Analysis of the cooling performance of a cylindrical hole designed for the suction side of the LS89 vane under transitional conditions

Secondary holes to a main film cooling hole are used to improve film cooling performance by creating anti-kidney vortices. The effects of injection angle of the secondary holes on both film cooling effectiveness and surrounding thermal and flow fields are investigated in this numerical study. Two kinds of primary hole shapes are adopted. One is a cylindrical hole, the other is a horn-shaped hole which is designed from a cylindrical hole by expanding the hole in the transverse direction to double the hole size at the exit. Two smaller cylindrical holes, the secondary holes, are located symmetrically about the centerline and downstream of the primary hole. Three compound injection angles (α = 30°, 45° and 60°, β = 30°) of the secondary holes are analyzed while the injection angle of the primary hole is kept at 45°. Cases with various blowing ratios are computed. It is shown from the simulation that cooling effectiveness of secondary holes with a horn-shaped primary hole is better than that with a cylindrical primary hole, especially at high blowing ratios. With a cylindrical primary hole, increasing inclination angle of the secondary holes provides better cooling effectiveness because the anti-kidney vortices created by shallow secondary holes cannot counteract the kidney vortex pairs adequately, enhancing mixing of main flow and coolant. For secondary holes with a horn-shaped primary hole, large secondary hole inclination angles provide better cooling performance at low blowing ratios; but, at high blowing ratios, secondary holes with small inclination angles are more effective, as the film coverage becomes wider in the downstream area.

Download Full-text

Heat Transfer Coefficient Measurements of Film-Cooling Holes With Expanded Exits

Volume 4: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/98-gt-028 ◽

1998 ◽

Cited By ~ 32

Author(s):

M. Gritsch ◽

A. Schulz ◽

S. Wittig

Keyword(s):

Heat Transfer ◽

Mach Number ◽

Film Cooling ◽

Cylindrical Hole ◽

Superposition Method ◽

Transfer Coefficients ◽

Cooling Performance ◽

Heat Transfer Coefficients ◽

Film Cooling Holes ◽

Injection Location

Detailed measurements of heat transfer coefficients in the nearfield of three different film-cooling holes are presented. The hole geometries investigated include a cylindrical hole and two holes with a diffuser shaped exit portion (i.e. a fan-shaped and a laidback fanshaped hole). They were tested over a range of blowing ratios M = 0.25…1.75 at an external crossflow Mach number of 0.6 and a coolant-to-mainflow density ratio of 1.85. Additionally, the effect of the internal coolant supply Mach number is addressed. Temperatures of the diabatic surface downstream of the injection location are measured by means of an infrared camera system. They are used as boundary conditions for a finite element analysis to determine surface heat fluxes and heat transfer coefficients. The superposition method is applied to evaluate the overall film-cooling performance of the hole geometries investigated. As compared to the cylindrical hole, both expanded holes show significantly lower heat transfer coefficients downstream of the injection location, particularly at high blowing ratios. The laidback fanshaped hole provides a better lateral spreading of the injected coolant than the fanshaped hole which leads to lower laterally averaged heat transfer coefficients. Coolant passage crossflow Mach number affects the flowfield of the jet being ejected from the hole and, therefore, has an important impact on film-cooling performance.

Download Full-text

Surface Curvature Effects on Film Cooling Performance for Shaped Holes on a Model Turbine Blade

Journal of Turbomachinery ◽

10.1115/1.4048582 ◽

2020 ◽

Vol 142 (11) ◽

Author(s):

Jacob D. Moore ◽

Christopher Yoon ◽

David G. Bogard

Keyword(s):

Flat Plate ◽

Turbine Blade ◽

Film Cooling ◽

Gas Turbines ◽

Convex Surface ◽

Adverse Pressure Gradient ◽

Suction Side ◽

Surface Curvature ◽

Cooling Performance ◽

Curvature Effects

Abstract Surface curvature has been shown to have significant effects on the film cooling performance of round holes, but the literature include few studies of its effects on shaped holes despite their prevalence in gas turbines. Experiments were performed using two rows of holes placed on the suction side of a scaled-up turbine blade in a low Mach number linear cascade wind tunnel with low freestream turbulence. The rows were placed in regions of high and low convex surface curvature. Geometries and flow conditions for the rows were matched to those from previous flat plate studies. Comparison of the adiabatic effectiveness results from the high curvature and flat plate rows revealed the same trends as those in the literature using round holes, with increased performance for the high curvature row at lower blowing ratios and the opposite at higher ones. The low curvature row had similar performance to the flat plate row at lower blowing ratios, suggesting the mild convex curvature had little beneficial effect. At higher blowing ratios, the low curvature row had inferior performance, which was attributed to the local freestream adverse pressure gradient that generated additional turbulence, promoting jet-to-mainstream mixing and decreasing performance.

