Effects of Target Channel Shapes on Double Swirl Cooling Performance at Gas Turbine Blade Leading Edge

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Junfei Zhou ◽  
Xinjun Wang ◽  
Jun Li ◽  
Weitao Hou
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Thermal Performance ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Leading Edge ◽  
Target Surface ◽  
Length Ratio ◽  
Maximum Enhancement ◽  
Cooling Performance

In order to further study the effects of the target channel shape on the cooling performance of the double swirl cooling (DSC), five double swirl channels formed by two overlapping elliptic cylinders with different length ratio between the vertical semi-axis and the horizontal semi-axis are applied. Numerical studies are carried out under three Reynolds numbers. The flow characteristics and heat transfer performance of five DSC cases are compared with the benchmark impingement cooling case. The flow losses, cross-flow development, generated vortices, and velocity distributions inside target channels are illustrated, analyzed, and compared. The spanwise averaged Nusselt number, Nusselt number distributions, and thermal performance are discussed and compared. Results indicate that the largest length ratio between the vertical semi-axis and the horizontal semi-axis of the target channel yields the lowest flow loss, largest overall averaged Nusselt number, and best thermal performance. With the decrease in the length ratio, the heat transfer distribution on the target surface becomes more uniform. The maximum enhancement of overall averaged Nusselt number and thermal performance in DSC is about 30% and 33%, respectively.

Effects of Extended Jet Holes to Heat Transfer and Flow Characteristics of the Jet Impingement Cooling

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Ahmet Ümit Tepe ◽  
Kamil Arslan ◽  
Yaşar Yetişken ◽  
Ünal Uysal
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Average Nusselt Number ◽  
Flat Surface ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Jet Impingement ◽  
Target Surface ◽  
Impingement Cooling ◽  
Compressor Power

In this study, effects of extended jet holes to heat transfer and flow characteristics of jet impingement cooling were numerically investigated. Cross-flow in the impinging jet cooling adversely affects the heat transfer on the target surface. The main purpose of this study is to reduce the negative effect of cross-flow on heat transfer by extending jet holes toward the target surface with nozzles. This study has been conducted under turbulent flow condition (15,000 ≤ Re  ≤  45,000). The surface of the turbine blade, which is the target surface, has been modeled as a flat plate. The effect of the ribs, placed on the target surface, on the heat transfer has been also investigated, and the results were compared with the flat surface. The parameters such as average and local Nusselt numbers on the target surface, flow characteristics, and compressor power have been examined in detail. It was obtained from the numerical results that the average Nusselt number increases with decreasing the gap between the target surface and the nozzle. In addition, the higher average Nusselt number was obtained on the flat surface than the ribbed surface. The lowest compressor power was achieved in the 5Dj nozzle gap for the flat surface and in the 4Dj nozzle gap for the ribbed surface.

Effects of Impinging Hole Shapes on Double Swirl Cooling Performance at Gas Turbine Blade Leading Edge

2018 ◽  
Author(s):  
Junfei Zhou ◽  
Xinjun Wang ◽  
Jun Li ◽  
Daren Zheng
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Thermal Performance ◽  
Heat Transfer Performance ◽  
Leading Edge ◽  
Transfer Performance ◽  
Cooling Performance ◽  
Impingement Cooling ◽  
Cooling Method ◽  
Blade Leading Edge

A double swirl cooling method has been raised recently to enhance the internal cooling performance at the blade leading edge. This paper mainly focuses on investigating the flow and heat transfer characteristics of the double swirl cooling method. Further more, four kinds of elliptical holes are applied to show effects of impinging hole shapes on the cooling performance. Results of all double swirl cooling cases are compared with that of an impingement cooling structure under four Reynolds numbers. Overall averaged Nusselt number, friction factor and thermal performance factor are compared in all cases, Vortexes induced by different impinging hole types and target chambers are studied and compared. The spanwise averaged Nusselt number, Nusselt number contours and Nusselt number distributions at several cross sections are studied and compared. Results show that the double swirl cooling method can significantly enhance the heat transfer performance compared with the traditional impingement cooling structure. Double swirl cooling with cylindrical impinging hole shows the best thermal performance and lowest flow losses. By applying the elliptical impinging hole with the sharp side faced the mainstream flow direction and a larger major to minor axis length ratio, the rotational vortex inside the double swirl chamber can be better developed and the heat transfer performance is also promoted.

