The Effect of Blade Tip Geometry on the Tip Leakage Flow in Axial Turbine Cascades

1992 ◽  
Vol 114 (3) ◽  
pp. 643-651 ◽  
Author(s):  
F. J. G. Heyes ◽  
H. P. Hodson ◽  
G. M. Dailey
Keyword(s):  
Turbine Blades ◽  
Suction Side ◽  
Generation Process ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip ◽  
Overall Performance ◽  
Turbine Cascades ◽  
Made In ◽  
Blade Tip Geometry

The phenomenon of tip leakage has been studied in two linear cascades of turbine blades. The investigation includes an examination of the performance of the cascades with a variety of tip geometries. The effects of using plain tips, suction side squealers, and pressure side squealers are reported. Traverses of the exit flow field were made in order to determine the overall performance. A method of calculating the tip discharge coefficients for squealer geometries is put forward. In linking the tip discharge coefficient and cascade losses, a procedure for predicting the relative performance of tip geometries is developed. The model is used to examine the results obtained using the different tip treatments and to highlight the important aspects of the loss generation process.

scholarly journals The Effect of Blade Tip Geometry on the Tip Leakage Flow in Axial Turbine Cascades

1991 ◽  
Author(s):  
F. J. G. Heyes ◽  
H. P. Hodson ◽  
G. M. Dailey
Keyword(s):  
Discharge Coefficient ◽  
Suction Side ◽  
Generation Process ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip ◽  
Overall Performance ◽  
Turbine Cascades ◽  
Made In ◽  
Blade Tip Geometry

The phenomenon of tip leakage has been studied in two linear cascades of turbine blades.The investigation includes an examination of the performance of the cascades with a variety of tip geometries. The effects of using plain tips, suction side squealers and pressure side squealers are reported. Traverses of the exit flow field were made in order to determine the overall performance. A method of calculating the tip discharge coefficients for squealer geometries is put forward. In linking the tip discharge coefficient and cascade losses a procedure for predicting the relative performance of tip geometries is developed. The model is used to examine the results obtained using the different tip treatments and to highlight the important aspects of the loss generation process.

scholarly journals Effects of Tip Clearance and Casing Recess on Heat Transfer and Stage Efficiency in Axial Turbines

1998 ◽  
Author(s):  
A. A. Ameri ◽  
E. Steinthorsson ◽  
David L. Rigby
Keyword(s):  
Heat Transfer ◽  
Suction Side ◽  
Tip Clearance ◽  
Flow Conditions ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip ◽  
Axial Turbines ◽  
Gap Height ◽  
Stage Efficiency

Calculations were performed to assess the effect of the tip leakage flow on the rate of heat transfer to blade, blade tip and casing. The effect on exit angle and efficiency was also examined. Passage geometries with and without casing recess were considered. The geometry and the flow conditions of the GE-E3 first stage turbine, which represents a modern gas turbine blade were used for the analysis. Clearance heights of 0%, 1%, 1.5% and 3% of the passage height were considered. For the two largest clearance heights considered, different recess depths were studied. There was an increase in the thermal load on all the heat transfer surfaces considered due to enlargement of the clearance gap. Introduction of recessed casing resulted in a drop in the rate of heat transfer on the pressure side but the picture on the suction side was found to be more complex for the smaller tip clearance height considered. For the larger tip clearance height the effect of casing recess was an orderly reduction in the suction side heat transfer as the casing recess height was increased. There was a marked reduction of heat load and peak values on the blade tip upon introduction of casing recess, however only a small reduction was observed on the casing itself. It was reconfirmed that there is a linear relationship between the efficiency and the tip gap height. It was also observed that the recess casing has a small effect on the efficiency but can have a moderating effect on the flow underturning at smaller tip clearances.

Effects of Tip Clearance on Unsteady Flow Characteristics in an Axial Turbine Stage

2009 ◽  
Author(s):  
Hao Sun ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Rotor Blade ◽  
Suction Side ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

The clearance between the rotor blade tip and casing wall in turbomachinery passages induces leakage flow loss and thus degrades aerodynamic performance of the machine. The flow field in turbomachinery is significantly influenced by the rotor blade tip clearance size. To investigate the effects of tip clearance size on the rotor-stator interaction, the turbine stage profile from Matsunuma’s experimental tests was adopted, and the unsteady flow fields with two tip clearance sizes of 0.67% and 2.00% of blade span was numerical simulated based on Harmonic method using NUMECA software. By comparing with the domain scaling method, the accuracy of the harmonic method was verified. The interaction mechanism between the stator wake and the leakage flow was investigated. It is found that the recirculation induced by the stator wake is separated by a significant “interaction line” from the flow field close to the suction side in the clearance region. The trend of the pressure fluctuation is contrary on both sides of the line. When the stator wakes pass by the suction side, the pressure field fluctuates and the intensity of the tip leakage flow varies. With the clearance size increasing, the “interaction line” is more far away from the suction side and the intensity of tip leakage flow also fluctuates more strongly.

