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Effect of Angle between the Primary and Auxiliary Holes of an Anti-vortex Film Cooling Hole
Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 99 (2015) 1492 – 1496
2014 Asia-Pacific International Symposium on Aerospace Technology, APISAT2014
Effect of Angle between the Primary and Auxiliary Holes of an Anti-vortex Film Cooling hole Younggi Moona, Soon Sang Parka, Jung Shin Parka, Jae Su Kwakb,* a
Graduate student, School of Aerospace and Mechanical Engineering, Korea Aerospace University b School of Aerospace and Mechanical Engineering, Korea Aerospace University
Abstract In this paper, we analytically investigated the effect of the angle between primary and auxiliary film cooling holes of an antivortex hole on the film cooling effectiveness. The effect of blowing ratio and the mainstream turbulence intensity were also considered. A commercial software, CFX was utilized and the RNG k-ε turbulence model was selected as the turbulence model for the analysis. The angle between primary and auxiliary hole was varied from 0 to 75 degrees and the blowing ratio was ranged from 0.25 to 2.0. Four different mainstream turbulence intensities were also considered. Results showed that the anti-vortex film cooling holes performed better than the cylindrical hole. Also, the film cooling effectiveness for the anti-vortex holes were strongly affected by the angle between primary and auxiliary holes of the anti-vortex film cooling hole and the mainstream turbulence intensity. © Authors. Published by Elsevier Ltd. ThisLtd. is an open access article under the CC BY-NC-ND license ©2015 2014The The Authors. Published by Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of Chinese Society of Aeronautics and Astronautics (CSAA). Peer-review under responsibility of Chinese Society of Aeronautics and Astronautics (CSAA)
Keywords: Film cooling, Anti-vortex film cooling, CFD
Nomenclature d D
Diameter of auxiliary hole Diameter of primary hole
L
Hole length
* Corresponding author. Tel.: +82-2-300-0103; fax: +82-2-3158-3189 E-mail address: [email protected]
1877-7058 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of Chinese Society of Aeronautics and Astronautics (CSAA)
doi:10.1016/j.proeng.2014.12.690
Younggi Moon et al. / Procedia Engineering 99 (2015) 1492 – 1496
M P u
Blowing ratio Primary hole to auxiliary hole space mainstream velocity (m/s
Greek Ƚ ɏ
Angle of between primary hole and auxiliary hole Density
1493
Subscripts c Coolant m Mainstream stream 1. Introduction Turbine inlet temperature (TIT) has been increased in order to increase the thermal efficiency and power output of gas turbines. The TIT of modern gas turbine already exceeded the allowable material temperature, so sophisticate cooling techniques should be applied to protect gas turbine components from the high and uneven heat load. For the internal cooling of gas turbine blade, various cooling techniques such as impingement, rib turbulated, dimple, and pin-fin cooling have been applied. For the blade external surface, the film cooling technique has been adopted. For film cooling, coolant is injected from tiny holes or slots and the coolant forms cooling film on the surface, and protect the surface from the hot combustion gas. Goldstein et al. [1] carried out fundamental film cooling research using the cylindrical film cooling hole. Many researchers have tried to improve the film cooling effectiveness by proposing different hole shapes. Gritsch et al. [2] researched the effect of various fan-shaped holes and compound angle holes design. Recently, a new concept of film cooling hole, anti-vortex film cooling hole, has been widely studied because of higher film cooling effectiveness and simpler fabrication. The anti-vortex film cooling hole has additional auxiliary holes near the primary hole and the coolant from the auxiliary hole dim inishes the effect of the kidney vortex which lifts up the coolant from the cooled surface. As the kidney vortex is weakened, the coolant can stay closer to the surface and the overall film cooling effectiveness increases. Various parameter of anti-vortex film cooling hole were studied in by Heidmann et al. [3]. But previous studies did not consider