Influence of Blade Leading Edge Geometry on Turbine Endwall Heat (Mass) Transfer

2005 ◽  
Vol 128 (4) ◽  
pp. 798-813 ◽  
Author(s):  
S. Han ◽  
R. J. Goldstein
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Leading Edge ◽  
Local Heat ◽  
Secondary Flows ◽  
Transfer Performance ◽  
Turbine Cascade ◽  
Suction Surface ◽  
Naphthalene Sublimation Technique ◽  
Passage Vortex

The secondary flows, including passage and other vortices in a turbine cascade, cause significant aerodynamic losses and thermal gradients. Leading edge modification of the blade has drawn considerable attention as it has been shown to reduce the secondary flows. However, the heat transfer performance of a leading edge modified blade has not been investigated thoroughly. Since a fillet at the leading edge blade is reported to reduce the aerodynamic loss significantly, the naphthalene sublimation technique with a fillet geometry is used to study local heat (mass) transfer performance in a simulated turbine cascade. The present paper compares Sherwood number distributions on an endwall with a simple blade and a similar blade having a modified leading edge by adding a fillet. With the modified blades, a horseshoe vortex is not observed and the passage vortex is delayed or not observed for different turbulence intensities. However, near the blade trailing edge the passage vortex has gained as much strength as with the simple blade for low turbulence intensity. Near the leading edge on the pressure and the suction surface, higher mass transfer regions are observed with the fillets. Apparently the corner vortices are intensified with the leading edge modified blade.

Influence of Blade Leading Edge Geometry on Turbine Endwall Heat(Mass) Transfer

2005 ◽  
Author(s):  
S. Han ◽  
R. J. Goldstein
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Leading Edge ◽  
Local Heat ◽  
Secondary Flows ◽  
Transfer Performance ◽  
Turbine Cascade ◽  
Suction Surface ◽  
Naphthalene Sublimation Technique ◽  
Passage Vortex

The secondary flows, including passage and other vortices in a turbine cascade cause significant aerodynamic losses and thermal gradients. Leading-edge modification of the blade has drawn considerable attention as it has been shown to reduce the secondary flows. However, the heat transfer performance of a leading-edge modified blade has not been investigated thoroughly. Since a fillet at the leading edge blade is reported to reduce the aerodynamic loss significantly, the naphthalene sublimation technique with a fillet geometry is used to study local heat (mass) transfer performance in a simulated turbine cascade. The present paper compares Sherwood number distributions on an endwall with a simple blade and a similar blade having modified leading-edge by adding a fillet. With the modified blades, a horseshoe vortex is not observed and the passage vortex is delayed or not observed for different turbulence intensities. However, near the blade trailing edge the passage vortex has gained as much strength as with the simple blade for low turbulence intensity. Near the leading edge on the pressure and the suction surface, higher mass transfer regions are observed with the fillets. Apparently the corner vortices are intensified with the leading-edge modified blade.

The Heat/Mass Transfer Analogy for a Simulated Turbine Endwall With Fillets

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
S. Han ◽  
R. J. Goldstein
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Measurement Data ◽  
Leading Edge ◽  
Secondary Flows ◽  
Alternative Methods ◽  
Experimental Conditions ◽  
Transfer Data ◽  
Naphthalene Sublimation Technique

Mass transfer measurements are employed as alternative methods for heat transfer measurement because of the difficulty of heat transfer measurements in thin boundary layers, complicated secondary flows, and large thermal gradients. Even though mass transfer experiments are fast and show detailed local measurement data, the conversion of mass transfer results to heat transfer data requires the heat/mass transfer analogy factors in detail. Therefore, the usefulness of mass transfer data depends on finding a simple analogy factor. The heat/mass transfer analogy on a simulated turbine endwall with fillets is evaluated in the present paper. Since the heat/mass transfer analogy factor may not be always the same, the heat/mass transfer analogy should be verified for other different geometries and experimental conditions. To utilize the heat/mass transfer analogy fully, it is necessary to check that the presence of different aerodynamic conditions caused by the fillets affects the heat/mass transfer analogy on a simulated turbine endwall with fillets. To compare heat transfer data and mass transfer data, heat transfer measurements on the endwall with fillets are conducted with a thermal boundary layer measurement technique and mass transfer measurements employing naphthalene sublimation technique on the endwall with the fillets are extracted from literature with equivalent experimental conditions and a similar geometry. As expected by heat transfer and mass transfer equations, the heat/mass transfer analogy factor is applied and shows a good agreement between heat transfer and mass transfer results on the endwall with the fillets from the leading edge to the trailing edge.

