Unsteady Effects in Turbine Tip Clearance Flows

2000 ◽  
Vol 122 (4) ◽  
pp. 621-627 ◽  
Author(s):  
Anil Prasad ◽  
Joel H. Wagner
Keyword(s):  
Tip Clearance ◽  
Time Resolved ◽  
Vena Contracta ◽  
Deviation Measurement ◽  
Blade Tip ◽  
Unsteady Effects ◽  
Heat Loads ◽  
High Work ◽  
Careful Comparison ◽  
Made In

The present study is concerned with the unsteady flow field on the blade outer air seal segments of high-work turbines; these segments are installed between the blade tip and outer casing and are usually subjected to extreme heat loads. Time-resolved measurements of the unsteady pressure on the blade outer air seal are made in a low-speed turbine rig. The present measurements indicate the existence of a separation zone on the blade tip, which causes a vena contracta to form at the entrance of the tip gap. In addition, a careful comparison between the ensemble-averaged pressure measurement and the corresponding result from steady computation suggests that the pressure on the blade outer air seal can largely be described as being due to a steady flow (in the rotating frame) sweeping past a stationary probe. The ensemble deviation measurement indicates that unsteadiness (from one revolution to the next) is confined to the tip gap. [S0889-504X(00)02304-7]

Unsteady Effects in Turbine Tip Clearance Flows

2000 ◽  
Author(s):  
Anil Prasad ◽  
Joel H. Wagner
Keyword(s):  
Tip Clearance ◽  
Time Resolved ◽  
Vena Contracta ◽  
Deviation Measurement ◽  
Blade Tip ◽  
Unsteady Effects ◽  
Heat Loads ◽  
High Work ◽  
Careful Comparison ◽  
Made In

The present study is concerned with the unsteady flow field on the blade outer air seal segments of high-work turbines; these segments are installed between the blade tip and outer casing and are usually subjected to extreme heat loads. Time-resolved measurements of the unsteady pressure on the blade outer air seal are made in a low-speed turbine rig. The present measurements indicate the existence of a separation zone on the blade tip which causes a vena contracta to form at the entrance of the tip gap. In addition, a careful comparison between the ensemble-averaged pressure measurement and the corresponding result from steady computation suggests that the pressure on the blade outer air seal can largely be described as being due to a steady flow (in the rotating frame) sweeping past a stationary probe. The ensemble deviation measurement indicates that unsteadiness (from one revolution to the next) is confined to the tip gap.

Evaluating the Influence of Rotor-Casing Eccentricity on Turbine Efficiency Including Time-Resolved Flow Field Measurements

2021 ◽  
pp. 1-33
Author(s):  
Eric DeShong ◽  
Shawn Siroka ◽  
Reid A. Berdanier ◽  
Karen A. Thole
Keyword(s):  
Flow Field ◽  
Magnetic Levitation ◽  
Field Measurements ◽  
Tip Clearance ◽  
Time Resolved ◽  
Flow Angle ◽  
Turbine Efficiency ◽  
Eccentric Rotor ◽  
Blade Tip ◽  
Manufacturing Techniques

Abstract The clearance that exists between the casing and turbine blade tips is one of the key drivers of efficiency in gas turbine engines. For this reason, engine manufacturers utilize precise manufacturing techniques and may employ clearance control systems to minimize tip clearances to reduce associated losses. Despite these efforts, turbines typically exhibit some nominal casing ovality or rotor-casing eccentricity, and changes to blade tip clearance during operation commonly occur due to thermal and mechanical stresses. The present study investigates non-axisymmetric tip clearance effects by creating a rotor-casing eccentricity in a one-stage axial test turbine operating in a continuous-duration mode at engine relevant conditions with engine representative hardware. A magnetic levitation bearing system was leveraged to move the turbine shaft to vary the rotor-casing eccentricity without test section disassembly. The results of this study indicate that rotor-casing eccentricity does not affect overall turbine efficiency over the range that was tested, but does locally influence efficiency and the rotor exit flow field. Comparisons of flow angle and secondary flow kinetic energy agreed with previous studies and existing analytical methods, respectively. Collectively, these results indicate that tip clearance can be studied locally on an eccentric rotor.

