Effects of Coating Blockage and Deposit on Film Cooling Effectiveness and Heat Transfer

Na, Sangkwon; Cunha, F. J.; Chyu, Minking K.; Shih, Tsan‐Hsing

doi:10.2514/6.2006-24

Cited by 6 publications

(6 citation statements)

References 13 publications

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“…When drilling with a long-pulsed laser, most of the material is removed by liquid molten sputtering by recoiling pressure caused by plasma, causing it to accumulate at the entrance and exit of the hole to form burrs [22]. The burrs will seriously affect the service life of the engine [23], which should be removed. Li et al used ceramic ller powder and silicone elastomer matrix to make a coating for laser drilling [24].…”

Section: Resultsmentioning

confidence: 99%

Fabrication of micro holes with high surface quality and mechanical properties by high-speed laser trepanning and electrochemical post-treatment

Liu,

Wang,

Yang

et al. 2024

Preprint

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Laser processing could drill micro holes with very high efficiency, but the micro holes suffer from recast layers, microcracks and heat-affected zones, which has limited its wide application in engineering. In this paper, the high-speed laser drilling and electrochemical post-treatment has been combined to improve the machining efficiency and surface quality. To reduce the surface sputtering and redeposit in laser drilling, avoid the stray current induced corrosion and improve the machining precision in electrochemical post-treatment, the double-side coating has been applied to the workpiece before processing. Influences of laser power ratio, frequency, duty cycle and defocus amount on the diameter and taper of the laser drilled micro holes were explored experimentally. Results showed that the micro hole diameter increased with the increase of laser power ratio, duty cycle and defocus amount and decreased with the increase of pulse frequency. The micro hole taper increased with the increase of frequency, duty cycle and defocus amount. A laser power ratio of larger than 70% was recommended to reduce the taper of the laser drilled micro holes. Additionally, orthogonal experiments were employed to study the effects of laser power ratio, frequency, duty cycle and defocus on laser drilled micro hole diameter, taper, and recast layer thickness. Results show that duty cycle has the greatest impact on aperture, and power ratio has the greatest impact on taper, and frequency has the greatest impact on the thickness of the recast layer. Micro holes with an average diameter of 0.58 mm, a taper angle of 1.77°, and an average recast layer thickness of 25 µm have been obtained by laser drilling utilizing the optimal parameters. Finally, electrochemical post-processing was adopted to improve the surface quality and mechanical properties of the laser drilled micro holes. Results had shown that micro holes without recast layer and micro cracks were obtained by electrochemical posttreatment with a processing time of 20 s. Moreover, the inner hole surface roughness has been reduced by 68.16% and the micro hardness was reduced by 63.40%. A surface roughness of Ra 0.71 μm has been achieved. The proposed laser and electrochemical machining could be applied to the fabrication of micro holes with high surface quality and high efficiency.

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Section: Resultsmentioning

confidence: 99%

Fabrication of micro holes with high surface quality and mechanical properties by high-speed laser trepanning and electrochemical post-treatment

Liu,

Wang,

Yang

et al. 2024

Preprint

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show abstract

“…To choose a suitable turbulent model in the calculation of film cooling, we calculate the film cooling of a single hole based on the reference [26] using four turbulent models. The particle deposition is not considered in this simulation.…”

Section: Simulation Validationmentioning

confidence: 99%

“…The geometry of the model is shown in Figure 3a. According to the settings in reference [26], we build a similar model with the mainstream channel having a length of 294 mm, a width of 18 mm, and a height of 90 mm. The diameter of the cooling hole is 6 mm and its inclination angle is 35 • .…”

Section: Simulation Validationmentioning

confidence: 99%

Particle Deposition in the Vicinity of Multiple Film Cooling Holes

Peng

Luo

et al. 2022

Micromachines

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Particle deposition on film cooling surface is an engineering issue that degrades the thermal protection of turbine blade. Here, we present a combined experimental and numerical investigation on the particle deposition in the vicinity of multiple film cooling holes to reveal the effect of interactions between cooling outflows on particle deposition. The numerical simulation of film cooling with a group of three rows of straight film cooling holes is conducted and validated by experimental data with blowing ratios ranging from 0 to 0.08. Wax particles with size range from 5 to 40 μm are added in the heated mainstream to simulate the particle deposition in the experiment. The simulation results show the decrease of particle deposition with blowing ratio and various deposition characteristics in different regions of the surface. The flow fields from numerical results are analyzed in detail to illustrate deposition mechanism of the particles in different regions under the interactions of cooling outflows. The cooling air from the holes in the first row reduces the particle concentration near the wall but causes particle deposition in or between the tail regions by the generated flow disturbance. The cooling air from the latter hole separates the diluted flow in the upstream from the wall, and creates a tail region without particle deposition. This revealed particle deposition characteristics under the effect of outflows interaction can benefit the understanding of particle deposition in engineering applications, where multi-row of cooling holes are utilized.

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“…Computational studies have also indicated that hole blockages reduce adiabatic effectiveness. The study by Na et al [6] ran simulations on unblocked and blocked cylindrical holes. Blocked holes were found to decrease film effectiveness, though this reduction was minimized by lowering the mass flow rate through the hole.…”

Section: Relevant Past Studiesmentioning

confidence: 99%

Blockage Effects From Simulated Thermal Barrier Coatings for Cylindrical and Shaped Cooling Holes

Whitfield

Schroeder

Thole

et al. 2015

Journal of Turbomachinery

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Film cooling and sprayed thermal barrier coatings (TBCs) protect gas turbine components from the hot combustion gas temperatures. As gas turbine designers pursue higher turbine inlet temperatures, film cooling and TBCs are critical in protecting the durability of turbomachinery hardware. One obstacle to the synergy of these technologies is that TBC coatings can block cooling holes when applied to the components, causing a decrease in the film cooling flow area thereby reducing coolant flow for a given pressure ratio (PR). In this study, the effect of TBC blockages was simulated on film cooling holes for widely spaced cylindrical and shaped holes. At low blowing ratios for shaped holes, the blockages were found to have very little effect on adiabatic effectiveness. At high blowing ratios, the area-averaged effectiveness of shaped and cylindrical holes decreased as much as 75% from blockage. The decrease in area-averaged effectiveness was found to scale best with the effective momentum flux ratio of the jet exiting the film cooling hole for the shaped holes.

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Effects of Coating Blockage and Deposit on Film Cooling Effectiveness and Heat Transfer

Cited by 6 publications

References 13 publications

Fabrication of micro holes with high surface quality and mechanical properties by high-speed laser trepanning and electrochemical post-treatment

Fabrication of micro holes with high surface quality and mechanical properties by high-speed laser trepanning and electrochemical post-treatment

Particle Deposition in the Vicinity of Multiple Film Cooling Holes

Blockage Effects From Simulated Thermal Barrier Coatings for Cylindrical and Shaped Cooling Holes

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