Onset of Transition in the Flow Over a Three-Dimensional Array of Rectangular Obstacles

1992 ◽  
Vol 114 (2) ◽  
pp. 251-255 ◽  
Author(s):  
S. V. Garimella ◽  
P. A. Eibeck
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Water Channel ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Channel Height ◽  
Circuit Boards ◽  
Three Dimensional Flow ◽  
Transfer Data ◽  
Array Geometry

Onset of transition is investigated in the flow over an array of protruding elements mounted on the bottom wall of a rectangular water channel simulating flow passages between adjacent circuit boards in computers. The element dimensions are held constant while the channel height and the element spacing are varied. Flow visualization and turbulence measurements are used to determine transition Reynolds numbers, which compare well with previous results obtained from heat transfer data. The complicated, three-dimensional flow field causes transition to be a function not only of flow rate and array geometry but also of location in the array. Transition occurs in the fully developed region of the array at a channel height-based Reynolds number of 700 for a channel height of 1.2 element heights, increasing to 1900 for a channel height of 3.6 element heights. However, when Reynolds number is defined based on element height, transition occurs at the same Reynolds number of 550 for all channel heights. Increasing the stream wise spacing between elements causes transition to occur at lower Reynolds numbers.

Numerical Investigation on Turbulence Statistics and Heat Transfer of a Circular Jet Impinging on a Roughened Flat Plate

2021 ◽  
Vol 13 (4) ◽  
Author(s):  
Abdulrahman Alenezi ◽  
Abdulrahman Almutairi ◽  
Hamad Alhajeri ◽  
Abdulaziz Gamil ◽  
Faisal Alshammari
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Numerical Study ◽  
Roughness Element ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Target Plate ◽  
Cross Sectional ◽  
Flow Physics ◽  
Baseline Case

Abstract A detailed heat transfer numerical study of a three-dimensional impinging jet on a roughened isothermal surface is presented and is investigated from flow physics vantage point under the influence of different parameters. The effects of the Reynolds number, roughness location, and roughness dimension on the flow physics and heat transfer parameters are studied. Additionally, the relations between average heat transfer coefficient (AHTC) and flow physics including pressure, wall shear and flow vortices with thermodynamic nonequilibrium are offered. This paper studies the effect of varying both location and dimension of the roughness element which took the shape of square cross-sectional continuous ribs to deliver a favorable trade-off between total pressure loss and heat transfer rate. The roughness element was tested for three different radial locations (R/D) = 1, 1.5, and 2 and at each location its height (i.e., width) (e) was changed from 0.25 to 1 mm in incremental steps of 0.25. The study used a jet angle (α) of 90 deg, jet-to-target distance (H/D = 6), and Re ranges from 10,000 to 50,000, where H is the vertical distance between the target plate and jet exit. The results show that the AHTC can be significantly affected by changing the geometry and dimensions of the roughness element. This variation can be either an augmentation of, or decrease in, the (HTC) when compared with the baseline case. An enhancement of 12.9% in the AHTC was achieved by using optimal location and dimensions of the roughness element at specific Reynolds number. However, a diminution between 10% and 30% in (AHTC) was attained by the use of rib height e = 1 mm at Re = 50k. The variation of both rib location and height showed better contribution in increasing heat transfer for low-range Reynolds numbers.

Pressure-driven flow in a channel with porous walls

2011 ◽  
Vol 679 ◽  
pp. 77-100 ◽  
Author(s):  
QIANLONG LIU ◽  
ANDREA PROSPERETTI
Keyword(s):  
Reynolds Number ◽  
Porous Medium ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Three Dimensional Flow ◽  
Porous Layers ◽  
Simple Cubic ◽  
Porous Walls ◽  
Pressure Driven Flow ◽  
Pressure Driven

