scholarly journals An Investigation on the Effect of Endwall Movement on the Tip Clearance Loss Using Annular Turbine Cascade

2011 ◽  
Vol 2011 ◽  
pp. 1-11 ◽  
Author(s):  
Hesham M. El-Batsh ◽  
Magdy Bassily Hanna
Keyword(s):  
Gas Turbines ◽  
Stokes Equations ◽  
Numerical Technique ◽  
Tip Clearance ◽  
Pressure Probe ◽  
Turbine Cascade ◽  
Tip Leakage Flow ◽  
Leakage Loss ◽  
Loss Mechanism ◽  
Tip Leakage

The aerodynamic losses in gas turbines are mainly caused by profile loss secondary flow, and tip leakage loss. This study focuses on tip leakage flow of high-pressure turbine stages. An annular turbine cascade was constructed with fixed blades on the casing, and the distance between blade tip and the hub was considered as tip clearance gap. The effect of endwall movement on loss mechanism was investigated by using experimental and numerical techniques. The measurements were obtained while the hub was fixed but the numerical calculations were carried out for both stationary and moving cascades. Upstream and downstream flows were measured by using a calibrated five-hole pressure probe. The steady incompressible turbulent flow was obtained by solving Reynolds averaged Navier-Stokes equations and by employing shear stress transport (SST)k-ωturbulence model. The total pressure loss coefficient obtained from the numerical technique was compared with the experimental measurements, and the comparison showed good agreement. Tip clearance vortices were observed in the tip clearance gap. It was found through this study that end-wall movement reduces tip leakage loss through the cascade.

A Proposal for Passive Wall Treatment Applied in High Performance Axial Flow Compressors

2020 ◽  
Author(s):  
Rubén Bruno Díaz ◽  
Jesuino Takachi Tomita ◽  
Cleverson Bringhenti ◽  
Francisco Carlos Elizio de Paula ◽  
Luiz Henrique Lindquist Whitacker
Keyword(s):  
Stokes Equations ◽  
Axial Compressor ◽  
Axial Flow ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Smooth Wall ◽  
Tip Leakage Flow ◽  
Viscous Effects ◽  
Stall Margin ◽  
Tip Leakage

Abstract Numerical simulations were carried out with the purpose of investigating the effect of applying circumferential grooves at axial compressor casing passive wall treatment to enhance the stall margin and change the tip leakage flow. The tip leakage flow is pointed out as one of the main contributors to stall inception in axial compressors. Hence, it is of major importance to treat appropriately the flow in this region. Circumferential grooves have shown a good performance in enhancing the stall margin in previous researches by changing the flow path in the tip clearance region. In this work, a passive wall treatment with four circumferential grooves was applied in the transonic axial compressor NASA Rotor 37. Its effect on the axial compressor performance and the flow in the tip clearance region was analyzed and set against the results attained for the smooth wall case. A 2.63% increase in the operational range of the axial compressor running at 100%N, was achieved, when compared with the original smooth wall casing configuration. The grooves installed at compressor casing, causes an increase in the flow entropy generation due to the high viscous effects in this gap region, between the rotor tip surface and casing with grooves. These viscous effects cause a drop in the turbomachine efficiency. For the grooves configurations used in this work, an efficiency drop of 0.7% was observed, compared with the original smooth wall. All the simulations were performed based on 3D turbulent flow calculations using Reynolds Averaged Navier-Stokes equations, and the flow eddy viscosity was determined using the two-equation SST turbulence model. The details of the grooves geometrical dimensions and its implementation are described in the paper.

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.

