Numerical Evaluation of 2D and 3D Steady and Unsteady Flows of a Pair of Opposing Confined Impinging Air Jets

2009 ◽  
Author(s):  
Victor Chiriac ◽  
Jorge L. Rosales
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Unsteady Flow ◽  
Flow Patterns ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
Complex Flow ◽  
Air Jets ◽  
2D And 3D ◽  
The Impact

The steady and unsteady laminar flow and heat transfer characteristics for a pair of opposing confined impinging slot jets in 2D and 3D were evaluated numerically at two Reynolds numbers. The present study continues the authors’ earlier work [1] and identifies the main similarities and differences arising from the expansion to the third dimension. At lower Reynolds number jet (Re = 300), the flow interaction produces a symmetric, steady flow hydrodynamic pattern with the jets being deflected laterally for the 2D flow. At Re = 300, the 3D slot jet produces almost the same values as the 2D case, yet the flow is slightly asymmetrical and unsteady. However, by further increasing the Reynolds number to 750, a complex and highly unsteady flow develops for both 2D and 3D simulations. The symmetry of both the 2D and 3D flows is disrupted and the resulting complex flow patterns reveal the vortex pairing effects, leading to the jet “buckling and sweeping” motion, enabling the enhanced local heat transfer. The convective heat transfer coefficients and the unsteady flow development between the jets are thoroughly investigated, with the flow unsteadiness also characterized by analyzing the stagnation point displacement on the channel walls. The comparison between the 2D and 3D flow patterns indicate that the 3D opposite jets enhance the unsteady effects compared to the 2D unsteady opposite jets. The complex vortex patterns resulting from the unsteady jets interaction, as well as the velocity, vorticity and temperature fields for both 2D and 3D cases are thoroughly evaluated. The comparison between the 2D and 3D impinging air jets is documented and the impact on chip/microelectronics cooling is highlighted.

The Cooling Impact of a Pair of Opposed Unsteady Confined Impinging Air Jets

2005 ◽  
Author(s):  
Victor Chiriac ◽  
Jorge L. Rosales
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Unsteady Flow ◽  
Jet Flow ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Air Jets ◽  
Laminar Jets ◽  
Vortex Patterns ◽  
Two Jets

A numerical investigation was performed at two Reynolds numbers to analyze the flow-field and heat transfer characteristics for a pair of laminar jets impinging on opposite walls in a channel. The present study is a continuation of the authors’ earlier work [1] in which the jets flowing out normal to the top channel wall produce a large stagnant bubble between the two jets which greatly reduce the heat transfer removal from the lower wall. In this case, the lower Reynolds number jet flow of 300 produces a symmetric, steady flow hydrodynamic pattern with the jets being deflected laterally. By further increasing the Reynolds number to 750, a complex asymmetric and highly unsteady flow develops between the two jets due to the opposite jet flow interaction. The convective heat transfer coefficients and the unsteady flow development between the jets are studied for each case. The flow unsteadiness is also characterized by analyzing the stagnation point displacement on the channel walls. The complex vortex patterns resulting from the jet interaction at the higher Reynolds number is investigated and its impact on the chip/microelectronics component cooling is thoroughly documented.   This paper was also originally published as part of the Proceedings of the ASME 2005 Heat Transfer Summer Conference.

The Microelectronics Cooling Impact and Comparison of 2D and 3D Unsteady Effects of a Pair of Opposed Confined Angled Impinging Air Jets

2011 ◽  
Author(s):  
Victor Adrian Chiriac ◽  
Jorge Luis Rosales
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Temperature Fields ◽  
Heat Sources ◽  
Air Jets ◽  
Nusselt Numbers ◽  
Target Wall ◽  
Third Dimension ◽  
Vortex Patterns ◽  
2D And 3D

