Film Cooling Study of Novel Orthogonal Entrance and Shaped Exit Holes

Transfer Coefficient ◽

Film Cooling ◽

Geometrical Parameters ◽

Cooling Effectiveness ◽

Cooling Hole ◽

Cooling Effects ◽

Internal Side

Film cooling effectiveness depends on several geometrical parameters like location on the airfoil, exit shape, orientation and arrangement of the holes. The focus of this investigation is to propose and explore a new film cooling hole geometry. The adiabatic film cooling effectiveness is determined experimentally, downstream of the exit of the film cooling holes on a flat plate using a steady state IR thermography technique. Coolant holes that are perpendicular to the direction of flow detach from the surface and enhance the heat transfer coefficient on the turbine blade without providing any coolant coverage, while angled holes along the mainstream direction result in superior film cooling effectiveness and lower heat transfer to the surface. The objective of this study is to examine the external cooling effects using coolant holes that are a combination of both angled shaped holes as well as perpendicular holes. The inlet of the coolant hole is kept perpendicular to the direction of flow to enhance the internal side heat transfer coefficient and the exit of the coolant hole is expanded and angled along the mainstream flow to prevent the coolant jet from lifting off from the blade external surface. A total of six different cases with variations in exit shape geometry are investigated at different blowing ratios (BR varying from 0.5 to 2.0). Results suggest that the film cooling effectiveness values obtained from these geometries are comparable with those of conventional angled holes. With the added advantage of enhanced heat transfer coefficient on the coolant channel internal side, as proven earlier by Byerley [3], overall superior cooling is accomplished. Furthermore this shaped hole can be made using the same technology being presently used in the industry.

Adiabatic Effectiveness and Heat Transfer Coefficient of Shaped Film Cooling Holes on a Scaled Guide Vane Pressure Side Model

International Journal of Rotating Machinery ◽

10.1155/s1023621x04000351 ◽

2004 ◽

Vol 10 (5) ◽

pp. 345-354 ◽

Cited By ~ 16

Author(s):

Jan Dittmar ◽

Achmed Schulz ◽

Sigmar Wittig

Keyword(s):

Heat Transfer ◽

Transfer Coefficient ◽

Film Cooling ◽

Guide Vane ◽

Inlet Temperature ◽

Test Model ◽

Pressure Side ◽

Cooling Effectiveness ◽

Film Cooling Effectiveness

The demand of improved thermal efficiency and high power output of modern gas turbine engines leads to extremely high turbine inlet temperature and pressure ratios. Sophisticated cooling schemes including film cooling are widely used to protect the vanes and blades of the first stages from failure and to achieve high component lifetimes. In film cooling applications, injection from discrete holes is commonly used to generate a coolant film on the blade's surface.In the present experimental study, the film cooling performance in terms of the adiabatic film cooling effectiveness and the heat transfer coefficient of two different injection configurations are investigated. Measurements have been made using a single row of fanshaped holes and a double row of cylindrical holes in staggered arrangement. A scaled test model was designed in order to simulate a realistic distribution of Reynolds number and acceleration parameter along the pressure side surface of an actual turbine guide vane. An infrared thermography measurement system is used to determine highly resolved distribution of the models surface temperature. Anin-situcalibration procedure is applied using single embedded thermocouples inside the measuring plate in order to acquire accurate local temperature data.All holes are inclined 35° with respect to the model's surface and are oriented in a streamwise direction with no compound angle applied. During the measurements, the influence of blowing ratio and mainstream turbulence level on the adiabatic film cooling effectiveness and heat transfer coefficient is investigated for both of the injection configurations.

