Experimental Investigation of Leading Edge Impingement Under High Rotation Numbers With Racetrack Shaped Jets

2014 ◽  
Author(s):  
Weston V. Harmon ◽  
Cassius A. Elston ◽  
Lesley M. Wright
Keyword(s):  
Heat Transfer ◽  
Rotation Number ◽  
Cross Flow ◽  
Leading Edge ◽  
Jet Impingement ◽  
Target Surface ◽  
Transfer Coefficients ◽  
Round Jet ◽  
Rotation Numbers ◽  
Circular Target

The effect of rotation on leading edge jet impingement is experimentally investigated in this study. Cooling air travels radially outward through a square supply channel, turns 90° into a cross-over hole, and impinges on a semi-circular surface. To eliminate the effect of jet cross-flow, regionally averaged heat transfer coefficients are measured on the surface surrounding a single jet. The heat transfer performance of a round jet is compared to that afforded by a 2:1 racetrack shaped jet. Two jet Reynolds numbers were investigated, Rejet = 15,000 and Rejet = 25,000. This, in addition to a varying rotational speed, allows for the consideration of rotation numbers varying from 0.0–0.076 (based on the jet velocity and jet hydraulic diameter). The results obtained are benchmarked against stationary results to highlight enhancement due to rotation. It is shown that as the rotation number increases, the heat transfer is enhanced on all regions of the semi-circular target surface. For rotation numbers of less than 0.030, enhancement due to rotation is marginal. Once rotation numbers breach this value, heat transfer begins to increase significantly on all surfaces. Additionally, it was shown that a racetrack shaped jet consistently out performs a round jet at an equivalent rotation number. The racetrack jet offers better and more consistent coverage of the leading edge surface, yielding higher average heat transfer enhancement.

Flow and Heat Transfer of Confined Impingement Jets Cooling

2000 ◽  
Author(s):  
Ting Wang ◽  
Mingjie Lin ◽  
Ronald S. Bunker
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Structure ◽  
Experimental Studies ◽  
Cross Flow ◽  
Jet Impingement ◽  
Target Surface ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Transfer Behavior

Experimental studies on heat transfer and flow structure in confined impingement jets were performed. The objective of this study was to investigate the detailed heat transfer coefficient distribution on the jet impingement target surface and flow structure in the confined cavity. The distribution of heat transfer coefficients on the target surface was obtained by employing the transient liquid crystal method coupled with a 3-D inverse transient conduction scheme under Reynolds number ranging from 1039 to 5175. The results show that the average heat transfer coefficients increased linearly with the Reynolds number as Nu = 0.00304 Pr0.42Re. The effects of cross flow on heat transfer were investigated. The flow structure were analyzed to gain insight into convective heat transfer behavior.

Leading Edge Jet Impingement Under High Rotation Numbers

2012 ◽  
Author(s):  
Cassius A. Elston ◽  
Lesley M. Wright
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rotation Number ◽  
Leading Edge ◽  
Jet Impingement ◽  
Target Surface ◽  
Test Cases ◽  
Nusselt Numbers ◽  
Supply Channel ◽  
Cooling Air

The effect of rotation on jet impingement cooling is experimentally investigated in this study. Pressurized cooling air is supplied to a smooth, square channel in the radial outward direction. To model leading edge impingement in a gas turbine, jets are formed from a single row of discrete holes. The cooling air from the first pass is expelled through the holes, with the jets impinging on a semi-circular, concave surface. The inlet Reynolds number varied from 10000–40000 in the square supply channel. The rotation number and buoyancy parameter varied from 0–1.4 and 0–6.6 near the inlet of the channel, and as coolant is extracted for jet impingement, the rotation and buoyancy numbers can exceed 10 and 500 near the end of the passage. The average jet Reynolds number varied from 6000–24000, and the jet rotation number varied from 0–0.13. For all test cases, the jet-to-jet spacing (s/djet = 4), the jet-to-target surface spacing (l/djet = 3.2), and the impingement surface diameter-to-diameter (D/djet = 6.4) were held constant. A steady state technique was implemented to determine regionally averaged Nusselt numbers on the leading and trailing surfaces inside the supply channel and three spanwise locations on the concave target surface. It was observed that in all rotating test cases, the Nusselt numbers deviated from those measured in a non-rotating channel. The degree of separation between the leading and trailing surface increased with increasing rotation number. Near the inlet of the channel, heat transfer was dominated by entrance effects, however moving downstream, the local rotation number increased and the effect of rotation was more pronounced. The effect of rotation on the target surface was most clearly seen in the absence of crossflow. With pure jet impingement, the deflection of the impinging jet combined with the rotation induced secondary flows offered increased mixing within the impingement cavity and enhanced heat transfer. In the presence of strong crossflow of the spent air, the same level of heat transfer is measured in both the stationary and rotating channels.

