Numerical Investigation of Film Cooling Enhancement Using Staggered Row Mixed Hole Arrangements

2017 ◽  
Vol 9 (2) ◽  
Author(s):  
Prakhar Jindal ◽  
Shubham Agarwal ◽  
R. P. Sharma ◽  
A. K. Roy
Keyword(s):  
Film Cooling ◽  
Vortex Pair ◽  
Temperature Fields ◽  
Flow Temperature ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Jet Interaction ◽  
Blowing Ratio ◽  
Cooling Enhancement ◽  
Counter Rotating Vortex Pair

The paper presents a novel study on film cooling effectiveness of a 3D flat plate with a multihole arrangement of mixed hole shapes. The film cooling arrangement consists of two rows of coolant holes, organized in a staggered pattern with an L/D (length to diameter ratio) of 10. The two rows consist of varied combinations of triangular and semi-elliptic shaped holes for the enhancement of film-cooling effectiveness. The results were obtained for a coolant to mainstream temperature ratio of 0.5 and a blowing ratio of 1.0. The computed flow temperature fields are presented in addition to the local two-dimensional streamwise and spanwise distribution of film cooling effectiveness. Validation of the results obtained from the turbulence model has been done with the experimental data of centerline film cooling effectiveness downstream of the cooling holes available in the open literature. The results showed the rapid merging of coolant jets emerging from front row of multiholes with the secondary staggered row of mixed holes. Due to the mainstream–coolant jet interaction, the strength of the counter rotating vortex pair was mitigated in the downstream region for certain arrangement of mixed hole shapes. The optimal hole combination with maximum overall effectiveness has been deduced from this study. The best configuration (M.R. VI) not only favored for the developed film, but also enhanced the averaged film cooling effectiveness to a large extent.

Interaction of Flow and Film-Cooling Effectiveness Between Double-Jet Film-Cooling Holes With Various Spanwise Distances

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Jiaxu Yao ◽  
Jin Xu ◽  
Ke Zhang ◽  
Jiang Lei ◽  
Lesley M. Wright
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Vortex Pair ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Film Cooling Holes ◽  
Two Jets ◽  
Compound Angle

The interaction of flow and film-cooling effectiveness between jets of double-jet film-cooling (DJFC) holes on a flat plate is studied experimentally. The time-averaged flow field in several axial positions (X/d = −2.0, 1.0, and 5.0) is obtained through a seven-hole probe. The downstream film-cooling effectiveness on the flat plate is measured by pressure sensitive paint (PSP). The inclination angle (θ) of all the holes is 35 deg, and the compound angle (β) is ±45 deg. Effects of the spanwise distance (p = 0, 0.5d, 1.0d, 1.5d, and 2.0d) between the two interacting jets of DJFC holes are studied, while the streamwise distance (s) is kept as 3d. The blowing ratio (M) varies as 0.5, 1.0, 1.5, and 2.0. The density ratio (DR) is maintained at 1.0. Results show that the interaction between the two jets of DJFC holes has different effects at different spanwise distances. For a small spanwise distance (p/d = 0), the interaction between the jets presents a pressing effect. The downstream jet is pressed down and kept attached to the surface by the upstream one. The effectiveness is not sensitive to blowing ratios. For mid-spanwise distances (p/d = 0.5 and 1.0), the antikidney vortex pair dominates the interaction and pushes both of the jets down, thus leading to better coolant coverage and higher effectiveness. As the spanwise distance becomes larger (p/d ≥ 1.5), the pressing effect almost disappears, and the antikidney vortex pair effect is weaker. The jets separate from each other and the coolant coverage decreases. At a higher blowing ratio, the interaction between the jets of DJFC holes happens later.

scholarly journals Numerical Investigation of Film Cooling Enhancement Using an Upstream Sand-Dune-Shaped Ramp

