Interaction of a Cold Wall Jet With a Natural Convective Flow in a Confined Opened Cavity

Volume 1 ◽  
2004 ◽  
Author(s):  
D. Couton ◽  
F. Marchal ◽  
S. Doan-Kim ◽  
Ch. Tanguy
Keyword(s):  
Reynolds Number ◽  
Convective Flow ◽  
Flow Behavior ◽  
Main Flow ◽  
Geometrical Parameters ◽  
Wall Jet ◽  
Mixture Flow ◽  
Free Jet ◽  
The Mean ◽  
Convective Plume

The aim of this experiment was to analyze the interaction and the development of two flows in the rectangular confined cavity described in this paper. The first was a forced convective flow generated by injecting air at low temperatures inside the cavity in a horizontal direction through an opened area located in the cavity front. Inside this cavity, a natural convective plume was developed simultaneously. Different experimental techniques were used in order to describe either the mean and fluctuating air flow or the mean and fluctuating temperature field, and also to analyze the interaction between these two flows. Firstly, our set-up was validated with the free jet configuration: we obtained a well-known three-dimensional turbulent free jet. Without plume, analysis of the results showed that injection flow behavior corresponded to a characteristic 3D wall jet along the upper wall, with an 15400 injection Reynolds number. The Coanda effect maintained the jet along the upper wall. We determined the parameters of the main velocity law in relation to those detailed in the literature. After that, the main flow developed simultaneously in the longitudinal and vertical directions, so that a recirculation zone appeared. With the plume that developed over an obstacle, we observed that cold flow behavior changed, because of the combination of some of the main parameters: geometrical parameters, injection Reynolds number and temperature gradient between injected flow and plume. For example, with an injection Reynolds number equal to 15400, we measured the influence of the plume on the main flow through the changes in the dynamic and temperature profiles. Three regimes were obtained: the main flow was maintained and no natural convective plume was observed; the transitional regime was characterized by the main flow development along the obstacles, in spite of the development of the natural convective plumes; the natural convective flow modified the wall jet and unsteady classical natural convective “mushrooms” were observed. The topical results deal with the parametric study. We worked on a critical number characterizing the mixture of the jet and the plume. This number is defined as the ratio of the Grashof number to the Reynolds number of the mixture flow. When this critical value was exceeded, the natural convective plume was able to stop the inlet wall jet.

Turbulence Measurements in the Corner Wall Jet

2014 ◽  
Author(s):  
Barrett Poole ◽  
Joseph W. Hall
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Turbulent Flow ◽  
Three Dimensional ◽  
Wall Jet ◽  
Hot Wire ◽  
Turbulence Measurements ◽  
Vertical Growth ◽  
The Mean ◽  
Turbulent Flow Field

The corner wall jet is similar to the standard three-dimensional wall jet with the exception that one half of the surface has been rotated counter-clockwise by 90 degrees. The corner wall jet investigated here is formed using a long round pipe with a Reynolds number of 159,000. Contours of the mean and turbulent flow field were measured using hot-wire anemometry. The results indicate that the ratio of lateral to vertical growth in the corner wall jet is approximately half of that in a standard turbulent three-dimensional wall jet.

scholarly journals Near-field flow structure of a confined wall jet on flat and concave rough walls

2008 ◽  
Vol 606 ◽  
pp. 27-49 ◽  
Author(s):  
I. ALBAYRAK ◽  
E. J. HOPFINGER ◽  
U. LEMMIN
Keyword(s):  
Shear Stress ◽  
Shear Layer ◽  
Outer Layer ◽  
Reynolds Shear Stress ◽  
Near Field ◽  
Wall Jet ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Free Jet ◽  
The Mean

Experimental results are presented of the mean flow and turbulence characteristics in the near field of a plane wall jet issuing from a nozzle onto flat and concave walls consisting of fixed sand beds. This is a flow configuration of interest for sediment erosion, also referred to as scouring. The measurements were made with an acoustic profiler that gives access to the three components of the instantaneous velocities. For the flat-wall flow, it is shown that the outer-layer spatial growth rate and the maxima of the Reynolds stresses approach the values accepted for the far field of a wall jet at a downstream distance x/b0 ≈ 8. These maxima are only about half the values of a plane free jet. This reduction in Reynolds stresses is also observed in the shear-layer region, x/b0 < 6, where the Reynolds shear stress is about half the value of a free shear layer. At distances x/b0 > 11, the maximum Reynolds shear stress approaches the value of a plane free jet. This change in Reynolds stresses is related to the mean vertical velocity that is negative for x/b0 < 8 and positive further downstream. The evolution of the inner region of the wall jet is found to be in good agreement with a previous model that explicitly includes the roughness length.On the concave wall, the mean flow and the Reynolds stresses are drastically changed by the adverse pressure gradient and especially by the development of Görtler vortices. On the downslope side of the scour hole, the flow is nearly separating with the wall shear stress tending to zero, whereas on the upslope side, the wall-friction coefficient is increased by a factor of about two by Görtler vortices. These vortices extend well into the outer layer and, just above the wall, cause a substantial increase in Reynolds shear stress.

