Numerical analysis of the aerodynamic performance and excitation forces in a transonic turbine cascade with flat-tip and squealer-tip blades

2020 ◽  
Vol 234 (22) ◽  
pp. 4377-4389
Author(s):  
Yang Pan ◽  
Qi Yuan ◽  
Gongge Huang ◽  
Guangyu Zhu ◽  
Pu Li
Keyword(s):  
Aerodynamic Performance ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Turbine Cascade ◽  
Tip Leakage Flow ◽  
Turbine Efficiency ◽  
Pressure Distributions ◽  
Sst Turbulence Model ◽  
Transonic Turbine ◽  
Excitation Force

The purpose of this paper is to numerically investigate the effect of blade tip clearance and its structure on the turbine aerodynamic performance and excitation force on blades in a transonic turbine cascade. Hence, circular cascades with flat-tip and squealer-tip blades and eight different tip clearances based on the SNECMA transonic turbine were established and the rotational effect was taking into consideration. The simulations were performed by solving the RANS equations and the SST turbulence model was used. The results show that tip clearance and tip structure have a significant influence on the turbine efficiency and excitation forces. Smaller tip clearance and squealer tip structure can reduce the tip leakage flow and leads to higher turbine efficiency. The tangential blade force varies nonlinearly with tip clearance since the leakage flow significantly changes the static pressure distributions on blade surfaces. Further, the excitation force factor was also calculated and illustrated.

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.

Tip Clearance Investigation of a Ducted Fan Used in VTOL UAVS: Part 1—Baseline Experiments and Computational Validation

2011 ◽  
Author(s):  
Ali Akturk ◽  
Cengiz Camci
Keyword(s):  
Total Pressure ◽  
Aerodynamic Performance ◽  
Test System ◽  
Tip Clearance ◽  
Computational Techniques ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Ducted Fan ◽  
Rans Simulations

Ducted fans that are popular choices in vertical take-off and landing (VTOL) unmanned aerial vehicles (UAV) offer a higher static thrust/power ratio for a given diameter than open propellers. Although ducted fans provide high performance in many VTOL applications, there are still unresolved problems associated with these systems. Fan rotor tip leakage flow is a significant source of aerodynamic loss for ducted fan VTOL UAVs and adversely affects the general aerodynamic performance of these vehicles. The present study utilized experimental and computational techniques in a 22″ diameter ducted fan test system that has been custom designed and manufactured. Experimental investigation consisted of total pressure measurements using Kiel total pressure probes and real time six-component force and torque measurements. The computational technique used in this study included a 3D Reynolds-Averaged Navier Stokes (RANS) based CFD model of the ducted fan test system. RANS simulations of the flow around rotor blades and duct geometry in the rotating frame of reference provided a comprehensive description of the tip leakage and passage flow. The experimental and computational analysis performed for various tip clearances were utilized in understanding the effect of the tip leakage flow on aerodynamic performance of ducted fans used in VTOL UAVs. The aerodynamic measurements and results of the RANS simulations showed good agreement especially near the tip region.

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.

scholarly journals Effects of Double-Side Labyrinth Seals on Aerodynamic Performance in a Transonic Shrouded Turbine Stage

2020 ◽  
Vol 142 (2) ◽  
Author(s):  
Weihang Li ◽  
Shaowen Chen ◽  
Hongyan Liu ◽  
Zhihua Zhou ◽  
Songtao Wang
Keyword(s):  
Labyrinth Seal ◽  
Aerodynamic Performance ◽  
Maximum Efficiency ◽  
Outlet Section ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Labyrinth Seals ◽  
Tip Leakage ◽  
Transonic Turbine

Abstract Labyrinth seals on both rotor casing and blade tip as an effective method to control the leakage flowrate of the shroud and improve aerodynamic performances in a transonic turbine stage are investigated in this study. Compared to the case without the labyrinth seal structure, the cases with three different types of sealing teeth have been shown to reduce significantly the tip leakage flow by computational simulations. The double-side sealing teeth case reduces the leakage flowrate mleakage/mpassage from 3.4% to 1.3% and increases the efficiency by 1.4%, which is the maximum efficiency improvement of all cases. The sealing structures increase the loss inside the shroud while reducing the momentum mixing between shroud leakage flow and mainstream. Therefore, the circumferential distribution of leakage velocity is changed, as well as the distribution of high-loss zones at turbine outlet. Furthermore, the leakage-vortex loss, which is associated with the blockage effect of sealing structure to the tip leakage flow, gains more improvement than the passage-vortex at the rotor outlet section in double-side seal case. In addition, it has also been found that with a larger gap at tip, the double-side seal has better effects of reducing the leakage flow and improving the aerodynamic performance in the transonic turbine stage.

Multi-Objective Optimization of Turbine Blade Tip With Film Cooling Holes

2021 ◽  
Author(s):  
Shuai Yang ◽  
Min Zhang ◽  
Yan Liu ◽  
Jinguang Yang
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Aerodynamic Performance ◽  
Tip Clearance ◽  
Pareto Optimum ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Multi Objective ◽  
Film Cooling Holes

Abstract Tip leakage flow is inevitable due to the tip clearance over rotor blades in turbines. This phenomenondeteriorates blade aerodynamic performance and induces severe thermal damage to the tip surface.Introduction of cooling jets to the tip can effectively controls the tip leakage flow and improves the tip heat transfer. Therefore, this paper aims to optimize film cooling holes on a flat tip of a subsonic cascade and an topology-optimized tip of a transonic cascade. A design variable is a material parameter defined at each grid node along the blade camber line. This idea is based on the topology optimization method. The objective is to minimize blade energy loss and maximize tip heat transfer intensity. A response surface optimization based on the design of experiment (DOE) analysis is employed, and a multi-objective Genetic Algorithm is used to get Pareto optimum solutions. During the DOE process, a CFD method using injection source terms is integrated for numerical simulations to reduce computational costs. Optimized tip film cooling holes are finally re-constructed. The influence of the newly designed tip cooling holes configuration on blade aero-thermal performance is evaluated via CFD simulations using body-fitted mesh. Results show that compared with the uniform arrangement of cooling film holes along the axial direction, all the optimized film cooling holes can improve both blade aerodynamic performance and tip heat transfer 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.