The Periodical Interaction of the Tip Clearance Flow in the Blade Rows of Axial Compressors

2001 ◽  
Author(s):  
Ronald Mailach ◽  
Helmut Sauer ◽  
Konrad Vogeler
Keyword(s):  
Flow Pattern ◽  
Flow Instability ◽  
Stability Limit ◽  
Tip Clearance ◽  
Time Resolved ◽  
Tip Clearance Flow ◽  
Blade Row ◽  
Clearance Flow ◽  
Blade Tip ◽  
Time Periodic

Current models on the tip clearance flow in turbomachines only describe the time-averaged behaviour of the flow structures. However, the real tip clearance flow is periodically fluctuating in time. This fact has to be considered for the design of turbomachine bladings especially with regard to blade vibrations and tip clearance noise. Detailed experimental investigations on the time-resolved behaviour of the flow in the rotor blade tip region were carried out in a four-stage low-speed research compressor. A strong time-periodic interaction of the blade tip vortices of adjacent blades can be shown for relatively large tip clearance of the rotor blades for operating points near the stability limit of the compressor. The resulting flow pattern, which frequency is not related to the rotor frequency, moves along the blade row. It can be described as a multicell configuration with strongly fluctuating cell number and size. The structure and propagation of the flow instability can be summarized in a model of the periodic fluctuating tip clearance flow (Mailach et al., 2000). Additional experiments were carried out in a straight cascade to improve the understanding of this flow phenomenon. It can be shown by means of time-resolved measurements that the same disturbance exists for comparable inlet flow conditions in the blade tip region of the cascade. Flow visualizations show that the blade tip vortex is strongly fluctuating and moves sometimes ahead of the leading edge of the adjacent blade. The result of this is a short-lengthscale flow pattern, which is propagating along the blade row. These experiments confirm the model of the time-periodic tip clearance flow proposed for compressors. A Strouhal-number for the estimation of the frequency of the flow fluctuation will be presented, which includes both design and aerodynamic parameters.

Effect of Tip Clearance on the Flow and Performance of a Centrifugal Compressor

2003 ◽  
Author(s):  
Soon-Sam Hong ◽  
Matthias Schleer ◽  
Reza S. Abhari
Keyword(s):  
Centrifugal Compressor ◽  
Fast Response ◽  
Tip Clearance ◽  
Wake Region ◽  
Clearance Ratio ◽  
Flow Measurements ◽  
Time Resolved ◽  
Compressor Impeller ◽  
Blade Tip ◽  
And Performance

To see the tip clearance effect on a centrifugal compressor, time-resolved flow measurements were carried out at the discharge of a centrifugal compressor impeller, which is 30 deg back swept from radial and operated at the blade tip speed of 260 m/s. Tested were six cases of tip clearance ratio ranged from 0.06 to 0.21. A fast response aerodynamic probe equipped with a single pressure sensor was used for the flow measurements. From the distribution of time-resolved relative velocity, the jet-wake structure was observed. The wake downstream of the splitter blade was located in the shroud-suction corner, but that downstream of the full blade was in the mid-shroud. By increasing the tip clearance, the wake region was increased and the deficit of the relative total pressure governed the wake region, therefore, the loss was enlarged.

Evaluating the Influence of Rotor-Casing Eccentricity on Turbine Efficiency Including Time-Resolved Flow Field Measurements

2021 ◽  
Author(s):  
Eric T. DeShong ◽  
Shawn Siroka ◽  
Reid A. Berdanier ◽  
Karen A. Thole
Keyword(s):  
Flow Field ◽  
Magnetic Levitation ◽  
Field Measurements ◽  
Tip Clearance ◽  
Time Resolved ◽  
Flow Angle ◽  
Turbine Efficiency ◽  
Eccentric Rotor ◽  
Blade Tip ◽  
Manufacturing Techniques

Abstract The clearance that exists between the casing and turbine blade tips is one of the key drivers of efficiency in gas turbine engines. For this reason, engine manufacturers utilize precise manufacturing techniques and may employ clearance control systems to minimize tip clearances to reduce associated losses. Despite these efforts, turbines typically exhibit some nominal casing ovality or rotor-casing eccentricity, and changes to blade tip clearance during operation commonly occur due to thermal and mechanical stresses. The present study investigates non-axisymmetric tip clearance effects by creating a rotor-casing eccentricity in a one-stage axial test turbine operating in a continuous-duration mode at engine relevant conditions with engine representative hardware. A magnetic levitation bearing system was leveraged to move the turbine shaft to vary the rotor-casing eccentricity without test section disassembly. The results of this study indicate that rotor-casing eccentricity does not affect overall turbine efficiency over the range that was tested, but does locally influence efficiency and the rotor exit flow field. Comparisons of flow angle and secondary flow kinetic energy agreed with previous studies and existing analytical methods, respectively. Collectively, these results indicate that tip clearance can be studied locally on an eccentric rotor.

