Effects of Shape and Arrangement of Dimples on Film Cooling Performance Over Cutback Surface at Airfoil Trailing Edge

2013 ◽  
Author(s):  
Satomi Nishida ◽  
Akira Murata ◽  
Hiroshi Saito ◽  
Yoji Okita ◽  
Chiyuki Nakamata ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Local Heat Transfer ◽  
Trailing Edge ◽  
Mean Velocity ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness

Trailing edge of a gas turbine blade is under very high thermal load because both sides are exposed to hot mainstream. The cooling film ejected from slots has to protect the cutback surface from the hot mainstream, and remove the heat from the surface. In this study, the film cooling performance of cutback surfaces with two types of dimples, spherical and teardrop-shaped dimples, were experimentally investigated with a transient infrared thermography method. Also, to examine the effects of arrangements, two different arrangements of the teardrop-shaped dimples, which are parallel and inclined to mainstream, were investigated. The dimples were arranged in two rows on the cutback surfaces. The Reynolds number of mainstream defined by the mean velocity and hydraulic diameter was 20,000, and profiles of local heat transfer coefficient and film cooling effectiveness on the cutback surface were measured for blowing ratios of 0.5–2.0. With the parallel teardrop-shaped dimples, reduction of the heat transfer in the upstream portion was less than that of the spherical dimples, and the heat transfer at downstream rims was higher. In the case of the inclined teardrop-shaped dimples, heat transfer enhancement at the downstream rims was higher than that of parallel one, and overall heat transfer coefficient was also higher. The film cooling effectiveness of all cases are almost equal values, namely, the dimpled surfaces could enhance heat transfer without reduction of the film cooling effectiveness; consequently significant cooling performance improvement was obtained for the teardrop-shaped dimple cases, especially with the introduction of inclined arrangement.

Numerical Study on the Effects of V-Shaped Rib Angle on Film Cooling Performance for Turbine Blade Trailing Edge

2018 ◽  
Author(s):  
Lin Ye ◽  
Cun-liang Liu ◽  
Hai-yong Liu ◽  
Qi-jiao He ◽  
Gang Xie
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbine Blade ◽  
Film Cooling ◽  
Trailing Edge ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio

The trailing edge of the high-pressure turbine blade presents significant challenges to cooling structure design. To achieve better cooling performance at turbine blade trailing edge, a novel ribbed cutback structure is proposed for trailing edge cooling, which has rib structures on the cutback surface for heat transfer enhancement. In this study, numerical simulations have been performed on the effects of V-shaped rib angle on the film cooling characteristics and flow physics. Three V-shaped rib angles of 30°, 45° and 60° are studied. The distributions of adiabatic cooling effectiveness and heat transfer coefficient are obtained under blowing ratios with the value of 0.5, 1.0 and 1.5 respectively. Due to the relatively small rib height, the effect of V-shaped ribs on the film cooling effectiveness is not notable. The disadvantage of V-shaped ribs mainly exhibits at the downstream area of cutback surface. With the increase of V-shaped rib angle, the film cooling effectiveness becomes lower, but the values are still above 0.9. The V-shaped ribs obviously enhance the heat transfer on trailing edge cutback surface. The area-averaged heat transfer coefficient of the V-rib case is higher than that of the smooth case by 26.3–41.2%. The 45° V-rib case has higher heat transfer intensity than the other two V-shaped rib cases under all the three blowing ratios. However, the heat transfer coefficient distribution of the 60° V-rib case is more uniform. The heat transfer intensity of the 30° V-rib case is higher in the downstream region than the other two cases, but lower in the upstream region in which the difference becomes smaller with the increase of blowing ratio. The 45° V-rib case and the 60° V-rib case both reach the maximum value of area-averaged heat transfer intensity under blowing ratio is 1.0. Under higher blowing ratio, the 30° V-rib case and the 45° V-rib case outperform 2.1% and 6.7% higher value relative to the 60° V-rib case respectively due to the smaller velocity gradient in the 60° V-rib case in the downstream.

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

2018 ◽  
Author(s):  
Lin Ye ◽  
Cun-liang Liu ◽  
Hai-yong Liu ◽  
Hui-ren Zhu ◽  
Jian-xia Luo
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Discharge Coefficient ◽  
Orientation Angle ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
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 Local Heat Transfer Coefficient and Film Cooling Effectiveness Through Discrete Holes

2000 ◽  
Author(s):  
R. F. Martinez-Botas ◽  
C. H. N. Yuen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
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.

