Film Cooling Effectiveness for Short Film Cooling Holes Fed by a Narrow Plenum

1999 ◽  
Author(s):  
C. A. Hale ◽  
M. W. Plesniak ◽  
S. Ramadhyani
Keyword(s):  
Film Cooling ◽  
Short Film ◽  
Injection Hole ◽  
Counter Flow ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Thin Walled ◽  
Film Cooling Holes

The adiabatic, steady-state liquid crystal technique was used to measure surface adiabatic film cooling effectiveness values in the near-hole region (X / D < 10). A parametric study was conducted for a single row of short holes (L / D ≤ 3) fed by a narrow plenum (H / D = 1). Film cooling effectiveness values are presented and compared for various L / D ratios (0.66 to 3.0), three different blowing ratios (0.5, 1.0, and 1.5), two different plenum feed configurations (co-flow and counter flow), and two different injection angles (35° and 90°). Injection hole geometery and plenum feed direction were found to significantly affect short hole film cooling performance. Under certain conditions, comparable or improved coverage was achieved with 90° holes as with 35° holes. This result has important implications for manufacturing of thin-walled film-cooled blades or vanes.

Film Cooling Effectiveness for Short Film Cooling Holes Fed by a Narrow Plenum

1999 ◽  
Vol 122 (3) ◽  
pp. 553-557 ◽  
Author(s):  
C. A. Hale ◽  
M. W. Plesniak ◽  
S. Ramadhyani
Keyword(s):  
Film Cooling ◽  
Short Film ◽  
Injection Hole ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Hole Geometry ◽  
Thin Walled ◽  
Film Cooling Holes

The adiabatic, steady-state liquid crystal technique was used to measure surface adiabatic film cooling effectiveness values in the near-hole region X/D<10. A parametric study was conducted for a single row of short holes L/D⩽3 fed by a narrow plenum H/D=1. Film cooling effectiveness values are presented and compared for various L/D ratios (0.66 to 3.0), three different blowing ratios (0.5, 1.0, and 1.5), two different plenum feed configurations (co-flow and counterflow), and two different injection angles (35 and 90 deg). Injection hole geometry and plenum feed direction were found to affect short hole film cooling performance significantly. Under certain conditions, similar or improved coverage was achieved with 90 deg holes compared with 35 deg holes. This result has important implications for manufacturing of thin-walled film-cooled blades or vanes. [S0889-504X(00)00603-6]

Rib Turbulator Effects on Crossflow-Fed Shaped Film Cooling Holes

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Dale W. Fox ◽  
Fraser B. Jones ◽  
John W. McClintic ◽  
David G. Bogard ◽  
Thomas E. Dyson ◽  
...  
Keyword(s):  
Film Cooling ◽  
Velocity Ratio ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Smooth Channel ◽  
Cooling Hole ◽  
Film Cooling Holes ◽  
Inlet Position ◽  
The Impact

Most studies of turbine airfoil film cooling in laboratory test facilities have used relatively large plenums to feed flow into the coolant holes. However, a more realistic inlet condition for the film cooling holes is a relatively small channel. Previous studies have shown that the film cooling performance is significantly degraded when fed by perpendicular internal crossflow in a smooth channel. In this study, angled rib turbulators were installed in two geometric configurations inside the internal crossflow channel, at 45 deg and 135 deg, to assess the impact on film cooling effectiveness. Film cooling hole inlets were positioned in both prerib and postrib locations to test the effect of hole inlet position on film cooling performance. A test was performed independently varying channel velocity ratio and jet to mainstream velocity ratio. These results were compared to the film cooling performance of previously measured shaped holes fed by a smooth internal channel. The film cooling hole discharge coefficients and channel friction factors were also measured for both rib configurations with varying channel and inlet velocity ratios. Spatially averaged film cooling effectiveness is largely similar to the holes fed by the smooth internal crossflow channel, but hole-to-hole variation due to inlet position was observed.

Effect of Unheated Starting Lengths on Film Cooling Experiments

2006 ◽  
Vol 128 (3) ◽  
pp. 579-588 ◽  
Author(s):  
Sarah M. Coulthard ◽  
Ralph J. Volino ◽  
Karen A. Flack
Keyword(s):  
Film Cooling ◽  
Infrared Camera ◽  
Stanton Number ◽  
Flow Structures ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Heat Transfer Coefficients ◽  
Film Cooling Holes

The effect of an unheated starting length upstream of a row of film cooling holes was studied experimentally to determine its effect on heat transfer coefficients downstream of the holes. Cases with a single row of cylindrical film cooling holes inclined at 35deg to the surface of a flat plate were considered at blowing ratios of 0.25, 0.5, 1.0, and 1.5. For each case, experiments were conducted to determine the film-cooling effectiveness and the Stanton number distributions in cases with the surface upstream of the holes heated and unheated. Measurements were made using an infrared camera, thermocouples, and hot and cold-wire anemometry. Ratios were computed of the Stanton number with film cooling (Stf) to corresponding Stanton numbers in cases without film cooling (Sto), but the same surface heating conditions. Contours of these ratios were qualitatively the same regardless of the upstream heating conditions, but the ratios were larger for the cases with a heating starting length. Differences were most pronounced just downstream of the holes and for the lower blowing rate cases. Even 12 diameters downstream of the holes, the Stanton number ratios were 10–15% higher with a heated starting length. At higher blowing rates the differences between the heated and unheated starting length cases were not significant. The differences in Stanton number distributions are related to jet flow structures, which vary with blowing rate.