the effect of angle between the primary hole and auxiliary holes on the film cooling effectiveness. In this study, we carried out three dimensional steady states numerical analysis in order to investigate the effect of angle between primary and auxiliary cooling holes of an anti-vortex film cooling hole. In order to isolate the angle effect on the film cooling effectiveness, all other design parameters such as the hole-to-hole distance and the hole length to diameter ratio were kept the same. 2. Method of numerical analysis Commercial software, CFX was used for the numerical simulation and the unstructured grid was used to ensure the mesh quality at film cooling holes. Fig. 1-(a) is boundary conditions for the analysis. One cylindrical hole or one set of anti-vortex hole was modelled and the periodic condition was applied as shown in Fig. 1-(a). Coolant was supplied form the bottom side and the adiabatic wall condition was applied to the film cooling surface. The velocity inlet condition and pressure outlet condition were applied to the inlet and exit, respectively, and mass flow rate was given as the coolant inlet condition. The mainstream velocity was 15m/s and the blowing ratio defined by Eq. (1) was varied from 0.25 to 2.0. (1) ڨ U ڊ ھ ې ھUۈ ې ۈ Fig. 1-(b) is the detailed view of the primary film cooling hole. The primary hole has 30 degrees angle with respect to the film cooled surface and the thickness of the cooled surface was two times of the primary film cooling hole diameter. The hole length-to-diameter ratio of the primary hole was 4. Figure 2 shows definition of the hole configuration for the cylindrical and anti-vortex hole. Diameters of primary
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Younggi Moon et al. / Procedia Engineering 99 (2015) 1492 – 1496
and auxiliary holes were 10 mm and 5 mm, respectively. Both the primary and auxiliary holes have 30 degree with respect to the surface in main stream direction, and the hole center-to-center distance between the primary and auxiliary holes (P) was two times of primary film cooling hole. The tested angle between the primary and auxiliary holes were 0˚, 15˚, 30˚, 45˚, 60˚ and 75˚. For the all angle cases, all other parameters such as hole center-to-center distance, thickness to diameter ratio, and diameter ratio are kept the same. Various turbulence models were tried to calculate the film cooling effectiveness and compared with the experimental results by Chen et al. [4]. In this study, the RNG k-ɂ model was selected as a turbulence model. Grid dependency test was performed for the efficient use of computer memory and the results are shown in Fig. 3. The number of grid varied from 0.66 million to 3.5 million and 2.3 million grid was chosen to be the optimal number of grid.
Fig. 1. (a) Boundary Condition; (b) Geometry of primary hole
Fig. 2. Figuration of film cooling hole Table 1. Anti-vortex hole configurations ſ
0, 15, 30, 45, 60, 75
Angle to flow
30
d
5 mm
D
10 mm
Hole length (L/D)
4
Hole to hole space (P/D)
1
Younggi Moon et al. / Procedia Engineering 99 (2015) 1492 – 1496
1495
Fig. 3. Grid dependency test results
3. Results and discussions In this study, we investigated the effect of the angle between primary and auxiliary holes of an anti-vortex hole on the film cooling effectiveness. The effects of blowing ratio and mainstream turbulence intensity were also considered. Fig. 4 is film cooling effectiveness contour for the cylindrical hole and anti-vortex hole with α=0˚, 15 ˚ and 30 ˚ at M=0.5. Note that the coolant flow rate for the all cases are the same, and as a results, the actual blowing ratio for the anti-vortex hole cases are lower than that for the cylindrical hole case. Results clearly shows that the anti-vortex hole cases causes higher film cooling effectiveness than that for the cylindrical hole case due to the reduced momentum ratio at the same blowing ratio and weakened kidney vortex. Results also showed that the overall film cooling effectiveness is strongly affected by the angle between primary and auxiliary film cooling holes.
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Younggi Moon et al. / Procedia Engineering 99 (2015) 1492 – 1496
Fig. 4. Film cooling effectiveness at M=0.5.