Analysis of heat transfer and fluid flow of a slot jet impinging on a confined concave surface with various curvature and small jet to target spacing

2019 ◽  
Vol 29 (8) ◽  
pp. 2885-2910 ◽  
Author(s):  
Dandan Qiu ◽  
Lei Luo ◽  
Songtao Wang ◽  
Bengt Ake Sunden ◽  
Xinhong Zhang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Thermal Performance ◽  
Flow Characteristics ◽  
Target Surface ◽  
Surface Curvature ◽  
Content Type ◽  
Curvature Effects ◽  
Target Spacing

Purpose This study aims to focus on the surface curvature, jet to target spacing and jet Reynolds number effects on the heat transfer and fluid flow characteristics of a slot jet impinging on a confined concave target surface at constant jet to target spacing. Design/methodology/approach Numerical simulations are used in this research. Jet to target spacing, H/B is varying from 1.0 to 2.2, B is the slot width. The jet Reynolds number, Rej, varies from 8,000 to 40,000, and the surface curvature, R2/B, varies from 4 to 20. Results of the target surface heat transfer, flow parameters and fluid flow in the concave channel are performed. Findings It is found that an obvious backflow occurs near the upper wall. Both the local and averaged Nusselt numbers considered in the defined region respond positively to the Rej. The surface curvature plays a positive role in increasing the averaged Nusselt number for smaller surface curvature (4-15) but affects little as the surface curvature is large enough (> 15). The thermal performance is larger for smaller surface curvature and changes little as the surface curvature is larger than 15. The jet to target spacing shows a negative effect in heat transfer enhancement and thermal performance. Originality/value The surface curvature effects are conducted by verifying the concave surface with constant jet size. The flow characteristics are first obtained for the confined impingement cases. Then confined and unconfined slot jet impingements are compared. An ineffective point for surface curvature effects on heat transfer and thermal performance is obtained.

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.

Enhancement of Impingement Cooling in a High Cross Flow Channel Using Shaped Impingement Cooling Holes

2009 ◽  
Vol 132 (2) ◽  
Author(s):  
Andrew C. Chambers ◽  
David R. H. Gillespie ◽  
Peter T. Ireland ◽  
Robert Kingston
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Cross Flow ◽  
Target Surface ◽  
Impingement Cooling ◽  
Turbine Cooling ◽  
Impingement Jet ◽  
Coefficient Distribution ◽  
Cooling Passage ◽  
Experimental Rig

Impingement systems are common place in many turbine cooling applications. Generally these systems consist of a target plate that is cooled by the impingement of multiple orthogonal jets. While it is possible to achieve high target surface heat transfer with this configuration, the associated pressure drop is generally high and the cooling efficiency low. Furthermore, especially in large impingement arrays, the buildup of cross flow from upstream jets can be significant and results in deflection of downstream impingement jets reducing the resultant heat transfer coefficient distribution. This paper presents a computational and experimental investigation into the use of shaped elliptical or elongated circular impingement holes designed to improve the penetration of the impinging jet across the coolant passage. This is of particular interest where there is significant cross flow. Literature review and computational investigations are used to determine the optimum aspect ratio of the impingement jet. The improved heat transfer performance of the modified design is then tested in an experimental rig with varying degrees of cross flow at engine representative conditions. In all cases, a 16% increase in the Nusselt number on the impingement target surface in the downstream half of the cooling passage was achieved. Under the first four impingement holes, a Nusselt number enhancement of 28–77% was achieved, provided no additional cross flow was present in the passage. When appropriately aligned, a significant reduction in the stress concentration factor caused by the addition of a hole can be achieved using this design.

