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.

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.

Numerical Analysis of Heat Transfer in a Laminar, Submerged, Slot Jet Impinging on an Oscillating Wall

2019 ◽  
Author(s):  
Srivathsan Ragunathan ◽  
Douglas J. Goering
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Electronics Cooling ◽  
Jet Impingement ◽  
Target Surface ◽  
Index Method ◽  
Laminar Jet ◽  
Nusselt Numbers ◽  
Grid Convergence Index ◽  
Two Parameters

Abstract Numerical simulation results of flow and heat transfer resulting from a confined, submerged liquid jet impinging on a planar oscillating surface are presented here. Laminar jets are employed in places where space and pumping capacity constraints exist (for example, in electronics cooling). However, in a laminar single jet, the cooled region due to the jet is small and is concentrated in the stagnation zone. One way to potentially enhance the heat transfer in a laminar jet impingement arrangement is by oscillating the heated impingement surface. This work extends the previous fluid dynamics analysis (by the same author) by a description and quantification heat transfer in such an arrangement. The problem is studied with respect to two parameters governing jet impingement :Jet Reynolds Number, distance from the jet inlet to the impinging wall (z/d ratios) and a parameter characterizing oscillation : the oscillatory peak Reynolds Number. OpenFOAM (foam-extend 3.2), an open-source CFD code based on the finite volume method is used to solve the problem. Quantification of discretization uncertainty is done by employing the Grid Convergence Index Method (GCI). The transport of the vortex structures formed due to the confined arrangement of the jets and due to the oscillation of the target wall has a strong influence on the temperature distribution on the target surface. The enhancement in heat transfer is estimated as a ratio of the Nusselt Numbers cases with oscillation to corresponding cases without oscillation. It is shown that the heat transfer enhancement is a strong function of the jet and the oscillatory parameters considered.

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.

Combined Effects of Jet Plate Thickness and Fillet Radius on Leading Edge Jet Impingement With Round and Racetrack Shaped Jets

2015 ◽  
Author(s):  
Weston V. Harmon ◽  
Lesley M. Wright ◽  
Daniel C. Crites ◽  
Mark C. Morris ◽  
Ardeshir Riahi
Keyword(s):  
Heat Transfer ◽  
Turbine Blades ◽  
Plate Thickness ◽  
Leading Edge ◽  
Jet Impingement ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Stagnation Region ◽  
Vena Contracta ◽  
Nusselt Numbers

The effect of jet plate thickness is considered as regionally averaged Nusselt numbers are measured on a concave surface, which models the leading edge of modern gas turbine blades. The performance of both round and racetrack shaped orifices for leading edge impingement is considered. Regionally averaged heat transfer coefficient distributions are obtained in a steady state experiment using heated aluminum plates. From this traditional heat transfer technique, the heat transfer afforded by jet plates of varying thickness is quantified. The thickness of the jet plate is varied from 1.33 to 4.0 diameters (for both the round and racetrack shaped jets). To model the modern, cast airfoil, the effect of an inlet and outlet radius on the jet orifice is also investigated. For all cases, the jet – to – target surface spacing (z/djet) is 4, the jet – to – jet spacing (s/djet) is 8, and the target surface diameter – to jet diameter (D/djet) is 5.33. Target surface Nusselt numbers are obtained for three separate Reynolds numbers. For the round orifices, jet Reynolds numbers of 14,000, 28,100, and 42,100 are used while the corresponding Reynolds numbers for the racetrack shaped jets are 11,800, 23,600, and 35,400. Although the Reynolds number is reduced for the racetrack shaped jets, the mass flow through each jet remains constant (from the round to the racetrack jets). The Nusselt numbers measured in the stagnation region of the target surface are relatively insensitive to the jet plate thickness. For all cases considered, the flow is not developed as it exits the orifice, so the flow structures of the jets ensuing from each of the plates are similar. When the inlet of the jet is rounded, the vena contracta effect within the orifice is minimized, and a more symmetrical jet develops within the orifice. For a fixed flow rate, the racetrack shaped jets provide enhanced heat transfer compared to the round jets for all geometries considered.