Film Cooling Effectiveness and Mass/Heat Transfer Coefficient Downstream of One Row of Discrete Holes

1999 ◽  
Vol 121 (2) ◽  
pp. 225-232 ◽  
Author(s):  
R. J. Goldstein ◽  
P. Jin ◽  
R. L. Olson
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Density Ratio ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness

A special naphthalene sublimation technique is used to study the film cooling performance downstream of one row of holes of 35 deg inclination angle with 3d hole spacing and relatively small hole length to diameter ratio (L/d = 6.3). Both film cooling effectiveness and mass/heat transfer coefficient are determined for blowing rates from 0.5 to 2.0 with density ratio of 1.0. The mass transfer coefficient is measured using pure air film injection, while the film cooling effectiveness is derived from comparison of mass transfer coefficients obtained following injection of naphthalene-vapor-saturated air with those from pure air injection. This technique enables one to obtain detailed local information on film cooling performance. The laterally averaged and local film cooling effectiveness agree with previous experiments. The difference between mass/heat transfer coefficients and previous heat transfer results indicates that conduction error may play an important role in the earlier heat transfer measurements.

Numerical Evaluation of Influence of Internal Ribs on Heat Transfer in Flat Plate Film Cooling

2013 ◽  
Author(s):  
Yukiko Agata ◽  
Toshihiko Takahashi ◽  
Eiji Sakai ◽  
Koichi Nishino
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Inlet Temperature ◽  
Turbine Inlet Temperature ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Turbine Inlet

To augment the thermal efficiency of combined power generation plants, the turbine inlet temperature of an industrial gas turbine has been increased. Cooling technology plays a vital role in the durability of gas turbine blades in situations in which the turbine inlet temperature exceeds the allowable temperature of the blade material. Cooling air is also directly associated with the reduction in thermal efficiency because bleed air from the compressor is used for turbine cooling. Thus, improvement in cooling performance has a marked impact on the further augmentation of thermal efficiency by increasing turbine inlet temperature. To evaluate film cooling performance on the basis of heat flux reduction, it is necessary to accurately estimate both heat transfer coefficient and adiabatic film cooling effectiveness. Most studies of film cooling, however, have focused on improving adiabatic film cooling effectiveness. In contrast, there are few studies focusing on heat transfer coefficient. One of the reasons for this is that adiabatic film cooling effectiveness is a performance parameter unique to film cooling. To preliminarily estimate the heat flux through a blade, heat transfer coefficient without film cooling can still be used as substitute. Moreover, the accurate CFD prediction of heat transfer coefficient with film cooling is difficult, compared with the evaluation of adiabatic film cooling effectiveness. Therefore, in this study, we addressed the CFD prediction of heat transfer coefficient with film cooling on a flat plate, and discussed its feasibility. Recent gas turbine blades operated at a turbine inlet temperature of over 1300 degree Celsius employ internal convection cooling with ribbed passages and external film cooling. These cooling technologies have been studied extensively, particularly regarding their individual effects. On the other hand, there are few investigations on the interaction between internal convection cooling and the film cooling. Although most of such film-cooling studies employed stagnant plenums to bleed cooling air, some researchers including the present authors have shown the marked impact of the conditions for supplying coolant air on film cooling performance. In this study, we focus particularly on the influence of internal rib orientation on external film cooling performance along the blade outer surface. CFD analysis is used to resolve the flow fields of the flat plate film cooling and to clarify the influence of rib orientation on heat-transfer.

On the effect of geometry of w-wave trenches on film cooling performance of gas turbine blades

2021 ◽  
pp. 095765092110082
Author(s):  
Alireza Bakhshinejad Bahambari ◽  
Mohammad Hassan Kayhani ◽  
Mahmood Norouzi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Stokes Equations ◽  
Uniform Structure ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio

In the present study, three types of w-wave trenches with different amplitude configurations are compared with transverse trench (TT), and the use of variable radius fillet (VRF) on downstream lips at different blowing ratio is numerically investigated to measure heat transfer coefficient, and cooling effectiveness. The numerical results are obtained by three-dimensional Reynolds average Navier–Stokes equations (RANS) while employing shear stress transport turbulence models, which are validated by comparing with experimental data. The trench width is kept constant in all cases, yet the three different amplitudes and variable fillet radiuses offered a variety of designs in trench film cooling. The results showed that w-wave trenches impressively improved film cooling effectiveness over the transverse trench, and utilizing fillets at downstream lips of the trench caused significant enhancement on both lateral averaged and centerline cooling performance. Due to the w-wave trench configuration, anti-counter-rotating vortices responsible for pushing coolant film toward the near-wall were formed throughout of downstream wall of the trench, and the cooling flow thus had a more uniform structure. The heat transfer coefficient distributions of filleted w-wave trenches are observed to be more uniform than simple w-wave and transverse trench under all blowing ratio conditions. Moreover, enlargement of the fillet radius in Cases 2 and 3 yielded to the growth of centerline coolant flow, which in turn resulted in the improvement of film cooling effectiveness at all blowing ratios.

scholarly journals Numerical study on film cooling and convective heat transfer characteristics in the cutback region of turbine blade trailing edge

