An Experimental Investigation of an Array of Inline Impinging Jets on a Surface With Varying Rib Orientations and Blockages

2017 ◽  
Author(s):  
Justin Hodges ◽  
Andrea Osorio ◽  
Erik J. Fernandez ◽  
Jayanta S. Kapat ◽  
Tryambak Gangopadhyay ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Flow Direction ◽  
Cross Flow ◽  
Jet Impingement ◽  
Target Surface ◽  
Channel Height ◽  
Streamwise Direction ◽  
Mean Flow ◽  
Roughness Elements ◽  
The Mean

This investigation focuses on multi-jet impingement configurations for gas turbine geometries in which the objective is to understand the influence of the roughness elements (ribs) on a target surface to the heat transfer and flow field. Existing studies in literature show the implementation of roughness elements for impingement configurations prove to increase heat transfer by 10–30%. Three different surface configurations are chosen for this multi-jet array impingement study: smooth surface (no ribs), small perpendicularly oriented ribs, and large perpendicularly oriented ribs. These roughness elements are non-continuous, broken rib turbulators which are square in cross section and oriented orthogonally to the mean flow direction within the cross flow duct. The roughness elements are oriented perpendicular to the mean flow direction. For each of the ribs tested, the two blockages tested, based on rib-to-channel height, were 20.83% and 41.67%. The jet impingement arrays are of an inline configuration. The Reynolds numbers tested, based on jet diameter, include 4,600, 13,300, 20,600, 30,200. The x/D (streamwise direction), y/D (spanwise direction), z/D (channel height direction) for the impingement array considered are 5 and 10, 8, and 3, respectively. A temperature sensitive paint technique was used to measure the heat transfer at the target surface, in which the local temperature was measured to estimate area averaged heat transfer coefficient (HTC), row averaged HTC, and stagnation region HTC. The spent air is made to exit from one direction only, thus generating a maximum cross flow situation. Keeping the jet diameter fixed at 5.1 mm, the pitch in the streamwise direction is doubled (x/D = 10) to study the effect of reducing coolant flow on the Nusselt Number distribution. Direct comparisons for heat transfer augmentation were done for all test nodes, including baseline flat/smooth plate cases. From the local heat transfer distributions of the different array patterns of the roughness elements, this study aims to determine the effect of including these elements on the target surface by the increases seen in heat transfer compared to a flat/smooth target plate.

Effects of Pin Shape and Array Orientation on Heat Transfer and Pressure Loss in Pin Fin Arrays

1984 ◽  
Vol 106 (1) ◽  
pp. 252-257 ◽  
Author(s):  
D. E. Metzger ◽  
C. S. Fan ◽  
S. W. Haley
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Pressure Loss ◽  
Flow Direction ◽  
Circular Cross Section ◽  
Cycle Performance ◽  
Mean Flow ◽  
Pin Fin ◽  
The Mean ◽  
Cooling Air

Modern high-performance gas turbine engines operate at high turbine inlet temperatures and require internal convection cooling of many of the components exposed to the hot gas flow. Cooling air is supplied from the engine compressor at a cost to cycle performance and a design goal is to provide necessary cooling with the minimum required cooling air flow. In conjunction with this objective, two families of pin fin array geometries which have potential for improving airfoil internal cooling performance were studied experimentally. One family utilizes pins of a circular cross section with various orientations of the array with respect to the mean flow direction. The second family utilizes pins with an oblong cross section with various pin orientations with respect to the mean flow direction. Both heat transfer and pressure loss characteristics are presented. The results indicate that the use of circular pins with array orientation between staggered and inline can in some cases increase heat transfer while decreasing pressure loss. The use of elongated pins increases heat transfer, but at a high cost of increased pressure loss. In conjunction with the present measurements, previously published results were reexamined in order to estimate the magnitude of heat transfer coefficients on the pin surfaces relative to those of the endwall surfaces. The estimate indicates that the pin surface coefficients are approximately double the endwall values.

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.