Experimental and Numerical Investigation of Impingement on a Rib-Roughened Leading-Edge Wall

2003 ◽  
Vol 125 (4) ◽  
pp. 682-691 ◽  
Author(s):  
M. E. Taslim ◽  
K. Bakhtari ◽  
H. Liu
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Cross Flow ◽  
Heat Removal ◽  
Leading Edge ◽  
Target Surface ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Edge Surface ◽  
Rib Roughened

Effective cooling of the airfoil leading edge is imperative in gas turbine designs. Among several methods of cooling the leading edge, impingement cooling has been utilized in many modern designs. In this method, the cooling air enters the leading edge cavity from the adjacent cavity through a series of crossover holes on the partition wall between the two cavities. The crossover jets impinge on a smooth leading-edge wall and exit through the film holes, and, in some cases, form a cross flow in the leading-edge cavity and move toward the end of the cavity. It was the main objective of this investigation to measure the heat transfer coefficient on a smooth as well as rib-roughened leading-edge wall. Experimental data for impingement on a leading-edge surface roughened with different conical bumps and radial ribs have been reported by the same authors previously. This investigation, however, deals with impingement on different horseshoe ribs and makes a comparison between the experimental and numerical results. Three geometries representing the leading-edge cooling cavity of a modern gas turbine airfoil with crossover jets impinging on (1) a smooth wall, (2) a wall roughened with horseshoe ribs, and (3) a wall roughened with notched-horseshoe ribs were investigated. The tests were run for a range of flow arrangements and jet Reynolds numbers. The major conclusions of this study were: (a) Impingement on the smooth target surface produced the highest overall heat transfer coefficients followed by the notched-horseshoe and horseshoe geometries. (b) There is, however, a heat transfer enhancement benefit in roughening the target surface. Among the three target surface geometries, the notched-horseshoe ribs produced the highest heat removal from the target surface, which was attributed entirely to the area increase of the target surface. (c) CFD could be considered as a viable tool for the prediction of impingement heat transfer coefficients on an airfoil leading-edge wall.

Leading Edge Jet Impingement Under High Rotation Numbers

2017 ◽  
Vol 9 (2) ◽  
Author(s):  
Cassius A. Elston ◽  
Lesley M. Wright
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rotation Number ◽  
Leading Edge ◽  
Jet Impingement ◽  
Target Surface ◽  
Test Cases ◽  
Nusselt Numbers ◽  
Supply Channel ◽  
Cooling Air

The effect of rotation on jet impingement cooling is experimentally investigated in this study. Pressurized cooling air is supplied to a smooth, square channel in the radial outward direction. To model leading edge impingement in a gas turbine, jets are formed from a single row of discrete holes. The cooling air from the first pass is expelled through the holes, with the jets impinging on a semi-circular, concave surface. The inlet Reynolds number varied from 10,000 to 40,000 in the square supply channel. The rotation number and buoyancy parameter varied from 0 to 1.4 and 0 to 6.6 near the inlet of the channel, and as coolant is extracted for jet impingement, the rotation and buoyancy numbers can exceed 10 and 500 near the end of the passage. The average jet Reynolds number varied from 6000 to 24,000, and the jet rotation number varied from 0 to 0.13. For all test cases, the jet-to-jet spacing (s/djet = 4), the jet-to-target surface spacing (l/djet = 3.2), and the impingement surface diameter-to-diameter (D/djet = 6.4) were held constant. A steady-state technique was implemented to determine regionally averaged Nusselt numbers on the leading and trailing surfaces inside the supply channel and three spanwise locations on the concave target surface. It was observed that in all rotating test cases, the Nusselt numbers deviated from those measured in a nonrotating channel. The degree of separation between the leading and trailing surface increased with increasing rotation number. Near the inlet of the channel, heat transfer was dominated by entrance effects, however moving downstream, the local rotation number increased, and the effect of rotation was more pronounced. The effect of rotation on the target surface was most clearly seen in the absence of crossflow. With pure jet impingement, the deflection of the impinging jet combined with the rotation-induced secondary flows offered increased mixing within the impingement cavity and enhanced heat transfer. In the presence of strong crossflow of the spent air, the same level of heat transfer is measured in both the stationary and rotating channels.