Computation ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 49 ◽  
Author(s):  
Sheng-Chang Zhang ◽  
Jing-Zhou Zhang ◽  
Xiao-Ming Tan
Keyword(s):  
Film Cooling ◽  
Sand Dune ◽  
Vortex Pair ◽  
Primary Flow ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Cooling Hole ◽  
Cooling Enhancement ◽  
Lateral Film ◽  
Film Layer

Film cooling enhancement by incorporating an upstream sand-dune-shaped ramp (SDSR) to the film hole exit was numerically investigated on a flat plate under typical blowing ratios ranging from 0.5 to 1.5. Three heights of SDSRs were designed: 0.25D, 0.5D, and 0.75D. The results indicated that the upstream SDSR effectively controlled the near-wall primary flow and subsequent mutual interaction with the coolant jet, which was the main mechanism of the film cooling enhancement. First, a pair of anti-kidney vortices was formed at the trailing ridges of the SDSR, which helped suppress the kidney vortex pair due to the interaction between the coolant jet and the primary flow. Second, a weak separation and a low pressure zone were induced behind the backside of the SDSR, which caused the coolant jet to spread around the film cooling hole and improve the lateral film coverage. With respect to the baseline cylindrical film cooling holes, the effect of the upstream SDSR was distinct under different blowing ratios. Under a low blowing ratio, the upstream SDSR shortened the streetwise film layer coverage in the vicinity of the film hole centerline but increased the span-wise film layer coverage. A relatively optimal ramp height seemed to be 0.5D. Under a high blowing ratio, both the streamwise and span-wise film layer coverages improved in comparison with the baseline case. The film cooling effectiveness improved gradually with increasing ramp height.

Effect of Jet Pulsing on Film Cooling: Part 1— Effectiveness and Flowfield Temperature Results

2006 ◽  
Author(s):  
Sarah M. Coulthard ◽  
Ralph J. Volino ◽  
Karen A. Flack
Keyword(s):  
Film Cooling ◽  
Infrared Camera ◽  
Temperature Fields ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Cold Wire ◽  
Duty Cycles ◽  
Cooling Behavior ◽  
Film Cooling Holes

Pulsed film cooling was studied experimentally to determine its effect on film cooling effectiveness. The film cooling jets were pulsed using solenoid valves in the supply air line. Cases with a single row of cylindrical film cooling holes inclined at 35 degrees to the surface of a flat plate were considered at blowing ratios of 0.25, 0.5, 1.0, and 1.5 for a variety of pulsing frequencies and duty cycles. Temperature measurements were made using an infrared camera, thermocouples, and cold wire anemometry. Hot wire anemometry was used for velocity measurements. The local film cooling effectiveness was calculated based on the measured temperatures and the results were compared to baseline cases with continuous blowing. Phase locked flow temperature fields were determined from cold wire surveys. Pulsing at high frequencies helped to improve film cooling effectiveness in some cases by reducing overall jet liftoff. At lower frequencies, pulsing tended to have the opposite effect. With the present geometry and a steady mainflow, pulsing did not provide an overall benefit. The highest overall effectiveness was achieved with continuous jets and a blowing ratio of 0.5. The present results may prove useful for understanding film cooling behavior in engines, where mainflow unsteadiness causes film cooling jet pulsation.

A Numerical and Experimental Investigation of the Slot Film-Cooling Jet With Various Angles

2005 ◽  
Vol 127 (3) ◽  
pp. 635-645 ◽  
Author(s):  
Rongguang Jia ◽  
Bengt Sundén ◽  
Petre Miron ◽  
Bruno Léger
Keyword(s):  
Film Cooling ◽  
Stokes Equations ◽  
Cross Flow ◽  
Turbulence Models ◽  
Temperature Fields ◽  
Cooling Effectiveness ◽  
Recirculation Bubble ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Present Solution