Wake Formation for an Oscillating Small-Incidence-Angle Cylinder Pair in Cross-Flow

2011 ◽  
Author(s):  
Mir M. Hayder
Keyword(s):  
Incidence Angle ◽  
Flow Direction ◽  
Incident Angle ◽  
Cross Flow ◽  
Wake Flow ◽  
Circular Cylinders ◽  
Mean Flow ◽  
Small Incidence ◽  
The Mean ◽  
Wake Formation

The wake region of a pair of equal-diameter staggered circular cylinders in cross-flow is investigated experimentally for Reynolds numbers, based on the mean flow velocity, U, and the cylinder diameter, D, within the range 540 ≤ Re ≤ 755. The centre-to-centre pitch ratio and stagger angle of the cylinders at their mean position are P/D = 2.0 and α = 16°, respectively. In an earlier study, wake formation of a small-incident-angle cylinder pair was investigated for forced oscillation (transverse to the flow direction) of the upstream cylinder only. The present study is aimed to reveal the modification of the wake when the oscillation is shifted from the upstream to downstream cylinder or vice versa. Results with cylinder excitation frequencies in the range 0.07 ≤ feD/U ≤ 1.10 are reported. It is observed that for both upstream and downstream cylinder oscillations with frequency feD/U ≤ 0.10 the wake flow patterns remain essentially the same as those of the corresponding static cases. However, for frequency feD/U > 0.10 the wake undergoes considerable modification vis-a`-vis when the cylinders are stationary, and the flow pattern within the wake is strongly dependent on feD/U value. As also observed in the previous study, there are distinct regions of synchronization between the dominant wake periodicities and the cylinder oscillation over the whole range of feD/U. These synchronizations involve sub- and super-harmonics as well as fundamental synchronizations and are the result of the formation of two rows of vortices, one on either side of the combined wake of the cylinder pair. The manner in which the wake responds to the cylinder oscillation depends strongly on whether it is the upstream or downstream cylinder which is oscillating. Flow-visualization images suggests that the synchronizations on the mean-flow side of the downstream cylinder occur from the outer vortices shed by the downstream cylinder, and those on the mean-flow side of the upstream cylinder occur from the vortices formed by the interaction of the two gap shear layers and the outer shear layer separated from the upstream cylinder.

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 Jet Diameter and Surface Roughness on Internal Cooling With Single Array of Jets

2013 ◽  
Author(s):  
Nicholas Miller ◽  
Sin Chien Siw ◽  
Minking K. Chyu ◽  
Mary Anne Alvin
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Cross Flow ◽  
Jet Impingement ◽  
Target Surface ◽  
Internal Cooling ◽  
Target Plate ◽  
Surface Features ◽  
Coefficient Distribution ◽  
Rib Turbulators

The current study focused on the effects of varying jet diameter and surface roughness on the target plate from jet impingement. A single row of five jets, plenum fed, expels air onto the flat target surface and the spent air is constrained to exit in only one direction, causing the jets to encounter maximum cross-flow. Baseline jet plates were equipped with pressure taps, one for each jet, to determine flow. The initial parameters, diameter D, height to diameter H/D, and jet spacing to diameter S/D is 9.53 mm (0.375 in), 2 and 4 respectively. Upon defining the optimum array of jet diameters, three test cases will be conducted using different surface features, 90 degree ribs, chevrons and X-shaped ribs on the target plate to further enhance the heat transfer performance of the jet impingement. The parameters, width W and height H, for the surface features will be set constant at 3.18 mm (0.125 in). The Reynolds number, Re, in this experimental study ranged from 50,000 to 80,000. A transient liquid crystal technique is employed in this study to determine the local and average heat transfer coefficient distribution on the target plate. The baseline tests revealed that the heat transfer is more predominate in the upstream jets impingement zones, however, by varying the diameters the heat transfer is more uniformly distributed downstream. The results also revealed that the rib-turbulators, especially X-shaped ribs, can further enhance heat transfer enhancement in the downstream jets where crossflow can affect impingement.

Turbulence Modulation by Particle Clustering in Dilute and Moderately Dilute Channel Flows

2014 ◽  
Author(s):  
Jesse Capecelatro ◽  
Olivier Desjardins
Keyword(s):  
Carrier Phase ◽  
Flow Direction ◽  
Channel Flows ◽  
Channel Height ◽  
Spontaneous Generation ◽  
Mean Flow ◽  
Particle Clustering ◽  
Fluid Turbulence ◽  
Velocity Statistics ◽  
The Mean

