Effects of Simulated Rotation on Tip Leakage in a Planar Cascade of Turbine Blades: Part I—Tip Gap Flow

1992 ◽  
Vol 114 (3) ◽  
pp. 652-659 ◽  
Author(s):  
M. I. Yaras ◽  
S. A. Sjolander
Keyword(s):  
Flow Field ◽  
Relative Motion ◽  
Wall Motion ◽  
Turbine Blades ◽  
Pressure Probe ◽  
Tip Leakage ◽  
Gap Flow ◽  
Axial Turbines ◽  
Downstream Flow ◽  
Tip Gap Flow

The paper presents further results from a continuing study on tip leakage in axial turbines. Rotation has been simulated in a linear cascade test section by using a moving-belt tip wall. Measurements were made inside the tip gap with a three-hole pressure probe for a clearance size of 3.8 percent of the blade chord. Two wall speeds are considered and the results are compared with the case of no rotation. As in other experiments, significant reduction in the gap mass flow rate is observed due to the relative motion. The detailed nature of the measurements allows the dominant physical mechanism by which wall motion affects the tip gap flow to be identified. Based on the experimental observations, an earlier model for predicting the tip gap flow field is extended to the case of relative wall motion. Part II of the paper examines the effect of the relative motion on the downstream flow field and the blade loading.

scholarly journals Effects of Simulated Rotation on Tip Leakage in a Planar Cascade of Turbine Blades: Part I — Tip Gap Flow

1991 ◽  
Author(s):  
M. I. Yaras ◽  
S. A. Sjolander
Keyword(s):  
Flow Field ◽  
Relative Motion ◽  
Wall Motion ◽  
Turbine Blades ◽  
Pressure Probe ◽  
Tip Leakage ◽  
Gap Flow ◽  
Axial Turbines ◽  
Downstream Flow ◽  
Tip Gap Flow

The paper presents further results from a continuing study on tip leakage in axial turbines. Rotation has been simulated in a linear cascade test section by using a moving-belt tip wall. Measurements were made inside the tip gap with a three-hole pressure probe for a clearance size of 3.8 percent of the blade chord. Two wall speeds are considered and the results are compared with the case of no rotation. As in other experiments, significant reduction in the gap mass flow rate is observed due to the relative motion. The detailed nature of the measurements allows the dominant physical mechanism by which wall motion affects the tip gap flow to be identified. Based on the experimental observations, an earlier model for predicting the tip gap flow field is extended to the case of relative wall motion. Part II of the paper examines the effect of the relative motion on the downstream flow field and the blade loading.

scholarly journals Effects of Simulated Rotation on Tip Leakage in a Planar Cascade of Turbine Blades: Part II — Downstream Flow Field and Blade Loading

1991 ◽  
Author(s):  
M. I. Yaras ◽  
S. A. Sjolander ◽  
R. J. Kind
Keyword(s):  
Flow Field ◽  
Turbine Blades ◽  
Companion Paper ◽  
Tip Vortex ◽  
Pressure Probe ◽  
Blade Loading ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Effects Of Rotation ◽  
Downstream Flow

This paper and its companion paper present experimental results on the effects of simulated rotation on the tip leakage in a linear turbine cascade test. Part II examines the downstream flow field. For clearance sizes of 2.4 and 3.8 percent of the blade chord measurements were made in two planes downstream of the trailing edge using a seven-hole pressure probe. Significant changes in the tip leakage vortex and passage vortex structures are observed with the introduction of relative motion. The effects of clearance size and rotation on the relationship between bound circulation and tip-vortex circulation are discussed. The validity of a previously developed tip-vortex model for the case of rotation is examined in the light of the measurements. Finally, for clearances of 1.5, 2.4 and 3.8 percent of the blade chord the effects of rotation on blade loading are studied through static pressure measurements on the blade surfaces. The distortion of the surface pressure field near the tip is found to be reduced with increasing wall speed. This is consistent with the reduced strength of the tip-leakage vortex as wall speed is increased. For all measurements two wall speeds are considered and the results are compared with the case of no rotation.