A Two∼Dimensional Wall Jet with Suction

1972 ◽  
Vol 1 (4) ◽  
pp. 182-188
Author(s):  
T.B. Hedley ◽  
J.F. Keffer
Keyword(s):  
Viscous Sublayer ◽  
Transport Processes ◽  
Wall Jet ◽  
Two Dimensional ◽  
Mean Flow ◽  
Law Of The Wall ◽  
Free Jet ◽  
The Mean ◽  
Turbulent Wall ◽  
Large Eddies

The mean flow field of a two-dimensional turbulent wall jet which encounters a uniform suction is examined. A marked increase in wall shear stress was observed for all suction levels as the jet moved into the suction zone. When the suction level is moderate a viscous sublayer exists next to the surface. The dominance of the flow by the free jet motion however prevents any law-of-the-wall representation for the adjacent turbulent region and a velocity defect model is found to be more satisfactory. One can interpret this lack of an extensive equilibrium layer to mean that the transport processes are controlled by the action of the large eddies over almost the entire wall jet zone, with or without suction.

Flow instability of cylinder embedded within two-parallel moving walls of cuboidal cavity at different radii sizes

2020 ◽  
Vol 31 (05) ◽  
pp. 2050063
Author(s):  
Basma Souayeh
Keyword(s):  
Reynolds Number ◽  
Steady State ◽  
Flow Instability ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Critical Value ◽  
The Other ◽  
Geometrical Parameters ◽  
Parallel Wall ◽  
Volume Method

A computational analysis has been performed to study the flow instability of two-parallel wall motions in a Cuboidal enclosure incorporated by a cylinder under different radii sizes. A numerical methodology based on the Finite Volume Method (FVM) and a full Multigrid acceleration is utilized in this paper. Left and right parallel walls of the cavity are maintained driven and all the other walls completing the domain are motionless. Different radii sizes ([Formula: see text], 0.1, 0.125, 0.15 and 0.175) are employed encompassing descriptive Reynolds numbers that range three orders of magnitude 100, 400 and 800 for the steady state. The obtained results show positions [Formula: see text] and [Formula: see text] of the inner cylinder promote cell distortion. Also, when the radius equates to [Formula: see text], it may lead to the birth of tertiary cells at [Formula: see text] which are more developed for [Formula: see text]. Thereafter, analysis of the flow evolution shows that with increasing Re beyond a certain critical value, the flow becomes unstable and undergoes a Hopf bifurcation. A nonuniform variation with the radius size of the inner cylinder is observed. Otherwise said, elongating the radius of the cylinder leads to decrease in the critical Reynolds number. Hence, the acceleration of the unsteadiness is realized. On the other hand, by further increasing Reynolds number more than the critical value from 1200 to 2100, we note that the kinetic energy is monotonously increasing with Reynolds number and a stronger motion in the velocity near the rear wall of the enclosure is observed. Furthermore, the symmetry of flow patterns observed in the steady state has been lost. Therefore, a systematic description of various effects illuminating the optimum geometrical parameters to achieve effective flow behavior in those systems has been successfully established through this paper.

scholarly journals Numerical modeling of a turbulent semi-confined slot jet impinging on a concave surface

2015 ◽  
Vol 19 (1) ◽  
pp. 129-140 ◽  
Author(s):  
Hadi Ahmadi ◽  
Mehran Rajabi-Zargarabadi ◽  
Arun Mujumdar ◽  
Javad Mohammadpour
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Local Nusselt Number ◽  
Numerical Study ◽  
Separation Distance ◽  
Heat Diffusion ◽  
Concave Surface ◽  
Geometrical Parameters ◽  
Wall Jet ◽  
Wall Region

This article presents results from a numerical study of a turbulent slot jet impinging on a concave surface. Five different low Reynolds number k-? models were evaluated to predict the heat transfer under a two dimensional steady turbulent jet. The effects of flow and geometrical parameters (e.g. jet Reynolds number and jet-to-target separation distance) have been investigated. The Yap correction is applied for reducing the over-prediction of Nusselt number in the near wall region. It is shown that among the models tested in this study, the LS-Yap model is capable of predicting local Nusselt number in good agreement with the experimental data in both stagnation and wall jet region. Moreover, after implementation of Yap correction, no significant effect of the nozzle-to-surface distance, h/B, on the predicted stagnation Nusselt number has been found. Finally it is demonstrated that the higher values of turbulent Prandtl number reduces the heat diffusion along the wall and consequently the predicted local Nusselt number is reduced especially in the wall jet region.