Turbulent wall-bounded particle-laden flows exhibit a variety of interesting phenomena that can greatly impact the underlying carrier-phase turbulence. At sufficiently low particle concentrations and mass loadings, it is well established that inertial particles will accumulate in regions of high strain and avoid regions of high vorticity. At larger concentrations and mass loadings, intimate coupling between the phases may lead to flow instabilities, resulting in the spontaneous generation of dense clusters that can completely reorganize the structure of the underlying fluid turbulence. This work aims at investigating the effect of particle clustering on the carrier-phase turbulence in both dilute and moderately-dilute channel flows with a friction Reynolds number Reτ=630 using highly-resolved Euler-Lagrange simulations. To study the effect of gravity on cluster dynamics, simulations are conducted with gravity aligned in the mean flow direction, as well as gravity opposing the mean flow direction (i.e., a riser configuration). Particle segregation and velocity statistics are compared for each case. It is shown that the fluid turbulence departs significantly from the initially fully-developed turbulent flow when subject to a moderately dilute suspension of particles. In the denser channel flows, the gas velocity retains a viscous sublayer, but displays a strongly reduced boundary layer thickness and a flatter velocity profile compared to the unladen and dilute flows, leading to larger friction velocity. The particle concentration profile along the channel height is not found to be modified greatly by the increased particle loading, but is found to depend strongly on the orientation of gravity.

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 in a Jet-Impingement Configuration With No Cross Flows About Impinging Jets

2012 ◽  
Author(s):  
C.-S. Lee ◽  
T. I-P. Shih ◽  
K. M. Bryden ◽  
R. Ames ◽  
R. A. Dennis
Keyword(s):  
Heat Transfer ◽  
Transport Model ◽  
Computational Study ◽  
Cross Flow ◽  
Jet Impingement ◽  
Target Surface ◽  
Impinging Jets ◽  
Mean Velocity ◽  
Wall Functions ◽  
Flow And Heat Transfer

Computations were performed to study the flow and heat transfer in a jet-impingement configuration in which there is no cross flow about the impinging cooling jets. The configuration consists of two sets of staggered arrays of holes with one array of holes for jets to impinge and cool a target wall with or without strategically positioned pin fins and a second array positioned midway relative to the first array of holes for the impinging jets to exit the configuration. For this configuration, the following parameter were investigated: distance between the jet-hole exit and the target surface to be cooled (H/d = 0.5, 1, 4), spacing between jets (S/d = 2, 4), and pin-fin height (Hp/d = 0, 1, 2) on the target surface, where d is the diameter of the holes in the arrays. Also, the jet-impingement velocity was varied to study a range Reynolds numbers based on the hole diameter d and the mean velocity of the jet in the hole (Red = 20,000, 40,000, and 60,000). For all cases studied, the temperature of the coolant air is 673 K; the wall to be cooled is maintained at 1,273 K; and the static pressure at the exit of the jet-impingement array is maintained at 25 bars. This computational study is based on steady RANS – compressible Navier-Stokes with the shear-stress transport model for turbulence where integration is to the wall (i.e., wall functions were not used) and temperature-dependent properties are accounted for.

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.

Experimental and Numerical Study of Array Jet Impingement Cooling on a Leading-Edge Curved Surface

2020 ◽  
Author(s):  
Jorge Torres ◽  
Husam Zawati ◽  
Erik Fernandez ◽  
Jayanta Kapat ◽  
Jose Rodriguez
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Numerical Study ◽  
Leading Edge ◽  
Jet Impingement ◽  
Target Surface ◽  
Suction Side ◽  
Navier Stokes ◽  
Mean Flow ◽  
Side Pressure

Abstract Aerothermal performance of an asymmetrical-profile, leading-edge jet impingement array is studied using numerical and experimental techniques. This array consists of a single row of 9 jets impinging on a leading edge of diameter ratio D/d = 2, and a distinct suction side/pressure side akin to that of an actual turbine blade. Two different jet-to-target heights are tested, while the jet spacing of 4 jet diameters is kept constant. A range of jet-averaged Reynolds numbers between 20k – 80k are tested. The mean flow field of the mid-jet plane is quantified experimentally, through a non-intrusive experimental method of Particle Image Velocimetry (PIV), while area-averaged heat transfer is measured by the constant temperature copper block technique. The target surface is divided into several copper blocks to investigate the area-averaged heat transfer at each jet. The numerical portion of the presented work serves to investigate the fidelity of the Reynolds Averaged Navier-Stokes (RANS) k-ω turbulence model and how well it can predict the flow field within the geometrical domain of the leading edge.

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