at the inlet of the computational domain to simulate the incoming swirling vortex. Incoming vortices with opposite directions were investigated. The vorticity of the positive incoming swirling vortex has a large vector in the same direction as that of the tip leakage vortex. In the case of the positive incoming swirling vortex, the vortex mixes with the tip leakage vortex to form one vortex near the tip as it transports downstream. The vortices interaction reduces the vorticity of the flow near the tip, as well as the loss by making up for the streamwise momentum within the tip leakage vortex core. In contrast, the negative incoming swirling vortex has little effects on the tip leakage vortex and the loss. As the negative incoming swirling vortex transports downstream, it is separated from the tip leakage vortex and forms two vortices. A triple-vortices-interaction kinetic analytical model and one-dimensional mixing model are proposed to explain the mechanism of vortex interaction on the aerodynamic performance.

Experimental study on axially non-uniform clearances in a linear turbine cascade with a cavity squealer tip

2018 ◽  
Vol 233 (5) ◽  
pp. 1645-1655
Author(s):  
Shaowen Chen ◽  
Qinghe Meng ◽  
Weihang Li ◽  
Zhihua Zhou ◽  
Songtao Wang
Keyword(s):  
Flow Field ◽  
Buffer Zone ◽  
Aerodynamic Performance ◽  
Field Structure ◽  
Tip Clearance ◽  
Turbine Cascade ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Passage Vortex ◽  
Flow Loss

The effects of axially non-uniform clearances on the tip leakage flow and aerodynamic performance in a linear turbine cascade with a cavity squealer tip were investigated in this study with the objective of improving the flow loss and tip flow field structure. A calibrated five-hole probe was used for the measurement of three-dimensional flows downstream of the cascade. The method of oil-flow visualization was used to show the endwall flow field structure. The distribution of endwall static pressure was measured particularly by using the special moveable endwall. The axially non-uniform clearance, as a novel strategy that has a non-negligible influence on tip clearance flow and clearance leakage loss, may become a potential technology for improving aerodynamic performance in turbine cascades. By using the expanding clearance, the flow loss at the outlet is reduced effectively and an apparent improvement of aerodynamic performance in the turbine cascade is gained. Under the tip clearances of 0.75% H and 2% H, the maximum reduction of overall total pressure loss coefficient at the outlet is separately about 2.3% and 3.5% compared with the uniform clearance. The shrinkage of the buffer zone is considered to be able to weaken the interaction of the tip leakage vortex and passage vortex and thus reduce the loss of passage vortex. For the shrinking clearance, a noticeable decline in the aerodynamic performance of turbine cascade with cavity squealer tip is exhibited at both on and off design conditions in contrast to the uniform clearance. In addition, the effects of axially non-uniform clearances on the aerodynamic performance at off-design conditions have been investigated.

Near Tip Loss Control with a Winglet Baffle Cavity Tip in a Turbine Cascade

2021 ◽  
Author(s):  
Li Li ◽  
Jiang Dengyu ◽  
Chao Zhou ◽  
Luo Hualing ◽  
Hou Weitao ◽  
...  
Keyword(s):  
Mass Flow ◽  
Large Scale ◽  
Experimental Studies ◽  
Suction Side ◽  
Aerodynamic Performance ◽  
Pressure Side ◽  
Tip Leakage ◽  
Flow Mixing ◽  
Geometry Feature ◽  
Blade Tip

Abstract The aerodynamic performance of a winglet baffle cavity tip is investigated at different inlet incidences from -12.5° to +12.5°. This blade tip shows geometry feature with a pressure side winglet and a baffle within the tip cavity. The experimental studies were carried out in a large scale linear cascade, and the numerical methods were also used to obtain the detail physics. The baffle on the tip divides the cavity vortex into two main parts, which increases the flow mixing over the tip. As the flow within the vortex exits the tip near the baffle and cavity corner, flow separation occurs over the suction side and reduces local tip leakage mass flow rate significantly. The additional pressure side winglet reduces the contraction coefficient on the pressure side squealer. It is found that the winglet baffle cavity tip can reduce the tip leakage mass flow by 12.1%, and the near tip loss by 4.2%, compared with the squealer tip. As the incidence of incoming flow decreases, the loss near the tip reduces mainly due to a reduction of the passage vortex, which develops from the casing endwall. At the same incidence, the aerodynamic performance of the winglet baffle cavity tip is better than the squealer tip.

