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

2017 ◽  
Author(s):  
Bo-lun Zhang ◽  
Li Zhang ◽  
Hui-ren Zhu ◽  
Jian-sheng Wei ◽  
Zhong-yi Fu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Numerical Study ◽  
Leading Edge ◽  
Cooling Effectiveness ◽  
Film 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.

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

2018 ◽  
Author(s):  
Rui-dong Wang ◽  
Cun-liang Liu ◽  
Hai-yong Liu ◽  
Hui-ren Zhu ◽  
Qi-ling Guo ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Leading Edge ◽  
Cooling Effectiveness ◽  
Film 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.

Investigations on the Film Cooling of Counter-Inclined Film-Hole Row Structures for Turbine Vane Leading Edge

2018 ◽  
Vol 35 (3) ◽  
pp. 291-303 ◽  
Author(s):  
Cun-Liang Liu ◽  
Dan Zhao ◽  
Ying-Ni Zhai ◽  
Hui-Ren Zhu ◽  
Yi-Hong He ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Leading Edge ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Blowing Ratio ◽  
Turbine Vane

AbstractNumerical simulations have been performed on the film cooling characteristics of counter-inclined structures, which have advantage in manufacturing relative to the usually used parallel-inclined film-hole row structure, on a turbine vane leading edge model. Single row structure and dual-row structure with counter-inclined film holes were applied in the simulation of leading edge film cooling of turbine vane. The effect of jet-interaction between counter-inclined film-hole rows was studied. The distributions of film cooling effectiveness and heat transfer coefficient were obtained at blowing ratios of 1.0 and 2.0. The results of single row structure show that the film cooling performances of counter-inclined film-hole row are not weakened compared to the traditional parallel-inclined film-hole row structure. The film cooling effectiveness of the counter-inclined film-hole row structure decreases with the increase of blowing ratio, while the heat transfer coefficient increases. The jet-interaction in the dual-row film cooling structure has more notable influence on the film cooling effectiveness than the heat transfer coefficient. Compared to the single row case, the interactions between the upstream counter-blowing jets and the downstream jet improve the film coverage performance and reduce the heat transfer intensity of this downstream jet under larger blowing ratio condition.

Influence of High Mainstream Turbulence on Leading Edge Film Cooling Heat Transfer: Effect of Film Hole Row Location

1992 ◽  
Vol 114 (4) ◽  
pp. 716-723 ◽  
Author(s):  
S. Ou ◽  
A. B. Mehendale ◽  
J. C. Han
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Leading Edge ◽  
Spanwise Direction ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Turbulence Effect

The effect of film hole row location on leading edge film cooling effectiveness and heat transfer coefficient under high mainstream turbulence conditions was experimentally determined for flow over a blunt body with semicylinder leading edge and a flat afterbody. Two separate cases of film injection film holes located only at ± 15 or ± 40 deg were studied. The holes were spaced three hole diameters apart in the spanwise direction and inclined 30 and 90 deg to the surface in the spanwise and streamwise directions, respectively. A bar grid (Tu = 5.07 percent), a passive grid (Tu = 9.67 percent), and a jet grid (Tu = 12.9 percent) produced high mainstream turbulence. The incident mainstream Reynolds number based on cylinder diameter was 100,000. Spanwise and streamwise distributions of film effectiveness and heat transfer coefficient in the leading edge and the flat sidewall were obtained for three blowing ratios. The results show mainstream turbulence adversely affects leading edge film effectiveness for the low blowing ratio (B = 0.4), but the effect reduces for higher blowing ratios (B = 0.8 and 1.2). The leading edge heat transfer coefficient increases with mainstream turbulence level for B = 0.4 and 0.8, but the effect is not systematic for B = 1.2. Mainstream turbulence effect is more severe for ±15 deg one-row injection than for ± 40 deg one-row injection. The surface heat load reduction for ± 15 deg one-row injection or ± 40 deg one-row injection is smaller than that for two-row injection.

Experimental Investigation on the Leading Edge Film Cooling of Cylindrical and Laid-Back Holes With Different Hole Pitches

2012 ◽  
Author(s):  
Cun-liang Liu ◽  
Hui-ren Zhu ◽  
Zong-wei Zhang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Leading Edge ◽  
Cooling Effectiveness ◽  
Large Hole ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Hole Model

Experimental investigation has been performed to study the film cooling performance of cylindrical and laid-back film holes on the turbine blade leading edge. Four test models are measured for four blowing ratios to investigate the influence of film hole shape and hole pitch on the film cooling performance. Film cooling effectiveness and heat transfer coefficient are obtained using transient heat transfer measurement technique with double thermochromic liquid crystals. As the blowing ratio increases, the trajectory of jets deviates to the spanwise direction and lifts off gradually. However, more area can benefit from the film protection under large blowing ratio, while the heat transfer coefficient is also higher. The basic distribution features of heat transfer coefficient are similar for all the four models. Heat transfer coefficient in the region where the jet core flows through is relatively lower, while heat transfer coefficient in the jet edge region is relatively higher. For the models with small hole pitch, the laid-back holes only give better film coverage performance than the cylindrical holes under large blowing ratio. For the models with large hole pitch, the advantage of laid-back holes in film cooling effectiveness is more obvious in the upstream region relative to the cylindrical holes. For the cylindrical hole model and the laid-back hole model with the same hole pitch, the laterally averaged heat transfer coefficients are nearly the same with each other under the same blowing ratios. Compared with the models with large hole pitch, the laterally averaged film cooling effectiveness and the laterally averaged heat transfer coefficient are larger for the models with small hole pitch because of larger proportion of film covering area and strong heat transfer region.

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.