Acknowledgements This work has been supported by Basic Science Research Program of the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2012R1A1A2003832 and 2012R1A1A2008083 References [1] R. J. Goldstein, E. R. G. Eckert, J. W. Ramsey, Film Cooling with Injection through Holes: Adiabatic Wall Temperatures Downstream of a Circular Hole, ASME Journal of Engineering for Power, 1968, pp. 384-393. [2] M. Gritsch, A. Schulz, S. Wittig, Effect of Crossflows on the Discharge Coefficient of Film Cooling Holes with Varying Angles of Inclination and Orientation, ASME Turbo Expo, 2001, 2001-GT-0134 [3] J. D. Heidmann, S. V. Ekkad, A Novel Anti-vortex Turbine Film Cooling Hole Concept,” ASME Turbo Expo 2007: Power for Land, Sea and Air, 2007, 2007-GT-27528 [4] Andrew F Chen, Shiou-Jiuan Li, Je-Chin Han, Film cooling with forward and backward injection for cylindrical and fan-shaped holes using PSP measurement technique, ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, 2014, 2014-GT-26232
ScienceDirect Procedia Engineering 99 (2015) 1492 – 1496
2014 Asia-Pacific International Symposium on Aerospace Technology, APISAT2014
Effect of Angle between the Primary and Auxiliary Holes of an Anti-vortex Film Cooling hole Younggi Moona, Soon Sang Parka, Jung Shin Parka, Jae Su Kwakb,* a
Graduate student, School of Aerospace and Mechanical Engineering, Korea Aerospace University b School of Aerospace and Mechanical Engineering, Korea Aerospace University
Abstract In this paper, we analytically investigated the effect of the angle between primary and auxiliary film cooling holes of an antivortex hole on the film cooling effectiveness. The effect of blowing ratio and the mainstream turbulence intensity were also considered. A commercial software, CFX was utilized and the RNG k-ε turbulence model was selected as the turbulence model for the analysis. The angle between primary and auxiliary hole was varied from 0 to 75 degrees and the blowing ratio was ranged from 0.25 to 2.0. Four different mainstream turbulence intensities were also considered. Results showed that the anti-vortex film cooling holes performed better than the cylindrical hole. Also, the film cooling effectiveness for the anti-vortex holes were strongly affected by the angle between primary and auxiliary holes of the anti-vortex film cooling hole and the mainstream turbulence intensity. © Authors. Published by Elsevier Ltd. ThisLtd. is an open access article under the CC BY-NC-ND license ©2015 2014The The Authors. Published by Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of Chinese Society of Aeronautics and Astronautics (CSAA). Peer-review under responsibility of Chinese Society of Aeronautics and Astronautics (CSAA)
Keywords: Film cooling, Anti-vortex film cooling, CFD
Nomenclature d D
Diameter of auxiliary hole Diameter of primary hole
L
Hole length
* Corresponding author. Tel.: +82-2-300-0103; fax: +82-2-3158-3189 E-mail address: [email protected]
1877-7058 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of Chinese Society of Aeronautics and Astronautics (CSAA)
doi:10.1016/j.proeng.2014.12.690
Younggi Moon et al. / Procedia Engineering 99 (2015) 1492 – 1496
M P u
Blowing ratio Primary hole to auxiliary hole space mainstream velocity (m/s
Greek Ƚ ɏ
Angle of between primary hole and auxiliary hole Density
1493
Subscripts c Coolant m Mainstream stream 1. Introduction Turbine inlet temperature (TIT) has been increased in order to increase the thermal efficiency and power output of gas turbines. The TIT of modern gas turbine already exceeded the allowable material temperature, so sophisticate cooling techniques should be applied to protect gas turbine components from the high and uneven heat load. For the internal cooling of gas turbine blade, various cooling techniques such as impingement, rib turbulated, dimple, and pin-fin cooling have been applied. For the blade external surface, the film cooling technique has been adopted. For film cooling, coolant is injected from tiny holes or slots and the coolant forms cooling film on the surface, and protect the surface from the hot combustion gas. Goldstein et al. [1] carried out fundamental film cooling research using the cylindrical film cooling hole. Many researchers have tried to improve the film cooling effectiveness by proposing different hole shapes. Gritsch et al. [2] researched the effect of various fan-shaped holes and compound angle holes design. Recently, a new concept of film cooling hole, anti-vortex film cooling hole, has been widely studied because of higher film cooling effectiveness and simpler fabrication. The anti-vortex film cooling hole has additional auxiliary holes near the primary hole and the coolant from the auxiliary hole dim inishes the effect of the kidney vortex which lifts up the coolant from the cooled surface. As the kidney vortex is weakened, the coolant can stay closer to the surface and the overall film cooling effectiveness increases. Various parameter of anti-vortex film cooling hole were studied in by Heidmann et al. [3]. But previous studies did not consider the effect of angle between the primary hole