Effects of Reynolds Number and Freestream Turbulence on Turbine Tip Clearance Flow

2005 ◽  
Vol 128 (1) ◽  
pp. 166-177 ◽  
Author(s):  
Takayuki Matsunuma
Keyword(s):  
Reynolds Number ◽  
Turbulence Intensity ◽  
Three Dimensional ◽  
Tip Clearance ◽  
Pressure Probe ◽  
Turbine Cascade ◽  
Freestream Turbulence ◽  
Tip Leakage Flow ◽  
Three Dimensional Flow ◽  
Dimensional Flow

Tip clearance losses represent a major efficiency penalty of turbine blades. This paper describes the effect of tip clearance on the aerodynamic characteristics of an unshrouded axial-flow turbine cascade under very low Reynolds number conditions. The Reynolds number based on the true chord length and exit velocity of the turbine cascade was varied from 4.4×104 to 26.6×104 by changing the velocity of fluid flow. The freestream turbulence intensity was varied between 0.5% and 4.1% by modifying turbulence generation sheet settings. Three-dimensional flow fields at the exit of the turbine cascade were measured both with and without tip clearance using a five-hole pressure probe. Tip leakage flow generated a large high total pressure loss region. Variations in the Reynolds number and freestream turbulence intensity changed the distributions of three-dimensional flow, but had no effect on the mass-averaged tip clearance loss of the turbine cascade.

Effect of Turbine Blade Tip Cooling Configuration on Tip Leakage Flow and Heat Transfer

2020 ◽  
Vol 142 (2) ◽  
Author(s):  
Sergen Sakaoglu ◽  
Harika S. Kahveci
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Gas Turbines ◽  
Thermal Response ◽  
Thermal Conditions ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

Abstract The pressure difference between suction and pressure sides of a turbine blade leads to tip leakage flow, which adversely affects the first-stage high-pressure (HP) turbine blade tip aerodynamics. In modern gas turbines, HP turbine blade tips are exposed to extreme thermal conditions requiring cooling. If the coolant jet directed into the blade tip gap cannot counter the leakage flow, it will simply add up to the pressure losses due to leakage. Therefore, the compromise between the aerodynamic loss and the gain in tip-cooling effectiveness must be optimized. In this paper, the effect of tip-cooling configuration on the turbine blade tip is investigated numerically from both aerodynamics and thermal aspects to determine the optimum configuration. Computations are performed using the tip cross section of GE-E3 HP turbine first-stage blade for squealer and flat tips, where the number, location, and diameter of holes are varied. The study presents a discussion on the overall loss coefficient, total pressure loss across the tip clearance, and variation in heat transfer on the blade tip. Increasing the coolant mass flow rate using more holes or by increasing the hole diameter results in a decrease in the area-averaged Nusselt number on the tip floor. Both aerodynamic and thermal response of squealer tips to the implementation of cooling holes is superior to their flat counterparts. Among the studied configurations, the squealer tip with a larger number of cooling holes located toward the pressure side is highlighted to have the best cooling performance.

Tip Leakage Flow in Axial Compressors

1991 ◽  
Vol 113 (2) ◽  
pp. 252-259 ◽  
Author(s):  
J. A. Storer ◽  
N. A. Cumpsty
Keyword(s):  
Pressure Field ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Local Pressure ◽  
Flow Measurements ◽  
Tip Leakage ◽  
Numerical Predictions

Experimental measurements in a linear cascade with tip clearance are complemented by numerical solutions of the three-dimensional Navier–Stokes equations in an investigation of tip leakage flow. Measurements reveal that the clearance flow, which separates near the entry of the tip gap, remains unattached for the majority of the blade chord when the tip clearance is similar to that typical of a machine. The numerical predictions of leakage flow rate agree very well with measurements, and detailed comparisons show that the mechanism of tip leakage is primarily inviscid. It is demonstrated by simple calculation that it is the static pressure field near the end of the blade that controls chordwise distribution of the flow across the tip. Although the presence of a vortex caused by the roll-up of the leakage flow may affect the local pressure field, the overall magnitude of the tip leakage flow remains strongly related to the aerodynamic loading of the blades.

