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.

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.

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.

Bump and Trench Modifications to Film-Cooling Holes at the Vane-Endwall Junction

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
N. Sundaram ◽  
K. A. Thole
Keyword(s):  
Film Cooling ◽  
Large Scale ◽  
Leading Edge ◽  
High Heat ◽  
Junction Region ◽  
High Heat Transfer ◽  
Turbine Vane ◽  
Cooling Hole ◽  
Adiabatic Effectiveness ◽  
Film Cooling Holes

The endwall of a first-stage vane experiences high heat transfer and low adiabatic effectiveness levels because of high turbine operating temperatures and formation of leading edge vortices. These vortices lift the coolant off the endwall and pull the hot mainstream gases toward it. The region of focus for this study is the vane-endwall junction region near the stagnation location where cooling is very difficult. Two different film-cooling hole modifications, namely, trenches and bumps, were evaluated to improve the cooling in the leading edge region. This study uses a large-scale turbine vane cascade with a single row of axial film-cooling holes at the leading edge of the vane endwall. Individual hole trenches and row trenches were placed along the complete row of film-cooling holes. Two-dimensional semi-elliptically shaped bumps were also evaluated by placing the bumps upstream and downstream of the film-cooling row. Tests were carried out for different trench depths and bump heights under varying blowing ratios. The results indicated that a row trench placed along the row of film-cooling holes showed a greater enhancement in adiabatic effectiveness levels when compared to individual hole trenches and bumps. All geometries considered produced an overall improvement to adiabatic effectiveness levels.

Bump and Trench Modifications to Film-Cooling Holes at the Vane Endwall Junction

2007 ◽  
Author(s):  
N. Sundaram ◽  
K. A. Thole
Keyword(s):  
Film Cooling ◽  
Large Scale ◽  
Leading Edge ◽  
High Heat ◽  
Junction Region ◽  
High Heat Transfer ◽  
Turbine Vane ◽  
Cooling Hole ◽  
Adiabatic Effectiveness ◽  
Film Cooling Holes

The endwall of a first stage vane experiences high heat transfer and low adiabatic effectiveness levels because of high turbine operating temperatures and formation of leading edge vortices. These vortices lift the coolant off the endwall and pull the hot mainstream gases towards it. The region of focus for this study is the vane-endwall junction region near the stagnation location where cooling is very difficult. Two different film-cooling hole modifications, namely trenches and bumps, were evaluated to improve the cooling in the leading edge region. This study uses a large-scale turbine vane cascade with a single row of axial film-cooling holes at the leading edge of the vane endwall. Individual hole trenches and row trenches were placed along the complete row of film-cooling holes. Two-dimensional semi-elliptically shaped bumps were also evaluated by placing the bumps upstream and downstream of the film-cooling row. Tests were carried out for different trench depths and bump heights under varying blowing ratios. The results indicated that a row trench placed along the row of film-cooling holes showed a greater enhancement in adiabatic effectiveness levels when compared to individual hole trenches and bumps. All geometries considered produced an overall improvement to adiabatic effectiveness levels.

Scaling of Performance for Varying Density Ratio Coolants on an Airfoil With Strong Curvature and Pressure Gradient Effects

2000 ◽  
Author(s):  
Marcia I. Ethridge ◽  
J. Michael Cutbirth ◽  
David G. Bogard
Keyword(s):  
Pressure Gradient ◽  
Film Cooling ◽  
Density Ratio ◽  
Flux Ratio ◽  
Leading Edge ◽  
Suction Side ◽  
Cooling Performance ◽  
Injection Angle ◽  
Adiabatic Effectiveness ◽  
Strong Curvature

An experimental study was conducted to investigate the film cooling performance on the suction side of a first stage turbine vane. Tests were conducted on a nine times scale vane model at density ratios of DR = 1.1 and 1.6 over a range of blowing conditions, 0.2 ≤ M ≤ 1.5 and 0.05 ≤ I ≤ 1.2. Two different mainstream turbulence intensity levels, Tu∞ = 0.5% and 20%, were also investigated. The row of coolant holes studied was located in a position of both strong curvature and strong favorable pressure gradient. In addition, its performance was isolated by blocking the leading edge showerhead coolant holes. Adiabatic effectiveness measurements were made using an infrared camera to map the surface temperature distribution. The results indicate that film cooling performance was greatly enhanced over holes with a similar 50° injection angle on a flat plate. Overall, adiabatic effectiveness scaled with mass flux ratio for low blowing conditions and with momentum flux ratio for high blowing conditions. However, for M < 0.5 there was a higher rate of decay for the low density ratio data. High mainstream turbulence had little effect at low blowing ratios, but degraded performance at higher blowing ratios.

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.

Film Cooling Performance of Waist-Shaped Slot Holes

2010 ◽  
Author(s):  
Cun-liang Liu ◽  
Hui-ren Zhu ◽  
Jiang-tao Bai ◽  
Du-chun Xu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Thermal Protection ◽  
Upstream Region ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Shaped Hole ◽  
The Heat Transfer Coefficient

Film cooling performance of a new shaped hole: waist-shaped slot hole is studied in this paper. Experimental measurement and numerical simulation are carried out to investigate the film cooling character and physics of this new shaped hole. And comparisons between the waist-shaped slot hole and two kinds of console holes are also performed. Both the cooling effectiveness distribution and the heat transfer coefficient distribution of the waist-shaped slot hole are similar with those of the console hole with large divergence angle because of the effect of the waist-shaped slot hole’s structure. The middle constriction structure of the waist-shaped slot hole and the coupled vortices make jets from the waist-shaped slot holes produce higher cooling effectiveness in the midspan region between adjacent holes. And also due to the effect of the middle constriction structure, the heat transfer coefficient of the waist-shaped slot hole is very high in the upstream midspan region. However, the heat transfer coefficient in the downstream midspan region is lower than that in the region near the hole centerline because of the effect of the coupled vortices. The waist-shaped slot holes provide the surface with very good thermal protection, especially in the upstream region. Although the console holes with small exit-entry area ratio provide better thermal protection than the waist-shaped slot holes due to small turbulence intensity, the flow resistance characteristic of the waist-shaped slot hole is much better.