Turbulence Measurements in a Corner Wall Jet1

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Barrett Poole ◽  
Joseph W. Hall
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Turbulent Flow ◽  
Three Dimensional ◽  
Numerical Code ◽  
Wall Jet ◽  
Hot Wire ◽  
Practical Applications ◽  
The Mean ◽  
Turbulent Flow Field

The corner wall jet is similar to the standard three-dimensional wall jet with the exception that one-half of the surface has been rotated counterclockwise by 90 deg. The corner wall jet is selected for study as the geometry occurs in practical applications and is an ideal benchmark case for numerical code validation. The corner wall jet investigated here is formed using a long round pipe with a Reynolds number of 159,000. Contours of the mean and turbulent flow field were measured using hot-wire anemometry from x/D = 0 to 40. The results indicate that the ratio of lateral-to-vertical growth in the corner wall jet is approximately half that in a standard turbulent three-dimensional wall jet. The results indicate that this behavior is not simply tied to a slower development of the corner wall jet.

The flow of liquid in a stream from the standard turbine impeller

1979 ◽  
Vol 44 (3) ◽  
pp. 700-710 ◽  
Author(s):  
Ivan Fořt ◽  
Hans-Otto Möckel ◽  
Jan Drbohlav ◽  
Miroslav Hrach
Keyword(s):  
Reynolds Number ◽  
Kinematic Viscosity ◽  
Momentum Flux ◽  
Relative Size ◽  
Mean Velocity ◽  
Axial Profile ◽  
The Mean ◽  
Hot Film ◽  
Turbine Impeller

Profiles of the mean velocity have been analyzed in the stream streaking from the region of rotating standard six-blade disc turbine impeller. The profiles were obtained experimentally using a hot film thermoanemometer probe. The results of the analysis is the determination of the effect of relative size of the impeller and vessel and the kinematic viscosity of the charge on three parameters of the axial profile of the mean velocity in the examined stream. No significant change of the parameter of width of the examined stream and the momentum flux in the stream has been found in the range of parameters d/D ##m <0.25; 0.50> and the Reynolds number for mixing ReM ##m <2.90 . 101; 1 . 105>. However, a significant influence has been found of ReM (at negligible effect of d/D) on the size of the hypothetical source of motion - the radius of the tangential cylindrical jet - a. The proposed phenomenological model of the turbulent stream in region of turbine impeller has been found adequate for values of ReM exceeding 1.0 . 103.

Entropy generation and heat transfer analysis for ferrofluid flow between two rotating disks with variable conductivity

2021 ◽  
pp. 095440622199118
Author(s):  
Anupam Bhandari
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Differential Equations ◽  
Entropy Generation ◽  
Heat Transfer Analysis ◽  
Entropy Generation Rate ◽  
Geometrical Parameters ◽  
Rotating Disks ◽  
Coupled Differential Equations ◽  
Lower Disk

Present model analyze the flow and heat transfer of water-based carbon nanotubes (CNTs) [Formula: see text] ferrofluid flow between two radially stretchable rotating disks in the presence of a uniform magnetic field. A study for entropy generation analysis is carried out to measure the irreversibility of the system. Using similarity transformation, the governing equations in the model are transformed into a set of nonlinear coupled differential equations in non-dimensional form. The nonlinear coupled differential equations are solved numerically through the finite element method. Variable viscosity, variable thermal conductivity, thermal radiation, and volume concentration have a crucial role in heat transfer enhancement. The results for the entropy generation rate, velocity distributions, and temperature distribution are graphically presented in the presence of physical and geometrical parameters of the flow. Increasing the values of ferromagnetic interaction number, Reynolds number, and temperature-dependent viscosity enhances the skin friction coefficients on the surface and wall of the lower disk. The local heat transfer rate near the lower disk is reduced in the presence of Harman number, Reynolds number, and Prandtl number. The ferrohydrodynamic flow between two rotating disks might be useful to optimize the use of hybrid nanofluid for liquid seals in rotating machinery.

Numerical Study of the Mean and Filtered Characteristics of Turbulent Jets Impinging on Convex and Flat Surfaces Using LES

2012 ◽  
Author(s):  
Adra Benhacine ◽  
Zoubir Nemouchi ◽  
Lyes Khezzar ◽  
Nabil Kharoua
Keyword(s):  
Convex Surface ◽  
Numerical Study ◽  
Three Dimensional ◽  
Turbulent Jets ◽  
Scale Model ◽  
Wall Jet ◽  
Potential Core ◽  
Flat Surfaces ◽  
Free Jet ◽  
Eddy Simulation

A numerical study of a turbulent plane jet impinging on a convex surface and on a flat surface is presented, using the large eddy simulation approach and the Smagorinski-Lilly sub-grid-scale model. The effects of the wall curvature on the unsteady filtered, and the steady mean, parameters characterizing the dynamics of the wall jet are addressed in particular. In the free jet upstream of the impingement region, significant and fairly ordered velocity fluctuations, that are not turbulent in nature, are observed inside the potential core. Kelvin-Helmholtz instabilities in the shear layer between the jet and the surrounding air are detected in the form of wavy sheets of vorticity. Rolled up vortices are detached from these sheets in a more or less periodic manner, evolving into distorted three dimensional structures. Along the wall jet the Coanda effect causes a marked suction along the convex surface compared with the flat one. As a result, relatively important tangential velocities and a stretching of sporadic streamwise vortices are observed, leading to friction coefficient values on the curved wall higher than those on the flat wall.

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