Effect of Endwall Motion on Blade Tip Heat Transfer

2003 ◽  
Vol 125 (2) ◽  
pp. 267-273 ◽  
Author(s):  
V. Srinivasan ◽  
R. J. Goldstein
Keyword(s):  
Mass Transfer ◽  
Suction Side ◽  
Tip Clearance ◽  
Pressure Gradients ◽  
Tip Leakage Flow ◽  
Blade Loading ◽  
Linear Cascade ◽  
Tip Leakage ◽  
Blade Tip ◽  
Wind Tunnel Data

Local mass transfer measurements were conducted on the tip of a turbine blade in a five-blade linear cascade with a blade-centered configuration. The tip clearance levels ranged from 0.6 to 6.9% of blade chord. The effect of relative motion between the casing and the blade tip was simulated using a moving endwall made of neoprene mounted on the top of the wind tunnel. Data were obtained for a single Reynolds number of 2.7×105 based on cascade exit velocity and blade chord. Pressure measurements indicate that the effect of endwall motion on blade loading at a clearance of 0.6% of blade chord is to reduce the pressure gradients driving the tip leakage flow. With the introduction of endwall motion, there is a reduction of about 9% in mass transfer levels at a clearance of 0.6% of chord. This is presumably due to the tip leakage vortex coming closer to the suction side of the blade and ‘blocking the flow,’ leading to reduced tip gap velocities and hence lower mass transfer.

Numerical Investigation of Tip Clearance Flow in an Axial Compressor Cascade

2014 ◽  
Vol 599-601 ◽  
pp. 368-371
Author(s):  
Zhi Hui Xu ◽  
He Bin Lv ◽  
Ru Bin Zhao
Keyword(s):  
Computational Simulation ◽  
Suction Side ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Compressor Cascade ◽  
Tip Leakage Flow ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Clearance Flow ◽  
Blade Tip

Using blade tip winglet to control the tip leakage flow has been concerned in the field of turbomachinery. Computational simulation was conducted to investigate the phenomenological features of tip clearance flow. The simulation results show that suction-side winglet can reduce leakage flow intensity. The tip winglet can also decrease tip leakage mass flow and weaken tip leakage flow mixing with the mainstream and therefore reduce the total pressure loss at the blade tip.

Axisymmetric Tip Gap Profiling in a Shroudless Axial Turbine

2020 ◽  
Author(s):  
M. Abda ◽  
M. G. Rose
Keyword(s):  
Mass Flow ◽  
Separation Bubble ◽  
Suction Side ◽  
Entropy Generation Rate ◽  
Tip Leakage Flow ◽  
Axial Turbine ◽  
Tip Leakage ◽  
Blade Tip ◽  
Design Value ◽  
Tip Mass

Abstract The inevitable gap between the rotor tips and the casing promotes flow leakage driven by the pressure difference between the pressure side and suction side of the blade. Axisymmetric tip gap profiling was applied at the blade tip and the casing endwall to reduce the tip leakage maintaining the same gap clearance. The investigation was held on a shroudless single stage axial turbine designed in ETH Zurich University named LISA D. The numerical calculation showed that axisymmetric tip gap profiling reduced the tip leakage flow and improved the efficiency by 0.65% and 0.1% respectively. However, the stage mass flow increased and as a result so did the rotor capacity. When the stage mass flow was reduced to the design value to maintain the design capacity, the effect of the axisymmetric tip gap profiling further improved, due to a reduction in the entropy generation rate of the tip leakage and passage vortices. The tip mass flow reduced by 2.39% and the efficiency improved significantly by 0.6%. It was observed that the tip profiling increased the size of the separation bubble in the PS/tip junction, which increased blockage effect in the gap. Hence, reduced the leaking flow to the SS, which results in weaker tip leakage vortex and its associated losses.

Effects of Tip Clearance and Casing Recess on Heat Transfer and Stage Efficency in Axial Turbines

1999 ◽  
Vol 121 (4) ◽  
pp. 683-693 ◽  
Author(s):  
A. A. Ameri ◽  
E. Steinthorsson ◽  
D. L. Rigby
Keyword(s):  
Heat Transfer ◽  
Suction Side ◽  
Tip Clearance ◽  
Flow Conditions ◽  
Tip Leakage Flow ◽  
Small Reduction ◽  
Tip Leakage ◽  
Blade Tip ◽  
Axial Turbines ◽  
Gap Height

Calculations were performed to assess the effect of the tip leakage flow on the rate of heat transfer to blade, blade tip, and casing. The effect on exit angle and efficiency was also examined. Passage geometries with and without casing recess were considered. The geometry and the flow conditions of the GE-E3 first-stage turbine, which represents a modern gas turbine blade, were used for the analysis. Clearance heights of 0, 1, 1.5, and 3 percent of the passage height were considered. For the two largest clearance heights considered, different recess depths were studied. There was an increase in the thermal load on all the heat transfer surfaces considered due to enlargement of the clearance gap. Introduction of recessed casing resulted in a drop in the rate of heat transfer on the pressure side, but the picture on the suction side was found to be more complex for the smaller tip clearance height considered. For the larger tip clearance height, the effect of casing recess was an orderly reduction in the suction side heat transfer as the casing recess height was increased. There was a marked reduction of heat load and peak values on the blade tip upon introduction of casing recess; however, only a small reduction was observed on the casing itself. It was reconfirmed that there is a linear relationship between the efficiency and the tip gap height. It was also observed that the recess casing has a small effect on the efficiency but can have a moderating effect on the flow underturning at smaller tip clearances.