The unsteady laminar flow and heat transfer characteristics for a pair of angled confined impinging air jets centered in a channel were studied numerically. The time-averaged heat transfer coefficient for a pair of heat sources centered in the channel was determined, as well as the oscillating jet frequency for the unsteady cases. The present study is a continuation of the authors’ previous investigations, identifying the similarities and differences arising from the expansion to the third dimension. It examines the interaction between the angled jets and the associated impact on the cooling of the heat sources placed on the board at a jet Reynolds number of 100 and 600. Maintaining the inlet jet width, W, at 1 cm, as in the previous studied cases, the interaction between the 45° angled jets leads to the formation of unsteady symmetrical jets that impinge on the two heat sources placed on the board at a Reynolds number of 100. A second case investigates the hydrodynamic interaction between the 45° angled jets at a Reynolds number of 600. In this case the jets interact and form a region of unsteady shear causing the jets to sweep the target board and the heated components placed on it. The nature of this unsteadiness depends on the proximity of the jet inlets, the channel dimensions and the jet Reynolds number. The jet unsteadiness causes the stagnation point locations to sweep back and forth over the impingement region causing the jets to “wash” a larger surface area on the target wall. The relevant trends for the 2D and 3D jet hydrodynamic and thermal fields are further documented by comparing the field plots and the Nusselt numbers on the target walls for the cases under evaluation. Although similar in nature, the unsteady 3D opposite jets produce results that deviate from the 2D unsteady opposite jets. The complex vortex patterns resulting from the jet interaction at various jet inlet locations, as well as the velocity, vorticity and temperature fields for both 2D and 3D cases are thoroughly evaluated.

Computational Study of Gas Turbine Blade Cooling Channel

2010 ◽  
Author(s):  
R. S. Amano ◽  
Krishna Guntur ◽  
Jose Martinez Lucci
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Gas Turbine ◽  
Turbulence Models ◽  
Flow Patterns ◽  
Higher Order ◽  
Secondary Flows ◽  
Complex Flow ◽  
Cooling Performance ◽  
Cooling Channels

It has been a common practice to use cooling passages in gas turbine blade in order to keep the blade temperatures within the operating range. Insufficiently cooled blades are subject to oxidation, to cause creep rupture, and even to cause melting of the material. To design better cooling passages, better understanding of the flow patterns within the complicated flow channels is essential. The interactions between secondary flows and separation lead to very complex flow patterns. To accurately simulate these flows and heat transfer, both refined turbulence models and higher-order numerical schemes are indispensable for turbine designers to improve the cooling performance. Power output and the efficiency of turbine are completely related to gas firing temperature from chamber. The increment of gas firing temperature is limited by the blade material properties. Advancements in the cooling technology resulted in high firing temperatures with acceptable material temperatures. To better design the cooling channels and to improve the heat transfer, many researchers are studying the flow patterns inside the cooling channels both experimentally and computationally. In this paper, the authors present the performance of three turbulence models using TEACH software code in comparison with the experimental values. To test the performance, a square duct with rectangular ribs oriented at 90° and 45° degree and placed at regular intervals. The channel also has bleed holes. The normalized Nusselt number obtained from simulation are validated with that of experiment. The Reynolds number is set at 10,000 for both the simulation and experiment. The interactions between secondary flows and separation lead to very complex flow patterns. To accurately simulate these flows and heat transfer, both refined turbulence models and higher-order numerical schemes are indispensable for turbine designers to improve the cooling performance. The three-dimensional turbulent flows and heat transfer are numerically studied by using several different turbulence models, such as non-linear low-Reynolds number k-omega and Reynolds Stress (RSM) models. In k-omega model the cubic terms are included to represent the effects of extra strain-rates such as streamline curvature and three-dimensionality on both turbulence normal and shear stresses. The finite volume difference method incorporated with the higher-order bounded interpolation scheme has been employed in the present study. The outcome of this study will help determine the best suitable turbulence model for future studies.

scholarly journals Highly Resolved Distribution of Heat Transfer for Turbine Leading Edge Film Cooling Including Reynolds Number and Blowing Rate Effects