Numerical Study on the Influence of Trench Width on Film Cooling Characteristics of Double-Wave Trench

Volume 5A: Heat Transfer ◽

10.1115/gt2017-63552 ◽

2017 ◽

Cited By ~ 2

Author(s):

Bo-lun Zhang ◽

Li Zhang ◽

Hui-ren Zhu ◽

Jian-sheng Wei ◽

Zhong-yi Fu

Keyword(s):

Heat Transfer ◽

Transfer Coefficient ◽

Film Cooling ◽

Numerical Study ◽

Leading Edge ◽

Cooling Effectiveness ◽

Blowing Ratio ◽

Trench Width

Film cooling performance of the double-wave trench was numerically studied to improve the film cooling characteristics. Double-wave trench was formed by changing the leading edge and trailing edge of transverse trench into cosine wave. The film cooling characteristics of transverse trench and double-wave trench were numerically studied using Reynolds Averaged Navier Stokes (RANS) simulations with realizable k-ε turbulence model and enhanced wall treatment. The film cooling effectiveness and heat transfer coefficient of double-wave trench at different trench width (W = 0.8D, 1.4D, 2.1D) conditions are investigated, and the distribution of temperature field and flow field were analyzed. The results show that double-wave trench effectively improves the film cooling effectiveness and the uniformity of jet at the downstream wall of the trench. The span-wise averaged film cooling effectiveness of the double-wave trench model increases 20–63% comparing with that of the transverse trench at high blowing ratio. The anti-counter-rotating vortices which can press the film on near-wall are formed at the downstream wall of the double-wave trench. With the double-wave trench width decreasing, the film cooling effectiveness gradually reduces at the hole center-line region of the downstream trench. With the increase of the blowing ratio, the span-wise averaged heat transfer coefficient increases. The span-wise averaged heat transfer coefficient of the double-wave trench with 0.8D and 2.1D trench width is higher than that of the double-wave trench with 1.4D trench width at the high blowing ratio conditions.

Investigations on the Influence of Rib Orientation Angle on Film Cooling Performance of Compound Holes

Volume 5C: Heat Transfer ◽

10.1115/gt2018-75794 ◽

2018 ◽

Author(s):

Lin Ye ◽

Cun-liang Liu ◽

Hai-yong Liu ◽

Hui-ren Zhu ◽

Jian-xia Luo

Keyword(s):

Heat Transfer ◽

Transfer Coefficient ◽

Film Cooling ◽

Discharge Coefficient ◽

Orientation Angle ◽

Cooling Effectiveness ◽

Cooling Performance ◽

Blowing Ratio

To investigate the effects of the inclined ribs on internal flow structure in film hole and the film cooling performance on outer surface, experimental and numerical studies are conducted on the effects of rib orientation angle on film cooling of compound cylindrical holes. Three coolant channel cases, including two ribbed cross-flow channels (135° and 45° angled ribs) and the plenum case, are studied under three blowing ratios (0.5, 1.0 and 2.0). 2D contours of film cooling effectiveness as well as heat transfer coefficient were measured by transient liquid crystal measurement technique (TLC). The steady RANS simulations with realizable k-ε turbulence model and enhanced wall treatment were performed. The results show that the spanwise width of film coverage is greatly influenced by the rib orientation angle. The spanwise width of the 45° rib case is obviously larger than that of the 135° rib case under lower blowing ratios. When the blowing ratio is 1.0, the area-averaged cooling effectiveness of the 135° rib case and the 45° rib case are higher than that of the plenum case by 38% and 107%, respectively. With the increase of blowing ratio, the film coverage difference between different rib orientation cases becomes smaller. The 45° rib case also produces higher heat transfer coefficient, which is higher than the 135° rib case by 3.4–8.7% within the studied blowing ratio range. Furthermore, the discharge coefficient of the 45° rib case is the lowest among the three cases. The helical motion of coolant flow is observed in the hole of 45° rib case. The jet divides into two parts after being blown out of the hole due to this motion, which induces strong velocity separation and loss. For the 135° rib case, the vortex in the upper half region of the secondary-flow channel rotates in the same direction with the hole inclination direction, which leads to the straight streamlines and thus results in lower loss and higher discharge coefficient.