scholarly journals Flow behaviors in a Kaplan turbine runner with different tip clearances

2021 ◽  
Vol 13 (5) ◽  
pp. 168781402110158
Author(s):  
Yue Ma ◽  
Bing Qian ◽  
Zhiguo Feng ◽  
Xuan Wang ◽  
Guangtai Shi ◽  
...  
Keyword(s):  
Flow Separation ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Stress Transfer ◽  
Suction Side ◽  
Tip Clearance ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Kaplan Turbine ◽  
Blade Tip

Tip clearance between the runner blade tip and shroud in a Kaplan turbine is inevitable, and the tip leakage flow (TLF) and tip leakage vortex (TLV) induced by the tip clearance have a considerable effect on the flow behaviors. To reveal the effect of the tip clearance on the flow characteristics, based on the Reynolds time-averaged Navier-Stokes (N-S) equation and the shear stress transfer (SST) k-ω turbulence model, the three-dimensional turbulence flow in a Kaplan turbine is simulated using ANSYS CFX. Meanwhile, the flow laws in the tip clearance are emphatically analyzed and summarized. Results show with the increase of the tip clearance, the negative pressure region in the blade suction side (SS) middle, the SS near the blade tip and the blade tip becomes more and more obvious. In the meantime, the flow behaviors on the blade pressure side (PS) are relatively stable, and the flow separation on the SS near blade tip merges. The larger the tip clearance is, the more obvious the flow separation phenomenon displays. In addition, the TLV is a spatial three-dimensional spiral structure formed by the entrainment effect of the TLF and main flow, and as the tip clearance increases, the TLV becomes more obvious.

Impact of Passive Tip-Injection on the Performance of Partially Shrouded Turbines: Basic Concept and Preliminary Results

2013 ◽  
Author(s):  
Pouya Ghaffari ◽  
Reinhard Willinger
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Gas Turbines ◽  
Turbine Blades ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip ◽  
Tip Injection ◽  
The Impact

In terms of efficiency improvement many methods for reducing the blade tip-leakage mass flow rate have been proposed. Some of these methods are based on increasing the flow resistance with aid of geometrical modifications of the blade tip (squealers, winglets, shrouded blades, etc.) whereas other methods take advantage of aerodynamical resistance with passive tip-injection as an example. The objective of this paper is a combination of both methods in order to achieve higher reduction in tip-leakage mass flow rate. In the first part of this work necessary characteristic parameters of modern low pressure turbine blades in aircraft gas turbines are estimated. These parameters are taken into consideration to calculate the range of physical quantities influencing tip-leakage flow. Subsequently a two dimensional flow model is obtained with the so called discharge coefficient as the ratio of the actual tip gap mass flow rate to its highest possible value. The investigations are based on dimensionless calculations. In the end the results obtained from dimensionless 2D CFD-simulations are presented and compared with the analytical results. This leads to conclusions regarding the impact of various parameters on the effectiveness of the passive tip-injection.

scholarly journals Effect of in-service burnout effect on the transonic leakage flows over cavity tip model

2021 ◽  
pp. 095765092110121
Author(s):  
Zainab J Saleh ◽  
Eldad J Avital ◽  
Theodosios Korakianitis
Keyword(s):  
Turbine Blades ◽  
High Heat ◽  
Navier Stokes ◽  
Gas Temperature ◽  
Flow Measurements ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Operational Life ◽  
Flow Interactions ◽  
Blade Tip

Increasing the gas temperature at the inlet to the high pressure turbine of gas turbine engines is known as a proven method to increase the efficiency of these engines. However, this will expose the blades’ surface to very high heat load and thermal damages. In the case of the un-shrouded turbine blades, the blade tip will be exposed to a significant thermal load due to the developed leakage flows in the tip gap, this leads to in-service burnout which degrades the blade tip and shortens its operational life. This paper studies the in-service burnout effect of the transonic tip flows over a cavity tip which is a configuration commonly used to reduce the tip leakage flows. This investigation is carried out experimentally within a transonic wind tunnel and computationally using steady and unsteady Reynolds Averaged Navier Stokes approaches. Various flow measurements are established and different flow behaviour including separation bubbles, shockwave development and distinct flow interactions are captured and discussed. It is found that when the tip is exposed to the in-service burnout, leakage flow behaves in a significantly different way. In addition, the effective tip gap becomes much larger and allows higher leakage mass flow rate in comparison to the sharp-edge tip (i.e. a tip at the beginning of its operational life). The tip leakage losses are found much higher for the round-edge cavity tip (i.e. a tip exposed to burn-out effect). Experimental and computational flow visualisations, surface pressure measurements and discharge coefficient variation are given and analysed for several pressure ratios across the tip gap.

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