Effect of Turbine Blade Tip Cooling Configuration on Tip Leakage Flow and Heat Transfer

2019 ◽  
Author(s):  
Sergen Sakaoglu ◽  
Harika S. Kahveci
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Gas Turbines ◽  
Thermal Response ◽  
Thermal Conditions ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

Abstract The pressure difference between suction and pressure sides of a turbine blade leads to the so-called phenomenon, the tip leakage flow, which most adversely affects the first-stage high-pressure (HP) turbine blade tip aerodynamics. In modern gas turbines, HP turbine blade tips are also exposed to extreme thermal conditions requiring the use of tip cooling. If the coolant jet directed into the blade tip gap cannot counter the leakage flow, it will simply add up to the pressure losses due to this leakage flow. Therefore, it is necessary to handle the design of tip cooling in such a way that the compromise between the aerodynamic loss and the gain in the tip cooling effectiveness is optimized. In this paper, the effect of tip cooling configuration on the turbine blade tip is investigated numerically both from the aerodynamics and thermal aspects in order to determine the optimum tip cooling configuration. The studies are carried out using the tip cross-section of General Electric E3 (Energy Efficient Engine) HP turbine first-stage blade for two different tip geometries, squealer tip and flat tip, where the number, location, and diameter of the cooling holes are varied. The study presents a discussion on the overall loss coefficient, the total pressure loss across the tip clearance, and the variation of heat transfer on the blade tip. The aerodynamic and heat transfer results are compared with the experimental data from literature. It is observed that increasing the coolant mass flow rate by using more holes or by increasing the hole diameter results in a decrease in the area-averaged Nusselt number on the tip floor, as expected. The findings show that both aerodynamic and thermal response of the squealer tips to the implementation of cooling holes is superior to their flat counterparts. Among the studied configurations, the squealer tip with larger number of cooling holes located towards the pressure side is highlighted as the configuration having the best cooling performance.

Effect of clearance height on tip leakage flow reduced by a honeycomb tip in a turbine cascade

2018 ◽  
Vol 233 (10) ◽  
pp. 3564-3576
Author(s):  
Fu Chen ◽  
Yunfeng Fu ◽  
Jianyang Yu ◽  
Yanping Song
Keyword(s):  
Flow Resistance ◽  
Flow Characteristics ◽  
Tip Clearance ◽  
Small Scale ◽  
Leakage Flow ◽  
Turbine Cascade ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Clearance Flow ◽  
Vortex Movement

In this paper, the control mechanism of the honeycomb tip structure on the tip leakage flow of a turbine cascade is studied experimentally and numerically, and the sensitivity of tip leakage flow characteristics to different clearance heights from 0.5% to 2% based on the blade span are mainly discussed. A flat tip is considered as a comparative case. The results show that a part of the leakage flow enters the tip honeycomb cavity, forming small-scale vortices and mixes with the upper leakage fluid, which increases the flow resistance within the clearance. In the range of clearance height variation investigated, honeycomb tip structure can effectively reduce the leakage flow, and reduce the size and strength of the leakage vortex, so that the loss of the cascade is reduced. At a large tip clearance height, the unstable split of the vortex cores causes the vortex in the honeycomb cavities near pressure side to grow in size, so that the vortex extends further into the upper gap, where the turbulent blocking effect of the vortices on the leakage flow is increased. However, due to the vortex movement and the mixing between honeycomb vortices and the upper clearance flow, there is no obvious advantage in reducing the total loss of the cascade compared to the small tip clearance height.

Numerical Study of the Effect of Honeycomb Tip on Tip Leakage Flow in Turbine Cascade

2016 ◽  
Author(s):  
Yunfeng Fu ◽  
Fu Chen ◽  
Cong Chen ◽  
Yanping Song
Keyword(s):  
Flow Rate ◽  
Numerical Study ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Turbine Cascade ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Honeycomb Seal ◽  
Leakage Flow Rate ◽  
Highly Loaded