2016 ◽  
Vol 20 (suppl. 3) ◽  
pp. 643-649
Author(s):  
Yong-Hui Xie ◽  
Dong-Ting Ye ◽  
Zhong-Yang Shen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Film Cooling ◽  
Convective Heat Transfer Coefficient ◽  
Trailing Edge ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness

Gas turbine blade trailing edge is easy to burn out under the exposure of high-temperature gas due to its thin shape. The cooling of this area is an important task in gas turbine blade design. The structure design and analysis of trailing edge is critical because of the complexity of geometry, arrangement of cooling channels, design requirement of strength, and the working condition of high heat flux. In the present paper, a 3-D model of the trailing edge cooling channel is constructed and both structures with and without land are numerically investigated at different blowing ratio. The distributions of film cooling effectiveness and convective heat transfer coefficient on cutback and land surface are analyzed, respectively. According to the results, it is obtained that the distributions of film cooling effectiveness and convective heat transfer coefficient both show the symmetrical characteristics as a result of the periodic structure of the trailing edge. The increase of blowing ratio significantly improves the film cooling effectiveness and convective heat transfer coefficient on the cutback surface, which is beneficial to the cooling of trailing edge. It is also found that the land structure is advantageous for enhancing the streamwise film cooling effectiveness of the trailing edge surface while the film cooling effectiveness on the land surface remains at a low level. Convective heat transfer coefficient exhibits a strong dependency with the blowing ratio, which suggests that film cooling effectiveness and convective heat transfer coefficient must be both considered and analyzed in the design of trailing edge cooling structure.

Effect of Hole Shape on Film Cooling Effectiveness Over a Flat Plate

2013 ◽  
Author(s):  
J. Felix ◽  
N. Harshavardhana ◽  
Y. Giridhara Babu ◽  
D. Rajanna ◽  
N. Vinod Kumar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flat Plate ◽  
Film Cooling ◽  
Thermal Image ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
The Heat Transfer Coefficient

Film cooling method of hot section components in the gas turbine engines is under continuous optimization for the enhanced cooling performance. In the present study, film cooling performance for a row of different shaped holes like triangular, circular and extended triangular have been considered. The adiabatic film effectiveness and the convective heat transfer coefficients are found experimentally on a flat plate. All the three test models are having holes of 5 mm diameter drilled at 20 mm pitch and inclined at an angle of 22 degrees. At the immediate downstream of these models, a flat plate is attached for finding the effect of these hole configurations. This flat plate is made with the low conductivity substrate and the stainless sheet of 0.2 mm thick is pasted over it in the flow path. The test model along with the flat plate is placed to the side wall of the rectangular duct where the mainstream air is supplied. The setup is made in such a way that the coolant air passed through the holes will create a film over the flat plate downstream. Infra Red camera is used to capture the thermal image of the entire test plate. The flat plate is connected with six thermocouples to have the reference surface temperature to correct the IR thermal image data. K-type thermocouples are used to measure the coolant and mainstream air temperatures. In both the heat transfer coefficient and adiabatic film cooling effectiveness experiments the blowing ratio is varied by 0.5 to 2.0, by keeping the constant mainstream air velocity of 20 m/s at ambient temperature. In the heat transfer coefficient experiments, the flat plate is heated with the constant heat flux conditions. In the adiabatic film cooling experiments, the coolant air is maintained at the temperature of −50°C with the help of liquid nitrogen heat exchanger bath. Results are plotted by taking the adiabatic film cooling effectiveness and convective heat transfer coefficient values from the centerline of holes downstream along the flow direction. From the results, the triangular and extended triangular hole models shown higher heat transfer coefficient and adiabatic film cooling effectiveness than the circular hole model.

scholarly journals Film Cooling Effectiveness and Mass/Heat Transfer Coefficient Downstream of One Row of Discrete Holes

1998 ◽  
Author(s):  
R. J. Goldstein ◽  
P. Jin ◽  
R. L. Olson
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Film Cooling ◽  
Density Ratio ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness

A special naphthalene sublimation technique is used to study the film cooling performance downstream of one row of holes of 35° inclination angle with 3d hole spacing and relatively small hole length to diameter ratio (L/d = 6.3). Both film cooling effectiveness and mass/heat transfer coefficient are determined for blowing rates from 0.5 to 2.0 with density ratio of 1.0. The mass transfer coefficient is measured using pure air film injection, while the film cooling effectiveness is derived from comparison of mass transfer coefficient obtained following injection of naphthalene-vapor-saturated air with that of pure air injection. This technique enables one to obtain detailed local information on film cooling performance. The laterally-averaged and local film cooling effectiveness agree with previous experiments. The difference between mass/heat transfer coefficients and previous heat transfer results indicates that conduction error may play an important role in the earlier heat transfer measurements.

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

2004 ◽  
Vol 10 (5) ◽  
pp. 345-354 ◽  
Author(s):  
Jan Dittmar ◽  
Achmed Schulz ◽  
Sigmar Wittig
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
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.

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