Measurement of Detailed Heat Transfer Coefficient and Film Cooling Effectiveness Distributions Using PSP and TSP

Volume 3: Heat Transfer, Parts A and B ◽

10.1115/gt2009-59975 ◽

2009 ◽

Cited By ~ 7

Author(s):

Rebekah A. Russin ◽

Daniel Alfred ◽

Lesley M. Wright

Keyword(s):

Heat Transfer ◽

Transfer Coefficient ◽

Film Cooling ◽

Optical Filters ◽

Experimental Investigations ◽

Transient Temperature ◽

Cooling Effectiveness ◽

Wide Range

This paper presents the development of a novel experimental technique utilizing both temperature and pressure sensitive paints (TSP and PSP). Through the combination of these paints, both detailed heat transfer coefficient and film cooling effectiveness distributions can be obtained from two short experiments. Using a mass transfer analogy, PSP has proven to be a powerful technique for measurement of film cooling effectiveness. This benefit is exploited to obtain detailed film cooling effectiveness distributions from a steady state flow experiment. This measured film cooling effectiveness is combined with transient temperature distributions obtained from a transient TSP experiment to produce detailed heat transfer coefficient distributions. Optical filters are used to differentiate the light emission from the florescent molecules comprising the PSP and TSP. Although two separate tests are needed to obtain the heat transfer coefficient distributions, the two tests can be performed in succession to minimize setup time and variability. The detailed film effectiveness and heat transfer enhancement ratios have been obtained for a generic, inclined angle (θ = 35°) hole geometry on a flat plate. Distinctive flow features over a wide range of blowing ratios have been captured with the proposed technique. In addition, the measured results have compared favorably to previous studies (both qualitatively and quantitatively), thus substantiating the use of the combined PSP / TSP technique for experimental investigations of three temperature mixing problems.

Investigation on the Leading Edge Film Cooling of Counter-Inclined Cylindrical and Laid-Back Holes With and Without Impingement: Part II — Heat Transfer Coefficient

Volume 5C: Heat Transfer ◽

10.1115/gt2018-76066 ◽

2018 ◽

Author(s):

Rui-dong Wang ◽

Cun-liang Liu ◽

Hai-yong Liu ◽

Hui-ren Zhu ◽

Qi-ling Guo ◽

...

Keyword(s):

Heat Transfer ◽

Transfer Coefficient ◽

Film Cooling ◽

Leading Edge ◽

Cooling Effectiveness ◽

Blowing Ratio ◽

The Heat Transfer Coefficient ◽

Tube Structure

Heat transfer of the counter-inclined cylindrical and laid-back holes with and without impingement on the turbine vane leading edge model are investigated in this paper. To obtain the film cooling effectiveness and heat transfer coefficient, transient temperature measurement technique on complete surface based on double thermochromic liquid crystals is used in this research. A semi-cylinder model is used to model the vane leading edge which is arranged with two rows of holes. Four test models are measured under four blowing ratios including cylindrical film holes with and without impingement tube structure, laid-back film holes with and without impingement tube structure. This is the second part of a two-part paper, the first part paper GT2018-76061 focuses on film cooling effectiveness and this study will focus on heat transfer. Contours of surface heat transfer coefficient and laterally averaged result are presented in this paper. The result shows that the heat transfer coefficient on the surface of the leading edge is enhanced with the increase of blowing ratio for same structure. The shape of the high heat transfer coefficient region gradually inclines to span-wise direction as the blowing ratio increases. Heat transfer coefficient in the region where the jet core flows through is relatively lower, while in the jet edge region the heat transfer coefficient is relatively higher. Compared with cylindrical hole, laid-back holes give higher heat transfer coefficient. Meanwhile, the introduction of impingement also makes heat transfer coefficient higher compared with cross flow air intake. It is found that the heat transfer of the combination of laid-back hole and impingement tube can be very high under large blowing ratio which should get attention in the design process.

