Adiabatic Effectiveness and Thermal Field Measurements of a Shaped Hole in the Showerhead of a Model Turbine Blade

2021 ◽  
Author(s):  
Jacob Moore ◽  
Matthew Horner ◽  
David Bogard
Keyword(s):  
Turbine Blade ◽  
Thermal Field ◽  
Field Measurements ◽  
Shaped Hole ◽  
Adiabatic Effectiveness

ADIABATIC EFFECTIVENESS AND THERMAL FIELD MEASUREMENTS OF A SHAPED HOLE IN THE SHOWERHEAD OF A MODEL TURBINE BLADE

2021 ◽  
pp. 1-37
Author(s):  
Jacob D. Moore ◽  
Matthew Horner ◽  
David G. Bogard
Keyword(s):  
Turbine Blade ◽  
Thermal Field ◽  
Leading Edge ◽  
Field Measurements ◽  
Injection Rate ◽  
Edge Region ◽  
Test Environment ◽  
Coolant Injection ◽  
Shaped Hole ◽  
Adiabatic Effectiveness

Abstract Few published studies incorporating shaped hole designs in the leading-edge region, or showerhead, of turbine airfoils have been performed; but among them is the indication that shaped holes may offer an improvement in coolant performance compared to cylindrical holes. A shaped hole was designed with the goal of high performance in the showerhead. The performance and physical behavior of this shaped hole design was studied in comparison to a traditional cylindrical hole design in a series of experiments. The geometries were built into the leading edge of a scaled-up turbine blade model for testing in a low-speed simulated linear cascade. To accomplish an engine-representative test environment, a nominally 5% approach turbulence level was used for this study. Adiabatic effectiveness as a function of coolant injection rate was measured for the two designs using infrared thermography. In addition, off-the-wall thermal field measurements were performed for each hole geometry in the leading-edge region. It was found that the shaped hole offered ~20-100% higher performance in terms of adiabatic effectiveness depending on the coolant injection rate. The thermal field measurements suggested that this was due to the better attachment of the jets exiting the shaped holes, the momenta of which were effectively reduced by the diffusers.

Adiabatic Effectiveness and Thermal Field Measurements of a Shaped Hole in the Showerhead of a Model Turbine Blade

2020 ◽  
Author(s):  
Jacob D. Moore ◽  
Matthew J. Horner ◽  
David G. Bogard
Keyword(s):  
Turbine Blade ◽  
Thermal Field ◽  
Leading Edge ◽  
Field Measurements ◽  
Injection Rate ◽  
Edge Region ◽  
Test Environment ◽  
Coolant Injection ◽  
Shaped Hole ◽  
Adiabatic Effectiveness

Abstract Few published studies incorporating shaped hole designs in the leading-edge region, or showerhead, of turbine airfoils have been performed; but among them is the indication that shaped holes may offer an improvement in coolant performance compared to cylindrical holes. A shaped hole was designed with the goal of high performance in the showerhead. The performance and physical behavior of this shaped hole design was studied in comparison to a traditional cylindrical hole design in a series of experiments. The geometries were built into the leading edge of a scaled-up turbine blade model for testing in a low-speed simulated linear cascade. To accomplish an engine-representative test environment, a nominally 5% approach turbulence level was used for this study. Adiabatic effectiveness as a function of coolant injection rate was measured for the two designs using infrared thermography. In addition, off-the-wall thermal field measurements were performed for each hole geometry in the leading-edge region. It was found that the shaped hole offered ∼20–100% higher performance in terms of adiabatic effectiveness depending on the coolant injection rate. The thermal field measurements suggested that this was due to the better attachment of the jets exiting the shaped holes, the momenta of which were effectively reduced by the diffusers.

scholarly journals Effects of Hole Shape on Film Cooling With Large Angle Injection