Effects of Simulated Rotation on Tip Leakage in a Planar Cascade of Turbine Blades: Part II—Downstream Flow Field and Blade Loading

1992 ◽  
Vol 114 (3) ◽  
pp. 660-667 ◽  
Author(s):  
M. I. Yaras ◽  
S. A. Sjolander ◽  
R. J. Kind
Keyword(s):  
Flow Field ◽  
Turbine Blades ◽  
Companion Paper ◽  
Tip Vortex ◽  
Pressure Probe ◽  
Blade Loading ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Effects Of Rotation ◽  
Downstream Flow

This paper and its companion paper present experimental results on the effects of simulated rotation on the tip leakage in a linear turbine cascade test. Part II examines the downstream flow field. For clearance sizes of 2.4 and 3.8 percent of the blade chord, measurements were made in two planes downstream of the trailing edge using a seven-hole pressure probe. Significant changes in the tip leakage vortex and passage vortex structures are observed with the introduction of relative motion. The effects of clearance size and rotation on the relationship between bound circulation and tip-vortex circulation are discussed. The validity of a previously developed tip-vortex model for the case of rotation is examined in the light of the measurements. Finally, for clearances of 1.5, 2.4, and 3.8 percent of the blade chord, the effects of rotation on blade loading are studied through static pressure measurements on the blade surfaces. The distortion of the surface pressure field near the tip is found to be reduced with increasing wall speed. This is consistent with the reduced strength of the tip-leakage vortex as wall speed is increased. For all measurements two wall speeds are considered and the results are compared with the case of no rotation.

The Reduction of Over Tip Leakage Loss in Unshrouded Axial Turbines Using Winglets and Squealers

2013 ◽  
Vol 136 (4) ◽  
Author(s):  
Zbigniew Schabowski ◽  
Howard Hodson
Keyword(s):  
Flow Pattern ◽  
Large Scale ◽  
Turbine Blades ◽  
Suction Side ◽  
Leakage Loss ◽  
Tip Leakage ◽  
Gap Flow ◽  
Computational Fluid Dynamics Cfd ◽  
Axial Turbines ◽  
The Impact

The possibilities of reducing the over tip leakage loss of unshrouded rotors have been investigated using a linear cascade of turbine blades and computational fluid dynamics (CFD). The large-scale blade profile is the same as that of the tip profile of a low-speed high-pressure research turbine facility. The impact of various combinations of squealer and winglet geometries on the turbine performance has been investigated. The influence of the thickness of the squealers has also been assessed. It was found that a 22% reduction in loss slope was possible, when compared to the flat tip blade, using simple tip modifications. The results obtained with the suction side squealer and cavity tip agreed well with the work of other researchers. Three winglet-based tip geometries were tested. One was a plain winglet, the other two had squealers applied. A significant impact of the squealers and their shape on the tip gap flow pattern and loss generation was found. The physical processes occurring within the tip gap region for the tested geometries are explained using both numerical and experimental results. The impact of the flow pattern within the tip gap on the loss generation is described. Good agreement between CFD and the experimental data was found. This shows that CFD can be used with confidence in the design process of shroudless turbines.

The Reduction of Over Tip Leakage Loss in Unshrouded Axial Turbines Using Winglets and Squealers

2007 ◽  
Author(s):  
Zbigniew Schabowski ◽  
Howard Hodson
Keyword(s):  
Flow Pattern ◽  
Large Scale ◽  
Turbine Blades ◽  
Suction Side ◽  
Leakage Loss ◽  
Tip Leakage ◽  
Gap Flow ◽  
Axial Turbines ◽  
The Impact ◽  
Good Agreement

The possibilities of reducing the over tip leakage loss of unshrouded rotors have been investigated using a linear cascade of turbine blades and CFD. The large-scale blade profile is the same as that of the tip profile of a low-speed HP research turbine facility. The impact of various combinations of squealer and winglet geometries on the turbine performance has been investigated. The influence of the thickness of the squealers has also been assessed. It was found that a 22% reduction in loss slope was possible, when compared to the flat tip blade, using simple tip modifications. The results obtained with the suction side squealer and cavity tip agreed well with the work of other researchers. Three winglet-based tip geometries were tested. One was a plain winglet, the other two had squealers applied. A significant impact of the squealers and their shape on the tip gap flow pattern and loss generation was found. The physical processes occurring within the tip gap region for the tested geometries are explained using both numerical and experimental results. The impact of the flow pattern within the tip gap on the loss generation is described. Good agreement between the CFD and the experimental data was found. This shows that the CFD can be used with confidence in the design process of shroudless turbines.