Numerical simulations coupled with laser Doppler velocimetry (LDV) experiments were carried out to investigate a slot jet issued into a cross flow, which is relevant in the film cooling of gas turbine combustors. The film-cooling fluid injection from slots or holes into a cross flow produces highly complicated flow fields. In this paper, the time-averaged Navier-Stokes equations were solved on a collocated body-fitted grid system with the shear stress transport k−ω, V2F k−ϵ, and stress-ω turbulence models. The fluid flow and turbulent Reynolds stress fields were compared to the LDV experiments for three jet angles, namely, 30, 60, and 90 deg, and the jet blowing ratio is ranging from 2 to 9. Good agreement was obtained. Therefore, the present solution procedure was also adopted to calculations of 15 and 40 deg jets. In addition, the temperature fields were computed with a simple eddy diffusivity model to obtain the film-cooling effectiveness, which, in turn, was used for evaluation of the various jet cross-flow arrangements. The results show that a recirculation bubble downstream of the jet exists for jet angles larger than 40 deg, but it vanishes when the angle is <30deg, which is in good accordance with the experiments. The blowing ratio has a large effect on the size of the recirculation bubble and, consequently, on the film cooling effectiveness. In addition, the influence of boundary conditions for the jet and cross flow are also addressed in the paper.

Numerical and Experimental Study of the Slot Film Cooling Jet With Various Angles

2003 ◽  
Author(s):  
Rongguang Jia ◽  
Bengt Sunde´n ◽  
Petre Miron ◽  
Bruno Le´ger
Keyword(s):  
Film Cooling ◽  
Stokes Equations ◽  
Cross Flow ◽  
Eddy Diffusivity ◽  
Temperature Fields ◽  
Cooling Effectiveness ◽  
Recirculation Bubble ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Present Solution

Numerical simulations coupled with LDV experiments were carried out to investigate a slot jet issued into a cross flow, which is relevant in the film cooling of gas turbine combustors. The film cooling fluid injection from slots or holes into a cross-flow produces highly complicated flow fields. In this paper, the time-averaged Navier-Stokes equations were solved on a collocated body-fitted grid system with the V2F turbulence model. The fluid flow and turbulent Reynolds stress fields were compared with the LDV experiments for three jet angles, namely, 30-deg, 60-deg, and 90-deg, and the jet blowing ratio is ranging from 2 to 9. Good agreement was obtained. Therefore, the present solution procedure was also adopted to calculations of 15-deg and 40-deg jets. In addition, the temperature fields, which were difficult to measure by experimental methods, were also computed with a simple eddy diffusivity model to obtain the film cooling effectiveness which was used for evaluation of the various jet-cross-flow arrangements. The results show that a recirculation bubble downstream the jet exists for jet angles larger than 40-deg, but it vanishes when the angle is less than 30-deg, which is in good accordance with the experiments. The blowing ratio has a large effect on the size of the recirculation bubble, and consequently on the film cooling effectiveness. In addition, the influence of boundary conditions for the jet and cross-flow are also addressed in the paper.

Effect of Jet Pulsing on Film Cooling—Part I: Effectiveness and Flow-Field Temperature Results

2006 ◽  
Vol 129 (2) ◽  
pp. 232-246 ◽  
Author(s):  
Sarah M. Coulthard ◽  
Ralph J. Volino ◽  
Karen A. Flack
Keyword(s):  
Film Cooling ◽  
Infrared Camera ◽  
Temperature Fields ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Cold Wire ◽  
Duty Cycles ◽  
Cooling Behavior ◽  
Film Cooling Holes