1998 ◽  
Author(s):  
K. Jung ◽  
D. K. Hennecke
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Heat Mass Transfer ◽  
Leading Edge ◽  
Transfer Coefficients ◽  
Complex Flow ◽  
Long Distance ◽  
Naphthalene Sublimation Technique

The effect of leading edge film cooling on heat transfer was experimentally investigated using the naphthalene sublimation technique. The experiments were performed on a symmetrical model of the leading edge suction side region of a high pressure turbine blade with one row of film cooling holes on each side. Two different lateral inclinations of the injection holes were studied: 0° and 45°. In order to build a data base for the validation and improvement of numerical computations, highly resolved distributions of the heat/mass transfer coefficients were measured. Reynolds numbers (based on hole diameter) were varied from 4000 to 8000 and blowing rate from 0.0 to 1.5. For better interpretation, the results were compared with injection-flow visualizations. Increasing the blowing rate causes more interaction between the jets and the mainstream, which creates higher jet turbulence at the exit of the holes resulting in a higher relative heat transfer. This increase remains constant over quite a long distance dependent on the Reynolds number. Increasing the Reynolds number keeps the jets closer to the wall resulting in higher relative heat transfer. The highly resolved heat/mass transfer distribution shows the influence of the complex flow field in the near hole region on the heat transfer values along the surface.

Parametric Study of a Transient Liquid Flow in a Microchannel of Square Cross-Section

2010 ◽  
Author(s):  
Guyh Dituba Ngoma ◽  
Amsini Sadiki
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Liquid Flow ◽  
Thermophysical Properties ◽  
Electric Potential ◽  
Thermal Characteristics ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
The Impact ◽  
Potential Pressure

Time-dependent laminar liquid flow and thermal characteristics in a square cross-section microchannel were numerically investigated using computational fluid dynamics code. In the numerical model developed the upper and bottom microchannel substrate properties, Joule heating caused by applying electric potential, pressure driven flow, electroosmosis, heat transfer coefficients on the microchannel bottom wall and variations in the liquid thermophysical properties were all taken into account. Liquid flow velocity distribution and temperature fields were calculated by solving both Navier-Stokes and energy equations, and electric field distribution was determined based on their electric potential. The results obtained demonstrate the impact that applied potential, pressure difference, heat transfer coefficient and microchannel dimensions have on liquid flow and thermal behaviors in a square microchannel. Finally, the results with the model developed were then compared with those of a liquid having constant thermophysical properties.

Thermo-Fluid-Dynamic Diagnostics in Multiple-Intersection Flow Network Using IR Thermometry and DPIV

2003 ◽  
Author(s):  
Herchang Ay ◽  
Chih-Hao Chou ◽  
Bing-Yi Chen
Keyword(s):  
Heat Transfer ◽  
Vascular System ◽  
Fluid Dynamic ◽  
Local Heat Transfer ◽  
Flow Patterns ◽  
Flow Networks ◽  
Transfer Coefficients ◽  
Complex Flow ◽  
Flip Flop ◽  
Flow Network

A multiple-intersecting flow network is common in biological and industrial systems such as the human vascular system, the internal coolant passage of turbine blade inside gas turbine engine, the liquid cooling channel inside electronic modules. An infrared thermovision system is used to map the detail local convective heat transfer coefficients for the multiple-intersection flow network consisting of a 30° intersection angle. In addition, a digital particle image velocimetry (DPIV) system had been developed to measure instantaneous and ensemble-averaged flow fields in the multiple-intersection flow networks. The flow at each intersection is characterizes by a collision of two flow streams, resulting in vortices on the two sides of the diamond-shaped pin in the post-intersecting region of the network. It is noticed that the vortex at one side increases, at the same time the vortex at the other side decreases with the flip-flop flow at the exit end of the flow network. The study also found the vortex ring places on interlacing surface of the downstream-half of the diamond-shaped pin between the two longitudinal rows. The complex flow patterns are found to play an important part in the local heat transfer performance. The main effort of the present study is attempt to interpret the DPIV measurement results to understand the detailed flow patterns inside the multiple-intersection flow networks and the heat transfer data using an infrared thermovision system.