Download Full-text

Experimental and Numerical Investigation on Film Cooling Performance and Flow Structure of Film Holes

Volume 5B: Heat Transfer ◽

10.1115/gt2019-90734 ◽

2019 ◽

Author(s):

Nan Cao ◽

Xue Li ◽

Ze-yu Wu ◽

Xiang Luo

Keyword(s):

Flow Visualization ◽

Numerical Investigation ◽

Flow Structure ◽

Film Cooling ◽

Cylindrical Hole ◽

Cooling Effectiveness ◽

Cooling Performance ◽

Blowing Ratio ◽

Visualization Experiment ◽

Shaped Hole

Abstract Discrete hole film cooling has been commonly used as an effective cooling technique to protect gas turbine blades from hot gas. There have been numerous investigations on the cylindrical hole and shaped hole, but few experimental investigations on the cooling mechanism of the novel film holes with side holes (anti-vortex hole and sister hole) are available. This paper presents an experimental and numerical investigation to study the film cooling performance and flow structure of four kinds of film holes (cylindrical hole, fan-shaped hole, anti-vortex hole and sister hole) on the flat plate. The film holes have the same main hole diameter of 4mm and the same inclination angle of 45°. The adiabatic film cooling effectiveness is obtained by the steady-state Thermochromic Liquid Crystal (TLC). The flow visualization experiment and numerical investigation are performed to investigate the flow structure and counter-rotating vortex pair (CRVP) intensity. The smoke is selected as the tracer particle in the flow visualization experiment. The mainstream Reynolds number is 2900, the blowing ratio ranges from 0.3 to 2.0, and the density ratio of coolant to mainstream is 1.065. Experimental results show that compared with the cylindrical hole, the film cooling performance of the anti-vortex hole and sister hole shows significant improvement at all blowing ratios. The sister hole can achieve the best cooling performance at blowing ratios of 0.3 to 1.5. The fan-shaped hole only performs well at high blowing ratios and it performs best at the blowing ratio of 2.0. Flow visualization experiment and numerical investigation reveal that the anti-vortex hole and sister hole can decrease the CRVP intensity of the main hole and suppress the coolant lift-off because of side holes, which increases the film coverage and cooling effectiveness. For the sister hole, the side holes are parallel to the main hole, but for the anti-vortex hole, there are lateral angles between them. The coolant interaction between the side holes and main hole of the sister hole is stronger than that of the anti-vortex hole. Therefore, the sister hole provides better film cooling performance than the anti-vortex hole.

Download Full-text

Effects of Obstructions and Surface Roughness on Film Cooling Effectiveness With and Without a Transverse Trench

Journal of Turbomachinery ◽

10.1115/1.2950063 ◽

2008 ◽

Vol 131 (1) ◽

Cited By ~ 5

Author(s):

Ruwan P. Somawardhana ◽

David G. Bogard

Keyword(s):

Surface Roughness ◽

Film Cooling ◽

Suction Side ◽

Cooling Effectiveness ◽

Cooling Performance ◽

Film Cooling Effectiveness ◽

Surface Conditions ◽

Turbine Vane ◽

Cylindrical Holes ◽

Better Than

Recent studies have shown that film cooling with holes embedded in a shallow trench significantly improves cooling performance. In this study, the performance of shallow trench configurations was investigated for simulated deteriorated surface conditions, i.e., increased surface roughness and near-hole obstructions. Experiments were conducted on the suction side of a scaled-up simulated turbine vane. Results from the study indicated that as much as 50% degradation occurred with upstream obstructions, but downstream obstructions actually enhanced film cooling effectiveness. However, the transverse trench configuration performed significantly better than the traditional cylindrical holes, both with and without obstructions and almost eliminated the effects of both surface roughness and obstructions.

Download Full-text

CFD Predictions of Film Cooling Adiabatic Effectiveness for Cylindrical Holes Embedded in Narrow and Wide Transverse Trenches

Volume 4: Turbo Expo 2007, Parts A and B ◽

10.1115/gt2007-28005 ◽

2007 ◽

Cited By ~ 13

Author(s):

Katharine L. Harrison ◽

David G. Bogard

Keyword(s):

Film Cooling ◽

Cylindrical Hole ◽

Dramatic Improvement ◽

Computational Simulations ◽

Cooling Performance ◽

Hole Configuration ◽

Cylindrical Holes ◽

Adiabatic Effectiveness

Recent studies have shown that film cooling adiabatic effectiveness can be significantly improved when holes are embedded in shallow, transverse trenches. In this study computational simulations were made using the commercial CFD code FLUENT to determine if the dramatic improvement in film cooling performance was predictable. Simulations were made of a baseline cylindrical hole configuration, and narrow and wide trench configurations. Simulations correctly predicted that the narrow trench outperformed the baseline row of cylindrical holes and the wide trench at all blowing ratios. Furthermore, the simulations showed that enhanced performance with the trench could be attributed to decreased separation of the coolant jets. The success of these predictions show that computational simulations can be used as a tool for studying and identifying promising film cooling configurations.

