A Flow Visualization Study of Axial Turbine Tip Desensitization by Coolant Injection From a Tip Trench

2004 ◽  
Author(s):  
Nikhil M. Rao ◽  
Cengiz Camci
Keyword(s):  
Flow Visualization ◽  
Flow Patterns ◽  
Surface Flow ◽  
Leakage Flow ◽  
Pressure Side ◽  
Suction Surface ◽  
Blade Height ◽  
Side Edge ◽  
Coolant Injection ◽  
Gap Height

The effect of coolant injection from a tip trench was investigated in a large-scale rotating turbine rig. Coolant is injected into the tip gap from discrete injection holes, located in a tip trench and directed towards the pressure-side. Surface flow patterns are visualized by a mixture of oil and paint. The mixture is applied on the blade pressure-side and allowed to seep onto the tip platform. Injection rates of 0.4%, 0.5%, 0.6%, and 0.7%, at a gap height of 1.40% blade height were investigated. Flow patterns for a gap height of 0.72% blade height are compared to the larger clearance gap. The flow visualization technique successfully identifies flow features like pressure-side edge separation, and reattachment and recirculation on the tip surface. The location of the reattachment line from the pressure-side edge varies little along the length of the blade and occurs at about two gap heights from the pressure-side edge. At the large gap height the tip gap flow is fully separated over the last 5% of the blade axial chord. Surface oil flow lines are directed almost normal to the camberline along most of the tip surface. Flow patterns with injection indicate that the ejected coolant effectively blocks the leakage flow. The coolant jets are turned towards the blade suction-side and appear to form a film on the tip surface. Some of the visualization material is carried by the leakage flow into the passage and is deposited on the blade suction surface, thereby giving an indication of the inception and growth of the leakage vortex. Suction surface patterns with injection indicate that leakage flow may be entering the adjacent passage at multiple locations.

Heat Transfer and Aerodynamics of Turbine Blade Tips in a Linear Cascade

2004 ◽  
Vol 128 (2) ◽  
pp. 300-309 ◽  
Author(s):  
P. J. Newton ◽  
G. D. Lock ◽  
S. K. Krishnababu ◽  
H. P. Hodson ◽  
W. N. Dawes ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Flow Visualization ◽  
Turbine Blade ◽  
Pressure Coefficient ◽  
Suction Side ◽  
Tip Clearance ◽  
Pressure Side ◽  
Linear Cascade ◽  
Side Edge ◽  
High Heat Transfer

Local measurements of the heat transfer coefficient and pressure coefficient were conducted on the tip and near tip region of a generic turbine blade in a five-blade linear cascade. Two tip clearance gaps were used: 1.6% and 2.8% chord. Data was obtained at a Reynolds number of 2.3×105 based on exit velocity and chord. Three different tip geometries were investigated: A flat (plain) tip, a suction-side squealer, and a cavity squealer. The experiments reveal that the flow through the plain gap is dominated by flow separation at the pressure-side edge and that the highest levels of heat transfer are located where the flow reattaches on the tip surface. High heat transfer is also measured at locations where the tip-leakage vortex has impinged onto the suction surface of the aerofoil. The experiments are supported by flow visualization computed using the CFX CFD code which has provided insight into the fluid dynamics within the gap. The suction-side and cavity squealers are shown to reduce the heat transfer in the gap but high levels of heat transfer are associated with locations of impingement, identified using the flow visualization and aerodynamic data. Film cooling is introduced on the plain tip at locations near the pressure-side edge within the separated region and a net heat flux reduction analysis is used to quantify the performance of the successful cooling design.