The finite-Reynolds-number three-dimensional flow in a channel bounded by one and two parallel porous walls is studied numerically. The porous medium is modelled by spheres in a simple cubic arrangement. Detailed results on the flow structure and the hydrodynamic forces and couple acting on the sphere layer bounding the porous medium are reported and their dependence on the Reynolds number illustrated. It is shown that, at finite Reynolds numbers, a lift force acts on the spheres, which may be expected to contribute to the mobilization of bottom sediments. The results for the slip velocity at the surface of the porous layers are compared with the phenomenological Beavers–Joseph model. It is found that the values of the slip coefficient for pressure-driven and shear-driven flow are somewhat different, and also depend on the Reynolds number. A modification of the relation is suggested to deal with these features. The Appendix provides an alternative derivation of this modified relation.

Heat Transfer and Turbulent Flow Characteristics of Isolated Three-Dimensional Protrusions in Channels

1991 ◽  
Vol 113 (3) ◽  
pp. 597-603 ◽  
Author(s):  
P. T. Roeller ◽  
J. Stevens ◽  
B. W. Webb
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Channel Wall ◽  
Three Dimensional ◽  
Three Dimensional Flow ◽  
Average Heat ◽  
Flow Acceleration ◽  
Dimensional Flow ◽  
Wall Spacing

The flow structure and average heat transfer characteristics of single, isolated three-dimensional protrusions in a flow channel have been investigated experimentally. This configuration has relevance in the electronics industry. The study was designed to identify the influence of the three-dimensional flow around a heated protrusion on its average heat transfer. Heated protrusions varying in width between 0.12 and 1.0 channel widths for a fixed protrusion height and streamwise length were studied in the channel Reynolds number range 500≤Re≤10,000. The channel wall spacing was also varied parametrically between 1.25 and 2.5 streamwise protrusion lengths. The study included both average heat transfer measurements, and detailed local velocity and turbulent flow structure measurements made using laser-Doppler velocimetry. The experimental results show that the Nusselt number increases with both decreasing channel wall spacing and decreasing protrusion width. The increase in heat transfer with decreasing wall spacing is explained by the accelerated flow due to the protrusion-obstructed channel. Increasing Nusselt number with decreasing protrusion width is a result of increased three-dimensional flow and associated turbulent mixing. Both of these flow-related phenomena are illustrated with local mean velocity and turbulence intensity measurements. The presence of recirculation zones both upstream and downstream of the module is revealed. The flow acceleration around the heated protrusions, and three dimensionality of the flow and heat transfer are competing mechanisms; the higher heat transfer due to flow acceleration around the protrusions for larger protrusions goes counter to the trend for higher heat transfer due to increased three-dimensional flow and transport for smaller protrusions. A Nusselt number correlation is developed as a function of channel Reynolds number and protrusion and channel geometric parameters, which describes the tradeoffs discussed.

Reynolds Number Effects on the Performance Characteristic of a Small Regenerative Pump

2009 ◽  
Vol 131 (6) ◽  
Author(s):  
Shin-Hyoung Kang ◽  
Su-Hyun Ryu
Keyword(s):  
Reynolds Number ◽  
Three Dimensional ◽  
Internal Flow ◽  
Reynolds Numbers ◽  
Maximum Efficiency ◽  
Three Dimensional Flow ◽  
One Dimensional ◽  
Rotating Speed ◽  
Dimensional Modeling ◽  
Reynolds Number Effects

This paper studies the effect of the Reynolds number on the performance characteristics of a small regenerative pump. Since regenerative pumps have low specific speeds, they are usually applicable to small devices such as micropumps. As the operating Reynolds number decreases, nondimensional similarity parameters such as flow and head coefficients and efficiency become dependent on the Reynolds number. In this study, the Reynolds number based on the impeller diameter and rotating speed varied between 5.52×103 and 1.33×106. Complex three-dimensional flow structures of internal flow vary with the Reynolds numbers. The coefficients of the loss models are obtained by using the calculated through flows in the impeller. The estimated performances obtained by using one-dimensional modeling agreed reasonably well with the numerically calculated performances. The maximum values of flow and head coefficients depended on the Reynolds number when it is smaller than 2.65×105. The critical value of the Reynolds number for loss coefficient and maximum efficiency variations with Reynolds number was 1.0×105.