Download Full-text

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

Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/2000-gt-0239 ◽

2000 ◽

Cited By ~ 7

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.

Download Full-text

Improvements of the Adiabatic Film Cooling by Using Two-Row Holes of Different Geometries and Arrangements

Journal of Energy Resources Technology ◽

10.1115/1.4047329 ◽

2020 ◽

Vol 142 (12) ◽

Author(s):

Guohua Zhang ◽

Jian Liu ◽

Bengt Sundén ◽

Gongnan Xie

Keyword(s):

Film Cooling ◽

Discharge Coefficient ◽

Three Dimensional ◽

Elliptical Hole ◽

Cylindrical Hole ◽

Maximum Deviation ◽

Cooling Effectiveness ◽

Cooling Performance ◽

Film Cooling Effectiveness ◽

Elliptical Holes

Abstract Existing researches on two-row film cooling mainly focused on double-jet film cooling. However, researches on the effects by combining different kinds of hole shapes on film cooling performance are quite limited. In order to improve the film cooling effectiveness, the three-dimensional numerical method is utilized to investigate the effects of a novel structure composed of two-row holes with different shapes and arrangements on the adiabatic film cooling effectiveness with the blowing ratio of M = 1.5. To achieve this purpose, 30 different cases with two-row holes are designed and their film cooling effectiveness are compared with those of other seven cases with a single hole. Cases with two-row holes are designed by setting cylindrical, elliptical, or super-elliptical holes as the first-row, and arranging cylindrical holes with 30 deg, 45 deg, 60 deg, and 90 deg compound angles as the second row. The realizable k–ɛ turbulence model with enhanced wall function is utilized for all cases under identical boundary conditions. Similar film cooling performances are observed for cases with elliptical and super-elliptical holes being the first row, since the maximum deviation of film cooling effectiveness is less than 10%. It is found that the case integrates both a cylindrical hole and a cylindrical hole with 90 deg compound angle can greatly improve the film cooling performance with a higher discharge coefficient. However, the staggered case with an elliptical hole as both first- and second row gives the best film cooling effectiveness and the worst discharge coefficient due to the biggest resistance for the coolant flowing into the film hole.

Download Full-text

Experimental Investigation on the Flat-Plate Film Cooling Enhancement Using the Vortex Generator Downstream for the Cylindrical Hole and Fan-Shaped Hole Configurations

Volume 5B: Heat Transfer ◽

10.1115/gt2019-90671 ◽

2019 ◽

Author(s):

Chao Zhang ◽

Jie Wang ◽

Xin Luo ◽

Liming Song ◽

Jun Li ◽

...

Keyword(s):

Film Cooling ◽

Vortex Generator ◽

Cylindrical Hole ◽

Combined Model ◽

Cooling Effectiveness ◽

Cooling Performance ◽

Film Cooling Effectiveness ◽

Blowing Ratio ◽

Shaped Hole ◽

Hole Model

Abstract In our experiments, the film cooling performance of the configurations combined the different hole with the vortex generator was investigated experimentally, measured by the infrared camera. Four different configurations were studied at the blowing ratio varying at M = 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0. In all cases, the Reynold number of the mainstream based on the hole diameter remained at Re = 8000, and the density ratio kept at DR = 1.7. Experimental results show that for the two models combining the cylindrical hole and fan-shaped hole with the vortex generator respectively, the film cooling performance becomes better when the blowing ratio increases from M = 0.5 to M = 2.0, and then decreases when the blowing ratio increases from M = 2.0 to M = 3.0. The model combining the fan-shaped hole with the vortex generator performs the best among the four models at each blowing ratio. Its film attachment holds the most extensive lateral distribution and its overall film cooling effectiveness could keep at a high level at a wide range of blowing ratios from M = 1.0 to M = 3.0. The combined model of the fan-shaped hole could improve the area-averaged film effectiveness at most 25.5% than that of the single hole model at M = 2.0. Moreover, the combined model of the cylindrical hole could improve the area-averaged film cooling effectiveness at most 431% than that of the single cylindrical hole model at M = 3.0.

Download Full-text