Impingement Heat Transfer Enhancement on a Cylindrical, Leading Edge Model With Varying Jet Temperatures

2012 ◽  
Author(s):  
Evan L. Martin ◽  
Lesley M. Wright ◽  
Daniel C. Crites
Keyword(s):  
Heat Transfer ◽  
Experimental Technique ◽  
Leading Edge ◽  
Jet Impingement ◽  
Target Surface ◽  
Large Temperature ◽  
Transfer Coefficients ◽  
Stagnation Region ◽  
Heat Transfer Coefficients ◽  
Impingement Heat Transfer

Stagnation region heat transfer coefficients are obtained from jet impingement onto a concave surface in this experimental investigation. A single row of round jets impinge on the cylindrical target surface to replicate leading edge cooling in a gas turbine airfoil. A modified, transient lumped capacitance experimental technique was developed (and validated) to obtain stagnation region Nusselt numbers with jet-to-target surface temperature differences ranging from 60°F (33.3°C) to 400°F (222.2°C). In addition to varying jet temperatures, the jet Reynolds number (5000–20000), jet-to-jet spacing (s/d = 2–8), jet-to-target surface spacing (ℓ/d = 2–8), and impingement surface diameter-to-jet diameter (D/d = 3.6, 5.5) were independently varied. This parametric investigation has served to develop and validate a new experimental technique which can be used for investigations involving large temperature differences between the surface and fluid. Furthermore, the study has broadened the range of existing correlations currently used to predict heat transfer coefficients for leading edge, jet impingement.

Impingement Heat Transfer Enhancement on a Cylindrical, Leading Edge Model With Varying Jet Temperatures

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Evan L. Martin ◽  
Lesley M. Wright ◽  
Daniel C. Crites
Keyword(s):  
Heat Transfer ◽  
Experimental Technique ◽  
Leading Edge ◽  
Jet Impingement ◽  
Target Surface ◽  
Large Temperature ◽  
Transfer Coefficients ◽  
Stagnation Region ◽  
Heat Transfer Coefficients ◽  
Impingement Heat Transfer

Stagnation region heat transfer coefficients are obtained from jet impingement onto a concave surface in this experimental investigation. A single row of round jets impinge on the cylindrical target surface to replicate leading edge cooling in a gas turbine airfoil. A modified, transient lumped capacitance experimental technique was developed (and validated) to obtain stagnation region Nusselt numbers with jet-to-target surface temperature differences ranging from 60 °F (33.3 °C) to 400 °F (222.2 °C). In addition to varying jet temperatures, the jet Reynolds number (5000–20,000), jet-to-jet spacing (s/d = 2–8), jet-to-target surface spacing (ℓ/d = 2–8), and impingement surface diameter-to-jet diameter (D/d = 3.6, 5.5) were independently varied. This parametric investigation has served to develop and validate a new experimental technique, which can be used for investigations involving large temperature differences between the surface and fluid. Furthermore, the study has broadened the range of existing correlations currently used to predict heat transfer coefficients for leading edge jet impingement.

Rotation Effect on Jet Impingement Heat Transfer in Smooth Rectangular Channels With Four Heated Walls and Radially Outward Cross Flow

1996 ◽  
Author(s):  
J. A. Parsons ◽  
J. C. Han ◽  
C. P. Lee
Keyword(s):  
Heat Transfer ◽  
Rotation Number ◽  
Temperature Difference ◽  
Flow Direction ◽  
Cross Flow ◽  
Jet Impingement ◽  
Coolant Temperature ◽  
Test Model ◽  
Transfer Coefficients ◽  
Side Walls

The effect of channel rotation on jet impingement cooling by arrays of circular jets in two channels was studied. Jet flow direction was in the direction of rotation in one channel and opposite to the rotation direction in the other channel. The jets impinged normally on two smooth target walls. Heat transfer results are presented for these two target walls, for the jet walls containing the jet producing orifices, and for side walls connecting the target and jet walls. The flow exited the channels in a single direction, radially outward, creating a cross flow on jets at larger radii. The mean test model radius to jet diameter ratio was 397. The jet rotation number was varied from 0.0 to 0.0028 and the isolated effects of jet Reynolds number (5000 and 10000), and wall-to-coolant temperature difference ratio (0.0855 and 0.129) were measured. The results for non-rotating conditions show that the Nusselt numbers for the target and jet walls in both channels are about the same and are greater than those for the side walls of both channels. However, as rotation number increases, the heat transfer coefficients for all walls in both channels decrease up to 20% below those results which correspond to non-rotating conditions. As the wall-to-coolant temperature difference ratio increases, heat transfer coefficient decreases up to 10% with other parameters held constant.