Theoretical Film Cooling Performance of Multi Trench Configurations on Flat Plate

2013 ◽  
Author(s):  
Antar M. M. Abdala ◽  
Qun Zheng ◽  
Fifi N. M. Elwekeel
Keyword(s):  
Film Cooling ◽  
Additional Benefit ◽  
The Other ◽  
Low Flow ◽  
Computational Simulations ◽  
Cooling Performance ◽  
Blowing Ratio ◽  
Ansys Cfx ◽  
Shaped Hole ◽  
Adiabatic Effectiveness

In the present work, computational simulations was made using ANSYS CFX to predict the improvements in film cooling performance with multi trench. Multi-trench configuration consists of two trenches together, one wider trench and the other is narrow trench that extruded from the wider one. Several blowing ratios in the range (0.5:5) were investigated. By using the multi trench configuration, the coolant jet impacted the trench wall two times allowing increasing the spreading of coolant laterally in the trench, reducing jet velocity and jet completely covered on the surface. The results indicate that this configuration increased adiabatic effectiveness as blowing ratio increased. No observed film blow-off at all blowing ratios. The adiabatic film effectiveness of multi trench case outperformed the narrow trench case, laidback fan-shaped hole, fan-shaped hole and cylinder hole at different blowing ratios. An additional benefit is the low flow rate will provide the same cooling effect by using multi trench configuration.

The Effect of an Upstream Ramp on Cylindrical and Fan-Shaped Hole Film Cooling: Part II — Adiabatic Effectiveness Results

2007 ◽  
Author(s):  
Giovanna Barigozzi ◽  
Giuseppe Franchini ◽  
Antonio Perdichizzi
Keyword(s):  
Thermal Analysis ◽  
Film Cooling ◽  
Thermal Protection ◽  
Intensity Level ◽  
Beneficial Effects ◽  
Turbulence Mixing ◽  
Shaped Hole ◽  
Hole Geometry ◽  
Adiabatic Effectiveness ◽  
Cooling Part

The present companion papers report the results of an experimental investigation on possible beneficial effects of an upstream ramp on discrete hole film cooling. This analysis was carried out on a flat plate model. Two hole geometries have been considered: cylindrical and fan-shaped with conical expanded exit. To compare different cooling schemes, a combined aero-thermal analysis was performed. Tests have been carried out at low speed and low inlet turbulence intensity level, with blowing ratios varied in the range 0.3–1.0. Part I was focused on the aerodynamic analysis: it has been shown that the introduction of a ramp is always detrimental, as it gives a strong loss increase (+5%). Fan-shaped hole was instead the best solution, as it gives losses comparable with the cylindrical one, reduced turbulence mixing and jet dilution. Part II of this paper faces the thermal analysis. The thermal behaviour of the cooled surface has been analysed using the wide banded TLC’s technique, so to obtain adiabatic effectiveness distributions. Additional air temperature measurements have been carried out by traversing a thermocouple downstream of injection holes. The upstream ramp was found to provide a thermal protection improvement (+40%) only at low blowing rate in the case of cylindrical hole. The application of a ramp upstream of a fanshaped hole was instead detrimental for all blowing conditions. The fan shaped hole geometry with no ramp resulted to be the best solution also in terms of adiabatic effectiveness (50% higher than the cylindrical one at BR = 0.5).

Rough Surface Effects on Film Cooling of the Suction Side Surface of a Turbine Vane

2003 ◽  
Author(s):  
David G. Bogard ◽  
Daniel Snook ◽  
Atul Kohli
Keyword(s):  
Surface Roughness ◽  
Film Cooling ◽  
Surface Wind ◽  
Density Ratio ◽  
Leading Edge ◽  
Test Facility ◽  
Roughness Effects ◽  
Cooling Performance ◽  
Coolant Injection ◽  
Adiabatic Effectiveness

In-service turbine airfoils generally have surface roughness much greater than new airfoils due to deposition, erosion, and spallation. This surface roughness has the effects of promoting early transition and increasing surface friction and heat transfer rates. When film cooling is used on the airfoil, the surface roughness affects film cooling performance by changing the approach boundary layer flow, and by increasing the turbulent mixing downstream of coolant injection. Previous studies of surface roughness effects on film cooling performance have used flat surface wind tunnel facilities. The present study was unique in using a simulated vane test facility. Hence it is the first study of surface roughness effects on film cooling of a highly curved surface. In our experiments, effects of roughness upstream and downstream of coolant injection were studied. Combined effects of leading edge showerhead injection and high mainstream turbulence levels were also investigated. In this study, determination of the effects on film cooling performance was limited to measurements of adiabatic effectiveness. Each configuration was tested over a range of blowing ratios and with a density ratio of 1.6. In each case roughness caused a significant degradation in adiabatic effectiveness. Roughness was observed to have a much greater effect on adiabatic effectiveness on the vane geometry than previous studies had observed using flat surfaces.

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