Direct Numerical Simulation of Flow and Heat Transfer From a Sphere in a Uniform Cross-Flow

2000 ◽  
Vol 123 (2) ◽  
pp. 347-358 ◽  
Author(s):  
P. Bagchi ◽  
M. Y. Ha ◽  
S. Balachandar
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Vortex Shedding ◽  
Axisymmetric Flow ◽  
Three Dimensional ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Temperature Fields ◽  
Flow And Heat Transfer

Direct numerical solution for flow and heat transfer past a sphere in a uniform flow is obtained using an accurate and efficient Fourier-Chebyshev spectral collocation method for Reynolds numbers up to 500. We investigate the flow and temperature fields over a range of Reynolds numbers, showing steady and axisymmetric flow when the Reynolds number is less than 210, steady and nonaxisymmetric flow without vortex shedding when the Reynolds number is between 210 and 270, and unsteady three-dimensional flow with vortex shedding when the Reynolds number is above 270. Results from three-dimensional simulation are compared with the corresponding axisymmetric simulations for Re>210 in order to see the effect of unsteadiness and three-dimensionality on heat transfer past a sphere. The local Nusselt number distribution obtained from the 3D simulation shows big differences in the wake region compared with axisymmetric one, when there exists strong vortex shedding in the wake. But the differences in surface-average Nusselt number between axisymmetric and three-dimensional simulations are small owing to the smaller surface area associated with the base region. The shedding process is observed to be dominantly one-sided and as a result axisymmetry of the surface heat transfer is broken even after a time-average. The one-sided shedding also results in a time-averaged mean lift force on the sphere.

Effects of Aeroderivative Combustor Turbulence on Endwall Heat Transfer Distributions Acquired in a Linear Vane Cascade

2002 ◽  
Author(s):  
Forrest E. Ames ◽  
Pierre A. Barbot ◽  
Chao Wang
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Combustion System ◽  
Three Dimensional Flow ◽  
Linear Cascade ◽  
High Turbulence ◽  
Turbulence Condition ◽  
Vortex Systems

Vane endwall heat transfer distributions are documented for a mock aeroderivative combustion system and for a low turbulence condition in a large-scale low speed linear cascade facility. Inlet turbulence levels range from below 0.7 percent for the low turbulence condition to 14 percent for the mock combustor system. Stanton number contours are presented at both turbulence conditions for Reynolds numbers based on true chord length and exit conditions ranging from 500,000 to 2,000,000. Low turbulence endwall heat transfer shows the influence of the complex three-dimensional flow field, while the effects of individual vortex systems are less evident for the high turbulence cases. Turbulent scale has been documented for the high turbulence case. Inlet boundary layers are relatively thin for the low turbulence case while inlet flow approximates a nonequilibrium or high turbulence channel flow for the mock combustor case. Inlet boundary layer parameters are presented across the inlet passage for the three Reynolds numbers and both the low turbulence and mock combustor inlet cases. Both midspan and 95 percent span pressure contours are included. This research provides a well-documented database taken across a range of Reynolds numbers and turbulence conditions for assessment of endwall heat transfer predictive capabilities.

