Performance analysis of different turbulence models in impinging jet cooling

2020 ◽  
Vol 31 (04) ◽  
pp. 2050051
Author(s):  
Shashikant Pawar ◽  
Devendra Kumar Patel
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Transfer Problem ◽  
Impinging Jet ◽  
Experimental Results ◽  
Wall Jet ◽  
Quadratic Formula ◽  
Upward Direction ◽  
Number Formula ◽  
Text Model

The characteristics of heat transfer from a hot wall surface for the oblique impingement of a free turbulent slot jet have been investigated numerically. Different turbulent models — the [Formula: see text]-[Formula: see text], [Formula: see text]-[Formula: see text], SST [Formula: see text]-[Formula: see text], cubic [Formula: see text]-[Formula: see text] and quadratic [Formula: see text]-[Formula: see text] models — are used for the prediction of heat transfer and their results were compared with experimental results reported in the literature. The comparison shows that the [Formula: see text]-[Formula: see text], quadratic [Formula: see text]-[Formula: see text] and SST [Formula: see text]-[Formula: see text] models give more unsatisfactory results for the investigated configuration, while the cubic [Formula: see text]-[Formula: see text] model is capable of predicting the local Nusselt number in wall-jet region only. The [Formula: see text]-[Formula: see text] model exhibits the best agreement with the experimental results in both stagnation and wall-jet regions. Further, the [Formula: see text]-[Formula: see text] model is applied to analyze the obliquely impinging jet heat transfer problem. The parametric effects of the jet inclination ([Formula: see text], [Formula: see text] and [Formula: see text]), jet-to-surface distance ([Formula: see text], 6 and 8), Reynolds number ([Formula: see text], 15[Formula: see text]000 and 20[Formula: see text]000), and turbulent intensity ([Formula: see text], [Formula: see text] and [Formula: see text]) have been presented. The heat transfer on the upward direction is seen to decrease, while that on the downward direction it rises for the increasing angle. It is to be noted that as the value of [Formula: see text] decreases, the point of maximum Nusselt number ([Formula: see text]) displaces toward the upward direction from the geometric center point as well as its value reduces. The shifting of the [Formula: see text] is found to be independent of Re and [Formula: see text] within the range considered for the study.

Very Large Eddy Simulation of Flow and Heat Transfer in a Pulsating Impinging Jet

2020 ◽  
Author(s):  
Fangyuan Liu ◽  
Junkui Mao ◽  
Xingsi Han ◽  
Zhaoyang Xia
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Large Eddy Simulation ◽  
Impinging Jet ◽  
Core Region ◽  
Wall Jet ◽  
The Core ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Pulsating Jets

Abstract The steady impinging jets applied in turbomachine have been comprehensively studied but the pulsating jets still need to be further researched. The flow field and heat transfer characteristics of pulsating impinging jet impinging on a flat plate have been simulated using the improved very large eddy simulation established with SST k–ω model. Two time-mean Reynolds numbers (6,000 and 23,000) in the conditions of frequency = 10Hz and steady state at the constant jet–to–surface distance (6D) were considered. The velocity, vortices, and Nusselt number distributions on the plate surface were investigated to emphasize on the vortex structures in the flow and its relation to the heat transfer. The investigation has revealed the advantage of the improved very large eddy simulation for predicting the dynamical generating process of flow structures in pulsating jets. Calculated results showed pairs of vortices were organized and induced from the jet exit, and propagated along with the jet region periodically. The vortices grew with the entrainment towards the ambient fluid and resulted in accelerated interaction in the wall jet region. Meanwhile, the vortices had strong interaction with the core region and weakened velocity in the core region. Results showed that the time–mean local Nusselt number of pulsating jet was lower in the stagnation region at both investigated Re numbers but not reduced in the wall jet region.