Measurements of the Tip-Leakage Flow in a Turbine Cascade With Large Clearances

1995 ◽  
Author(s):  
S. De Cecco ◽  
M. I. Yaras ◽  
S. A. Sjolander
Keyword(s):  
Static Pressure ◽  
Unit Area ◽  
Field Measurements ◽  
Leakage Flow ◽  
Unexpected Result ◽  
Turbine Cascade ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Pressure Distributions ◽  
Gap Flow

Measurements have been made for tip clearances up to 15% of chord in a turbine cascade which has been used previously to study the tip-leakage flow at smaller clearances. The work is part of a study of the aerodynamics of turbines which have experienced in-service damage and is related to Engine Health Monitoring. Detailed flow field measurements have been made upstream and downstream of the cascade and static pressure distributions have been measured on the endwall and at the midspan of the blade. The most unexpected result was that the blade end losses (that is, the sum of the secondary and tip-leakage losses) reached a maximum for a clearance of about 6% of chord. At the largest clearance of 15%, the end losses were substantially reduced and were in fact comparable with the secondary losses measured for zero clearance. The paper discusses in some detail the physics of the flow and the reasons for the observed reduction in losses. The pressure difference across the gap was found to be considerably attenuated at the largest clearance. This would have the effect of reducing the mass flow rate per unit area through the gap as well as the kinetic energy of the gap flow. These effects appear to account for a large part of the reduction in losses. As might be expected, the turning of the flow near the endwall was considerably reduced at the large clearances.

An Experimental Investigation of the Effects of Grooved Tip Geometry on the Flow Field in a Turbine Cascade Passage Using Stereoscopic PIV

2017 ◽  
Author(s):  
Yangtao Tian ◽  
Hongwei Ma ◽  
Lixiang Wang
Keyword(s):  
Flow Field ◽  
Vortex Breakdown ◽  
Tracer Particle ◽  
Tip Clearance ◽  
Small Scale ◽  
Turbine Cascade ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Turbine Efficiency

In the unshrouded axial turbine, the tip clearance gap can cause the losses of turbine efficiency and the penalty of turbine performance. Based on previous investigations, changing the blade tip geometry plays an important role in improving the turbine efficiency and performance. In this paper, the Stereoscopic Particle Imaging Velocimetry (SPIV) measurements were conducted to study the effects of grooved tip geometry on the flow field inside a turbine cascade passage. During the measurements, the double-frame CCD cameras were configured at different sides of the laser light sheet. Additionally, the Diisooctyl Sebacate (DEHS) was treated as the tracer particle. The tip clearance gap of both grooved tip and flat tip was set to 1.18% of the blade chord. The groove height was specified as 2.94% of the blade chord. In this study, the flow field results of eight measured planes were presented. Some typical features of the complicated flow structures, such as tip leakage vortex formation, development, breakdown and the dissipation, the variations of turbulence intensity and Reynolds stress, the blockage characteristic, were discussed as well. The experimental results show that the tip leakage flow/vortex is weakened by the grooved tip. The blockage effect and the flow capacity of the turbine passage are also improved. The tip leakage vortex breaks down at about 70% camber line, but the pattern of leakage vortex has changed into an ellipse at 60% camber line, which is an indication of the vortex breakdown. As for the decomposed and reconstructed flow, the first modal flow is the most similar to the original flow field. And it can capture the dominant flow features in flow field. And the flow of mode 2 and mode 3 generates many eddies with small scale.

Effect of endwall suction on aerodynamic performance of compressor cascade with tip clearance at a large incidence angle

2021 ◽  
pp. 095765092098395
Author(s):  
Botao Zhang ◽  
Bo Liu ◽  
Hejian Wang ◽  
Xiaochen Mao
Keyword(s):  
Boundary Layer ◽  
Incidence Angle ◽  
Boundary Layer Separation ◽  
Aerodynamic Performance ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Compressor Cascade ◽  
Tip Leakage Flow ◽  
Control Effect ◽  
Tip Leakage

In order to deeply analyze the application prospect of the boundary layer suction technique on the compressor, the flow control effect of endwall suction scheme on the tip leakage flow of a compressor cascade at a large incidence angle with complex internal flow structure and different loss proportion from the case at design incidence angle, was studied numerically, as well as on the overall aerodynamic performance. The results show that the suction scheme directly affects the structure of the tip leakage flow and makes the onset position of the tip leakage vortex move backward, which weakens the intensity and influence range of the tip leakage flow, thus improving the cascade performance in the tip region. At the large incidence angle, large flow suction makes the boundary layer separation in the low span area advance, and the corner separation region at the gap-free end expands to the upper. The position of the separation vortex shedding rises from 10% blade span under the condition without suction to about 70% blade span under the condition with the suction flow rate of 0.7%, and the separation loss increases. The overall performance of the cascade at the large incidence angle mainly depends on the increase of separation loss, while the effect of the decrease of leakage loss on it is greatly reduced. With suction, the total pressure loss coefficient of the cascade increases by about 5.7% at the incidence angle of +8°.

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