Wake–Boundary Layer Interactions in an Axial Flow Turbine Rotor at Off-Design Conditions

1989 ◽  
Vol 111 (2) ◽  
pp. 181-192 ◽  
Author(s):  
H. P. Hodson ◽  
J. S. Addison
Keyword(s):  
Rotor Blade ◽  
Axial Flow ◽  
Leading Edge ◽  
Surface Flow ◽  
Design Flow ◽  
Flow Coefficient ◽  
Experimental Investigations ◽  
Pressure Side ◽  
Suction Surface ◽  
Edge Separation

A series of experimental investigations has been undertaken in a single-stage low-speed turbine. The measurements involved rotor blade surface flow visualization, surface-mounted hot-film anemometry, and exit pitot traverses. The effects of varying the flow coefficient and Reynolds number upon the performance of the rotor blade at midspan are described. At the design flow coefficient (φ = 0.495), the rotor pressure surface flow may be regarded as laminar, while on the suction surface, laminar flow gives way to unsteady stator wake-induced transition and then to turbulent flow. Over the range of Reynolds numbers investigated (1.8×105–3.3×105), the rotor midspan performance is dominated by the suction surface transition process; suction surface separation is prevented and the rotor midspan loss coefficient remains approximately constant throughout the range. At positive incidence, suction surface leading edge separation and transition are caused by a velocity overspeed. Reattachment occurs as the flow begins to accelerate toward the throat. The loss associated with the separation becomes significant with increasing incidence. At negative incidence, a velocity overspeed causes leading edge separation of the pressure side boundary layers. Reattachment generally occurs without full transition. The suction surface flow is virtually unaffected. Therefore, the rotor midspan profile loss remains unchanged from the zero incidence value until pressure side stall occurs.

Assessment of the Flow Quality of a Transonic Turbine Cascade

2009 ◽  
Author(s):  
R. Woodason ◽  
A. Asghar ◽  
W. D. E. Allan
Keyword(s):  
Flow Visualization ◽  
Surface Flow ◽  
Turbine Cascade ◽  
Suction Surface ◽  
Flow Quality ◽  
Transonic Turbine ◽  
Turboshaft Engine ◽  
Nozzle Guide ◽  
Nozzle Guide Vanes ◽  
Surface Flow Visualization

The assessment of flow quality through a newly constructed transonic turbine cascade is presented. Although the main objective of this research was to investigate the effect of the modification of a vane profile due to repair on pressure loss, only the results for checking the flow periodicity, two-dimensionality of the flow and transonic exit flow condition are described in this paper. The cascade blades were constructed using the profiles of nozzle guide vanes of a low pressure turbine of an in-service turboshaft engine. The assessment of the flow quality in the cascade was carried out using three methods: wall static pressure measurements at the inlet and exit of each flow passage of the cascade to check the flow periodicity, surface flow visualization using blackened paraffin oil to check the two dimensionality of the flow and thirdly, Schlieren flow visualization to verify the periodicity and transonic flow conditions at the exit of the cascade. The cascade inlet and exit wall pressure showed that the flow was nominally periodic in the cascade. The surface flow visualization of the suction surface showed that the flow was two-dimensional on approximately 70% of the central span and also indicated flow separations on the suction surface. The Schlieren flow visualization confirmed the flow periodicity and revealed the existence of shock waves on the suction surface and near the trailing edge of the blades.

Numerical Investigations on Application of Cantilever Stator on Aerodynamic Performance of Tandem Bladed Axial-Flow Compressor

2021 ◽  
Author(s):  
Bhanu Pratap Singh Tanwar ◽  
Ajey Singh ◽  
Chetan S. Mistry
Keyword(s):  
Secondary Flow ◽  
Operating Conditions ◽  
Design Flow ◽  
Leakage Flow ◽  
Pressure Side ◽  
Tip Leakage Flow ◽  
Suction Surface ◽  
Flow Angle ◽  
Bladed Rotor ◽  
End Wall

