scholarly journals Numerical Study on Plane and Radial Wall Jets to Validate the 2D Assumption for an Idealized Downburst Outflow

2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Yongli Zhong ◽  
Zhitao Yan ◽  
Yan Li ◽  
Jie Luo ◽  
Hua Zhang
Keyword(s):  
Reynolds Number ◽  
Numerical Study ◽  
Critical Value ◽  
Plane Wall ◽  
Cloud Base ◽  
Jet Flows ◽  
Wall Jet ◽  
Wall Jets ◽  
Radial Wall ◽  
Velocity Decay

Turbulent radial and plane wall jets have been extensively investigated both experimentally and numerically over the past few decades. Previous studies mostly focused on the heat and mass transfers involved in jet flows. In this study, a comprehensive investigation was conducted on turbulent radial and plane wall jets, considering both jet spread and velocity decay for different parameters. The numerical results were compared with existing experimental measurements. The comparison focused on the velocity profile, jet spread, and velocity decay, and revealed that the Reynolds stress model (RSM) performs well in the simulation of both radial and plane wall jets. The results show that with a typical ratio of cloud base height to diameter for most downburst events, the effects of nozzle height and Reynolds number on the evolution of the radial wall jet are not significant. Both the jet spread and velocity decay exhibit a clear dependence on the Reynolds number below a critical value. Above this critical value, the plane wall jet becomes asymptotically independent of the Reynolds number. The co-flow was found to have a significant influence on the evolution of the plane wall jet. Comparatively, the jet spread and velocity of the radial wall jet were faster than those of the plane jet. For applications in civil engineering, it is valid to approximate the downburst outflow with a two-dimensional (2D) assumption from the perspective of longitudinal evolution of the flows.

Numerical Study of Pulsed Turbulent Plane Wall Jet by Low-Reynolds-Number k–ε Model

2007 ◽  
Vol 52 (10) ◽  
pp. 935-957 ◽  
Author(s):  
Jamel Kechiche ◽  
Hatem Mhiri ◽  
Georges Le Palec ◽  
Philippe Bournot
Keyword(s):  
Reynolds Number ◽  
Numerical Study ◽  
Low Reynolds Number ◽  
Plane Wall ◽  
Wall Jet ◽  
Turbulent Plane ◽  
Low Reynolds

Three-Dimensional Curved Wall Jets

1972 ◽  
Vol 94 (2) ◽  
pp. 339-344 ◽  
Author(s):  
U. M. Patankar ◽  
K. Sridhar
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Maximum Velocity ◽  
Ambient Air ◽  
Jet Flow ◽  
Jet Flows ◽  
Wall Jet ◽  
Wall Jets ◽  
Potential Core ◽  
Velocity Decay

This paper presents an experimental investigation of mean velocities of turbulent, three-dimensional incompressible air jets from various rectangular orifices issuing tangentially to and flowing along the surface of a curved wall into quiescent ambient air. An experimental study of the jet separation is also presented. The three-dimensional curved wall jet is found to be drastically different in its mean property behavior from its so-called two-dimensional counterpart. Velocity contour plots show the resultant effect on the jet flow of two diverging tendencies—the free jet flow and the Coanda flow. This effect is found to occur earlier with smaller aspect-ratio orifices. Within the range of variables studied, three-dimensional curved wall jets may be characterized by three regions of maximum velocity decay. The rate of maximum velocity decay is dependent on orifice aspect ratio, except in the potential core region. Further, the curved wall jet differs from other three-dimensional jet flows in its growth behavior.

Radial Wall Jet Flow Over Sigmoidal Surfaces

2020 ◽  
Author(s):  
Leonard F. Pease ◽  
Michael J. Minette ◽  
Judith Ann Bamberger
Keyword(s):  
Velocity Profile ◽  
Jet Flows ◽  
Wall Jet ◽  
Radial Wall ◽  
Modest Contribution ◽  
Velocity Decay ◽  
Conservation Of Momentum ◽  
Fixed Beds ◽  
Wall Jet Flow ◽  
Particle Bed

Abstract Radial wall jet flows across flat smooth surfaces have been studied for decades. These studies show that the radial velocity of these jets decays inversely with distance from the nozzle with modest contribution from friction (Poreh, et al., 1967; Rajaratnam, 1976). However, the extent to which flat surface results apply to curved surfaces remains unclear. In this paper we explore the influence of settled particle bed slope on radial wall jet velocity profiles. Jet flows over particle beds often introduce curvature in the particle bed profile, but the influence of the developed curvature on the velocity profile has not been explored. We model the step change in thickness as a sigmoidal curve of variable steepness and use conservation of momentum to evaluate the velocity profile for steady fixed beds. We find that surface curvature has a significant influence on the velocity decay coefficients, provided there is a slip velocity in the vicinity of the particle bed interface, which is strictly true for particle surfaces. We show that the velocity profile attenuates because of curvature. Indeed, conservation of momentum predicts conditions where the forward momentum of the flow is directed completely upward. The solution identifies two new dimensionless groups that determine whether a curved surface is sufficient to block radial flow and force flow vertically.