and auxiliary holes on the film cooling effectiveness. In this study, we carried out three dimensional steady states numerical analysis in order to investigate the effect of angle between primary and auxiliary cooling holes of an anti-vortex film cooling hole. In order to isolate the angle effect on the film cooling effectiveness, all other design parameters such as the hole-to-hole distance and the hole length to diameter ratio were kept the same. 2. Method of numerical analysis Commercial software, CFX was used for the numerical simulation and the unstructured grid was used to ensure the mesh quality at film cooling holes. Fig. 1-(a) is boundary conditions for the analysis. One cylindrical hole or one set of anti-vortex hole was modelled and the periodic condition was applied as shown in Fig. 1-(a). Coolant was supplied form the bottom side and the adiabatic wall condition was applied to the film cooling surface. The velocity inlet condition and pressure outlet condition were applied to the inlet and exit, respectively, and mass flow rate was given as the coolant inlet condition. The mainstream velocity was 15m/s and the blowing ratio defined by Eq. (1) was varied from 0.25 to 2.0. (1) ڨ U ڊ ھ ې ھUۈ ې ۈ Fig. 1-(b) is the detailed view of the primary film cooling hole. The primary hole has 30 degrees angle with respect to the film cooled surface and the thickness of the cooled surface was two times of the primary film cooling hole diameter. The hole length-to-diameter ratio of the primary hole was 4. Figure 2 shows definition of the hole configuration for the cylindrical and anti-vortex hole. Diameters of primary
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Younggi Moon et al. / Procedia Engineering 99 (2015) 1492 – 1496
and auxiliary holes were 10 mm and 5 mm, respectively. Both the primary and auxiliary holes have 30 degree with respect to the surface in main stream direction, and the hole center-to-center distance between the primary and auxiliary holes (P) was two times of primary film cooling hole. The tested angle between the primary and auxiliary holes were 0˚, 15˚, 30˚, 45˚, 60˚ and 75˚. For the all angle cases, all other parameters such as hole center-to-center distance, thickness to diameter ratio, and diameter ratio are kept the same. Various turbulence models were tried to calculate the film cooling effectiveness and compared with the experimental results by Chen et al. [4]. In this study, the RNG k-ɂ model was selected as a turbulence model. Grid dependency test was performed for the efficient use of computer memory and the results are shown in Fig. 3. The number of grid varied from 0.66 million to 3.5 million and 2.3 million grid was chosen to be the optimal number of grid.
Fig. 1. (a) Boundary Condition; (b) Geometry of primary hole
Fig. 2. Figuration of film cooling hole Table 1. Anti-vortex hole configurations ſ
0, 15, 30, 45, 60, 75
Angle to flow
30
d
5 mm
D
10 mm
Hole length (L/D)
4
Hole to hole space (P/D)
1
Younggi Moon et al. / Procedia Engineering 99 (2015) 1492 – 1496
1495
Fig. 3. Grid dependency test results
3. Results and discussions In this study, we investigated the effect of the angle between primary and auxiliary holes of an anti-vortex hole on the film cooling effectiveness. The effects of blowing ratio and mainstream turbulence intensity were also considered. Fig. 4 is film cooling effectiveness contour for the cylindrical hole and anti-vortex hole with α=0˚, 15 ˚ and 30 ˚ at M=0.5. Note that the coolant flow rate for the all cases are the same, and as a results, the actual blowing ratio for the anti-vortex hole cases are lower than that for the cylindrical hole case. Results clearly shows that the anti-vortex hole cases causes higher film cooling effectiveness than that for the cylindrical hole case due to the reduced momentum ratio at the same blowing ratio and weakened kidney vortex. Results also showed that the overall film cooling effectiveness is strongly affected by the angle between primary and auxiliary film cooling holes.
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Fig. 4. Film cooling effectiveness at M=0.5.
Acknowledgements This work has been supported by Basic Science Research Program of the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2012R1A1A2003832 and 2012R1A1A2008083 References [1] R. J. Goldstein, E. R. G. Eckert, J. W. Ramsey, Film Cooling with Injection through Holes: Adiabatic Wall Temperatures Downstream of a Circular Hole, ASME Journal of Engineering for Power, 1968, pp. 384-393. [2] M. Gritsch, A. Schulz, S. Wittig, Effect of Crossflows on the Discharge Coefficient of Film Cooling Holes with Varying Angles of Inclination and Orientation, ASME Turbo Expo, 2001, 2001-GT-0134 [3] J. D. Heidmann, S. V. Ekkad, A Novel Anti-vortex Turbine Film Cooling Hole Concept,” ASME Turbo Expo 2007: Power for Land, Sea and Air, 2007, 2007-GT-27528 [4] Andrew F Chen, Shiou-Jiuan Li, Je-Chin Han, Film cooling with forward and backward injection for cylindrical and fan-shaped holes using PSP measurement technique, ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, 2014, 2014-GT-26232