Aerodynamic Investigation of the Tip Leakage Flow for Blades With Different Tip Squealer Geometries at Transonic Conditions

2009 ◽  
Author(s):  
Toma´sˇ Hofer ◽  
Tony Arts
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Suction Side ◽  
Loss Coefficient ◽  
Leakage Flow ◽  
Pressure Side ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Gap Flow ◽  
Tip Gap Flow

Modern high pressure turbines operate at high velocity and high temperature conditions. The gap existing above a turbine rotor blade is responsible for an undesirable tip leakage flow. It is a source of high aerodynamic losses and high heat transfer rates. A better understanding of the tip flow behaviour is needed to provide a more efficient cooling design in this region. The objective of this paper is to investigate the tip leakage flow for a blade with two different squealer tips and film-cooling applied on the pressure side and through tip dust holes in a non-rotating, linear cascade arrangement. The experiments were performed in the VKI Light Piston Compression Tube facility, CT-2. The tip gap flow was investigated by oil flow visualisations and by wall static and total pressure measurements. Two geometries were tested — a full squealer and a partial suction side squealer. The measurements were performed in the blade tip region, including the squealer rim and on the corresponding end-wall for engine representative values of outlet Reynolds and Mach numbers. The main flow structures in the cavity were put in evidence. Positive influence of the coolant on the tip gap flow and on the aerodynamic losses was found for the full squealer tip case: increasing the coolant mass-flow increased the tip gap flow resistance. The flow through the clearance therefore slows down, the tip gap mass-flow and the heat transfer respectively decreases. No such effect of cooling was found in the case of the partial suction side squealer geometry. The absence of a pressure side squealer rim resulted in a totally different tip gap flow topology, indifferent to cooling. The influence of cooling on the overall mass-weighted thermodynamic loss coefficient, which takes into account the different energies of the mainstream and coolant flows was found marginal for both geometries. Finally the overall loss coefficient was found to be higher for the partial suction side squealer tip than for the full squealer tip.

scholarly journals Measurements of the Flow Field Within a Compressor Outlet Guide Vane Passage

1993 ◽  
Author(s):  
J. F. Carrotte ◽  
K. F. Young ◽  
S. J. Stevens
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Guide Vane ◽  
Pressure Probe ◽  
Streamwise Vorticity ◽  
Measured Velocity ◽  
Tip Leakage ◽  
Blade Row ◽  
Flow Features ◽  
Novel Design

A series of tests have been carried out to investigate the flow in a Compressor Outlet Guide Vane (OGV) blade row downstream of a single stage rotor. The subsequent flow field that developed within an OGV passage was measured, at intervals of 10% axial chord, using a novel design of miniature 5 hole pressure probe. In addition to indicating overall pressure levels and the growth of regions containing low energy fluid, secondary flow features were identified from calculated axial vorticity contours and flow vectors. Close to each casing the development of classical secondary flow was observed, but towards the centre of the annulus large well defined regions of opposite rotation were measured. These latter flows were due to the streamwise vorticity at inlet to the blade row associated with the skewed inlet profile. Surface static pressures were also measured and used to obtain the blade pressure force at 3 spanwise locations. These values were compared with the local changes in flow momentum calculated from the measured velocity distributions. With the exception of the flow close to the outer casing, which is affected by rotor tip leakage, good agreement was found between these quantities indicating relatively weak radial mixing.