scholarly journals Highly Resolved Distribution of Heat Transfer for Turbine Leading Edge Film Cooling Including Reynolds Number and Blowing Rate Effects

1998 ◽  
Author(s):  
K. Jung ◽  
D. K. Hennecke
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Heat Mass Transfer ◽  
Leading Edge ◽  
Transfer Coefficients ◽  
Complex Flow ◽  
Long Distance ◽  
Naphthalene Sublimation Technique

The effect of leading edge film cooling on heat transfer was experimentally investigated using the naphthalene sublimation technique. The experiments were performed on a symmetrical model of the leading edge suction side region of a high pressure turbine blade with one row of film cooling holes on each side. Two different lateral inclinations of the injection holes were studied: 0° and 45°. In order to build a data base for the validation and improvement of numerical computations, highly resolved distributions of the heat/mass transfer coefficients were measured. Reynolds numbers (based on hole diameter) were varied from 4000 to 8000 and blowing rate from 0.0 to 1.5. For better interpretation, the results were compared with injection-flow visualizations. Increasing the blowing rate causes more interaction between the jets and the mainstream, which creates higher jet turbulence at the exit of the holes resulting in a higher relative heat transfer. This increase remains constant over quite a long distance dependent on the Reynolds number. Increasing the Reynolds number keeps the jets closer to the wall resulting in higher relative heat transfer. The highly resolved heat/mass transfer distribution shows the influence of the complex flow field in the near hole region on the heat transfer values along the surface.

Film Cooling Effect of Rotor-Stator Purge Flow on Endwall Heat/Mass Transfer

2011 ◽  
Vol 134 (4) ◽  
Author(s):  
M. Papa ◽  
V. Srinivasan ◽  
R. J. Goldstein
Keyword(s):  
Mass Transfer ◽  
Leading Edge ◽  
Recirculation Region ◽  
Pressure Side ◽  
Blade Profile ◽  
Suction Surface ◽  
Cooling Effectiveness ◽  
Blowing Ratio ◽  
Passage Vortex ◽  
Purge Flow

Mass transfer measurements on the endwall and blade suction surfaces are performed in a five-blade linear cascade with a high-performance rotor blade profile. The effects of purge flow from the wheelspace cavity entering the hot gas path are simulated by injecting naphthalene-free and naphthalene-saturated air through a slot upstream of the blade row at 45 deg to the endwall, for a Reynolds number of 6×105 based on blade true chord and cascade exit velocity, and blowing ratios of 0.5, 1, and 1.5. Oil-dot visualization indicates that with injection, a recirculation region is set up upstream of the leading edge, and the growth of the passage vortex is altered. The coolant exiting from the slot is drawn to the suction side of the blade and is pushed up along the suction surface of the blade by the secondary flow. For blowing ratios of 0.5 and 1.0, only a little coolant reaches the pressure side in the aft part of the passage. However, at a blowing ratio of 1.5, there is a dramatic change in the flow structure. Both the oil-dot visualization and the cooling effectiveness maps indicate that at this blowing ratio, the coolant exiting the slot has sufficient momentum to closely follow the blade profile and is not significantly entrained into the passage vortex. As a result, high cooling effectiveness values are obtained at the pressure side of the endwall, well into the midchord and aft portions of the blade passage.

Effect of Inlet Skew on Heat/Mass Transfer From a Simulated Turbine Blade

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Kalyanjit Ghosh ◽  
R. J. Goldstein
Keyword(s):  
Mass Transfer ◽  
Turbine Blade ◽  
Sherwood Number ◽  
Heat Mass Transfer ◽  
Velocity Ratio ◽  
Transition To Turbulence ◽  
Suction Surface ◽  
Freestream Velocity ◽  
Pressure Surface ◽  
Passage Vortex

Heat (mass) transfer experiments are conducted to study the effect of an inlet skew on a simulated gas-turbine blade placed in a linear cascade. The inlet skew simulates the relative motion between rotor and stator endwalls in a single turbine stage. The transverse motion of a belt, placed parallel to and upstream of the turbine cascade, generates the inlet skew. With the freestream velocity constant at approximately 16 m/s, which results in a Reynolds number (based on the blade chord length of 0.184 m) of 1.8 × 105, a parametric study was conducted for three belt-to-freestream velocity ratios. The distribution of the Sherwood number on the suction surface of the blade shows that the inlet skew intensifies the generation of the horseshoe vortex close to the endwall region. This is associated with the development of a stronger passage vortex for a higher velocity ratio, which causes an earlier transition to turbulence. Corresponding higher mass transfer coefficients are measured between the midheight of the blade and the endwall, at a midchord downstream location. However, a negligible variation in transport properties is measured above the two-dimensional region of the blade at the higher velocity ratios. In contrast, the inlet skew has a negligible effect on the distribution of the Sherwood number on the entire pressure surface of the blade. This is mainly because the skew is directed along the passage vortex, which is from the pressure surface of the airfoil to the suction surface of the adjacent airfoil.

