Flow Measurements in a First Stage Nozzle Cascade Having Leakage and Assembly Features: Effects of Endwall Steps and Leakage on Aerodynamic Losses

2005 ◽  
Author(s):  
J. D. Piggush ◽  
T. W. Simon
Keyword(s):  
Secondary Flows ◽  
Flow Measurements ◽  
Flow Rates ◽  
Leakage Flows ◽  
Assembly Features ◽  
Transition Piece ◽  
Improved Performance ◽  
Flow Effects ◽  
Work Supports ◽  
Aerodynamic Losses

This work supports new gas turbine designs for improved performance by evaluating endwall leakage and assembly features in a cascade that is representative of a first stage stator passage. The present paper documents component misalignment and leakage flow effects on the aerodynamic losses within a passage having one contoured and one straight endwall. Steps on the endwall and leakage flows through the endwall can lead to thicker endwall boundary layers, stronger secondary flows and possibly additional vortex structures in the passage. The paper compares losses with steps of various geometries and leakage of various flow rates to assess their importance on aerodynamic losses in this contoured passage. In particular, features associated with the combustor-to-turbine transition piece and the slash-face gap, a gap between two vane segments on the vane platform, are addressed.

Flow Measurements in a First Stage Nozzle Cascade Having Endwall Contouring, Leakage and Assembly Features

2005 ◽  
Author(s):  
J. D. Piggush ◽  
T. W. Simon
Keyword(s):  
Secondary Flows ◽  
Flow Measurements ◽  
Leakage Flows ◽  
Assembly Features ◽  
Transition Piece ◽  
Endwall Contouring ◽  
Improved Performance ◽  
Flow Effects ◽  
Work Supports ◽  
Aerodynamic Losses

This work supports new gas turbine designs for improved performance by evaluating the use of endwall contouring in a cascade that is representative of a first stage stator passage. Contouring accelerates the flow, reducing the thickness of the endwall inlet boundary layer to the turbine stage and reducing the strength of secondary flows within the passage. Reduction in secondary flows leads to less mixing in the endwall region. This allows improved cooling of the endwall and airfoil surfaces with injected and leakage flows. The present paper documents component misalignment and leakage flow effects on the aerodynamic losses within a passage having one contoured and one straight endwall. Steps on the endwall and leakage flows through the endwall can lead to thicker endwall boundary layers, stronger secondary flows and possibly additional vortex structures in the passage. The paper compares losses with steps of various geometries and leakage of various flow rates to assess their importance on aerodynamic losses in this contoured passage. In particular, features associated with the combustor-to-turbine transition piece and the slashface gap, a gap between two vane segments on the vane platform, are addressed. An n-factorial study is used to quantify the importance of such effects on aerodynamic losses.

Flow Measurements in a First Stage Nozzle Cascade Having Endwall Contouring, Leakage, and Assembly Features

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
J. D. Piggush ◽  
T. W. Simon
Keyword(s):  
Secondary Flows ◽  
Flow Measurements ◽  
Leakage Flows ◽  
Assembly Features ◽  
Transition Piece ◽  
Endwall Contouring ◽  
Improved Performance ◽  
Flow Effects ◽  
Work Supports ◽  
Aerodynamic Losses

This work supports new gas turbine designs for improved performance by evaluating the use of endwall contouring in a cascade that is representative of a first stage stator passage. Contouring accelerates the flow, reducing the thickness of the endwall inlet boundary layer to the turbine stage and reducing the strength of secondary flows within the passage. The reduction in secondary flows leads to less mixing in the endwall region. This allows for an improved cooling of the endwall and airfoil surfaces with injected and leakage flows. The present paper documents the component misalignment and injected and leakage flow effects on the aerodynamic losses within a passage that has one contoured and one straight endwall. Steps and injected flows within the passage can lead to thicker endwall boundary layers, stronger secondary flows, and possibly additional vortex structures in the passage. The paper compares losses with various steps, gaps, and leakage flows to assess their importance in this contoured passage. In particular, features associated with the combustor-to-turbine transition piece and the slashface on the vane platform are addressed. An n-factorial study is used to quantify the importance of such effects on aerodynamic losses.