1999 ◽  
Author(s):  
Atui Kohil ◽  
David G. Bogard
Keyword(s):  
Velocity Field ◽  
Film Cooling ◽  
Field Measurements ◽  
Round Hole ◽  
Cooling Performance ◽  
Injection Angle ◽  
Hole Shape ◽  
Shaped Hole ◽  
Adiabatic Effectiveness ◽  
Better Than

In this study the film cooling performance of a single row of discrete holes inclined at an injection angle of 55° is investigated at a density ratio of DR = 1.6. Three different hole geometries were used in this study, a round hole and two shaped holes. One shaped hole had forward and lateral expansions of 15°, and the other a 15° lateral with a 25° forward expansion. For reference, a round hole with an injection angle of 35° was also tested. The film cooling performance of each hole shape was evaluated using adiabatic effectiveness, thermal field, and velocity field measurements. The shaped holes showed higher spatially averaged adiabatic effectiveness than the round hole over the whole range of momentum flux ratios (I) investigated. The effectiveness values for the shaped holes were only marginally better than the round hole at the low I, but at the high I, the shaped holes performed much better than the round hole. The temperature and velocity field measurements near the hole exit suggest that there is a slight detachment of the jet from the wall for the round hole, while the jets remain attached for the two shaped holes. The shaped hole with the larger forward expansion had a warmer jet with a higher trajectory at the hole exit suggesting ingestion of mainstream fluid and flow separation within the hole.

Effects on Film Cooling Performance in the Showerhead From Geometric Parameterization of Shaped Hole Designs

2021 ◽  
Author(s):  
Jacob D. Moore ◽  
Christopher C. Easterby ◽  
David G. Bogard
Keyword(s):  
Film Cooling ◽  
Thermal Protection ◽  
Leading Edge ◽  
Field Measurements ◽  
High Heat ◽  
Area Ratio ◽  
Cooling Performance ◽  
Shaped Hole ◽  
Adiabatic Effectiveness ◽  
Marginal Improvement

Abstract The high heat loads at the leading-edge regions of turbine vanes and blades necessitate the most robust thermal protection, typically accomplished via a dense array of film cooling holes, nicknamed the “showerhead.” Although research has shown that film cooling using shaped holes provides more reliable thermal protection than that using cylindrical holes, the effects on cooling performance from varying the geometric details of the shaped hole design are not well characterized. In this study, adiabatic effectiveness and off-the-wall thermal field measurements were conducted for two shaped hole geometries designed as successors to a baseline hole geometry presented in a previous study. One geometry with a 40% increase in area ratio exhibited only a marginal improvement in adiabatic effectiveness (∼10%). A second design with a 12° forward and lateral expansion angle with a breakout area 40% larger performed marginally worse than its matched area ratio counterpart (∼15% lower), suggesting a negative sensitivity to breakout area. Such changes in performance for different shaped hole designs were small compared to the boost in performance gained by switching from a cylindrical hole to a shaped hole, which suggests cooling performance is insensitive to specific shaped hole details provided the exterior coolant flow is well-attached.

Thermal Field Measurements for a Shaped Hole at Low and High Freestream Turbulence Intensity

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Robert P. Schroeder ◽  
Karen A. Thole
Keyword(s):  
Turbulence Intensity ◽  
Gas Turbines ◽  
Thermal Field ◽  
Vertical Direction ◽  
Field Measurements ◽  
Superior Performance ◽  
Turbulent Shear ◽  
Freestream Turbulence ◽  
Thermal Fields ◽  
Shaped Hole

Shaped holes are increasingly selected for airfoil cooling in gas turbines due to their superior performance over that of cylindrical holes, especially at high blowing ratios. The performance of shaped holes is regarded to be the result of the diffused outlet, which slows and laterally spreads coolant, causing coolant to remain close to the wall. However, few thermal field measurements exist to verify this behavior at high blowing ratio or to evaluate how high freestream turbulence alters the coolant distribution in jets from shaped holes. The present study reports measured thermal fields, along with measured flowfields, for a shaped hole at blowing ratios up to three at both low and high freestream turbulence intensities of 0.5% and 13.2%. Thermal fields at low freestream turbulence intensity showed that the coolant jet was initially attached, but far downstream of the hole the jet lifted away from the surface due to the counter-rotating vortex pair. Elevated freestream turbulence intensity was found to cause strong dilution of the coolant jet and also increased dispersion, almost exclusively in the lateral as opposed to the vertical direction. Dominance of lateral dispersion was due to the influence of the wall on freestream eddies, as indicated from changes in turbulent shear stress between the low and high freestream turbulence cases.