Measurement of Local Heat Transfer Coefficient and Film Cooling Effectiveness Through Discrete Holes

Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/2000-gt-0243 ◽

2000 ◽

Cited By ~ 3

Author(s):

R. F. Martinez-Botas ◽

C. H. N. Yuen

Keyword(s):

Heat Transfer ◽

Liquid Crystal ◽

Transfer Coefficient ◽

Film Cooling ◽

Density Ratio ◽

Local Heat Transfer ◽

Double Row ◽

Cooling Effectiveness ◽

Film Cooling Effectiveness

An efficient steady-state wide band liquid crystal technique is used to study the film cooling performance of a variety of geometries in a flat plate: a single row of holes, a double row of holes (both in-line and staggered), and a single cooling hole. This method allows temperature information to be captured in one image, without the difficulty involved in a transient experiment. The streamwise inclinations tested are 30°, 60°, and 90°. The freestream is maintained at 13m/s, and at ambient temperature. The range of blowing ratios varied from 0.33 to 2.0. Both heat transfer coefficient and adiabatic cooling effectiveness are measured for all the cases. Air is used to produce a density ratio near unity. From the range of blowing ratios tested, the most effective film cooling is achieved at a value close to 0.5, for near unity density ratio. It has been revealed that film cooling effectiveness is improved when the jet remains attached to the surface, however, this is generally coupled with an augmentation in heat transfer owing to the disturbance the attached jet causes to the boundary layer. The 30° inclined holes show to be the most effective. Results demonstrate the full coverage capability of liquid crystal thermography.

Combined Effects of Wakes and Jet Pulsing on Film Cooling

Volume 4: Turbo Expo 2007, Parts A and B ◽

10.1115/gt2007-27921 ◽

2007 ◽

Author(s):

Kristofer M. Womack ◽

Ralph J. Volino ◽

Michael P. Schultz

Keyword(s):

Heat Transfer ◽

Transfer Coefficient ◽

Film Cooling ◽

Temperature Fields ◽

Constant Current ◽

Wake Effect ◽

Cooling Effectiveness ◽

Cold Wire

Pulsed film cooling jets subject to periodic wakes were studied experimentally. The wakes were generated with a spoked wheel upstream of a flat plate. Cases with a single row of cylindrical film cooling holes inclined at 35 degrees to the surface were considered at blowing ratios, B, of 0.50, and 1.0 with jet pulsing and wake Strouhal numbers of 0.15, 0.30, and 0.60. Wake timing was varied with respect to the pulsing. Temperature measurements were made using an infrared camera, thermocouples, and constant current (cold wire) anemometry. The local film cooling effectiveness and heat transfer coefficient were determined from the measured temperatures. Phase locked flow temperature fields were determined from cold wire surveys. With B = 0.5, wakes and pulsing both lead to a reduction in film cooling effectiveness, and the reduction is larger when wakes and pulsing are combined. With B = 1.0, pulsing again causes a reduction in effectiveness, but wakes tend to counteract this effect somewhat by reducing jet liftoff. At low Strouhal numbers, wake timing had a significant effect on the instantaneous film cooling effectiveness, but wakes in general had very little effect on the time averaged effectiveness. At high Strouhal numbers, the wake effect was stronger, but the wake timing was less important. Wakes increased the heat transfer coefficient strongly and similarly in cases with and without film cooling, regardless of wake timing. Heat transfer coefficient ratios, like the time averaged film cooling effectiveness, did not depend strongly on wake timing for the cases considered.