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.

Experimental and Numerical Study on Impingement Heat Transfer and Flow Characteristics on a Semicircular Ribbed Target Surface

2021 ◽  
Author(s):  
Wang-Hao-Tai Kang ◽  
Hui-Ren Zhu
Keyword(s):  
Heat Transfer ◽  
Flow Resistance ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Target Surface ◽  
High Heat ◽  
Transfer Effect ◽  
High Heat Transfer ◽  
Special Cases ◽  
The Impact

Abstract Impact cooling is an effective way to enhance heat transfer, especially in the gas turbine blades. In the leading edge of the blade where has the high heat load, jet impingement cooling is widely used due to its high heat transfer characteristic in stagnation region. The focus is on finding a cooling structure that can improve the heat transfer effect of the internal impact structure at the leading edge without increasing the internal flow resistance. In this paper, using transient liquid crystal experiments researches for the flow and heat transfer characteristics of a semi-circular structure, which is simplified from the real blade leading edge ’s inside surface and have different rib structures. This paper studies five cases:no rib, round-shaped raised structure, oblique rib, round-shaped raised structure and oblique rib and span-wise rib and arc rib to find their heat transfer and flow characteristics. Some rib-shaped protrusion has three heights, which are 30%, 50%, 70% of the impact distance H. Experimental conditions of Reynolds number are Re = 10000, 15000, 20000, 25000, 30000. The experimental verification results show that the internally strengthened heat transfer structures studied in this paper can improve the heat transfer effect of the leading edge array of the turbine blade impact target surface without increasing the flow resistance. The structure with both oblique ribs and round-shaped raised structures has the highest surface average Nusselt number of the target plate and the lowest discharge coefficient of the channel. The structure with both span-wise ribs and arc ribs has a staggered high heat transfer area distribution, which can maybe use in some special cases.

Experimental Leading-Edge Impingement Cooling Through Racetrack Crossover Holes

2001 ◽  
Author(s):  
M. E. Taslim ◽  
L. Setayeshgar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Cross Flow ◽  
Leading Edge ◽  
Target Surface ◽  
Transfer Enhancement ◽  
Experimental Heat ◽  
Circular Holes

Proper and efficient cooling of the turbine airfoil leading edge is imperative in increasing the airfoil life and overall efficiency of the gas turbine. To enhance the heat transfer coefficient in the leading-edge cavities, they are often roughened on three walls with ribs of different geometries. The cooling flow for these geometries usually enters the cavity from the airfoil root and flows radially to the airfoil tip or, in the most recent designs, enters the leading edge cavity from the adjacent cavity through a series of crossover holes on the partition wall between the two cavities. In the latter case, the cross-over jets impinge on a smooth leading-edge wall and exit through the showerhead film holes, “gill” film holes on the pressure and suction sides, and, in some cases, forms a cross-flow in the leading-edge cavity and is ejected through the airfoil tip hole. In this investigation, the impingement heat transfer coefficient was measured on both smooth and roughened leading-edge walls. Most reported studies cover the impingement on a flat smooth surface with round jets. This investigation dealt with two new features in airfoil leading-edge cooling concept: a curved and roughened target surface as well as impingement with racetrack shaped holes. Results of circular crossover jets impinging on the same surface geometries were reported by these authors previously. Experimental heat transfer results are presented for the impingement of racetrack shaped cross-over jets, with major hole (jet) axes at 0° and 45° angles to the cooling cavity’s radial axis, on 1) a smooth curved leading-edge wall, 2) a wall roughened with conical bumps, and 3) a wall roughened with tapered radial ribs. The tests were run for a range of inlet and exit flow arrangements and jet Reynolds numbers and the results were compared with those of round cross-over jets. The major conclusions of this study are: a) racetrack crossover holes are much more efficient than circular holes in cooling of the leading-edge surface, b) the overall heat transfer performance of 0° racetrack cross-over holes is superior to that of 45° racetrack cross-over holes, c) there is a heat transfer enhancement of up to 70% for roughening the target surface, and d) the driving factor in heat transfer enhancement is the increase in surface area.