Optimal Arrangement of the Film Cooling Holes Considering the Manufacturing Tolerance for High Pressure Turbine Nozzle

2016 ◽  
Author(s):  
Sanga Lee ◽  
Dong-Ho Rhee ◽  
Kwanjung Yee
Keyword(s):  
High Pressure ◽  
Film Cooling ◽  
Leading Edge ◽  
High Pressure Turbine ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Manufacturing Tolerance ◽  
Cooling Hole ◽  
Film Cooling Holes

In spite of a myriad of researches on the optimal shape of film cooling holes, only a few attempts have been made to optimize the hole arrangement for film cooling so far. Moreover, although the general scale of film cooling hole is so small that manufacturing tolerance has substantial effects on the cooling performance of turbine, the researches on this issue are even scarcer. If it is possible to obtain optimal hole arrangement which not only improve the film cooling performance but also is robust to the manufacturing tolerance, then overall cooling performance of a turbine would become more reliable and useful from the practical point of view. To this end, the present study proposed a robust design optimization procedure which takes the manufacturing uncertainties into account. The procedure was subsequently applied to the film cooling holes on high pressure turbine nozzle pressure side to obtain the robust array shape under the uncertainty of the manufacturing tolerance. First, the array of the holes was parameterized by 5 design variables using the newly suggested shape functions, and 2 representative factors were considered for the manufacturing tolerance of the film cooling hole. Probabilistic process that consists of Kriging surrogate model and Monte Carlo Simulation with descriptive sampling method was coupled with the design optimization process using Genetic Algorithm. Through this, film cooling hole array which shows the high performance, yet robust to the manufacturing tolerance was obtained, and the effects of the manufacturing tolerance on the cooling performance was carefully investigated. As a result, the region where the film cooling effectiveness is noticeable, as well as the maximum width of the variation of the film cooling effectiveness were reduced through optimization, and it is also confirmed that the tolerance of the holes near the leading edge is more influential to the cooling performance because the film cooling effectiveness is more sensitive to the manufacturing tolerance of the leading edge than that of the trailing edge.

Film Cooling and Thermal Field Measurements for Staggered Rows of Rectangular-Shaped Film Cooling Holes

2003 ◽  
Author(s):  
Dong Ho Rhee ◽  
Youn Seok Lee ◽  
Young Bong Kim ◽  
Hyung Hee Cho
Keyword(s):  
Film Cooling ◽  
Lateral Spreading ◽  
Temperature Fields ◽  
Test Surface ◽  
Spanwise Direction ◽  
Rectangular Hole ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Film Cooling Holes

An experimental study has been conducted to measure the temperature fields and the local film cooling effectiveness for two and three staggered rows of the rectangular-shaped film cooling holes with various blowing rates. Three different cooling hole shapes such as a straight rectangular hole, a rectangular hole with laterally expanded exit and a circular hole are tested. The rectangular cross-section has the aspect ratio of 2 at the hole inlet with the hydraulic diameter of 10 mm. The area ratio of the exit to the hole inlet is 1.8 for the rectangular hole with expanded exit, which is similar to a two-dimensional slot. The holes are spaced 3d apart in the spanwise direction and 4d apart in the streamwise direction with a staggered arrangement. Temperature fields are acquired using a three-axis traversing system equipped with a thermocouple rake. A thermochromic liquid crystals technique is applied to determine adiabatic film cooling effectiveness values and heat transfer coefficients on the test surface. The results show that the rectangular-shaped holes provide better performance than the cylindrical holes because the penetration of coolant is reduced and the lateral spreading of coolant is promoted. For rows of film cooling holes, the film cooling performance decreases with increasing blowing rate. However, the difference of hole shapes and blowing rates for film cooling performance is reduced with increasing the row of cooling holes.

