scholarly journals Simulation of Film Cooling Enhancement With Mist Injection

2005 ◽  
Author(s):  
Xianchang Li ◽  
Ting Wang
Keyword(s):  
Film Cooling ◽  
Injection Rate ◽  
Round Hole ◽  
Gas Temperature ◽  
Cooling Effectiveness ◽  
Droplet Dynamics ◽  
Blowing Ratio ◽  
Jet Cooling ◽  
Cooling Enhancement ◽  
Conventional Cooling

Cooling of gas turbine hot section components such as combustor liners, combustor transition pieces, turbine vanes (nozzles) and blades (buckets) is a critical task for improving the life and reliability of hot-section components. Conventional cooling techniques using air-film cooling, impingement jet cooling, and turbulators have significantly contributed to cooling enhancements in the past. However, the increased net benefits that can be continuously harnessed by using these conventional cooling techniques seem to be incremental and are about to approach their limit. Therefore, new cooling techniques are essential for surpassing these current limits. This paper investigates the potential of film cooling enhancement by injecting mist into the coolant. The computational results show that a small amount of injection (2% of the coolant flow rate) can enhance the cooling effectiveness about 30% ∼ 50%. The cooling enhancement takes place more strongly in the downstream region, where the single-phase film cooling becomes less powerful. Three different holes are used in this study including a 2-D slot, a round hole, and a fan-shaped diffusion hole. A comprehensive study is performed on the effect of flue gas temperature, blowing angle, blowing ratio, mist injection rate, and droplet size on the cooling effectiveness with 2-D cases. Analysis on droplet history (trajectory and size) is undertaken to interpret the mechanism of droplet dynamics.

Simulation of Film Cooling Enhancement With Mist Injection

2005 ◽  
Vol 128 (6) ◽  
pp. 509-519 ◽  
Author(s):  
Xianchang Li ◽  
Ting Wang
Keyword(s):  
Film Cooling ◽  
Injection Rate ◽  
Round Hole ◽  
Gas Temperature ◽  
Cooling Effectiveness ◽  
Droplet Dynamics ◽  
Jet Cooling ◽  
Adiabatic Cooling ◽  
Cooling Enhancement ◽  
Conventional Cooling

Cooling of gas turbine hot-section components, such as combustor liners, combustor transition pieces, and turbine vanes (nozzles) and blades (buckets), is a critical task for improving the life and reliability of them. Conventional cooling techniques using air-film cooling, impingement jet cooling, and turbulators have significantly contributed to cooling enhancements in the past. However, the increased net benefits that can be continuously harnessed by using these conventional cooling techniques seem to be incremental and are about to approach their limit. Therefore, new cooling techniques are essential for surpassing these current limits. This paper investigates the potential of film-cooling enhancement by injecting mist into the coolant. The computational results show that a small amount of injection (2% of the coolant flow rate) can enhance the adiabatic cooling effectiveness about 30–50%. The cooling enhancement takes place more strongly in the downstream region, where the single-phase film cooling becomes less powerful. Three different holes are used in this study including a two-dimensional (2D) slot, a round hole, and a fan-shaped diffusion hole. A comprehensive study is performed on the effect of flue gas temperature, blowing angle, blowing ratio, mist injection rate, and droplet size on the cooling effectiveness with 2D cases. Analysis on droplet history (trajectory and size) is undertaken to interpret the mechanism of droplet dynamics.

Combined Effects of Freestream Pressure Gradient and Density Ratio on the Film Cooling Effectiveness of Round and Shaped Holes on a Flat Plate

2016 ◽  
Author(s):  
Kyle R. Vinton ◽  
Travis B. Watson ◽  
Lesley M. Wright ◽  
Daniel C. Crites ◽  
Mark C. Morris ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Round Hole ◽  
Combined Effects ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Lift Off

The combined effects of a favorable, mainstream pressure gradient and coolant-to-mainstream density ratio have been investigated. Detailed film cooling effectiveness distributions have been obtained on a flat plate with either cylindrical (θ = 30°) or laidback, fan-shaped holes (θ = 30°, β = γ = 10°) using the pressure sensitive paint (PSP) technique. In a low speed wind tunnel, both non-accelerating and accelerating flows were considered while the density ratio varied from 1–4. In addition, the effect of blowing ratio was considered, with this ratio varying from 0.5 to 1.5. The film produced by the shaped hole outperformed the round hole under the presence of a favorable pressure gradient for all blowing and density ratios. At the lowest blowing ratio, in the absence of freestream acceleration, the round holes outperformed the shaped holes. However, as the blowing ratio increases, the shaped holes prevent lift-off of the coolant and offer enhanced protection. The effectiveness afforded by both the cylindrical and shaped holes, with and without freestream acceleration, increased with density ratio.