Effect of Wake-Disturbed Flow on Heat (Mass) Transfer to a Turbine Blade

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
S. Olson ◽  
S. Sanitjai ◽  
K. Ghosh ◽  
R. J. Goldstein
Keyword(s):  
Mass Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Heat Mass Transfer ◽  
Turbine Blades ◽  
Freestream Turbulence ◽  
Suction Surface ◽  
Disturbed Flow ◽  
Linear Cascade ◽  
Naphthalene Sublimation Technique

This study investigates the effect of wakes in the presence of varying levels of background freestream turbulence on the heat (mass) transfer from gas turbine blades. Measurements using the naphthalene sublimation technique provide local values of the mass transfer coefficient on the pressure and suction surfaces of a simulated turbine blade in a linear cascade. Experimental parameters studied include the pitch of the wake-generating blades (vanes), blade-row separation, Reynolds number, and the freestream turbulence level. The disturbed flow strongly affects the mass transfer Stanton number on both sides of the blade, particularly along the suction surface. An earlier transition to a turbulent boundary layer occurs with increased background turbulence, higher Reynolds number, and from wakes shed from vanes placed upstream of the linear cascade. Note that once the effects on mass transfer are known, similar variation on heat transfer can be inferred from the heat/mass transfer analogy.

Film Cooling Effect of Rotor-Stator Purge Flow on Endwall Heat/Mass Transfer

2010 ◽  
Author(s):  
M. Papa ◽  
V. Srinivasan ◽  
R. J. Goldstein
Keyword(s):  
Mass Transfer ◽  
Leading Edge ◽  
Recirculation Region ◽  
Pressure Side ◽  
Blade Profile ◽  
Suction Surface ◽  
Cooling Effectiveness ◽  
Blowing Ratio ◽  
Passage Vortex ◽  
Purge Flow

Mass transfer measurements on the endwall and blade suction surfaces are performed in a five-blade linear cascade with a high-performance rotor blade profile. The effects of purge flow from the wheelspace cavity entering the hot gas path are simulated by injecting air through a slot upstream of the blade row at 45° to the endwall, for Reynolds number of 6×105 based on blade true chord and cascade exit velocity, and blowing ratios of 0.5, 1 and 1.5. Detailed maps of cooling effectiveness on the passage endwall and blade suction surface are generated for the cases of injection of naphthalene-free and naphthalene-saturated air. Oil-dot visualization indicates that with injection, a recirculation region is set up upstream of the leading edge, and the growth of the passage vortex is altered. The coolant exiting from the slot is drawn to the suction side of the blade and is pushed up along the suction surface of the blade by the secondary flow. For blowing ratios of 0.5 and 1.0, only a little coolant reaches the pressure side in the aft part of the passage. However, at a blowing ratio of 1.5, there is a dramatic change in the flow structure. Both the oil dot visualization and the cooling effectiveness maps indicate that at this blowing ratio, the coolant exiting the slot has sufficient momentum to closely follow the blade profile, and is not significantly entrained into the passage vortex. As a result, high cooling effectiveness values are obtained at the pressure side of the endwall, well into the mid-chord and aft portions of the blade passage.

Darryl E. Metzger Memorial Session Paper: The Influence of Secondary Flows Near the Endwall and Boundary Layer Disturbance on Convective Transport From a Turbine Blade

1995 ◽  
Vol 117 (4) ◽  
pp. 657-665 ◽  
Author(s):  
R. J. Goldstein ◽  
H. P. Wang ◽  
M. Y. Jabbari
Keyword(s):  
Mass Transfer ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Leading Edge ◽  
Flow Region ◽  
Suction Side ◽  
Convective Transport ◽  
Pressure Side ◽  
Suction Surface ◽  
Passage Vortex