Effect of Variation of Pin-fin Height on Jet Impingement Heat Transfer on a Rotating Surface

2021 ◽  
Author(s):  
Pratik S. Bhansali ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Gas Turbine ◽  
Average Nusselt Number ◽  
Jet Impingement ◽  
Impinging Jet ◽  
Rotating Disc ◽  
Disc Surface ◽  
Pin Fins

Abstract Heat transfer over rotating surfaces is of particular interest in rotating machinery such as gas turbine engines. The rotation of the gas turbine disc creates a radially outward flow on the disc surface, which may lead to ingress of hot gases into the narrow cavity between the disc and the stator. Impingement of cooling jet is an effective way of cooling the disc and countering the ingress of the hot gases. Present study focusses on investigating the effect of introducing pin-fins over the rotating disc on the heat transfer. The jet Reynolds number has been varied from 5000 to 18000, and the rotating Reynolds number has been varied from 5487 to 12803 for an aluminum disc of thickness 6.35mm and diameter 10.16 cm, over which square pins have been arranged in an inline fashion. Steady state temperature measurements have been taken using thermocouples embedded in the disc close to the target surface, and area average Nusselt number has been calculated. The effects of varying the height of the pin-fins, distance between nozzle and the disc surface and the inclination of the impinging jet with the axis of rotation have also been studied. The results have been compared with those for a smooth aluminum disc of equal dimensions and without any pin-fins. The average Nusselt number is significantly enhanced by the presence of pin fins. In the impingement dominant regime, where the effect of disc rotation is minimal for a smooth disc, the heat transfer increases with rotational speed in case of pin fins. The effect of inclination angle of the impinging jet is insignificant in the range explored in this paper (0° to 20°).

Uncoupling the Conjugate Heat Transfer Problem in a Horizontal Plate Under the Influence of a Laminar Flow

2003 ◽  
Author(s):  
Ricardo S. Va´squez ◽  
Antonio J. Bula
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Conjugate Heat Transfer ◽  
Energy Equation ◽  
Transfer Problem ◽  
Heat Transfer Problem ◽  
Interface Temperature ◽  
Horizontal Plate ◽  
Steady State Condition ◽  
Heated Body

The conjugate heat transfer process of cooling a horizontal plate in steady state condition is studied. The model considers both solid and fluid regions in Cartesian coordinates. The problem was solved analytically, considering the fluid flowing in a laminar condition and hydrodynamically developed before any interaction with the heated body. The height of the fluid considered was enough to allow the generation of a thermal boundary layer without any restriction. The conservation of mass, momentum and energy equations were considered to turn the problem into a non dimensional form. The heated body presented a constant heat flux at the bottom side, and convective heat transfer at the top side in contact with the fluid. The other two boundary conditions are adiabatic. The energy equation was considered in the solid to turn it into a non dimensional form. The interface temperature was obtained from a regression using the Chebyshev polynomial approximation. As the problem deals with the cooling of a electronics components, the solution presents the mathematical solution of the energy equation for the solid, including the isothermal lines. The non dimensional form allows a thorough analysis of the problem, considering the influence of the different parameters in the conjugate heat transfer problem. The solution is compared with numerical solution of different problems, and the parameters considered are Reynolds number, plate thickness, Prandtl number, and solid thermal conductivity. The results obtained present isothermal lines, local Nusselt number, and average Nusselt number.

Study of a Cooling Feed Pipe With a Covering Plate on a Ribbed Turbine Case

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Fangyuan Liu ◽  
Junkui Mao ◽  
Chao Han ◽  
Yuanjian Liu ◽  
Xingsi Han ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Experimental Tests ◽  
Impinging Jet ◽  
Nusselt Numbers ◽  
Spacing Ratio ◽  
Wall Flow ◽  
Complicated Geometry ◽  
Clearance Control

Considering the complicated geometry in an active clearance control (ACC) system, the design of an improved cooling feed pipe with a covering plate for a high pressure ribbed turbine case was investigated. Numerical calculations were analyzed to obtain the interactions between the impinging jet arrays fed by the pipe. Experimental tests were performed to explore the effect of the Reynolds number (2000–20,000) and the jet-to-surface spacing ratio (6–10) on the streamwise-averaged Nusselt numbers. Additionally, the effect of the crossflow produced by the configuration was investigated. Results showed a confined curved channel was formed by the pipe and ribbed case, which resulted in crossflow. The crossflow evolved into vortices and the streamwise-averaged Nusselt number on the high ribs was subsequently increased. Furthermore, the distribution of the heat transfer on the entire surface became more uniform compared with that of traditional impinging jet arrays. A higher Nusselt number was achieved by decreasing the jet-to-surface spacing and increasing the Reynolds number. This investigation has revealed a cooling configuration for controlling the wall flow and evening the heat transfer on the case surface, especially for the ribs.