Investigation of a Novel Discrete Slot Film Cooling Scheme

2014 ◽  
Author(s):  
Karim M. Shalash ◽  
Lamyaa A. El-Gabry ◽  
Mohamed M. Abo El-Azm
Keyword(s):  
Film Cooling ◽  
Cross Flow ◽  
Sensitivity Study ◽  
Round Hole ◽  
Blade Surface ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Jet In Cross Flow ◽  
Slot Film Cooling

The future of the gas turbine industry is strongly relying on the development of new efficient cooling schemes. Film cooling is one popular and reliable cooling technique, one way to increase the film cooling effectiveness is through the use of shaped holes. In this paper two proposed shaped holes are being studied and compared thoroughly against the conventional round hole film cooling. The two proposed holes are based on the theoretically perfect continuous slot film cooling, however, these slots are not continuous, and preserves the solid surface to the total blade surface ratio. The first design to be studied is the Rectangular Divergent Slot, and the second is the Aeroslot, which is a discrete aerodynamically shaped slot; both designs showed an increase in the centerline film cooling effectiveness when compared to the conventional round holes. The Aeroslot showed a large increase in film cooling effectiveness for the same blowing ratio, and mass flow rate of coolant, when compared to the other shapes. A sensitivity study of the blowing ratio to the centerline film cooling effectiveness is carried out for several blowing ratios, covering different jet in cross flow behaviors, fully attached jet, and detached-reattached jet.

Effect of Row Spacing on the Accuracy of Film Cooling Superposition Method

2018 ◽  
Author(s):  
Lang Wang ◽  
Xueying Li ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Film Cooling ◽  
Row Spacing ◽  
Superposition Method ◽  
Round Hole ◽  
Cooling Effectiveness ◽  
Blowing Ratio ◽  
Cooling Hole ◽  
Shaped Hole ◽  
The Difference ◽  
Density Ratios

Film cooling technique is widely used in a modern gas turbine. Many applications in hot sections require multiple film cooling rows to get better cooled. In most situation, the additive effect is computed using Sellers superposition method, but it is not accurate when the hole rows are close to each other. In this paper, row spacing between two rows of cooling hole was investigated by numerical method, which was validated by PSP results. The validation experiments are performed on flat test bench and the freestream is maintained at 25m/s. The inlet boundary conditions of numerical simulations were same with the experiment. Both round hole and shaped hole were investigated at blowing ratio M = 0.5, density ratios DR = 1.5 and row spacing S/D = 6, 10, 15, 20. It is found that the round hole results by Sellers method are similar to experiment results only at large row spacing, and the results of Sellers are always higher than experimental results. The boundary layer has a big effect on cooling effectiveness for round hole, but very little effect on shaped hole. When the row spacing increase, the difference between experiment and prediction become smaller. The vortex is the major factor to effect the accuracy of superposition method.

Enhancement of Film Cooling Effectiveness Using Dean Vortices

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Pingting Chen ◽  
Lang Wang ◽  
Xueying Li ◽  
Jing Ren ◽  
Hongde Jiang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Gas Turbines ◽  
Wall Region ◽  
Round Hole ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Dean Vortices ◽  
Curved Hole

Abstract Film cooling technology is widely used in gas turbines. With the additive manufacturing anticipated in the future, there will be more freedom in film cooling hole design. Exploiting this freedom, the present authors tried using curved holes to generate Dean vortices within the delivery line. These vortices have opposite direction of rotation to the vorticity of the kidney vortices and, thus, there is interaction between these vortices in the mixing region. It is shown that as a result of the inclusion of Dean vortices, the curved hole delivery leads to enhanced film cooling effectiveness. Numerical results, including film cooling effectiveness values, tracking of vortices in the flow field, heat transfer coefficients, and net heat flux reduction (NHFR), are compared between the curved hole, round hole, and a laidback, fan-shaped hole with blowing ratios, M, of 0.5, 1.0, 1.5, 2.0, and 2.5. The comparison shows that film cooling effectiveness values with the curved hole are higher than those with cylindrical film cooling holes at every blowing ratio studied. The curved hole has lower film cooling effectiveness values than the laidback, fan-shaped holes when M = 0.5 and 1.0, but shows advantages when the blowing ratio is higher than 1.0. There is heat transfer enhancement for the curved hole case due to a higher kinetic energy transferred to the near-wall region, however. Nevertheless, the curved hole still displays a higher NHFR when the blowing ratio is high.