A naphthalene sublimation technique is used to investigate convective transport from a simulated turbine blade in a stationary linear cascade. In some of the tests undertaken, a trip wire is stretched along the span of the blade near the leading edge. The disturbance produced by tripping the boundary layers on the blade near the leading edge causes early boundary layer transition, creates high mass transfer rate on the pressure side and in the laminar flow region on the suction side, but lowers the transfer rate in the turbulent flow region on the suction side. Comparison is made with other heat and mass transfer studies in the two-dimensional region far from the endwall and good agreement is found. Near the endwall, flow visualization indicates a strong secondary flow pattern. The impact of vortices initiated near the endwall on the laminar–turbulent transition extends three-dimensional effects to about 0.8 chord lengths on the suction side and to about 0.2 chord lengths on the pressure side away from the endwall. The effect of the passage vortex and the new vortex induced by the passage vortex on mass transfer is clearly seen and can be traced along the suction surface of the blade. Close to the endwall the highest mass transfer rate on the suction surface is not found near the leading edge. It occurs at about 27 percent of the curvilinear distance from the stagnation line to the trailing edge where a strong main flow and the secondary passage flow from the pressure side of the adjacent blade interact. The influences of some small but very intense corner vortices and the passage vortex on mass transfer are also observed on both surfaces of the blade.

Effect of Rib Angle on Local Heat/Mass Transfer Distribution in a Two-Pass Rib-Roughened Channel

1988 ◽  
Vol 110 (2) ◽  
pp. 233-241 ◽  
Author(s):  
P. R. Chandra ◽  
J. C. Han ◽  
S. C. Lau
Keyword(s):  
Mass Transfer ◽  
Sherwood Number ◽  
Heat Mass Transfer ◽  
Local Heat ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
Test Channel ◽  
Mass Transfer Coefficients ◽  
Square Duct ◽  
Naphthalene Sublimation Technique

The heat transfer characteristics of turbulent air flow in a two-pass channel were studied via the naphthalene sublimation technique. The test section, which consisted of two straight, square channels joined by a sharp 180 deg turn, resembled the internal cooling passages of gas turbine airfoils. The top and bottom surfaces of the test channel were roughened by rib turbulators. The rib height-to-hydraulic diameter ratio (e/D) was 0.063 and the rib pitch-to-height ratio (P/e) was 10. The local heat/mass transfer coefficients on the roughened top wall, and on the smooth divider and side walls of the test channel, were determined for three Reynolds numbers of 15,000, 30,000, and 60,000, and for three angles of attack (α) of 90, 60, and 45 deg. The results showed that the local Sherwood numbers on the ribbed walls were 1.5 to 6.5 times those for a fully developed flow in a smooth square duct. The average ribbed-wall Sherwood numbers were 2.5 to 3.5 times higher than the fully developed values, depending on the rib angle-of-attack and the Reynolds number. The results also indicated that, before the turn, the heat/mass transfer coefficients in the cases of α = 60 and 45 deg were higher than those in the case of α = 90 deg. However, after the turn, the heat/mass transfer coefficients in the oblique-rib cases were lower than those in the traverse-rib case. Correlations for the average Sherwood number ratios for individual channel surfaces and for the overall Sherwood number ratios are reported.

scholarly journals The Influence of Secondary Flows Near the Endwall and Boundary Layer Disturbance on Convective Transport From a Turbine Blade

1994 ◽  
Author(s):  
R. J. Goldstein ◽  
H. P. Wang ◽  
M. Y. Jabbari
Keyword(s):  
Mass Transfer ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Leading Edge ◽  
Flow Region ◽  
Suction Side ◽  
Convective Transport ◽  
Pressure Side ◽  
Suction Surface ◽  
Passage Vortex

A naphthalene sublimation technique is used to investigate convective transport from a simulated turbine blade in a stationary linear cascade. In some of the tests undertaken a trip wire is stretched along the span of the blade near the leading edge. The disturbance produced by tripping the boundary layers on the blade near the leading edge causes early boundary layer transition, creates high mass transfer rate on the pressure side and in the laminar flow region on the suction side, but lowers the transfer rate in the turbulent flow region on the suction side. Comparison is made with other heat and mass transfer studies in the two dimensional region far from the endwall and good agreement is found. Near the endwall, flow visualization indicates a strong secondary flow pattern. The impact of vortices initiated near the endwall on the laminar-turbulent transition extends three dimensional effects to about 0.8 chord lengths on the suction side and to about 0.2 chord lengths on the pressure side away from the endwall. The effect of the passage vortex and the new vortex induced by the passage vortex on mass transfer is clearly seen and can be traced along the suction surface of the blade. Close to the endwall the highest mass transfer rate on the suction surface is not found near the leading edge. It occurs at about 27% of the curvilinear distance from the stagnation line to the trailing edge where a strong main flow and the secondary passage flow from the pressure side of the adjacent blade interact. The influences of some small but very intense corner vortices and the passage vortex on mass transfer are also observed on both surfaces of the blade.

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