Heat Transfer in Leading Edge, Triangular Shaped Cooling Channels With Angled Ribs Under High Rotation Numbers

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Yao-Hsien Liu ◽  
Michael Huh ◽  
Dong-Ho Rhee ◽  
Je-Chin Han ◽  
Hee-Koo Moon
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Rotation Number ◽  
Leading Edge ◽  
Gas Turbine Blade ◽  
Cooling Channels ◽  
Triangular Channel ◽  
Buoyancy Parameter ◽  
Rotation Numbers

The gas turbine blade/vane internal cooling is achieved by circulating compressed air through the cooling channels inside the turbine blade. Cooling channel geometries vary to fit the blade profile. This paper experimentally investigated the rotational effects on heat transfer in an equilateral triangular channel (Dh=1.83 cm). The triangular shaped channel is applicable to the leading edge of the gas turbine blade. Angled 45 deg ribs are placed on the leading and trailing surfaces of the test section to enhance heat transfer. The rib pitch-to-rib height ratio (P/e) is 8 and the rib height-to-channel hydraulic diameter ratio (e/Dh) is 0.087. Effect of the angled ribs under high rotation numbers and buoyancy parameters is also presented. Results show that due to the radially outward flow, heat transfer is enhanced with rotation on the trailing surface. By varying the Reynolds numbers (10,000–40,000) and the rotational speeds (0–400 rpm), the rotation number and buoyancy parameter reached in this study are 0–0.58 and 0–1.9, respectively. The higher rotation number and buoyancy parameter correlate very well and can be used to predict the rotational heat transfer in the equilateral triangular channel.

Experimental and Numerical Impingement Heat Transfer in an Airfoil Leading-Edge Cooling Channel With Cross-Flow

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
M. E. Taslim ◽  
D. Bethka
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Convective Heat Transfer Coefficient ◽  
Cross Flow ◽  
Internal Heat ◽  
Leading Edge ◽  
Impinging Jet ◽  
Experimental Results ◽  
Transfer Coefficients ◽  
Impingement Heat Transfer

To enhance the internal heat transfer around the airfoil leading-edge area, a combination of rib-roughened cooling channels, film cooling, and impingement cooling is often employed. Experimental data for impingement on various leading-edge geometries are reported by these and other investigators. The effects of strong cross-flows on the leading—edge impingement heat transfer, however, have not been studied to that extent. This investigation dealt with impingement on the leading edge of an airfoil in the presence of cross-flows beyond the cross-flow created by the upstream jets (spent air). Measurements of heat transfer coefficients on the airfoil nose area as well as the pressure and suction side areas are reported. The tests were run for a range of axial to jet mass flow rates (Maxial∕Mjet) ranging from 1.14 to 6.4 and jet Reynolds numbers ranging from 8000 to 48,000. Comparisons are also made between the experimental results of impingement with and without the presence of cross-flow and between representative numerical and measured heat transfer results. It was concluded that (a) the presence of the external cross-flow reduces the impinging jet effectiveness both on the nose and sidewalls; (b) even for an axial to jet mass flow ratio as high as 5, the convective heat transfer coefficient produced by the axial channel flow was less than that of the impinging jet without the presence of the external cross-flow; and (c) the agreement between the numerical and experimental results was reasonable with an average difference ranging from −8% to −20%.

scholarly journals Verification of Thermal Models of Internally Cooled Gas Turbine Blades

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Igor Shevchenko ◽  
Nikolay Rogalev ◽  
Andrey Rogalev ◽  
Andrey Vegera ◽  
Nikolay Bychkov
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Turbine Blades ◽  
Heat Removal ◽  
Leading Edge ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Transfer Coefficients ◽  
Single Experiment ◽  
Heat Transfer Coefficients

Numerical simulation of temperature field of cooled turbine blades is a required element of gas turbine engine design process. The verification is usually performed on the basis of results of test of full-size blade prototype on a gas-dynamic test bench. A method of calorimetric measurement in a molten metal thermostat for verification of a thermal model of cooled blade is proposed in this paper. The method allows obtaining local values of heat flux in each point of blade surface within a single experiment. The error of determination of local heat transfer coefficients using this method does not exceed 8% for blades with radial channels. An important feature of the method is that the heat load remains unchanged during the experiment and the blade outer surface temperature equals zinc melting point. The verification of thermal-hydraulic model of high-pressure turbine blade with cooling allowing asymmetrical heat removal from pressure and suction sides was carried out using the developed method. An analysis of heat transfer coefficients confirmed the high level of heat transfer in the leading edge, whose value is comparable with jet impingement heat transfer. The maximum of the heat transfer coefficients is shifted from the critical point of the leading edge to the pressure side.

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