PIV Study of Laminar Wall Jets of Non-Newtonian Fluids

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
K. F. K. Adane ◽  
M. F. Tachie
Keyword(s):  
Reynolds Number ◽  
Three Dimensional ◽  
Maximum Velocity ◽  
Reynolds Numbers ◽  
Newtonian Fluids ◽  
Jet Flows ◽  
Wall Jet ◽  
Fluid Type ◽  
Particle Image Velocimetry Technique ◽  
Velocity Decay

Three-dimensional laminar wall jet flows of shear-thinning non-Newtonian fluids have been studied using a particle image velocimetry technique. The non-Newtonian fluids were prepared from xanthan gum solutions of various concentrations. The velocity measurements were performed in various streamwise-transverse and streamwise-spanwise planes at various inlet Reynolds numbers. From these measurements, the maximum velocity decay, jet half-widths, and velocity profiles were obtained to study the effects of Reynolds number and fluid type on the characteristics of the wall jet flows. It was observed that the maximum velocity decay and jet half-widths depend on inlet Reynolds number and fluid but the similarity velocities profiles are independent of both Reynolds number and specific fluid type.

scholarly journals A numerical study of a plane wall jet with heat transfer

2017 ◽  
Vol 63 ◽  
pp. 99-107 ◽  
Author(s):  
Iftekhar Z. Naqavi ◽  
James C. Tyacke ◽  
Paul G. Tucker
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Plane Wall ◽  
Wall Jet

Numerical Study of Flow and Dilution Behavior of Radial Wall Jet

2010 ◽  
Vol 22 (5) ◽  
pp. 681-688 ◽  
Author(s):  
Zhi-wei Li ◽  
Wen-xin Huai ◽  
Zhong-dong Qian ◽  
Yu-hong Zeng ◽  
Zhong-hua Yang
Keyword(s):  
Numerical Study ◽  
Wall Jet ◽  
Radial Wall

Comparison of 2-D Turbulent Particle Laden Density Current and Wall Jets

2006 ◽  
Author(s):  
S. Hormozi ◽  
B. Firoozabadi ◽  
H. Ghasvari Jahromi ◽  
H. Afshin
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Suspended Solids ◽  
Turbidity Currents ◽  
Density Current ◽  
Wall Jet ◽  
Density Currents ◽  
Ambient Water ◽  
Wall Jets ◽  
Good Agreement

Dense underflows are continuous currents, which move down the slope due to the fact that, their density are heavier than ambient water. In turbidity currents the density differences arises from suspended solids. Vicinity of the wall make density currents and wall jets similar in some sense but Variation of density cause this flows more complex than wall jets. An improved form of ‘near-wall’ k-ε turbulence model is chosen which preserve all characteristics of both density and wall jet currents and a compression is made between them. Then the outcomes from low Reynolds number k-ε model is compared with v2–f model which show similarity. Also results show good agreement with experimental data.

Flow Characteristics of Three-Dimensional Curved Wall Jets on a Cylinder

2017 ◽  
Vol 140 (4) ◽  
Author(s):  
Mirae Kim ◽  
Hyun Dong Kim ◽  
Eunseop Yeom ◽  
Kyung Chun Kim
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Turbulence Intensity ◽  
Flow Separation ◽  
Reynolds Shear Stress ◽  
Three Dimensional ◽  
Cylinder Surface ◽  
Cylinder Wall ◽  
Wall Jet ◽  
Wall Jets

Three-dimensional (3D) curved wall jets are a significant topic in various applications related to local heat and mass transfer. This study investigates the effects of the impinging angle and Reynolds number with a fixed distance from the nozzle to the surface of a cylinder. The particle image velocimetry (PIV) method was used to measure the mean streamwise velocity profiles, which were normalized by the maximum velocity along the centerline of the impinging jet onto the cylinder. After the impingement of the circular jet, a 3D curved wall jet develops on the cylinder surface due to the Coanda effect. At a given Reynolds number, the initial momentum of the wall jet increases, and flow separation occurs further downstream than in normal impingement as the impinging angle increases. At a given impinging angle, flow separation is delayed with increasing Reynolds number. A self-preserving wall jet profile was not attained in the 3D curved wall jet. The turbulence intensity and the Reynolds shear stress were obtained to analyze the turbulence characteristics. The radial turbulence intensity showed similar tendencies to a two-dimensional (2D) curved wall jet, but the streamwise turbulence intensity was dissimilar. The Reynolds shear stress decreases downstream of the cylinder wall due to the decreased velocity and centrifugal force.