Experimental Study of Tip Clearance Effects Under Transonic Flow Conditions

1996 ◽  
Author(s):  
M. Wehner ◽  
A. Bölcs ◽  
J. Bütikofer
Keyword(s):  
Test Section ◽  
Static Pressure ◽  
Suction Side ◽  
Tip Clearance ◽  
Tip Vortex ◽  
Blade Loading ◽  
Gap Flow ◽  
Inlet Conditions ◽  
Axial Turbines ◽  
Tip Gap Flow

An idealized 3 blade test section has been used to study tip clearance effects which occur in transonic axial turbines. At subsonic inlet conditions (Mis1 = 0.56) the flow leaves the test section supersonic (Mis2 = 1.26). The tip clearance was varied from 0 to 15% of the chord length. Extensive laser-2-focus anemometry was used to determine the tip gap mass flow based on the velocity vectors for gaps with 6, 10 and 15% chord. At small clearances the tip gap flow is mainly influenced by the pressure drop between pressure and suction side, while for larger gaps the main flow field dominates the tip gap flow. The variation of the blade loading with the tip clearance was measured by static pressure tappings at 50% and 90% Span. Furthermore the static pressure along the tip surface was measured for varying tip clearances. Pitot probe traverses in the tip vortex region at different downstream positions revealed the vortex structures and vortex core evolution. For tip gaps of 3 and 6%, multiple vortices were detected which were not fully mixed downstream. The origin of these vortices moves towards the trailing edge for larger gaps.

Measurements of the Flow Field Within a Compressor Outlet Guide Vane Passage

1995 ◽  
Vol 117 (1) ◽  
pp. 29-37 ◽  
Author(s):  
J. F. Carrotte ◽  
K. F. Young ◽  
S. J. Stevens
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Guide Vane ◽  
Pressure Probe ◽  
Streamwise Vorticity ◽  
Measured Velocity ◽  
Tip Leakage ◽  
Blade Row ◽  
Flow Features ◽  
Novel Design

A series of tests have been carried out to investigate the flow in a Compressor Outlet Guide Vane (OGV) blade row downstream of a single-stage rotor. The subsequent flow field that developed within an OGV passage was measured, at intervals of 10 percent axial chord, using a novel design of miniature five-hole pressure probe. In addition to indicating overall pressure levels and the growth of regions containing low-energy fluid, secondary flow features were identified from calculated axial vorticity contours and flow vectors. Close to each casing the development of classical secondary flow was observed, but toward the center of the annulus large well-defined regions of opposite rotation were measured. These latter flows were due to the streamwise vorticity at inlet to the blade row associated with the skewed inlet profile. Surface static pressures were also measured and used to obtain the blade pressure force at three spanwise locations. These values were compared with the local changes in flow momentum calculated from the measured velocity distributions. With the exception of the flow close to the outer casing, which is affected by rotor tip leakage, good agreement was found between these quantities indicating relatively weak radial mixing.

The Physical Mechanism of Tip Leakage Loss Reduction by Means of Passive Injection in Low Mach Number Flows

2018 ◽  
Author(s):  
Maximilian Passmann ◽  
Stefan aus der Wiesche ◽  
Franz Joos ◽  
Reinhard Willinger
Keyword(s):  
Physical Mechanism ◽  
Experimental Tests ◽  
Tip Clearance ◽  
Loss Reduction ◽  
Present Contribution ◽  
Tip Leakage ◽  
Gap Flow ◽  
Novel Method ◽  
Tip Injection ◽  
Tip Gap Flow

Tip clearance losses represent a major source of efficiency losses in turbomachinery. A novel method based on passive injection for reducing tip leakage losses in axial turbine cascades has been proposed in 2007 by Willinger and co-workers, and first experimental demonstrations of the potential of this approach were reported recently. However, these experimental tests were limited to linear cascade experiments w6ith stationary endwalls, and they were not able to explain the underlying physical mechanism of the observed loss reduction. In the present contribution, results of detailed experimental and numerical analyses of the tip gap flow, the interaction of the passive tip injection jet with the gap and the main flow, and the effect of the moving endwall are presented. Both numerical and experimental results indicated that the beneficial effect of the passive injection mainly results from a weaker tip gap vortex and not so much from a simple blockage of the tip gap flow itself.

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