Experimental and Numerical Film Effectiveness Downstream a Row of Compound Angle Film Holes

2003 ◽  
Author(s):  
A. Khanicheh ◽  
M. E. Taslim
Keyword(s):  
High Temperature ◽  
Film Cooling ◽  
Computational Study ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Cooling Hole ◽  
Cylindrical Holes ◽  
Film Cooling Holes ◽  
Compound Angle

High component lifetimes of modern gas turbines can be achieved by cooling the airfoils effectively. Film cooling is commonly employed on the airfoils and other engine hot section surfaces in order to protect them from the high thermal stress fields created by exposure to combustion gases. Complex geometries as well as optimized cooling considerations often dictate the use of compound-angled film cooling hole. In the present experimental and computational study, the effects that two different compound angle film cooling hole injection configurations have on film cooling effectiveness are investigated. Film cooling effectiveness measurements have been made downstream of a single row of compound angle cylindrical holes with a diameter of 7.5 mm, and a single row of compound angle, diffuser-shaped holes with an inlet diameter of 7.5 mm. The cylindrical holes were inclined (α=25°) with respect to the coverage surface and were oriented perpendicular to the high-temperature airflow direction. The diffuser-shaped holes had a compound angle of 45 degrees with respect to the high temperature air flow direction and, similar to the cylindrical film holes, a 25-deg angle with the coverage surface. Both geometries were tested over a blowing ratio range of 0.7 to 4.0. Surface temperatures were measured along four longitudinal rows of thermocouples covering the downstream area between two adjacent holes. The results showed that the best overall protection over the widest range of blowing ratios was provided by the diffuser-shaped film cooling holes. Compared with the cylindrical hole results, the diffuser-shaped expansion holes produced higher film cooling effectiveness downstream of the film cooling holes, particularly at high blowing ratios. The increased cross sectional area at the shaped hole exit compared to that of the cylindrical hole lead to a reduction of the mean velocity, thus the reduction of the momentum flux of the jet exiting the hole. Therefore, the penetration of the jet into the main flow was reduced, resulting in an increased cooling effectiveness. A commercially available CFD software package was used to study film cooling effectiveness downstream of the row of holes. Comparisons between the experimentally measured and numerically calculated film effectiveness distributions showed that the computed results are in reasonable agreement with the measured results. Therefore, CFD can be considered as a viable tool to predict the cooling performance of different film cooling configurations in a parametric study. A more realistic turbulence model, possibly adopting a two-layer model that incorporates boundary layer anisotropy, in the computational study may improve the predicted results.

The Effect of High Freestream Turbulence on Film Cooling Effectiveness

1994 ◽  
Author(s):  
Jeffrey P. Bons ◽  
Charles D. MacArthur ◽  
Richard B. Rivir
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Plate Boundary ◽  
Constant Density ◽  
Freestream Turbulence ◽  
Injection Hole ◽  
Adiabatic Wall ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Single Row

This study investigated the adiabatic wall cooling effectiveness of a single row of film cooling boles injecting into a turbulent flat plate boundary layer below a turbulent, zero pressure gradient freestream. Levels of freestream turbulence (Tu) up to 17.4% were generated using a method which simulates conditions at a gas turbine combustor exit. Film cooling was injected from a single row of five 35 degree slant-hole injectors (length/diameter = 3.5. pitch/diameter = 3.0) at blowing ratios from 0.55 to 1.85 and at a nearly constant density ratio (coolant density/freestream density) of 0.95. Film cooling effectiveness data is presented for Tu levels ranging from 0.9% to 17% at a constant freestream Reynolds number based on injection hole diameter of 19000. Results show that elevated levels of freestream turbulence reduce film cooling effectiveness by up to 70% in the region directly downstream of the injection hole due to enhanced mixing. At the same time, high freestream turbulence also produces a 50–100% increase in film cooling effectiveness in the region between injection boles. This is due to accelerated spanwise diffusion of the cooling fluid, which also produces an earlier merger of the coolant jets from adjacent holes.

scholarly journals Film Cooling From a Row of Holes Supplemented With Anti Vortex Holes

2007 ◽  
Author(s):  
Alok Dhungel ◽  
Yiping Lu ◽  
Wynn Phillips ◽  
Srinath V. Ekkad ◽  
James Heidmann
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Circular Cross Section ◽  
Flux Ratio ◽  
Upstream Region ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Cylindrical Holes ◽  
Film Cooling Holes

The primary focus of this paper is to study the film cooling performance for a row of cylindrical holes each supplemented with two symmetrical anti vortex holes which branch out from the main holes. The anti-vortex design was originally developed at NASA-Glenn Research Center by Dr. James Heidmann, co-author of this paper. This “anti-vortex” design is unique in that it requires only easily machinable round holes, unlike shaped film cooling holes and other advanced concepts. The hole design is intended to counteract the detrimental vorticity associated with standard circular cross-section film cooling holes. The geometry and orientation of the anti vortex holes greatly affect the cooling performance downstream, which is thoroughly investigated. By performing experiments at a single mainstream Reynolds number of 9683 based on the free stream velocity and film hole diameter at four different coolant-to-mainstream blowing ratio of 0.5, 1, 1.5, 2 and using the transient IR thermography technique, detailed film cooling effectiveness and heat transfer coefficients are obtained simultaneously from a single test. When the anti vortex holes are nearer to the primary film cooling holes and are developing from the base of the primary holes, better film cooling is accomplished as compared to other anti vortex hole orientations. When the anti vortex holes are laid back in the upstream region, film cooling diminishes considerably. Although an enhancement in heat transfer coefficient is seen in cases with high film cooling effectiveness, the overall heat flux ratio as compared to standard cylindrical holes is much lower. Thus cases with anti vortex holes placed near the main holes certainly show promising results.