Comparison of Numerical Investigations With Measured Heat Transfer Performance of a Film Cooled Turbine Vane

Volume 4: Heat Transfer, Parts A and B ◽

10.1115/gt2008-50623 ◽

2008 ◽

Cited By ~ 10

Author(s):

D. Charbonnier ◽

P. Ott ◽

M. Jonsson ◽

Th. Ko¨bke ◽

F. Cottier

Keyword(s):

Heat Transfer ◽

Liquid Crystal ◽

Transfer Coefficient ◽

Film Cooling ◽

Measurement Data ◽

External Flow ◽

Test Model ◽

Cooling Effectiveness ◽

Film Cooling Effectiveness

Detailed surface measurements of the heat transfer coefficient and the film cooling effectiveness by application of the transient liquid crystal method were carried out on a heavily film cooled nozzle guide vane (NGV) in a linear cascade wind tunnel at the EPFL as part of the European Research Project TATEF2 (Turbine Aero-Thermal External Flows 2). The external cooling setup included a showerhead cooling scheme and suction and pressure side of the airfoil several rows of fan-shaped cooling holes. By testing two different cooling flow rates at a NGV exit Reynolds number of 1.46E+06, detailed aerodynamic and heat transfer measurement data were obtained that can be used for validation of numerical codes and design tools for cooled airfoils. The data include the NGV surface static pressure distribution and wall heat transfer and film cooling effectiveness obtained by application of the transient liquid crystal technique. An engine representative density ratio between the coolant and the external hot gas flow was achieved by using CO2 as coolant gas. For the coupled simulation of internal cooling and external flow the numerical model was composed of the cooling air feeding the internal plenum, the cooling holes, and the outer external flow domain. An unstructured mesh was generated for the simulations by applying two different commercial CFD codes (Fluent and CFX). Identical boundary conditions were chosen in order to allow for a direct comparison of both codes. The computations were carried in two ways, first using a built-in transition model and second by imposing fully turbulent flow starting at the leading edge. For both codes the same built-in turbulence models were applied. The computations were set up to solve for the aerodynamic flow quantities both within and around the test model and for the thermal quantities on the vane surface, i.e. heat transfer coefficient and film cooling effectiveness. The computational results from the two codes are compared and validated against the results from the experiments. The numerical results were able to confirm a suspicion that the cross flow in the feeding plenum causes an observed non-symmetry of the measured film cooling effectiveness at the outlet of some cooling holes.

Effects of Surface Geometry on Film Cooling Performance at Airfoil Trailing Edge

Journal of Turbomachinery ◽

10.1115/1.4004828 ◽

2012 ◽

Vol 134 (5) ◽

Cited By ~ 7

Author(s):

Akira Murata ◽

Satomi Nishida ◽

Hiroshi Saito ◽

Kaoru Iwamoto ◽

Yoji Okita ◽

...

Keyword(s):

Heat Transfer ◽

Transfer Coefficient ◽

Film Cooling ◽

Surface Geometry ◽

Enhanced Heat Transfer ◽

Cooling Effectiveness ◽

Blowing Ratio ◽

The Heat Transfer Coefficient

Cooling at the trailing edge of a gas turbine airfoil is one of the most difficult problems because of its thin shape, high thermal load from both surfaces, hard-to-cool geometry of narrow passages, and at the same time demand for structural strength. In this study, the heat transfer coefficient and film cooling effectiveness on the pressure-side cutback surface was measured by a transient infrared thermography method. Four different cutback geometries were examined: two smooth cutback surfaces with constant-width and converging lands (base and diffuser cases) and two roughened cutback surfaces with transverse ribs and spherical dimples. The Reynolds number of the main flow defined by the mean velocity and two times the channel height was 20,000, and the blowing ratio was varied among 0.5, 1.0, 1.5, and 2.0. The experimental results clearly showed spatial variation of the heat transfer coefficient and the film cooling effectiveness on the cutback and land top surfaces. The cutback surface results clearly showed periodically enhanced heat transfer due to the periodical surface geometry of ribs and dimples. Generally, the increase of the blowing ratio increased both the heat transfer coefficient and the film cooling effectiveness. Within the present experimental range, the dimple surface was a favorable cutback-surface geometry because it gave the enhanced heat transfer without deterioration of the high film cooling effectiveness.