Heat Transfer Measurements in a First-Stage Nozzle Cascade Having Endwall Contouring: Misalignment and Leakage Studies

2006 ◽  
Vol 129 (4) ◽  
pp. 782-790 ◽  
Author(s):  
J. D. Piggush ◽  
T. W. Simon
Keyword(s):  
Heat Transfer ◽  
Secondary Flows ◽  
Transfer Coefficients ◽  
Transfer Rates ◽  
Leakage Flows ◽  
Heat Transfer Coefficients ◽  
Assembly Features ◽  
Transition Piece ◽  
Improved Performance ◽  
Work Supports

This work supports new gas turbine designs for improved performance by evaluating endwall heat transfer rates in a cascade that is representative of a first-stage stator passage and incorporates endwall assembly features and leakage. Assembly features, such as gaps in the endwall and misalignment of those gaps, disrupt the endwall boundary layer, typically leading to enhanced heat transfer rates. Leakage flows through such gaps within the passage can also affect endwall boundary layers and may induce additional secondary flows and vortex structures in the passage near the endwall. The present paper documents leakage flow and misalignment effects on the endwall heat transfer coefficients within a passage which has one axially contoured and one straight endwall. In particular, features associated with the combustor-to-turbine transition piece and the assembly joint on the vane platform are addressed.

Heat Transfer Measurements in a First Stage Nozzle Cascade Having Endwall Contouring: Misalignment and Leakage Studies

2006 ◽  
Author(s):  
J. D. Piggush ◽  
T. W. Simon
Keyword(s):  
Heat Transfer ◽  
Secondary Flows ◽  
Transfer Coefficients ◽  
Transfer Rates ◽  
Leakage Flows ◽  
Heat Transfer Coefficients ◽  
Assembly Features ◽  
Transition Piece ◽  
Improved Performance ◽  
Work Supports

This work supports new gas turbine designs for improved performance by evaluating endwall heat transfer rates in a cascade that is representative of a first stage stator passage and incorporates endwall assembly features and leakage. Assembly features, such as gaps in the endwall and misalignment of those gaps, disrupt the endwall boundary layer, typically leading to enhanced heat transfer rates. Leakage flows through such gaps within the passage can also affect endwall boundary layers and may induce additional secondary flows and vortex structures in the passage near the endwall. The present paper documents leakage flow and misalignment effects on the endwall heat transfer coefficients within a passage which has one axially-contoured and one straight endwall. In particular, features associated with the combustor-to-turbine transition piece and the assembly joint on the vane platform are addressed.

Heat Transfer Measurements in a First Stage Nozzle Cascade Having Endwall Contouring, Leakage and Assembly Features

2005 ◽  
Author(s):  
J. D. Piggush ◽  
T. W. Simon
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Secondary Flows ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Flow Rates ◽  
Assembly Features ◽  
Improved Performance ◽  
Flow Effects ◽  
Work Supports

This work supports new gas turbine designs for improved performance by evaluating sealing flow effects in a cascade representative of a contoured first stage stator passage. Contouring accelerates the flow, reducing the thickness of the endwall inlet boundary layer to the turbine stage and reducing the strength of secondary flows within the passage. Injected flows, used to seal gaps and cool surfaces, may affect endwall boundary layers, increase secondary flows and possibly create additional vortex structures in the passage. The present paper documents injected flow effects on the endwall heat transfer within a passage with one contoured and one straight endwall. The paper discusses heat transfer distributions measured with different leakage flow rates. In particular, leakage is from the gap between the combustor and turbine sections and from the gap at the assembly joint on the vane platform between two vanes.

Axisymmetric Endwall Contouring in a Four-Stage Turbine: Comparison of Experimental and Numerical Results

2002 ◽  
Author(s):  
Dieter E. Bohn ◽  
Norbert Su¨rken ◽  
Qing Yu ◽  
Franz Kreitmeier
Keyword(s):  
Flow Field ◽  
Positive Influence ◽  
Secondary Flows ◽  
Navier Stokes ◽  
Flow Measurements ◽  
Flow Angle ◽  
Numerical Predictions ◽  
Before And After ◽  
Endwall Contouring ◽  
Aerodynamic Losses

Secondary flows and leakage flows lead to complex vortex structures in the 3-D flow field of a turbine blading. Aerodynamic losses are the consequence. Reducing these aerodynamic losses by axisymmetric endwall contouring is the subject of a current experimental and numerical investigation of the flow field in a 4-stage test turbine with repeating stages. Numerical 4-stage simulations for the reconstructed turbine with an axisymmetric off-set arc endwall contour at the casing have been performed and compared to corresponding numerical investigations of the original machine without endwall modifications. The 3-D flow fields have been calculated by application of a steady 3-D Navier-Stokes code. Based on these results the experimental setup is modified to the off-set arc endwall design. The characteristics of the reconstructed machine are measured and compared to the original test rig. Special emphasis is put on the determination of the aerodynamic efficiencies over the four stages. For a detailed assessment of the radial and spanwise flow field properties inside the blading, 5-hole pressure probes are used for steady flow measurements in the narrow axial gaps before and after the 3rd stage. Finally, the measured radial distributions of the flow field properties and the machine characteristics are compared to the corresponding numerical predictions. All results show a significant positive influence of the endwall contouring on the radial distribution of the flow angle, the pressure field and the aerodynamic efficiency.