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.

Unsteady Aerodynamics of a Flat Tip and a Winglet Tip in a High-Pressure Turbine

2016 ◽  
Author(s):  
Kai Zhou ◽  
Chao Zhou
Keyword(s):  
High Pressure ◽  
Unsteady Aerodynamics ◽  
Suction Side ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
High Pressure Turbine ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Passage Vortex

In an unshrouded high-pressure turbine, tip leakage flow results in a loss of efficiency. In this paper, the aerodynamic performance of the tip leakage flow is investigated in a turbine stage by numerical methods. A flat tip and a closed squealer tip combined with a suction side winglet are used for the rotor tips, and the two turbines are named as ‘Flat Configuration’ and ‘Winglet Configuration’. The ability of the CFD methods in predicting the unsteady flow and the tip leakage flow is validated. The steady calculations using a mixing plane between the stator and the rotor are presented first. Then, the unsteady flows of the turbine stage with a flat rotor tip and a winglet rotor tip are simulated by solving Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. Compared with the ‘Flat Configuration’, the ‘Winglet Configuration’ reduces the size of the passage vortex and the tip leakage vortex. A surprising observation is that although the ‘Winglet Configuration’ reduces the size of the tip leakage vortex, its maximum swirl strength of the tip leakage vortex is about 40% higher than that for the ‘Flat Configuration’. The steady calculation shows that the entropy generation for the turbine stage is 12.1% lower with the ‘Winglet Configuration’ than that with the ‘Flat Configuration’. The mixed-out entropy predicted in the unsteady calculation is higher than that of the steady calculation for both tips. The stator casing passage vortex has a periodic effect on the vortex near the tip gap of the rotor. The unsteady interaction of the vortices seems to be beneficial in terms of the loss. As a result, the ‘Winglet Configuration’ produces 9.4% less entropy than the ‘Flat Configuration’, which is lower than that in the case of the steady calculation.

scholarly journals An Experimental Investigation on the Aerodynamic Performance and Flowfield Structure of a Film-Cooled Turbine Cascade

1999 ◽  
Author(s):  
Chen Fu ◽  
Yang Hong
Keyword(s):  
Surface Pressure ◽  
Great Majority ◽  
Suction Side ◽  
Aerodynamic Performance ◽  
Surface Flow ◽  
Air Injection ◽  
Blade Surface ◽  
Turbine Cascade ◽  
Suction Surface ◽  
Passage Vortex

Experiments have been performed to study the aerodynamic performance and internal flows in a linear turbine cascade with air injection from various locations of the blade surface. Data were obtained by using pneumatic probe, static pressure taps and surface flow visualization techniques. The experimental results showed that the suction side injection would affect the development of the passage vortex significantly. The passage vortex was strengthened and pushed away from the injection surface, a triangular-shaped region uncovered by the injected air always existed on the suction surface due to the existence of the passage vortex. The passage vortex was weakened with air injection from pressure surface, which would cause a smaller amount of low momentum fluids to migrate into the comer region between suction surface and end wall. Although the scale and intensity of kidney-shaped vortices were different when air was injected from various positions, these vortices might always exist near the blade surface, mixing with mainflow in the flow passage and with wakes at the cascade exit while they moved downstream. The energy loss increased near the blade surface from which air was injected due mainly to the mixing process between mainflow and injected air, and to the formation of kidney-shaped vortices. In contrast to the pressure side injection, the changes of blade surface pressure distribution were more sensitive to the amount of injected air and the locations of injection holes for the suction side injection. In the great majority of cases, the surface pressure decreases owing to the existence of low-pressure zone downstream of the injection holes were more significant than the pressure increases caused by mainflow stagnation upstream of the holes.