Pulsed film cooling was studied experimentally to determine its effect on film-cooling effectiveness. The film-cooling jets were pulsed using solenoid valves in the supply air line. Cases with a single row of cylindrical film-cooling holes inclined at 35 deg to the surface of a flat plate were considered at blowing ratios of 0.25, 0.5, 1.0, and 1.5 for a variety of pulsing frequencies and duty cycles. Temperature measurements were made using an infrared camera, thermocouples, and cold-wire anemometry. Hot-wire anemometry was used for velocity measurements. The local film-cooling effectiveness was calculated based on the measured temperatures, and the results were compared to baseline cases with continuous blowing. Phase-locked flow temperature fields were determined from cold-wire surveys. Pulsing at high frequencies helped to improve film-cooling effectiveness in some cases by reducing overall jet liftoff. At lower frequencies, pulsing tended to have the opposite effect. With the present geometry and a steady mainflow, pulsing did not provide an overall benefit. The highest overall effectiveness was achieved with continuous jets and a blowing ratio of 0.5. The present results may prove useful for understanding film-cooling behavior in engines, where mainflow unsteadiness causes film-cooling jet pulsation.

Influence of Blowing Ratio on the Double-Jet Ejection of Cooling Air

2007 ◽  
Author(s):  
Karsten Kusterer ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
Ryozo Tanaka
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Vortex Pair ◽  
Mixing Processes ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Secondary Vortices ◽  
Cooling Air ◽  
Combined Cooling

Further improvement of the thermal efficiency of modern gas turbines can be achieved by a further reduction of the cooling air amount. Therefore, it is necessary to increase the cooling effectiveness so that the available cooling air fulfils the cooling task even if the amount has been reduced. In particular, the cooling effort for the vanes and blades of the first stage in a modern gas turbine is very high. The task of the film-cooling is to protect the blade material from the hot gas attack to the surface. Unfortunately, aerodynamic mixing processes are enhanced by secondary vortices in the cooling jets and, thus, the film-cooling effectiveness is reduced shortly behind the cooling air ejection through the holes. By improvement of the hole positioning, the negative interaction effects can be reduced. One approach is the Double-jet Film-cooling (DJFC) Technology presented recently by the authors. It has been shown by numerical simulations that for a special and precise arrangement of two holes, the interaction of the secondary vortices can be used for a significant increase in film-cooling effectiveness. This is reached by establishing an anti-kidney vortex pair in a combined jet from two jets starting from two cylindrical ejection holes. The influence of the blowing ratio on the double-jet ejection is investigated numerically. The configurations of the double-hole arrangements have been investigated only for a relative high blowing ratio (M = 1.7). The present investigations focus on moderate blowing ratios (1.0 &lt; M &lt; 1.5) and on a higher blowing ratio of M = 2.0. It can be shown that also for moderate blowing ratios the anti-kidney vortex pair is generated in the combined cooling jet. Thus, high adiabatic film-cooling effectiveness can be reached also for the case with a moderate blowing ratio. The lateral distribution of the cooling air is reduced compared to the cases of higher blowing ratios (M = 1.7, M = 2.0).

Effect of Blowing Ratio on Mist-Assisted Air Film Cooling of a Flat Plate: An Experimental Study

2020 ◽  
Vol 13 (3) ◽  
Author(s):  
Mallikarjuna Rao Pabbisetty ◽  
B. V. S. S. S. Prasad
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Test Facility ◽  
Cooling Effectiveness ◽  
Ir Camera ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Cooling Enhancement ◽  
Air Film

Abstract A novel mist-assisted air film cooling scheme is proposed by Li and Wang (2006, “Simulation of Film Cooling Enhancement With Mist Injection,” ASME J. Heat Transfer, 128, pp. 509–519) to increase the film cooling effectiveness of a gas turbine cooled vane/blade. This scheme is further investigated experimentally in this article to determine the effect of the blowing ratio. The coolant is made to pass through the film holes on a flat plate mounted in a test facility. Tiny water droplets, characterized by Rosin-Rammler mean diameter of about 36.7 μm measured with a phase Doppler particle analyzer (PDPA) system is introduced into the cooling air. The effectiveness values are evaluated by measuring the plate surface temperature with the infrared (IR) camera. The maximum percentage of the mist-assisted film cooling effectiveness is 26% more than air film cooling effectiveness when 2.1% of mist is added to the air. In addition, the coolant coverage on the plate is found to be much better with mist cooling in both the streamwise and the spanwise directions. The net enhancement due to the mist-assisted air film cooling effectiveness (Δη) decreases with the increasing values of the blowing ratio in the range of 0.55–2.58 at a density ratio of 2.2.

