Numerical Evaluation of Surface Roughness Effects on Film-Cooling Performance in a Laidback Fan-Shaped Hole

2021 ◽  
Author(s):  
Ali Zamiri ◽  
Sung Jin You ◽  
Jin Taek Chung
Keyword(s):  
Surface Roughness ◽  
Film Cooling ◽  
Numerical Evaluation ◽  
Roughness Effects ◽  
Cooling Performance ◽  
Shaped Hole

Numerical Evaluation of Surface Roughness Effects on Film-Cooling Performance in a Laidback Fan-Shaped Hole

2020 ◽  
Author(s):  
Ali Zamiri ◽  
Sung Jin You ◽  
Jin Taek Chung
Keyword(s):  
Surface Roughness ◽  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Roughness Height ◽  
Constant Density ◽  
Cooling Performance ◽  
Cooling Hole ◽  
Shaped Hole ◽  
Grain Roughness

Abstract This study numerically investigates the influences of cooling hole surface roughness in a laidback fan-shaped hole on the flow structure and film-cooling effectiveness. The three-dimensional compressible LES approach (large eddy simulation) is conducted in a baseline 7-7-7 laidback fan-shaped hole. The cooling hole is located on a flat plate surface with a 30-degree injection angle at a constant density ratio DR = 1.5 and two blowing ratios M = 1.5 and 3. The computational results were validated by the measurements in terms of velocity and thermal fields for both the smooth and rough holes. In order to numerically consider the influences of the surface roughness on cooling hole side, the equivalent sand grain roughness method was utilized. Different correlations between the equivalent sand grain roughness height and arithmetic average roughness height were numerically tested to find an accurate correlation in comparison to the measurements. The computational data revealed that the surface roughness of the hole interior walls increases the thickness of the boundary layers within the hole. This leads to a higher jet core flow at the hole exit and lower film-cooling performance at the surface of flat plate compared to those of the smooth cooling hole. The minimum area-averaged film-cooling performance was observed in the case of the highest blowing ratio and the largest surface roughness height. The present work reveals that the current LES approach by considering the proper equivalent sand grain roughness height is a powerful tool to obtain the accurate solution in the prediction of the heat transfer characteristics and the flow structures in the fan-shaped cooling holes.

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.

Film Cooling From Novel Sister Shaped Single-Holes

2014 ◽  
Author(s):  
Siavash Khajehhasani ◽  
Bassam Jubran
Keyword(s):  
Film Cooling ◽  
Three Dimensional ◽  
Lateral Spreading ◽  
Navier Stokes ◽  
The Novel ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Shaped Hole ◽  
Lift Off

A numerical investigation of the film cooling performance from novel sister shaped single-holes (SSSH) is presented in this paper and the obtained results are compared with a single cylindrical hole, a forward diffused shaped hole, as well as discrete sister holes. Three types of the novel sister shaped single-hole schemes namely downstream, upstream and up/downstream SSSH, are designed based on merging the discrete sister holes to the primary hole in order to reduce the jet lift-off effect and increase the lateral spreading of the coolant on the blade surface as well as a reduction in the amount of coolant in comparison with discrete sister holes. The simulations are performed using three-dimensional Reynolds-Averaged Navier Stokes analysis with the realizable k–ε model combined with the standard wall function. The upstream SSSH demonstrates similar film cooling performance to that of the forward diffused shaped hole for the low blowing ratio of 0.5. While it performs more efficiently at M = 1, where the centerline and laterally averaged effectiveness results improved by 70% and 17%, respectively. On the other hand, the downstream and up/downstream SSSH schemes show a considerable improvement in film cooling performance in terms of obtaining higher film cooling effectiveness and less jet lift-off effect as compared with the single cylindrical and forward diffused shaped holes for both blowing ratios of M = 0.5 and 1. For example, the laterally averaged effectiveness for the downstream SSSH configuration shows an improvement of approximately 57% and 110% on average as compared to the forward diffused shaped hole for blowing ratios of 0.5 and 1, respectively.

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.

Experimental Investigation and Optimal Design on the Film Cooling Performance of Fan-Shaped Hole With Vortex Generator Fed by Crossflow

2021 ◽  
Author(s):  
Jie Wang ◽  
Chao Zhang ◽  
Xuebin Liu ◽  
Liming Song ◽  
Jun Li ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Film Cooling ◽  
Vortex Generator ◽  
Optimized Design ◽  
Combined Model ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Shaped Hole

Abstract Aiming at investigating the effects of crossflow and vortex generator on film cooling characteristics of fan-shaped hole, the film cooling performance was measured experimentally by infrared camera. The blowing ratio is fixed at 0.5 and 1.5. The Reynolds number of the mainstream based on the hole diameter remains at 7000 and the inlet Reynolds number of crossflow is 40000. The experimental results show that the film cooling performance becomes better when the blowing ratio increases from 0.5 to 1.5 for each model, and the film cooling performance becomes worse under the influence of crossflow. When the blowing ratio is 1.5, the area-averaged film cooling effectiveness of the fan-shaped hole model with vortex generator decreases by 16.6% because of the influence of crossflow. The combined model always performs better compared with the model without vortex generator under all working conditions. When the blowing ratio becomes 1.5, under the influence of crossflow, the area-averaged film cooling effectiveness of the combined model could increase by 14.8%, compared with the model without vortex generator. To further improve the film cooling performance, the global optimization algorithm based on the Kriging method and the CFD technology are coupled to optimize the combined model under crossflow condition at the high blowing ratio, and the optimized design is verified by experiments. The experimental results show that the area-averaged film cooling effectiveness of the optimized design increases by 17.8% compared with the reference model.

Effects of Free-Stream Turbulence and Surface Roughness on Film Cooling

1996 ◽  
Author(s):  
Donald L. Schmidt ◽  
David G. Bogard
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Momentum Flux ◽  
Free Stream ◽  
Cooling Performance ◽  
Free Stream Turbulence ◽  
Adiabatic Effectiveness

A flat plate test section was used to study how high free-stream turbulence with large turbulence length scales, representative of the turbine environment, affect the film cooling adiabatic effectiveness and heat transfer coefficient for a round hole film cooling geometry. This study also examined cooling performance with combined high free-stream turbulence and a rough surface which simulated the roughness representative of an in-service turbine. The injection was from a single row of film cooling holes with injection angle of 30°. The density ratio of the injectant to the mainstream was 2.0 for the adiabatic effectiveness tests, and 1.0 for the heat transfer coefficient tests. Streamwise and lateral distributions of adiabatic effectiveness and heat transfer coefficients were obtained at locations from 2 to 90 hole diameters downstream. At small to moderate momentum flux ratios, which would normally be considered optimum blowing conditions, high free-stream turbulence dramatically decreased adiabatic effectiveness. However, at large momentum flux ratios, conditions for which the film cooling jet would normally be detached, high free-stream turbulence caused an increase in adiabatic effectiveness. The combination of high free-stream turbulence with surface roughness resulted in an increase in adiabatic effectiveness relative to the smooth wall with high free-stream turbulence. Heat transfer rates were relatively unaffected by a film cooling injection. The key result from this study was a substantial increase in the momentum flux ratios for maximum film cooling performance which occurred for high free-stream turbulence and surface roughness conditions which are more representative of actual turbine conditions.

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

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.

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

2008 ◽  
Vol 131 (1) ◽  
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.

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