Impingement Heat Transfer on a Cylindrical, Concave Surface With Varying Jet Geometries

2012 ◽  
Author(s):  
C. Neil Jordan ◽  
Lesley M. Wright ◽  
Daniel C. Crites
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Mass Flow Rate ◽  
Flow Rate ◽  
Leading Edge ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Hole Shape ◽  
Cylindrical Holes

Jet impingement is often employed within the leading edge of modern turbine airfoils to combat the extreme heat loads incurred within this region. This experimental investigation employs a transient liquid crystal technique to obtain detailed Nusselt number distributions on a concave, cylindrical surface that models the leading edge of a turbine airfoil. The effect of hole shape as well as differing hole inlet and exit conditions are investigated. Two hole shapes are studied: cylindrical and racetrack shaped holes; for each hole shape, the hydraulic diameter and mass flow rate into the array of jets is conserved. As a result, the jet’s Reynolds number (Rejet) varies between the two jet arrays. Reynolds numbers of 13600, 27200, and 40700 are investigated for the cylindrical holes and Reynolds numbers of 11500, 23000, and 34600 are investigated for the racetrack holes. Three inlet and exit conditions are investigated for each hole shape: a square edged, a partially filleted, and a fully filleted hole. The ratio of the fillet radius to hole hydraulic diameter (r / dH,Jet) is set at 0.25 and 0.667 for the partially and fully filleted holes, respectively. The relative jet–to–jet spacing (s / dH,Jet) is maintained at 8, the jet–to–target surface spacing (z / dH,Jet) is maintained at 4, the jet–to–target surface curvature (D / dH,Jet) is maintained at 5.33, and the relative jet plate thickness (t / dH,Jet) is maintained at 1.33. Results show the Nusselt number is directly related to the jet Reynolds number for both cylindrical and racetrack shaped holes. The racetrack holes are shown to provide enhanced heat transfer compared to the cylindrical holes for a set mass flow rate. The degree of filleting at the inlet and outlet of the holes affects whether the heat transfer on the leading edge model is further enhanced or degraded.

Enhancement of Impingement Cooling in a High Cross Flow Channel Using Shaped Impingement Cooling Holes

2006 ◽  
Author(s):  
Andrew C. Chambers ◽  
David R. H. Gillespie ◽  
Peter T. Ireland ◽  
Mark Mitchell
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Cross Flow ◽  
Target Surface ◽  
Impingement Cooling ◽  
Turbine Cooling ◽  
Impingement Jet ◽  
Coefficient Distribution ◽  
Cooling Passage ◽  
Experimental Rig

Impingement systems are common place in many turbine cooling applications. Generally these systems consist of a target plate that is cooled by the impingement of multiple orthogonal jets. While it is possible to achieve high target surface heat transfer with this configuration, the associated pressure drop is generally high and the cooling efficiency low. Furthermore, especially in large impingement arrays, the build-up of cross flow from upstream jets can be significant and result in deflection of downstream impingement jets reducing the resultant heat transfer coefficient distribution. This paper presents a computational and experimental investigation into the use of shaped elliptical or elongated circular impingement holes designed to improve the penetration of the impinging jet across the coolant passage. This is of particular interest where there is significant cross flow. Literature review and computational investigations are used to determine the optimum aspect ratio of the impingement jet. The improved heat transfer performance of the modified design is then tested in an experimental rig with varying degrees of cross flow at engine representative conditions. In all cases a 16% increase in the Nusselt number on the impingement target surface in the downstream half of the cooling passage was achieved. Under the first 4 impingement holes Nusselt number enhancement of enhancement of 28–77% was achieved provided no additional cross flow was present in the passage. When appropriately aligned, a significant reduction in the stress concentration factor caused by the addition of a hole can be achieved using this design.

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