Effect of the Tip Clearance on End Wall Heat-Transfer in a HP Turbine

2013 ◽  
Author(s):  
Marc H.-O. Biester ◽  
Dimitri Karapetrow ◽  
Joerg R. Seume
Keyword(s):  
Heat Transfer ◽  
Aircraft Engine ◽  
Tip Clearance ◽  
Time Resolved ◽  
Velocity Gradients ◽  
Blade Tip ◽  
High Level ◽  
Radial Gap ◽  
End Wall ◽  
Tip Clearance Vortex

The present investigation analyzes the effect of the extension of the radial gap on the heat transfer at the blade tip and the casing within a high-pressure turbine stage of an aircraft engine. Due to the rotation and the interaction of the adjacent blade-rows, the flow field in the tip region of an unshrouded rotor-blade is characterized by a high level of unsteadiness. Furthermore, the casing is exposed to the passing blade-gap and corresponding changes in the velocity-profile, the resulting near-wall velocity-gradients, and the resulting changes in heat transfer. In order to account for these effects, time-resolved RANS computations of three different radial gaps are performed and evaluated. The present analysis shows an influence of the radial gap on the characteristics of the steady and unsteady heat transfer and a correlation with the size of the tip-clearance vortex can be shown.

scholarly journals Creep-Based Reliability Evaluation of Turbine Blade-Tip Clearance with Novel Neural Network Regression

Materials ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 3552 ◽  
Author(s):  
Chun-Yi Zhang ◽  
Jing-Shan Wei ◽  
Ze Wang ◽  
Zhe-Shan Yuan ◽  
Cheng-Wei Fei ◽  
...  
Keyword(s):  
Neural Network ◽  
High Pressure ◽  
Reliability Analysis ◽  
Response Surface ◽  
Response Surface Method ◽  
Tip Clearance ◽  
Strong Nonlinearity ◽  
Surface Method ◽  
Blade Tip ◽  
Blade Tip Clearance

To reveal the effect of high-temperature creep on the blade-tip radial running clearance of aeroengine high-pressure turbines, a distributed collaborative generalized regression extremum neural network is proposed by absorbing the heuristic thoughts of distributed collaborative response surface method and the generalized extremum neural network, in order to improve the reliability analysis of blade-tip clearance with creep behavior in terms of modeling precision and simulation efficiency. In this method, the generalized extremum neural network was used to handle the transients by simplifying the response process as one extremum and to address the strong nonlinearity by means of its nonlinear mapping ability. The distributed collaborative response surface method was applied to handle multi-object multi-discipline analysis, by decomposing one “big” model with hyperparameters and high nonlinearity into a series of “small” sub-models with few parameters and low nonlinearity. Based on the developed method, the blade-tip clearance reliability analysis of an aeroengine high-pressure turbine was performed subject to the creep behaviors of structural materials, by considering the randomness of influencing parameters such as gas temperature, rotational speed, material parameters, convective heat transfer coefficient, and so forth. It was found that the reliability degree of the clearance is 0.9909 when the allowable value is 2.2 mm, and the creep deformation of the clearance presents a normal distribution with a mean of 1.9829 mm and a standard deviation of 0.07539 mm. Based on a comparison of the methods, it is demonstrated that the proposed method requires a computing time of 1.201 s and has a computational accuracy of 99.929% over 104 simulations, which are improvements of 70.5% and 1.23%, respectively, relative to the distributed collaborative response surface method. Meanwhile, the high efficiency and high precision of the presented approach become more obvious with the increasing simulations. The efforts of this study provide a promising approach to improve the dynamic reliability analysis of complex structures.