Effect of Film Extraction on Impingement Heat Transfer Characteristics of Jet Arrays on Spherical-Dimpled Surfaces

2015 ◽  
Author(s):  
Xing Yang ◽  
Zhao Liu ◽  
Zhenping Feng
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Coupling Effect ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Separation Distance ◽  
Plate Spacing

Detailed heat transfer distributions are numerically investigated on a multiple jet impingement target surface with staggered arrays of spherical dimples where coolant can be extracted through film holes for external film cooling. The three dimensional Reynolds-averaged Navier-Stokes analysis with SST k-ω turbulence model is conducted at jet Reynolds number from 15,000 to 35,000. The separation distance between the jet plate and the target surface varies from 3 to 5 jet diameters and two jet-induced crossflow schemes are included to be referred as large and small crossflow at one and two opposite exit openings correspondingly. Flow and heat transfer results for the dimpled target plate with three suction ratios of 2.5%, 5.0% and 12.0% are compared with those on dimpled surfaces without film holes. The results indicate the presence of film holes could alter the local heat transfer distributions, especially near the channel outlets where the crossflow level is the highest. The heat transfer enhancements by applying film holes to the dimpled surfaces is improved to different degrees at various suction ratios, and the enhancements depend on the coupling effect of impingement and channel flow, which is relevant to jet Reynolds number, jet-to-plate spacing and crossflow scheme.

Convective Heat Transfer From Heated Extended Surfaces With a Confined Slot Jet Impingement

2004 ◽  
Author(s):  
L. K. Liu ◽  
M. C. Wu ◽  
C. J. Fang ◽  
Y. H. Hung
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Number ◽  
Mixed Convection ◽  
Average Nusselt Number ◽  
Jet Impingement ◽  
Separation Distance ◽  
Nusselt Numbers ◽  
Transfer Behavior ◽  
Extended Surfaces

A series of experimental investigations with stringent measurement methods on the studies related to mixed convection from the horizontally confined extended surfaces with a slot jet impingement have been successfully conducted. The relevant parameters influencing mixed convection performance due to jet impingement and buoyancy include the Grashof number, ratio of jet separation distance to nozzle width, ratio of extended surfaces height to nozzle width and jet Reynolds number. The range of these parameters studied are Grs = 3.77 × 105 – 1.84 × 106, H/W = 1–10, Hs/W = 0.74–3.40 and Re = 63–1383. In the study, the heat transfer behavior on the extended surfaces with confined slot jet impingement such as the temperature distribution, local and average Nusselt numbers on the extended surfaces has been systematically explored. The results manifest that the effect of steady-state Grashof number on heat transfer behavior such as stagnation, local and average Nusselt number is not significant; while the heat transfer performance increases with decreasing jet separation distance or with increasing extended surface height and jet Reynolds number. Besides, two new correlations of local and average Nusselt numbers in terms of H/W, Hs/W and Re are proposed for the cases of extended surfaces. A satisfactory agreement is achieved between the results predicted by these correlations and the experimental data. Finally, a complete composite correlation of steady-state average Nusselt number for mixed convection due to jet impingement and buoyancy is proposed. The comparison of the predictions evaluated by this correlation with all the present experimental data is made. The maximum and average deviations of the predictions from the experimental data are 7.46% and 2.87%, respectively.

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.

Heat Transfer Measurements in a Leading Edge Geometry With Racetrack Holes and Film Cooling Extraction

2012 ◽  
Author(s):  
Luca Andrei ◽  
Carlo Carcasci ◽  
Riccardo Da Soghe ◽  
Bruno Facchini ◽  
Francesco Maiuolo ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Film Cooling ◽  
Large Scale ◽  
Internal Heat ◽  
Leading Edge ◽  
Jet Impingement ◽  
Internal Surface ◽  
Test Facility ◽  
Supply Channel