Abstract Adoption of a tandem bladed rotor configuration brings special flow features at the exit compared to the conventional rotor. For tandem bladed rotor, there is the presence of strong dual-tip leakage flow, atypical exit flow angle distributions, corner blade separations leading to thicker dual wakes at the exit of the rotor to name a few. This makes the aerodynamic design of downstream stator more challenging in terms of overall performance as well as operational stability. The modern compressor requisite of being lighter and cost-efficient needs to be taken care of both aerodynamic and mechanical requirements. To overcome all these challenges, the cantilever type stator (without hub rotation) has been chosen and been analyzed for the present study. The effects of different hub gap sizes of the cantilever stator in combination with the tandem bladed axial compressor stage are investigated in order to explore passive flow control mechanism near the hub. The goal of the work is to get further insights into the aerodynamic aspects of flow using a detailed flow field analysis. The numerical study was performed using ANSYS TurboGrid® for mesh generation and the commercial package ANSYS CFX® 18.0 was used as solver for steady-state simulation. Stationary hub boundary conditions have been employed for the stator in all 3 cases [baseline, 1% and 2% (of span) part clearance]. For no clearance case, the regions of momentum deficit were observed in the vicinity of the hub endwall and suction surface of the stator. The region keeps growing along both streamwise and spanwise direction as a low momentum bubble is formed near trailing edge. This low momentum bubble seems to be transported along the span and moved more towards the suction surface. The solution strategy explored to mitigate the effect of hub corner separation by adapting hub clearance. The role played by secondary flow in feeding the low momentum flow along the span is seen to be moderated by the high momentum leakage flow from the pressure side. The hub leakage flow from the blade pressure side reenergized the low momentum fluid on the suction side refraining it to travel along the span and mitigate its effect by suppressing the separation tendency near end wall region. The formation of large size bubble gets reduced in overall size both in the circumferential and span-wise direction. This phenomenon compels the low momentum flow to pass along the low span region. Numerically obtained results provide an insightful mechanism of the interaction of secondary flow structures and the influence of hub clearance flow. Hub corner stall, which is the consequence of low momentum fluid sweeping across the blade passage near the end wall got wiped out in the presence of hub clearance. This phenomenon diminishes the extent and overall effect of the hub corner stall. The interaction of hub leakage vortex and passage vortex leads to mitigation of overall secondary flow adverse effects. As a result, performance improvement at design flow conditions have been elucidated by implementation of cantilever stator. The peak pressure operation is dominated by mid-span flow complexities and as a result cantilevered stator doesn’t show much improvements. Nevertheless, the improvements in design point operating conditions do justify the study for gaining physical insights.

Effects of Winglet Geometry on the Aerodynamic Performance of Tip Leakage Flow in a Turbine Cascade

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Chao Zhou ◽  
Howard Hodson ◽  
Ian Tibbott ◽  
Mark Stokes
Keyword(s):  
Pressure Difference ◽  
Leading Edge ◽  
Suction Side ◽  
Aerodynamic Performance ◽  
Driving Pressure ◽  
Leakage Flow ◽  
Pressure Side ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Side Edge

Experimental and numerical methods were used to investigate the aerodynamic performance of a winglet tip in a linear cascade. A flat tip and a cavity tip were studied as baseline cases. The flow patterns over the three tips were studied. For the cavity tip and the winglet tip, vortices appear in the cavity and the gutter. These vortices reduce the discharge coefficient of the tip leakage flow. The purpose of using a winglet tip is to reduce the driving pressure difference. The pressure side winglet of the winglet geometry studied in this paper has little effect in reducing the driving pressure difference. It is found that the suction side winglet reduces the driving pressure difference of the tip leakage flow near the leading edge, but increases the driving pressure difference from midchord to the trailing edge. This is also used to explain the findings and discrepancies in other studies. Compared with the flat tip, the cavity tip and the winglet tip achieve a reduction of loss. The effects of the rounding of the pressure side edge of the tips were studied to simulate the effects of deterioration. As the size of the pressure side edge radius increases, the tip leakage mass flow rate and the loss increase. The improvement of the aerodynamic performance by using a winglet remains similar when comparing with a flat tip or a cavity tip with the same pressure side radius.

Effects of Winglet Geometry on the Aerodynamic Performance of Tip Leakage FLow in a Turbine Cascade

2012 ◽  
Author(s):  
Chao Zhou ◽  
Howard Hodson ◽  
Ian Tibbott ◽  
Mark Stokes
Keyword(s):  
Pressure Difference ◽  
Leading Edge ◽  
Suction Side ◽  
Aerodynamic Performance ◽  
Driving Pressure ◽  
Leakage Flow ◽  
Pressure Side ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Side Edge