Three-Dimensional Laminar Wall Jet Flows

2009 ◽  
Author(s):  
Kofi K. Adane ◽  
Mark F. Tachie
Keyword(s):  
Numerical Study ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Navier Stokes ◽  
Jet Flows ◽  
Wall Jet ◽  
Navier Stokes Equation ◽  
Flow Geometry

The present article reports on both experimental and numerical study of three-dimensional laminar wall jet flows. The wall jet was created using a circular pipe of diameter 7 mm and flows into an open channel. The Reynolds numbers based on the pipe diameter and jet exit velocity were varied from 310 to 1300. A particle image velocimetry (PIV) was used to conduct detailed velocity measurements at various streamwise-transverse and streamwise-spanwise planes. A complete nonlinear incompressible Navier-Stokes equation was also solved using a co-located finite volume based in-house computational fluid dynamic (CFD) code. This code was used to compute the experimental flow geometry. From the PIV measurements and CFD results, velocities profiles and jet-half-widths were extracted at selected locations. It was observed that the numerical results are in reasonable agreement with the experimental data. The distributions of the velocities, jet-half-widths and visualisation of the secondary flows were used to provide insight into the characteristics of three-dimensional wall jet flows.

Large-scale motions in a plane wall jet

2019 ◽  
Vol 877 ◽  
pp. 239-281 ◽  
Author(s):  
Ebenezer P. Gnanamanickam ◽  
Shibani Bhatt ◽  
Sravan Artham ◽  
Zheng Zhang
Keyword(s):  
Reynolds Number ◽  
Shear Layer ◽  
Large Scale ◽  
Plane Wall ◽  
Shear Stresses ◽  
Wall Jet ◽  
Wall Region ◽  
Free Shear Layer ◽  
Large Scale Structures ◽  
Scale Structures

The plane wall jet (PWJ) is a wall-bounded flow in which a wall shear layer develops in the presence of extremely energetic flow structures of the outer free-shear layer. The structure of a PWJ, developing in still air, was studied with the focus on the large scales in the flow. Wall-normal hot-wire anemometry (HWA) measurements along with double-frame particle image velocimetry (PIV) measurements (wall-normal–streamwise plane) were carried out at streamwise distances up to $162b$, where $b$ is the slot width of the PWJ exit. The nominal PWJ Reynolds number based on exit parameters was $Re_{j}\approx 5940$. Comparisons with a zero-pressure-gradient boundary layer (ZPGBL) at nominally matched friction Reynolds number $Re_{\unicode[STIX]{x1D70F}}$ were also carried out as appropriate, to highlight key features of the PWJ structure. Consistent with previous work, the PWJ showed a dependence of the peak turbulent stresses on the jet exit Reynolds number. The turbulent production showed a peak corresponding to the near-wall cycle similar to the peak seen in the ZPGBL. However, another turbulent production peak was observed in the outer free-shear layer that was an order of magnitude larger than the inner one. Along with the change in sign of the viscous and Reynolds shear stresses, the PWJ was shown to have a region of very low turbulent production between these two peaks. The dissipation rate increased over the PWJ layer with a peak also in the outer region. Visualizations of the flow and two-point correlations reveal that the most energetic large-scale structures within a PWJ are vortical motions in the wall-normal–streamwise plane similar to those structures seen in free-shear layers. These structures are referred to as J (for jet) type structures. In addition two-point correlations reveal the existence of large-scale structures in the wall region which have a signature similar to those structures seen in canonical boundary layers. These structures are referred to as W (for wall) type structures. Instantaneous PIV realizations and flow visualizations reveal that these W type large-scale features are consistent with the paradigm of hairpin vortex packets in the wall region. The J type structures were seen to intrude well into the wall region while the W type structures were also seen to extend into the outer shear layer. Further, these large-scale structures were shown to modulate the amplitude of the finer scales of the flow.

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