Effect of Cylinder Aspect Ratio and Channel Dimensions on the Fluid Flow and Heat Transfer in Parallel-Plate Channel Heat Exchangers

2002 ◽  
Author(s):  
A. K. Saha ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Heat Exchangers ◽  
Parallel Plate ◽  
Numerical Study ◽  
Three Dimensional ◽  
Channel Height ◽  
Flow And Heat Transfer ◽  
Plate Channel

A comparative numerical study has been carried out to analyze the unsteady three-dimensional flow and heat transfer in a parallel-plate channel heat exchangers with in-line arrays of periodically mounted square cylinders (pins) at various Reynolds number and geometrical configurations. The geometry considered represents the narrow trailing edge region of the blade where pin fins are used to serve both a structural and a heat transfer role. The three-dimensional unsteady Navier-Stokes and energy equations are solved using higher order temporal and spatial discretizations. The simulations have been carried out for a range of Reynolds number based on cylinder width (180–600) and a Prandtl number of 6.99 (corresponding to water). Conjugate heat transfer calculations have been employed to account for the conduction in the solid cylinder and convection in the fluid. The thermal performance factor (TPF) increases significantly when the flow becomes unsteady. The choice of aspect ratio of the cylinders is judged by their relative increase in friction factor and heat transfer at transitional Reynolds number. The TPF is found to increase with the increase in pitch of the cylinders. The increase in channel height enhances the TPF though the heat transfer decreases at higher channel height.

Heat Transfer Measurements and Correlations for Air-Water Two-Phase Slug Flow in a Horizontal Pipe

Volume 3 ◽  
2004 ◽  
Author(s):  
Afshin J. Ghajar ◽  
Kapil Malhotra ◽  
Jae-Yong Kim ◽  
Steve A. Trimble
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Slug Flow ◽  
Reynolds Numbers ◽  
Mean Deviation ◽  
Heat Transfer Correlation ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Transfer Data ◽  
Heat Transfer Coefficients

Local heat transfer coefficients and flow parameters were measured for air-water slug flow in a horizontal 25.4 mm stainless steel schedule 10S pipe with a length to diameter ratio of 100. For this systematic study, a total of 83 data points were taken by carefully coordinating the liquid and gas superficial Reynolds number combinations. The heat transfer data were measured under a uniform wall heat flux boundary condition ranging from about 3800 to 16000 W/m2. The superficial Reynolds numbers ranged from about 3160 to 30290 for water and from about 1480 to 5840 for air. Comparison of heat transfer data for slug flow revealed that the heat transfer results were significantly dependent on the liquid and gas superficial Reynolds numbers. Overall, the experimental heat transfer data showed that the liquid phase dominated the heat transfer. However, it was found that the heat transfer data having a fixed liquid superficial Reynolds number showed that the heat transfer coefficients decreased as the gas superficial Reynolds number increased. A general heat transfer correlation for two-phase gas-liquid flow was fitted to our experimental horizontal slug flow heat transfer data with a mean deviation of −2.77% and an RMS deviation of 9.92%. Furthermore, a simplified heat transfer correlation for slug flow was developed based on the trends of heat transfer coefficient over the superficial liquid and gas Reynolds numbers. The proposed correlation predicted the experimental data with a mean deviation of −1.44% and an RMS deviation of 5.15%.

Three-dimensional flow over two spheres placed side by side

1993 ◽  
Vol 246 ◽  
pp. 465-488 ◽  
Author(s):  
Inchul Kim ◽  
Said Elghobashi ◽  
William A. Sirignano
Keyword(s):  
Reynolds Number ◽  
Vortical Structure ◽  
Three Dimensional ◽  
Numerical Data ◽  
Reynolds Numbers ◽  
Near Wake ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Confined Flow ◽  
Small Spacing

Three-dimensional flow over two identical (solid or liquid) spheres which are held fixed relative to each other with the line connecting their centres normal to a uniform I stream is investigated numerically at Reynolds numbers 50, 100, and 150. We consider the lift, moment, and drag coefficients on the spheres and investigate their dependence on the distance between the two spheres. The computations show that, for a given Reynolds number, the two spheres are repelled when the spacing is of the order of the diameter but are weakly attracted at intermediate separation distances. For small spacing, the vortical structure of the near wake is significantly different from that of the axisymmetric wake that establishes at large separations. The partially confined flow passing between the two spheres entrains the flows coming around their other sides. Our results agree with available experimental and numerical data.

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