An experimental survey on a state of the art leading edge cooling scheme was performed to evaluate heat transfer coefficients (HTC) on a large scale test facility simulating an high pressure turbine airfoil leading edge cavity. Test section includes a trapezoidal supply channel with three large racetrack impingement holes. On the internal surface of the leading edge, four big fins are placed in order to confine impingement jets. The coolant flow impacts the leading edge internal surface and it is extracted from the leading edge cavity through 24 showerhead holes and 24 film cooling holes. The aim of the present study is to investigate the combined effects of jet impingement and mass flow extraction on the internal heat transfer of the leading edge. A non uniform mass flow extraction was also imposed to reproduce the effects of pressure side and suction side external pressure. Measurements were performed by means of a transient technique using narrow band Thermo-chromic Liquid Crystals (TLC). Jet Reynolds number and crossflow conditions into the supply channel were varied in order to cover the typical engine conditions of these cooling systems (Rej = 10000–40000). Experiments were compared with a numerical analysis on the same test case in order to better understand flow interaction inside the cavity. Results are reported in terms of detailed 2D maps, radial-wise and span-wise averaged values of Nusselt number.

Heat Transfer Measurements in a Leading Edge Geometry With Racetrack Holes and Film Cooling Extraction

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Luca Andrei ◽  
Carlo Carcasci ◽  
Riccardo Da Soghe ◽  
Bruno Facchini ◽  
Francesco Maiuolo ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Film Cooling ◽  
Large Scale ◽  
Internal Heat ◽  
Leading Edge ◽  
Jet Impingement ◽  
Internal Surface ◽  
Test Facility ◽  
Supply Channel

An experimental survey on a state of the art leading edge cooling scheme was performed to evaluate heat transfer coefficients (HTC) on a large scale test facility simulating a high pressure turbine airfoil leading edge cavity. The test section includes a trapezoidal supply channel with three large racetrack impingement holes. On the internal surface of the leading edge, four big fins are placed in order to confine impingement jets. The coolant flow impacts the leading edge internal surface, and it is extracted from the leading edge cavity through 24 showerhead holes and 24 film cooling holes. The aim of the present study is to investigate the combined effects of jet impingement and mass flow extraction on the internal heat transfer of the leading edge. A nonuniform mass flow extraction was also imposed to reproduce the effects of the pressure side and suction side external pressure. Measurements were performed by means of a transient technique using narrow band thermochromic liquid crystals (TLCs). Jet Reynolds number and crossflow conditions into the supply channel were varied in order to cover the typical engine conditions of these cooling systems (Rej=10,000-40,000). Experiments were compared with a numerical analysis on the same test case in order to better understand flow interaction inside the cavity. Results are reported in terms of detailed 2D maps, radial-wise, and span-wise averaged values of Nusselt number.

Effects of Jetting Orifice Geometry Parameters and Channel Reynolds Number on Bended Channel Cooling for a Novel Internal Cooling Structure

2019 ◽  
Author(s):  
Wei He ◽  
Qinghua Deng ◽  
Juan He ◽  
Tieyu Gao ◽  
Zhenping Feng
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Leading Edge ◽  
Jet Impingement ◽  
Suction Side ◽  
Outer Wall ◽  
Internal Cooling ◽  
Cooling Effectiveness ◽  
Blade Leading Edge

Abstract A novel internal cooling structure has been raised recently to enhance internal cooling effectiveness and reduce coolant requirement without using film cooling. This study mainly focuses on verifying the actual cooling performance of the structure and investigating the heat transfer mechanism of the leading edge part of the structure, named bended channel cooling. The cooling performances of the first stage of GE-E3 turbine with three different blade leading edge cooling structures (impingement cooling, swirl cooling and bended channel cooling) were simulated using the conjugate heat transfer method. Furthermore, the effects of jetting orifice geometry and channel Reynolds number were studied with simplified models to illustrate the flow and heat transfer characteristics of the bended channel cooling. The results show that the novel internal cooling structure has obvious advantages on the blade leading edge and suction side under operating condition. The vortex core structure in the bended channel depends on orifice width, but not channel Reynolds number. With the ratio of orifice width to outer wall thickness smaller than a critical value of 0.5, the coolant flows along the external surface of the channel in the pattern of “inner film cooling”, which is pushed by centrifugal force and minimizes the mixing with spent cooling air. Namely, the greatly organized coolant flow generates higher cooling effectiveness and lower coolant demand. Both the Nusselt number on the channel surfaces and total pressure loss increase significantly when the orifice width falls or channel Reynolds increases, but the wall jet impingement distance appears to be less influential.

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