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

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Akira Murata ◽  
Satomi Nishida ◽  
Hiroshi Saito ◽  
Kaoru Iwamoto ◽  
Yoji Okita ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Surface Geometry ◽  
Enhanced Heat Transfer ◽  
Cooling Effectiveness ◽  
Film 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.

Effects of Oscillations in the Mainstream on Film Cooling at Various Blowing Ratios

2017 ◽  
Author(s):  
Seung Il Baek ◽  
Savas Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Jet Flow ◽  
Main Flow ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Lift Off

The objective of this study is to understand the effects of flow oscillations in the mainstream and film cooling jets on film cooling at various blowing ratios (0.5, 0.78, 1.0 and 1.5). These oscillations could be caused by the combustion instabilities. They are approximated in sinusoidal form for the current study. The effects of different frequencies (0, 2, 16, 32 Hz) on film cooling are investigated. Simulations are performed using URANS Realizable k-epsilon and LES Smagorinsky-Lilly turbulence models. The results indicate that if the frequencies of the mainstream and the jet flow are increased at a low average blowing ratio of M = 0.5, the adiabatic film cooling effectiveness is decreased and the heat transfer coefficient is increased due to increased disturbance in jet and main flow interaction with increasing frequency. It was observed that when the frequency of the mainstream and the cooling jet flow is increased at M = 0.5, the amplitude of the pressure difference between the mainstream and the plenum is increased resulting in increased amplitude of coolant flow rate oscillations leading to more jet lift off and more disturbance in the main flow and coolant interaction. Consequently, adiabatic film cooling effectiveness is decreased and heat transfer coefficient is increased. If the frequency of the mainstream is increased from 0 Hz to 2, 16, or 32 Hz at M = 0.5, the centerline effectiveness is decreased about 10%, 12%, or 47% and the spanwise-averaged Stanton number ratio is increased about 4%, 5%, or 9% respectively. If the frequencies of the main flow and the jet flow are increased at higher blowing ratios of M = 1.0 and 1.5, adiabatic effectiveness is increased and the spanwise-averaged heat transfer coefficient are decreased. Under steady flow conditions jet lift off is generated for these high blowing ratios. If the frequency of the mainstream and the jet flow is increased, the amplitude of coolant jet flow rate oscillation is increased for the same reason as mentioned above for M = 0.5. This leads to less jet lift off during the cycle resulting in more frequent coolant contact with the wall and consequently increased centerline effectiveness as frequency increases. In addition, the entrainment of hot gases underneath the jet doesn’t lead to higher mixing between the hot mainstream and the coolant and this results in decreased heat transfer coefficient. This is also indicated by the turbulent kinetic energy levels. Some representative results are: when the frequency of the main flow is increased from 0 Hz to 2, 16, or 32 Hz at M = 1.0, the centerline effectiveness is increased about 8%, 19%, or 320%. Also, if the oscillation frequency is increased from 2 Hz to 16, or 32 Hz at M = 1.0, the spanwise-averaged Stanton number ratio is decreased around 2%, to 5% respectively. It seems like the cut off point for low and high blowing ratio behavior of cooling jets is around M = 0.78.

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.

scholarly journals A Transient Method Using Liquid Crystal for Film Cooling Over a Convex surface

2001 ◽  
Vol 7 (3) ◽  
pp. 153-164 ◽  
Author(s):  
Ping-Hei Chen ◽  
Min-Sheng Hung ◽  
Pei-Pei Ding
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystal ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Convex Surface ◽  
Density Ratio ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio

In order to explore the effect of blowing ratio on film cooling over a convex surface, the present study adopts the transient liquid crystal thermography for the film cooling measurement on a straight circular hole configuration. The test piece has a strength of curvature(2r/D)of 92.5, pitch to diameter ratio(P/D)of 3 and streamwise injection angle(γ)of35∘All measurements were conducted under the mainstream Reynolds number(Red)of 1700 with turbulence intensity(Tu)of 3.8%, and the density ratio between coolant and mainstream(ρc/ρm)is 0.98. In current study, the effect of blowing ratio(M)on film cooling performance is investigated by varying the range of blowing ratio from 0.5 to 2.0. Two transient tests of different injection flow temperature were conducted to obtain both detailed heat transfer coefficient and film cooling effectiveness distributions of measured region. The present measured results show that both the spanwise averaged heat transfer coefficient and film cooling effectiveness increase with decreased blowing ratio.

Numerical Prediction of Film Cooling and Heat Transfer on the Leading Edge of a Rotating Blade With Two Rows Holes in a 1-1/2 Turbine Stage at Design and Off Design Conditions

2005 ◽  
Author(s):  
Huitao Yang ◽  
Hamn-Ching Chen ◽  
Je-Chin Han ◽  
Hee-Koo Moon
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Leading Edge ◽  
Suction Side ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Rotating Speed ◽  
Rotating Blade

Numerical simulations were performed to predict the film cooling effectiveness and the associated heat transfer coefficient on the leading edge of a rotating blade in a 1-1/2 turbine stage using a Reynolds stress turbulence model together with a non-equilibrium wall function. Simulations were performed for both the design and off-design conditions to investigate the effects of blade rotation on the leading edge film cooling effectiveness and heat transfer coefficient distributions. It was found that the tilt stagnation line on the leading edge of rotor moves from the pressure side to the suction side, and the instantaneous coolant streamlines shift from the suction side to the pressure side with increasing rotating speed. This trend was supported by the experimental results. The result also showed that the heat transfer coefficient increases, but film cooling effectiveness decreases with increasing rotating speed. In addition, the unsteady characteristics of the film cooling and heat transfer at different time phases, as well as different rotating speeds, were also reported.

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