ZnCdO/ZnMgO and ZnO/AlGaN Heterostructures for UV and Visible Light Emitters

2005 ◽  
Vol 892 ◽  
Author(s):  
Andrei Osinsky ◽  
Jianwei Dong ◽  
J. Q. Xie ◽  
B. Hertog ◽  
A. M. Dabiran ◽  
...  
Keyword(s):  
Molecular Beam ◽  
Compositional Analysis ◽  
Optical Emission ◽  
Rf Plasma ◽  
Light Emitters ◽  
Time Resolved ◽  
Light Emitting ◽  
Spatially Resolved ◽  
Time Resolved Photoluminescence ◽  
Made In

AbstractThis paper reviews of some of the progress made in the development of ZnO-based light emitting diodes (LEDs). n-ZnO/p-AlGaN-based heterostructures have been successfully for the fabrication of UV emitting LEDs that have operated at temperatures up to 650K, suggesting an excitonic origin for the optical transitions. RF-plasma-assisted molecular beam epitaxy has been used to grow epitaxial CdxZn1-xO films on GaN/sapphire structure. These films have a single-crystal wurtzite structure as demonstrated by structural and compositional analysis. High quality CdxZn1-xO films were grown with up to x=0.78 mole fraction as determined by RBS and SIMS techniques. Optical emission ranging from purple (Cd0.05Zn0.95O) to yellow (Cd0.29Zn0.71O) was observed. Compositional fluctuations in a Cd0.16Zn0.84O films were not detected by spatially resolved CL measurements, although intensity fluctuation with features of ∼0.5 μm diameter were seen on the intensity maps. Time resolved photoluminescence shows multi-exponential decay with 21 psec. and 49±3 psec. lifetimes, suggesting that composition micro-fluctuations may be present in Cd0.16Zn0.84O film.

Influence of tip clearance and cavity depth on heat transfer in a cutback squealer tip

2020 ◽  
pp. 095441002096469
Author(s):  
Weijie Wang ◽  
Shaopeng Lu ◽  
Hongmei Jiang ◽  
Qiusheng Deng ◽  
Jinfang Teng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Suction Side ◽  
High Heat ◽  
Tip Clearance ◽  
Tip Leakage Flow ◽  
Trailing Edge ◽  
Cavity Depth ◽  
High Heat Transfer ◽  
Blade Tip ◽  
High Heat Transfer Coefficient

Numerical simulations are conducted to present the aerothermal performance of a turbine blade tip with cutback squealer rim. Two different tip clearance heights (0.5%, 1.0% of the blade span) and three different cavity depths (2.0%, 3.0%, and 6.0% of the blade span) are investigated. The results show that a high heat transfer coefficient (HTC) strip on the cavity floor appears near the suction side. It extends with the increase of tip clearance height and moves towards the suction side with the increase of cavity depth. The cutback region near the trailing edge has a high HTC value due to the flush of over-tip leakage flow. High HTC region shrinks to the trailing edge with the increase of cavity depth since there is more accumulated flow in the cavity for larger cavity depth. For small tip clearance cases, high HTC distribution appears on the pressure side rim. However, high HTC distribution is observed on suction side rim for large tip clearance height. This is mainly caused by the flow separation and reattachment on the squealer rims.

Numerical Modeling of Heat Transfer and Pressure Losses for Uncooled Gas Turbine Blade Tip: Effect of Tip Clearance and Tip Geometry

2007 ◽  
Author(s):  
Lamyaa A. El-Gabry
Keyword(s):  
Heat Transfer ◽  
Mach Number ◽  
Gas Turbine ◽  
Computational Study ◽  
Numerical Models ◽  
Pressure Ratio ◽  
Tip Clearance ◽  
Pressure Losses ◽  
Blade Tip ◽  
Exit Mach Number

A computational study has been performed to predict the heat transfer distribution on the blade tip surface for a representative gas turbine first stage blade. CFD predictions of blade tip heat transfer are compared to test measurements taken in a linear cascade, when available. The blade geometry has an inlet Mach number of 0.3 and an exit Mach number of 0.75, pressure ratio of 1.5, exit Reynolds number based on axial chord of 2.57×106, and total turning of 110 deg. Three blade tip configurations were considered; they are flat tip, a full perimeter squealer, and an offset squealer where the rim is offset to the interior of the tip perimeter. These three tip geometries were modeled at three tip clearances of 1.25, 2.0, and 2.75% of blade span. The tip heat transfer results of the numerical models agree fairly well with the data and are comparable to other CFD predictions in the open literature.

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