Heat Transfer in Cavities Having a Fixed Amount of Solid Material

2005 ◽  
Author(s):  
Edimilson J. Braga ◽  
Marcelo J. S. de Lemos
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Continuum Model ◽  
Average Nusselt Number ◽  
Numerical Solutions ◽  
Solid Phase ◽  
Transfer Problem ◽  
Void Space ◽  
Fixed Amount ◽  
The Continuum

This work compares two different approaches for obtaining numerical solutions for laminar natural convection within a square cavity, which is filled by a fixed amount of a solid conducting material. The first model considered, namely, porous-continuum model, is based on the assumption that the solid and the fluid phases are seen as the same medium, over which volume-averaged transport equations apply. Secondly, a continuum model is considered to solve the momentum equations for the fluid phase that would resemble a conjugate heat transfer problem in both the solid and the void space. In the continuum model, the solid phase is composed of square obstacles, equally spaced within the cavity. In both models, governing equations are numerically solved using the finite volume method. The average Nusselt number at the hot wall, obtained from the porous-continuum model, for several Darcy numbers, are compared with those obtained with the second approach, namely the continuum model, with different number of obstacles. When comparing the two methodologies, this study shows that the average Nusselt number calculated for each approach for the same Ram differs between each other and that this discrepancy increases as the Darcy number decreases, in the porous-continuum model, or the number of blocks increases and their size decreases, in the continuum model. A correlation is suggested to modify the macroscopic thermal expansion coefficient in order to match the average Nusselt numbers calculated by the two models for Ram = const = 104 and Da ranging from 1.2060×10−4 to 1.

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

2007 ◽  
Author(s):  
M. E. Taslim ◽  
D. Bethka
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Convective Heat Transfer Coefficient ◽  
Internal Heat ◽  
Leading Edge ◽  
Impinging Jet ◽  
Suction Side ◽  
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. Effects of strong crossflows 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 crossflows beyond the crossflow 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 and jet Reynolds numbers ranging from 8000 to 48000. Comparisons are also made between the experimental results of impingement with and without the presence of crossflow and between representative numerical and measured heat transfer results. It was concluded that the presence of the external crossflow reduces the impinging jet effectiveness both on the nose and side walls, 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 crossflow, and the agreement between the numerical and experimental results was reasonable with an average difference ranging from −8% to −20%.

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 Enhancement of Impinging Jet Heat Transfer Using Two Parallel Confining Plates Mounted near Rectangular Nozzle Exit

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Yoshiaki Haneda ◽  
Akiko Souma ◽  
Hideo Kurasawa ◽  
Shouichiro Iio ◽  
Toshihiko Ikeda
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Nozzle Exit ◽  
Impinging Jet ◽  
Parallel Plates ◽  
Target Plate ◽  
Rectangular Nozzle ◽  
Gap Ratio ◽  
Type Flow ◽  
The One

Impinging jet heat transfer on a target plate was enhanced by using two parallel confining plates mounted between a rectangular nozzle end plate and a jet target plate. The target plate was set equal to 2, 3, 4, and 5 times the jet exit width, h, and the gap ratio of two parallel confining plates, W/h, were changed from 2.7 to 8.0 only by impinging length H=5h and from 2.7 to 6.7 by H≠5h. Two confining parallel plates mounted near the jet exit produced swing-type flow under some conditions. As a result, the maximum Nusselt number attained around the stagnation point was augmented by about 50% compared to the one for normal impinging jet without the two parallel plates and then spatial mean Nusselt number was increased by about 40%.

Heat Transfer Characteristics of a Swirling Laminar Impinging Jet

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
Koichi Ichimiya ◽  
Koji Tsukamoto
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Local Heat Transfer ◽  
Impinging Jet ◽  
Local Heat ◽  
Experimental Results ◽  
Governing Equations ◽  
Constant Wall Temperature ◽  
Numerical Heat Transfer ◽  
Narrow Space

This paper describes the characteristics of the heat transfer and flow of a swirling laminar impinging jet in a comparatively narrow space with a confined wall. Air is impinged on a flat surface with constant wall temperature. The heat transfer and flow field were analyzed numerically by solving three-dimensional governing equations. Heat transfer experiment and flow visualization were also performed. Numerical heat transfer was compared with experimental results. Temperature distribution and velocity vectors in the space were obtained for various swirl numbers at Reynolds number Re=2000. The numerical and experimental results show that the swirling jet enhances or depresses the local heat transfer, and the average Nusselt number ratio with and without swirl takes a peak at a certain swirl number.

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