Effects of Casing Relative Motion on Aerodynamic Performance With Modified Designs of Winglet and Squealer Tip

2020 ◽  
Author(s):  
Anmol Garg ◽  
Sachin Singh Rawat ◽  
B. V. S. S. S. Prasad
Keyword(s):  
Heat Transfer ◽  
Relative Motion ◽  
Flow Rate ◽  
Rotor Blade ◽  
Aerodynamic Performance ◽  
Base Case ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Passage Vortex

Abstract For unshrouded high pressure turbines, the design of rotor blade tips is a dynamic multi-purpose process. The model should have least aerodynamic and heat transfer losses caused by the flow through the tip gap and the blade. Recent studies show that by the modification of the blade tip, there is some improvement in efficiency and reduced tip gap flow. These include mainly parametric study of cavity tip and winglet tip modifications. Previous studies confirm the benefit of overhang in reducing tip leakage loss and heat transfer by changing the location of the tip leakage vortex away from the blade. But, to the best of authors’ knowledge none of the study reports the effect of casing relative motion on modified winglet and squealer tip. In the present study, novel modified tip blade geometry is introduced named as Top Squealer with Bottom Winglet (TSBW). Tip gap physics and loss generation has been investigated on three other different designs of squealer and winglet geometries and compared with the novel design. These designs are named as Flat Winglet, Cavity Squealer, Top Squealer with Bottom Winglet (new design) and Top Winglet with Bottom Squealer (TWBS). The flat tip rotor blade is considered as the base case for comparison. Three-dimensional computational study using ANSYS CFX 18.2 has been performed in order to examine the effect of casing relative motion on various designs of winglet and squealer tip. Structured mesh is created using ANSYS ICEM 18.2. At the downstream of trailing edge, distinct regions of momentum deficits named as the tip leakage vortex (LV), tip passage vortex (TPV), wakes and hub passage vortex (HPV) has been observed. Wakes formed due to the interaction of scraping vortex (SV), Tip passage vortex (TPV) and the leakage vortex. It has been found that Cavity Squealer and Top Squealer with Bottom Winglet (TSBW)gave the lowest total pressure loss coefficient and lowest tip leakage flow rate. But in casing relative motion case, cavity squealer with bottom wingletout runs the cavity squealer aerodynamic performance. This is due to the enlarged cavity at the tip. The incoming pass over flow got blocked because of enhanced interaction of LV and Scraping vortex (SV) in the tip cavity. As a result, tip leakage losses and tip leakage mass flow rate decreased.

Numerical Investigation of Effects of Non-Uniform Tip Clearance on Flow Field Inside a Turbine Cascade

2016 ◽  
Author(s):  
Hongwei Ma ◽  
Yangtao Tian
Keyword(s):  
Flow Field ◽  
Suction Side ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Pressure Side ◽  
Turbine Cascade ◽  
Leakage Loss ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Turbine Performance

In the unshrouded axial turbine, the tip clearances can result in the loss of turbine efficiency and the penalty of turbine performance. Therefore, investigating the blade tip geometry of improving the turbine performance has a great significance. This paper is to study the effects of non-uniform tip clearance on the flow field in a turbine cascade. The numerical works are performed at the incidence angle of 0 degree and the exit Reynolds number of 1.7 × 105 based on the blade chord. In the investigations, the flat tip (Basic) geometry was employed as a benchmark, and three different tip geometries, including the pressure side squealer (PSQ), suction side squealer (SSQ) and grooved tip (Grooved), were studied. The tip clearances are all specified as 1.18% of the chord. The squealer height is set to 2.94% of the chord. The endwall static pressure, tip leakage loss, flow capacity and the development of tip leakage vortex are discussed. And the numerical results show that the grooved tip which can obtain the least total pressure loss, is helpful to smooth the pressure change from pressure side to suction side and suppress the intensity of tip leakage vortex. The tip clearance flow in the pre semi-passage is mainly involved in the passage vortex, and in the post semi-passage it is added to the tip leakage vortex. Compared with the Basic, PSQ and SSQ tips, the Grooved tip contributes to reducing the tip leakage flow and the tip leakage loss. And the leakage flow can be strengthened in the middle passage for the PSQ. The difference between the area averaged streamwise coefficient and mass averaged loss is almost opposite for the SSQ and Grooved tip, which is uncertain the performance of the turbine cascade with the SSQ and Grooved tip is better than the Basic tip.

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