Effects of Inlet Swirl on Endwall Film Cooling in Neighboring Vane Passages

2017 ◽  
Author(s):  
Yang Zhang ◽  
Yifei Li ◽  
Xiutao Bian ◽  
Xin Yuan
Keyword(s):  
Film Cooling ◽  
Rotating Flow ◽  
Leakage Flow ◽  
Cooling Effectiveness ◽  
Inlet Flow ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Inlet Swirl ◽  
Endwall Film Cooling ◽  
Film Cooling Holes

The distribution of film cooling effectiveness of endwall film-cooling holes is considered to be periodic between neighboring high pressure turbine passages in most cascade experiments. In reality, because of the difference in the number of combustors and vanes, the flow fields of neighboring passages are completely different. The secondary flow, especially the passage vortex, is dominated by the upstream inlet rotating flow whose relative flow direction is the reverse between the neighboring vane passages. Specifying the direction of rotation to simulate inlet swirl introduces new challenges in film-cooling design. The present experiment compares five groups of endwall film-cooling with anticlockwise rotating flows at inlet at different clocking positions, and the film-cooling effect is analyzed to investigate the effects of inlet rotating flow. The inlet flow condition of neighboring passages is simulated by switching the position of a swirler fan. Hence, different rotating inlet flow conditions in different positions are achieved. The GE-E3 airfoil was used in the cascade rig, with a scaled-up factor of 1.95. The inlet Reynolds number is 1.48 × 105 and the Mach number is 0.07. The effects of the blowing ratio and relative positions of the swirler are investigated in the experiment. Adiabatic film-cooling effectiveness is probed by using pressure-sensitive paint (PSP). The coolant is simulated by nitrogen with which a density ratio of around 1.0 can be achieved. Fan-shaped film-cooling holes are introduced into the endwall surface as well as trailing edge discharge holes. The cooling performance of the combustor-turbine gap leakage flow is not considered. Fan-shaped film-cooling holes are introduced into the endwall surface as well as upstream slot. The cooling performance of the combustor-turbine gap leakage flow is considered in this case. A Pair of nozzle guide vane (NGV) passages are investigated simultaneously by which the film cooling effectiveness can be compared for the same case at the endwall surface. The inlet rotating flow is simulated by an upstream swirler, with five relative positions along the pitchwise direction. According to the experimental results, the inlet rotating flow dominates the film cooling effectiveness distribution at the endwall. The averaged film cooling effectiveness changes substantially with the change in swirler position. The rotating flow at the endwall region mainly interacts with the main flow to modify incidence angle. The influence of the inlet rotating flow is more obvious at the upstream portion. Meanwhile the downstream portion is not as sensitive to rotating flow as the upstream portion.

Rib Turbulator Effects on Crossflow-Fed Shaped Film Cooling Holes

2018 ◽  
Author(s):  
Dale W. Fox ◽  
Fraser B. Jones ◽  
John W. McClintic ◽  
David G. Bogard ◽  
Thomas E. Dyson ◽  
...  
Keyword(s):  
Film Cooling ◽  
Velocity Ratio ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Smooth Channel ◽  
Cooling Hole ◽  
Film Cooling Holes ◽  
Inlet Position ◽  
The Impact

Most studies of turbine airfoil film cooling in laboratory test facilities have used relatively large plenums to feed flow into the coolant holes. However, a more realistic inlet condition for the film cooling holes is a relatively small channel. Previous studies have shown that the film cooling performance is significantly degraded when fed by perpendicular internal crossflow in a smooth channel. In this study, angled rib turbulators were installed in two geometric configurations inside the internal crossflow channel, at 45° and 135°, to assess the impact on film cooling effectiveness. Film cooling hole inlets were positioned in both pre-rib and post-rib locations to test the effect of hole inlet position on film cooling performance. A test was performed independently varying channel velocity ratio and jet to mainstream velocity ratio. These results were compared to the film cooling performance of previously measured shaped holes fed by a smooth internal channel. The film cooling hole discharge coefficients and channel friction factors were also measured for both rib configurations with varying channel and inlet velocity ratios. Spatially-averaged film cooling effectiveness is largely similar to the holes fed by the smooth internal crossflow channel, but hole-to-hole variation due to inlet position was observed.

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