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.

Combined Effects of Freestream Pressure Gradient and Density Ratio on the Film Cooling Effectiveness of Round and Shaped Holes on a Flat Plate

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Kyle R. Vinton ◽  
Travis B. Watson ◽  
Lesley M. Wright ◽  
Daniel C. Crites ◽  
Mark C. Morris ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Round Hole ◽  
Combined Effects ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Lift Off

The combined effects of a favorable, mainstream pressure gradient and coolant-to-mainstream density ratio have been investigated. Detailed film cooling effectiveness distributions have been obtained on a flat plate with either cylindrical (θ = 30 deg) or laidback, fan-shaped holes (θ = 30 deg and β = γ = 10 deg) using the pressure-sensitive paint (PSP) technique. In a low-speed wind tunnel, both nonaccelerating and accelerating flows were considered, while the density ratio varied from 1 to 4. In addition, the effect of blowing ratio was considered, with this ratio varying from 0.5 to 1.5. The film produced by the shaped hole outperformed the round hole under the presence of a favorable pressure gradient for all the blowing and density ratios. At the lowest blowing ratio, in the absence of freestream acceleration, the round holes outperformed the shaped holes. However, as the blowing ratio increases, the shaped holes prevent lift-off of the coolant and offer enhanced protection. The effectiveness afforded by both the cylindrical and shaped holes, with and without freestream acceleration, increased with density ratio.

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.

The Effect of Using Ramps with Trench Cylindrical Holes on Film Cooling Effectiveness

2015 ◽  
Vol 3 (2) ◽  
pp. 15-27
Author(s):  
Ahmed A. Imram ◽  
Humam K. Jalghef ◽  
Falah F. Hatem
Keyword(s):  
Numerical Simulation ◽  
Film Cooling ◽  
Air Injection ◽  
Baseline Model ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Hot Air ◽  
Test Study ◽  
Cylindrical Holes

     The effect of introducing ramp with a cylindrical slot hole on the film cooling effectiveness has been investigated experimentally and numerically. The film cooling effectiveness measurements are obtained experimentally. A test study was performed at a single mainstream with Reynolds number 76600 at three different coolant to mainstream blowing ratios 1.5, 2, and 3. Numerical simulation is introduced to primarily estimate the best ramp configurations and to predict the behavior of the transport phenomena in the region linked closely to the interaction between the coolant air injection and the hot air mainstram flow. The results showed that using ramps with trench cylindrical holes would enhanced the overall film cooling effectiveness by 83.33% compared with baseline model at blowing ratio of 1.5, also  the best overall flim cooling effectevness was obtained at blowing ratio of 2 while it is reduced at blowing ratio of 3.

Numerical Study of the Effect of Blowing Angle on Cooling Effectiveness of an Effusion Cooling

2004 ◽  
Author(s):  
Yaping Hu ◽  
Honghu Ji
Keyword(s):  
Film Cooling ◽  
Numerical Study ◽  
Coolant Flow ◽  
Cooling Effectiveness ◽  
Absolute Value ◽  
Blowing Ratio ◽  
Conventional Film

The paper numerically investigates the influences of the blowing angle α of coolant flow on the cooling effectiveness of effusion cooling of a plate. Nine cases were studied which cover three blowing angles of α = 30°, 60°, 90° and for each angle three blowing ratios of M = 0.5, 1.0, 2.0 are calculated, respectively. The results show that with the increase of α the cooling effectiveness reduces for all the calculated cases. For the cases of α = 30° and 60° the distribution of cooling effectiveness η along the whole plate are very similar for any given blowing ratio, especially when M = 1.0 and 2.0. Whereas for the cases of α = 90°, the distributions of cooling effectiveness are quite different from other two blowing angles for a given blowing ratio, especially for M = 1.0 and in the trailing region of the plate. Although the cooling effectiveness of the cases with α = 90° for any given blowing ratio is the worst one among the three angles (α = 30°, 60°, and 90°) stated, its absolute value is still quite high comparing to the conventional film cooling.

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