Experimental and numerical methods were used to investigate the aerodynamic performance of a winglet tip in a linear cascade. A flat tip and a cavity tip are studied as baseline cases. The flow patterns over the three tips are studied. The flow separates over the pressure side edge. For the cavity tip and the winglet tip, vortices appear in the cavity. These vortices reduce the discharge coefficient of the tip. The purpose of using a winglet tip is to reduce the driving pressure difference. The pressure side winglet of the winglet geometry studied in this paper has little effect in reducing the driving pressure difference. It is found that the suction side winglet reduces the driving pressure difference of the tip leakage flow near the leading edge, but increases the driving pressure difference from midchord to the trailing edge. This is also used to explain the findings and discrepancies in other studies. Compared with the flat tip, the cavity tip and the winglet tip achieve a reduction of the loss to the size of the tip gap. The effects of the rounding of the pressure side edge of the tips were studied to simulate the effects of deterioration. As the size of the pressure side edge radius increase, the tip leakage mass flow rate and the loss increase. The improvement of the aerodynamic performance by using a winglet remains similar when comparing with a flat tip or a cavity tip with the same pressure side radius.

Measurements of turbulent crossflow separation created by a curved body of revolution

2007 ◽  
Vol 589 ◽  
pp. 353-374 ◽  
Author(s):  
P. A. GREGORY ◽  
P. N. JOUBERT ◽  
M. S. CHONG
Keyword(s):  
Flow Visualization ◽  
Skin Friction ◽  
Cross Sections ◽  
Separated Flow ◽  
Surface Flow ◽  
The Body ◽  
Body Of Revolution ◽  
Outer Flow ◽  
Friction Measurements ◽  
Surface Flow Visualization

Using the method pioneered by Gurzhienko (1934), the crossflow separation produced by a body of revolution in a steady turn is examined using a stationary deformed body placed in a wind tunnel. The body of revolution was deformed about a radius equal to three times the body's length. Surface pressure and skin-friction measurements revealed regions of separated flow occurring over the rear of the model. Extensive surface flow visualization showed the presence of separated flow bounded by a separation and reattachment line. This region of separated flow began just beyond the midpoint of the length of the body, which was consistent with the skin-friction data. Extensive turbulence measurements were performed at four cross-sections through the wake including two stations located beyond the length of the model. These measurements revealed the location of the off-body vortex, the levels of turbulent kinetic energy within the shear layer producing the off-body vorticity and the large values of 〈uw〉 stress within the wake. Velocity spectra measurements taken at several points in the wake show evidence of the inertial sublayer. Finally, surface flow topologies and outer-flow topologies are suggested based on the results of the surface flow visualization.

Surface flow patterns on an ogive-cylinder at incidence

AIAA Journal ◽  
1992 ◽  
Vol 30 (1) ◽  
pp. 272-274 ◽  
Author(s):  
David Degani ◽  
Murray Tobak ◽  
G. G. Zilliac
Keyword(s):  
Flow Patterns ◽  
Surface Flow

Investigation of Leakage Flow and Heat Transfer in a Gas Turbine Blade Tip With Emphasis on the Effect of Rotation

2008 ◽  
Author(s):  
Dianliang Yang ◽  
Xiaobing Yu ◽  
Zhenping Feng
Keyword(s):  
Heat Transfer ◽  
Relative Motion ◽  
Turbulence Models ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Blade Height ◽  
Tip Leakage ◽  
Flow And Heat Transfer ◽  
Blade Rotation ◽  
Blade Tip

In this paper, numerical methods have been applied to the investigation of the effect of rotation on the blade tip leakage flow and heat transfer. Using the first stage rotor blade of GE-E3 engine high pressure turbine, both flat tip and squealer tip have been studied. The tip gap height is 1% of the blade height, and the groove depth of the squealer tip is 2% of the blade height. Heat transfer coefficient on tip surface obtained by using different turbulence models was compared with experimental results. And the grid independence study was carried out by using the Richardson extrapolation method. The effect of the blade rotation was studied in the following cases: 1) blade domain is rotating and shroud is stationary; 2) blade domain is stationary and shroud is rotating; and 3) both blade domain and shroud are stationary. In this approach, the effects of the relative motion of the endwall, the centrifugal force and the Coriolis force can be investigated respectively. By comparing the results of the three cases discussed, the effects of the blade rotation on tip leakage flow and heat transfer are revealed. It indicated that the main effect of the rotation on the tip leakage flow and heat transfer is resulted from the relative motion of the shroud, especially for the squealer tip blade.

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