Measurements in Film Cooling With Lateral Injection: Adiabatic Effectiveness Values and Temperature Fields

2000 ◽  
Author(s):  
Rohit A. Oke ◽  
Terrence W. Simon
Keyword(s):  
Film Cooling ◽  
Thermal Field ◽  
Additional Data ◽  
Field Measurements ◽  
Diameter Ratio ◽  
Temperature Fields ◽  
Near Surface ◽  
Blowing Ratio ◽  
Adiabatic Effectiveness ◽  
Lift Off

Temperature fields were taken in a film cooling lateral injection configuration with pitch-to-hole-diameter of 3.0. These measurements were done with a traversing thermocouple. Momentum flux ratios of 0.25, 1.0 and 2.25 were used. Results are presented as fields of dimensionless temperatures, given by θ=Tprobe-T∞Tc-T∞. Near-surface values of this quantity over an unheated surface are adiabatic effectiveness values. Streamwise evolutions of these temperature fields are documented. It is seen how with higher blowing ratio the film cooling jets tend to lift off the surface. Comparisons are made to previous data and computational results. It is verified that lateral injection yields a more uniform distribution of effectiveness immediately downstream of injection. It is shown also how interaction of adjacent film cooling jets leads to such improved uniformity. This interaction depends on the pitch to diameter ratio, P/D. In order to study the effect of this parameter, additional data with P/D = 6.0 are presented. The present thermal field data complement previous velocity field measurements taken in the same flow.

Effect of In-Hole Roughness on Film Cooling From a Shaped Hole

2016 ◽  
Author(s):  
Robert P. Schroeder ◽  
Karen A. Thole
Keyword(s):  
Film Cooling ◽  
Thermal Field ◽  
Core Flow ◽  
Blowing Ratio ◽  
Cooling Hole ◽  
Flow Through ◽  
Shaped Hole ◽  
Adiabatic Effectiveness ◽  
Cool Gas ◽  
Interior Walls

While much is known about how macro-geometry of shaped holes affects their ability to successfully cool gas turbine components, little is known about the influence of surface roughness on cooling hole interior walls. For this study a baseline shaped hole was tested with various configurations of in-hole roughness. Adiabatic effectiveness measurements at blowing ratios up to three showed that in-hole roughness caused decreased adiabatic effectiveness relative to smooth holes. Decreases in area-averaged effectiveness grew more severe with larger roughness size and with higher blowing ratios for a given roughness. Decreases of more than 60% were measured at a blowing ratio of three for the largest roughness values. Thermal field and flowfield measurements showed that in-hole roughness caused increased velocity of core flow through the hole, which increased the jet penetration height and turbulence intensity resulting in increased mixing between coolant and the mainstream. Effectiveness reductions due to roughness were also observed when roughness was isolated to only the diffused outlet of holes, and when the mainstream was highly turbulent.

Thermal Field Measurements for a Shaped Hole at Low and High Freestream Turbulence Intensity

2016 ◽  
Author(s):  
Robert P. Schroeder ◽  
Karen A. Thole
Keyword(s):  
Turbulence Intensity ◽  
Gas Turbines ◽  
Thermal Field ◽  
Vertical Direction ◽  
Field Measurements ◽  
Superior Performance ◽  
Turbulent Shear ◽  
Freestream Turbulence ◽  
Thermal Fields ◽  
Shaped Hole