Interaction of Flow and Film-Cooling Effectiveness Between Double-Jet Film-Cooling Holes With Various Spanwise Distances

2017 ◽  
Author(s):  
Jiaxu Yao ◽  
Jin Xu ◽  
Ke Zhang ◽  
Jiang Lei ◽  
Lesley M. Wright
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Vortex Pair ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Film Cooling Holes ◽  
Two Jets ◽  
Compound Angle

The interaction of flow and film-cooling effectiveness between jets of double-jet film-cooling (DJFC) holes on a flat plate is studied experimentally. The time-averaged secondary flow field in several axial positions (X/d = −2.0, 1.0, and 5.0) is obtained through a seven-hole probe. The downstream film-cooling effectiveness on the flat plate is achieved by Pressure Sensitive Paint (PSP). The inclination angle (θ) of all holes is 35°, and the compound angle (β) is ±45°. Effects of spanwise distance (p = 0, 0.5d, 1.0d, 1.5d, 2.0d) between the two interacting jets of DJFC holes are studied while streamwise distance (s) is kept as 3d. The blowing ratio (M) varies as 0.5, 1.0, 1.5, and 2.0. The density ratio (DR) is maintained at 1.0. Results show that the interaction between two jets of DJFC holes has different effects for different spanwise distance. For a small spanwise distance (p/d = 0), the interaction between jets presents a pressing effect. The downstream jet is pressed down and kept attached to the surface by the upstream one. The effectiveness is not sensitive to blowing ratios. For mid spanwise distances (p/d = 0.5 and 1.0), the anti-kidney vortex pair dominates the interaction, and pushes both of the jets down, thus leads to better coolant coverage and higher effectiveness. As spanwise distance becomes larger (p/d≥1.5), the pressing effect almost disappears, and the anti-kidney vortex pair effect is weaker. The jets separate from each other and the coolant coverage decreases. At higher blowing ratio, the interaction between the two jets of DJFC holes moves more downstream.

scholarly journals Numerical Investigation of Partial Blockage Effect on Film Cooling Effectiveness

2014 ◽  
Vol 2014 ◽  
pp. 1-13 ◽  
Author(s):  
Pan Cheng-xiong ◽  
Zhang Jing-zhou ◽  
Huang Ke-nan
Keyword(s):  
Film Cooling ◽  
Peak Velocity ◽  
Three Dimensional ◽  
Vertical Direction ◽  
Leading Edge ◽  
Streamwise Direction ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Jet Interaction ◽  
Blowing Ratio

Three-dimensional numerical calculation was performed to investigate the effects of partial blockage inside cylindrical film holes on the film cooling effectiveness over a flat plate. Five blockage ratios ranged from 0.1 to 0.5 and a series of blockage positions were considered under the blowing ratios of 0.3–1.5. It is found that the blockage position has a significant influence on mainstream-coolant jet interaction. The partial blockage located at the leading edge of coolant-hole exit mitigates the primary vortices due to mainstream-coolant jet interaction. The coolant jet penetration along vertical direction is suppressed and the peak velocity along streamwise direction is augmented under the action of partial blockage at the upstream side of film holes, providing an increment of film cooling effectiveness, especially under high blowing ratio. While the partial blockages located at the trailing or lateral edges of coolant-hole exit weaken the film cooling effectiveness. In relation to the partial blockage located in the vicinity of coolant-hole exit, the partial blockage located in the vicinity of coolant-hole inlet or middle has less impaction on the film cooling effectiveness under low blowing ratio.

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