Local Heat Transfer to Staggered Arrays of Impinging Circular Air Jets

1983 ◽  
Vol 105 (2) ◽  
pp. 354-360 ◽  
Author(s):  
A. I. Behbahani ◽  
R. J. Goldstein
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flat Plate ◽  
Flow Direction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Air Jets ◽  
Impingement Surface

Measurements are made of the local heat transfer from a flat plate to arrays of impinging circular air jets. Fluid from the spent jets is constrained to flow out of the system in one direction. Two different jet-to-jet spacings, 4 and 8 jet diameters, are employed. The parameters that are varied include jet-orifice-plate to impingement-surface spacing and jet Reynolds number. Local heat transfer coefficients vary periodically both in the flow direction and across the span with high values occurring in stagnation regions. Stagnation regions of individual jets as determined by local heat transfer coefficients move further in the downstream direction as the amount of crossflow due to upstream jet air increases. Local heat transfer coefficients are averaged numerically to obtain spanwise and streamwise-spanwise averaged heat transfer coefficients.

scholarly journals Local Heat Transfer to Staggered Arrays of Impinging Circular Air Jets

1982 ◽  
Author(s):  
A. I. Behbahani ◽  
R. J. Goldstein
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flat Plate ◽  
Flow Direction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Air Jets ◽  
Impingement Surface

Measurements are made of the local heat transfer from a flat plate to impinging arrays of staggered circular air jets. Fluid from the spent jets is constrained to flow out in one direction. Two different jet-to-jet spacings, 4 and 8 jet diameters, are employed. The parameters that are varied include jet-orifice-plate to impingement-surface spacing and jet Reynolds number. Local heat transfer coefficients vary periodically both in the flow direction and across the span with high values occurring at stagnation regions. Stagnation regions of individual jets as determined by local heat transfer coefficients move further in the downstream direction as the amount of crossflow due to upstream jet air increases. Local heat transfer coefficients are averaged numerically to obtain spanwise and streamwise-spanwise averaged heat transfer coefficients.

Heat Transfer to Arrays of Impinging Jets in a Crossflow

1987 ◽  
Vol 109 (4) ◽  
pp. 564-571 ◽  
Author(s):  
B. R. Hollworth ◽  
G. H. Cole
Keyword(s):  
Heat Transfer ◽  
Impinging Jets ◽  
Hole Diameter ◽  
Transfer Coefficients ◽  
Target Plate ◽  
Heat Transfer Coefficients ◽  
Air Jets ◽  
Local Measurements ◽  
Geometric Variables ◽  
2D And 3D

Convective heat transfer measurements are reported for staggered arrays of round turbulent air jets impinging upon a heated flat surface. Spent air was constrained by skirts to exit at one end of the test section, thus establishing a crossflow. Geometric variables included the jet hole diameter d, the streamwise spacing X and spanwise spacing Y between jet holes, and the standoff distance Z between the orifice plate and the target plate. Three patterns of holes, all having d = 3.5 mm, were tested. Their (X, Y) were (4d, 4d), (4d, 8d), and (8d, 4d). Values of the standoff were Z = d, 2d, and 3d; and tests were run for 4, 6, and 8 rows of holes. The airflow was varied to achieve a range of mean jet Reynolds number from 2500 to 25,000. Microfoil heat flux sensors were used to determine streamwise variations in (spanwise-averaged) heat transfer. Excellent resolution was obtained by employing a sensor whose streamwise dimension is considerably less than one hole diameter d. Heat transfer profiles were periodic, with a peak corresponding to each spanwise row of holes. Such peaks were displaced in the steamwise direction by the crossflow, and those nearest the exhaust end of the channel exhibited the largest deflections. Array-averaged heat transfer coefficients were obtained by numerically averaging the local measurements; values agree well with the results of other experiments on similar impingement-with-crossflow systems.

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