Off-Design Flow Measurements in a Centrifugal Compressor Vaneless Diffuser

1995 ◽  
Vol 117 (4) ◽  
pp. 602-608 ◽  
Author(s):  
A. Pinarbasi ◽  
M. W. Johnson
Keyword(s):  
Flow Rate ◽  
Centrifugal Compressor ◽  
Secondary Flows ◽  
Design Flow ◽  
Vaneless Diffuser ◽  
Flow Measurements ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Flow Rates ◽  
Study Results

Detailed measurements have been taken of the three-dimensional velocity field within the vaneless diffuser of a backswept low speed centrifugal compressor using hot-wire anemometry. A 16 percent below and an 11 percent above design flow rate were used in the present study. Results at both flow rates show how the blade wake mixes out more rapidly than the passage wake. Strong secondary flows inherited from the impeller at the higher flow rate delay the mixing out of the circumferential velocity variations, but at both flow rates these circumferential variations are negligible at the last measurement station. The measured tangential/radial flow angle is used to recommend optimum values for the vaneless space and vane angle for design of a vaned diffuser.

Influence of Endwall Contouring in Axial Gaps on the Flow Field in a Four-Stage Turbine

2000 ◽  
Author(s):  
Dieter E. Bohn ◽  
Karsten Kusterer ◽  
Norbert Sürken ◽  
Franz Kreitmeier
Keyword(s):  
Flow Field ◽  
Flow Analysis ◽  
Numerical Data ◽  
Positive Influence ◽  
Secondary Flows ◽  
Maximum Deviation ◽  
Leakage Flows ◽  
Endwall Contouring ◽  
D Values ◽  
Aerodynamic Losses

Secondary flows and leakage flows are leading to complex vortex structures in the 3-D flow field of a turbine blading. Aerodynamic losses are the consequence. Reducing the aerodynamic losses related to tip leakage flows by endwall contouring is subject of an actual numerical investigation of the flow field in a 4-stage test turbine with repeating stages. The 3-D flow field for various geometric configurations with endwall contouring is calculated by application of a 3-D Navier-Stokes code. Here, the numerical results of configurations with arc-like and wave-like contours (bumps) at the shaft and the casing with a maximum deviation from the reference contour in the axial gap between stator and rotor are presented. Furthermore, the results are compared to the experimental and numerical data of the test turbine with a reference contour without endwall contouring. The results show a significant influence of the bumps on the radial velocity distribution in the flow field and the static pressure field. By application of a subtraction method where the reference flow field is subtracted from the flow fields of the bump-configurations, it can be shown that the leakage flows are reduced. A detailed flow analysis shows the presence of a leakage vortex. For a measure of the flow field inhomogeneity and for reducing the complex 3-D data to 2-D and 1-D values a balance-based averaging method is used. The method is based on a hypothetical equilibration process between two infinitesimal neighbouring control surfaces. During this physically based averaging process, equilibration coefficients can be derived which are a measure for the flow inhomogeneity. It can be shown that arc-like and wave-like endwall contouring has a positive influence on the homogeneity of the flow field. Thus, this effect leads to higher aerodynamic stage efficiencies for repeating stages.

scholarly journals Investigation of Separation Phenomena in a Radial Pump at Reduced Flow Rate by Large-Eddy Simulation

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Antonio Posa ◽  
Antonio Lippolis ◽  
Elias Balaras
Keyword(s):  
Reverse Flow ◽  
Leading Edge ◽  
Suction Side ◽  
Secondary Flows ◽  
Vaned Diffuser ◽  
Flow Rates ◽  
Turbulent Statistics ◽  
Large Eddy ◽  
Radial Pump ◽  
Reduced Flow

Turbopumps operating at reduced flow rates experience significant separation and backflow phenomena. Although Reynolds-Averaged Navier–Stokes (RANS) approaches proved to be usually able to capture the main flow features at design working conditions, previous numerical studies in the literature verified that eddy-resolving techniques are required in order to simulate the strong secondary flows generated at reduced loads. Here, highly resolved large-eddy simulations (LES) of a radial pump with a vaned diffuser are reported. The results are compared to particle image velocimetry (PIV) experiments in the literature. The main focus of the present work is to investigate the separation and backflow phenomena occurring at reduced flow rates. Our results indicate that the effect of these phenomena extends up to the impeller inflow: they involve the outer radii of the impeller vanes, influencing significantly the turbulent statistics of the flow. Also in the diffuser vanes, a strong spanwise evolution of the flow has been observed at the reduced load, with reverse flow, located mainly on the shroud side and on the suction side (SS) of the stationary channels, especially near the leading edge of the diffuser blades.

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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