Shaped holes are increasingly selected for airfoil cooling in gas turbines due to their superior performance over that of cylindrical holes, especially at high blowing ratios. The performance of shaped holes is regarded to be result of the diffused outlet which slows and laterally-spreads coolant, causing coolant to remain close to the wall. However, few thermal field measurements exist to verify this behavior at high blowing ratio or to evaluate how high freestream turbulence alters the coolant distribution in jets from shaped holes. The present study reports measured thermal fields, along with measured flowfields, for a shaped hole at blowing ratios up to 3 at both low and high freestream turbulence intensities of 0.5% and 13.2%. Thermal fields at low freestream turbulence intensity showed that the coolant jet was initially attached, but far downstream of the hole the jet lifted away from the surface due to the counter-rotating vortex pair. Elevated freestream turbulence intensity was found to cause strong dilution of the coolant jet and also increased dispersion, almost exclusively in the lateral as opposed to the vertical direction. Dominance of lateral dispersion was due to the influence of the wall on freestream eddies, as indicated from changes in turbulent shear stress between the low and high freestream turbulence cases.

scholarly journals Effect of In-Hole Roughness on Film Cooling From a Shaped Hole

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Robert P. Schroeder ◽  
Karen A. Thole
Keyword(s):  
Film Cooling ◽  
Thermal Field ◽  
Core Flow ◽  
Blowing Ratio ◽  
Cooling Hole ◽  
Flow Through ◽  
Shaped Hole ◽  
Adiabatic Effectiveness ◽  
Cool Gas ◽  
Interior Walls

While much is known about how macrogeometry of shaped holes affects their ability to successfully cool gas turbine components, little is known about the influence of surface roughness on cooling hole interior walls. For this study, a baseline-shaped hole was tested with various configurations of in-hole roughness. Adiabatic effectiveness measurements at blowing ratios up to 3 showed that the in-hole roughness caused decreased adiabatic effectiveness relative to smooth holes. Decreases in area-averaged effectiveness grew more severe with larger roughness size and with higher blowing ratios for a given roughness. Decreases of more than 60% were measured at a blowing ratio of 3 for the largest roughness values. Thermal field and flowfield measurements showed that in-hole roughness caused increased velocity of core flow through the hole, which increased the jet penetration height and turbulence intensity resulting in an increased mixing between the coolant and the mainstream. Effectiveness reductions due to roughness were also observed when roughness was isolated to only the diffused outlet of holes, and when the mainstream was highly turbulent.

Experimental and Computational Investigation of Film Cooling Performance and External Flowfield Effects due to Impingement Coolant Feed in the Leading Edge of a Turbine Blade

2021 ◽  
Author(s):  
Jacob D. Moore ◽  
Christopher C. Easterby ◽  
David G. Bogard
Keyword(s):  
Film Cooling ◽  
Leading Edge ◽  
Field Measurements ◽  
Suction Side ◽  
Computational Investigation ◽  
Exterior Surface ◽  
Cooling Performance ◽  
Root Cause ◽  
Shaped Hole ◽  
Adiabatic Effectiveness

Abstract The effects that leading-edge impingement coolant feeds have on the external flowfield and on film cooling performance in the showerhead have not been studied thoroughly in the literature. To isolate the influence of the impingement feed, experimental adiabatic effectiveness and off-the-wall thermal field measurements were made using a shaped hole geometry fed by an ideal plenum coolant feed and by an engine-realistic impingement coolant feed. The impingement configuration exhibited around 10% higher adiabatic effectiveness levels than the plenum configuration did — a finding in agreement with the few studies isolating this effect. CFD RANS simulations of the impingement and the pseudo-plenum configurations from a companion study were consulted to investigate the root cause of this difference in performance because the experimental data alone did not sufficiently explain it. In the impingement feed simulation, flow remained better attached throughout the hole (both at the inlet and at the diffuser) due to a rotation caused by the impingement flow, leading to better attachment on the exterior surface. This was most significant for the suction side holes at higher blowing ratios wherein the pseudo-plenum caused much more severe separation in the holes than the impingement configuration did.

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