Experiments on laminar film flow along a periodic wall

2002 ◽  
Vol 457 ◽  
pp. 133-156 ◽  
Author(s):  
M. VLACHOGIANNIS ◽  
V. BONTOZOGLOU
Keyword(s):  
Film Flow ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Imaging Method ◽  
Three Dimensional Flow ◽  
Numerical Studies ◽  
High Reynolds Numbers ◽  
Gravity Driven ◽  
Temporary Decrease ◽  
High Reynolds

Experimental results are reported on the structure of gravity-driven film flow along an inclined periodic wall with rectangular corrugations. A fluorescence imaging method is used to capture the evolution of film height in space and time with accuracy of a few microns. The steady flow is found to exhibit a statically deformed free surface, as predicted by previous asymptotic and numerical studies. Though usually unstable, its characteristics determine much of the subsequent non-stationary dynamics. Travelling disturbances are observed to evolve into solitary multi-peaked humps, and pronounced differences from the respective phenomena along a flat wall are noted. Finally, a remarkable stabilization of the flow at high Reynolds numbers is documented, which proceeds through the development of a three-dimensional flow structure and leads to a temporary decrease in film thickness and recession of solitary waves.

New thermal-hydraulic correlations for printed circuit heat exchangers (PCHEs) with zigzag channels under high Reynolds numbers

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Carolina P. Naveira-Cotta ◽  
Jian Su ◽  
Paulo Lucena Kreppel Paes ◽  
Philippe R. Egmont ◽  
Rodrigo P. M. Moreira ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Design Parameters ◽  
Channel Diameter ◽  
Content Type ◽  
Printed Circuit ◽  
High Reynolds Numbers ◽  
High Reynolds ◽  
The Impact

Purpose The purpose of this paper is to investigate the impact of semi-circular zigzag-channel printed circuit heat exchanger (PCHE) design parameters on heat transfer and pressure drop of flows under high Reynolds numbers and provide new thermal-hydraulic correlations relevant to conditions encountered in natural gas processing plants. Design/methodology/approach The correlations were developed using three-dimensional steady-state computational fluid dynamics simulations with varying semicircular channel diameter (from 1 to 5 mm), zigzag angle (from 15° to 45°) and Reynolds number (from 40,000 to 100,000). The simulation results were validated by comparison with experimental results and existing correlations. Findings The results revealed that the thermal-hydraulic performance was mostly affected by the zigzag angle, followed by the ratio of the zigzag channel length to the hydraulic diameter. Overall, smaller zigzag angles favored heat transfer intensification while keeping reasonably low pressure drops. Originality/value This study is, to date, the only one providing thermal-hydraulic correlations for PCHEs with zigzag channels under high Reynolds numbers. Besides, the broad range of parameters considered makes the proposed correlations valuable PCHE design tools.

How Turbulence Models Perform in Simulating Pipeflow Response to Targeted Wall-Shapes?

2021 ◽  
Author(s):  
Mehran Masoumifar ◽  
Suyash Verma ◽  
Arman Hemmati
Keyword(s):  
Three Dimensional ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Flow Response ◽  
High Reynolds Numbers ◽  
Flow Features ◽  
Rans Models ◽  
Response And Recovery ◽  
High Reynolds

Abstract This study evaluates how Reynolds-Averaged-Navier-Stokes (RANS) models perform in simulating the characteristics of mean three-dimensional perturbed flows in pipes with targeted wall-shapes. Capturing such flow features using turbulence models is still challenging at high Reynolds numbers. The principal objective of this investigation is to evaluate which of the well-established RANS models can best predict the flow response and recovery characteristics in perturbed pipes at moderate and high Reynolds numbers (10000-158000). First, the flow profiles at various axial locations are compared between simulations and experiments. This is followed by assessing the well-known mean pipeflow scaling relations. The good agreement between our computationally predicted data using Standard k-epsilon model and those of experiments indicated that this model can accurately capture the pipeflow characteristics in response to introduced perturbation with smooth sinusoidal axial variations.

Studies of Flow Patterns in a Diffuser Designed to Generate Longitudinal Vortices

1989 ◽  
Vol 111 (2) ◽  
pp. 111-117
Author(s):  
L. N. Goenka ◽  
R. L. Panton ◽  
D. G. Bogard
Keyword(s):  
Three Dimensional ◽  
Low Frequency ◽  
Reynolds Numbers ◽  
Flow Patterns ◽  
Three Dimensional Flow ◽  
Low Reynolds Numbers ◽  
Longitudinal Vortices ◽  
Turbulent Vortex ◽  
Transverse Pressure ◽  
High Reynolds

This paper describes flow visualization studies on a three-dimensional diffuser that generates two longitudinal vortices. The premise is that the three-dimensional flow patterns of this diffuser may have attributes that are superior to the two-dimensional flows of conventional diffusers. The diffuser geometry consists of a wide-angle, plane-wall diffuser with a pyramid-shaped insert attached to its expansion wall. The upsweep on the insert upper surface increases the pressure of the incoming flow, which rolls over into the expansion region in the presence of a transverse pressure gradient to form two symmetric, longitudinal vortices. At low Reynolds numbers (below 6000 based on the diffuser inlet height), the flow exhibited three flow patterns with subtle distinctions. The flowfield contained longitudinal vortices that modified and reduced in extent the separated regions that were present along the diffuser expansion wall. At high Reynolds numbers (above 6000), the separated regions along the diffuser expansion wall were replaced by a turbulent vortex. The lack of closed separated regions in the flow implies the absence of low-frequency effects that are characteristic of such regions. In addition, the flowfield exhibited little or no hysteresis with respect to changes in Reynolds number. These flowfield features are desirable in certain applications, such as exhaust diffusers for turbomachinery.

The vortex-induced forces on a multi-column platform in current at high Reynolds numbers

2018 ◽  
Vol 32 (29) ◽  
pp. 1850356 ◽  
Author(s):  
Xiaofeng Hu ◽  
Xinshu Zhang ◽  
Yunxiang You
Keyword(s):  
Numerical Simulations ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Transverse Force ◽  
Single Cylinder ◽  
Force Coefficients ◽  
High Reynolds Numbers ◽  
The Mean ◽  
High Reynolds ◽  
Current Incidence

The unsteady vortex-induced forces on a multi-column platform in current from subcritical up to supercritical Reynolds numbers have been investigated using three-dimensional numerical simulations. Two different current incidences, 0[Formula: see text] and 45[Formula: see text], are considered. The results show that for 0[Formula: see text] current incidence, the mean streamwise force coefficients [Formula: see text] increase with the rise of [Formula: see text] when [Formula: see text], while they grow slightly when [Formula: see text]. For 45[Formula: see text] current incidence, a decrease of streamwise force with increasing [Formula: see text] is observed. Similar to a single cylinder, the fluctuating transverse force coefficients [Formula: see text] of the multi-column platform drop at [Formula: see text] for 0[Formula: see text] and 45[Formula: see text] current incidences. In addition, it is found that for 0[Formula: see text] current incidence, the [Formula: see text] values of the downstream columns are much larger than those of the upstream columns, while for 45[Formula: see text] current incidence, the [Formula: see text] values of each column are similar. Furthermore, the results of correlations between the forces on each column and total forces indicates that for 0[Formula: see text] current incidence, the fluctuating transverse forces on the downstream columns are mainly responsible for the total fluctuating transverse force on the multi-column platform.

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