A novel leakage flow control strategy with honeycomb seal applied on the tip of the rotor blades in a highly-loaded turbine cascade is proposed. The numerical method is used to study the tip leakage flow in a highly-loaded turbine cascades with flat tip and with honeycomb seal structure, the mechanism of honeycomb tip on inhibiting leakage flow is analyzed, the influence of various relative gap heights is also been investigated. The discussions of the action of the honeycomb-tip structure in reducing leakage flow and improving the turbine efficiency provide the according for control methods of tip leakage flow. Through the comparative study among three different tip structures of honeycomb tip, honeycomb casing and flat tip, the results show that both honeycomb tip and honeycomb casing inhibit the leakage flow effectively, but honeycomb tip has positive effect on reducing the flow loss in cascade. For the cascade with honeycomb tip, on one hand, the vortices rolled up in the regular hexagon honeycomb cavities dissipate the energy of the tip leakage flow, and the range of influence of the vortices is nearly one third of the tip clearance height. On the other hand, the radial jets caused by the honeycomb obstruct the tip leakage flow like a “pneumatic fence”, resulting in weaker leakage flow and less leakage flow rate. Besides, the honeycomb tip reduces the scale of the leakage vortex, thus the leakage loss also decreases. Compared with the flat tip cascade at the clearance height of 1%H, the honeycomb tip cascade with the same clearance height obtains decrease of the leakage flow rate and leakage flow speed in circumference by 10.16% and 20%. As a result, the leakage vortex in honeycomb tip cascade is undermined, the loss is reduced by nearly 4.43%. Considering the abradable property of the honeycomb seal that can protect the blade tips from damage, the cascade with honeycomb tip structure can obtain a smaller clearance height and achieve better sealing effect. Compared to cascade with the flat tip at the clearance height of 2%H, the amount of leakage flow using inlet flow in the honeycomb tip cascades decreases by 17.33%, 36.63% and 54.79% at the clearance heights of 2%H, 1.5%H and 1%H, the losses related to the leakage flow is reduced by nearly 5.71%, 14.33% and 25.24%, respectively.

Interaction Between Inlet Boundary Layer, Tip-Leakage and Secondary Flows in a Low-Speed Turbine Cascade

1994 ◽  
Author(s):  
J. K. K. Chan ◽  
M. I. Yaras ◽  
S. A. Sjolander
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Large Scale ◽  
Field Measurements ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Turbine Cascade ◽  
Streamwise Vorticity ◽  
Tip Leakage Flow ◽  
Tip Leakage

An experiment has been conducted in a large-scale linear turbine cascade to examine the interaction between the inlet endwall boundary layer, tip-leakage and secondary flows. Detailed flow field measurements have been made upstream and downstream of the blade row for two values of inlet boundary layer thickness (δ*/c of about 0.015 and 0.04) together with three values of tip clearance (gap heights of 0.0, 1.5 and 5.5 percent of blade chord). In the downstream plane, the total pressure deficits associated with the tip-leakage and secondary flows were discriminated by examining the sign of the streamwise vorticity. For this case, the streamwise vorticity of the two flows have opposite signs and this proved an effective criterion for separating the flows despite their close proximity in space. It was found that with clearance the loss associated with the secondary flow was substantially reduced from the zero clearance value, in contradiction to the assumption made in most loss prediction schemes. Further work is needed, notably to clarify the influence of relative tip-wall motion which in turbines reduces the tip-leakage flow while enhancing the secondary flow.

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

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Kai Zhou ◽  
Chao Zhou
Keyword(s):  
Numerical Study ◽  
Leakage Flow ◽  
Computational Domain ◽  
Turbine Cascade ◽  
Tip Leakage Flow ◽  
Loss Mechanism ◽  
Flow Physics ◽  
Tip Leakage ◽  
Swirl Generator ◽  
Secondary Vortices

In turbines, secondary vortices and tip leakage vortices form in the blade passage and interact with each other. In order to understand the flow physics of this vortices interaction, the effects of incoming vortex on the downstream tip leakage flow are investigated by experimental, numerical, and analytical methods. In the experiment, a swirl generator was used upstream of a linear turbine cascade to generate the incoming vortex, which could interact with the downstream tip leakage vortex (TLV). 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 (SV). The effects of the directions of the incoming vortices were investigated. In the case of a positive incoming SV, which has a large vorticity vector in the same direction as that of the TLV, the vortex mixes with the TLV to form one major vortex near the casing as it transports downstream. This vortices interaction reduces the loss by increasing the streamwise momentum within the TLV core. However, the negative incoming SV has little effects on the TLV and the loss. As the negative incoming SV transports downstream, it travels away from the TLV and two vortices can be identified near the casing. A triple-vortices-interaction kinetic model is used to explain the flow physics of vortex interaction, and a one-dimensional mixing analytical model are proposed to explain the loss mechanism.

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