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.

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 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.

scholarly journals Raman temperature and density measurements in supersonic jets

2021 ◽  
Vol 62 (3) ◽  
Author(s):  
Mark P. Wernet ◽  
Nicholas J. Georgiadis ◽  
Randy J. Locke
Keyword(s):  
Flow Field ◽  
Supersonic Jet ◽  
Ambient Air ◽  
Jet Flow ◽  
Supersonic Jets ◽  
Jet Flows ◽  
Turbulent Heat ◽  
Flow Measurements ◽  
Potential Core ◽  
The Mean

AbstractPrediction of flow-field properties in supersonic jets using computational fluid dynamics (CFD) code predictions has become routine; however, obtaining accurate solutions becomes more challenging when there is a significant temperature difference between the jet core and the ambient air and/or compressibility effects are significant. Benchmark sets of flow field property data are required in order to assess current CFD capabilities and develop better modeling approaches for these turbulent flow fields where accurate calculation of temperatures and turbulent heat flux is important. Particle Image Velocimetry, spontaneous rotational Raman scattering spectroscopy, and Background-Oriented Schlieren (BOS) have been previously used to acquire measurements of the mean and root-mean-square (rms) velocities, the mean and rms gas temperatures, and density gradients in subsonic jet flows and film cooling flows. In this work, the ability to measure density is added to the list of measurands available using the acquired Raman spectra. The suite of measurement techniques are now applied to supersonic jet flows. The computation of the local gas pressure in the potential core of an over-expanded jet is demonstrated using the Raman measured gas temperature and density. Additionally, a unique density feature in temperature matched, perfectly expanded jet flow shear layers identified using BOS was verified using the Raman measurement technique. These non-intrusive flow measurements are compared against RANS predictions of the supersonic jet flow properties as a means of assessing their prediction accuracy. Graphic abstract

Three-Dimensional Free Jets

1967 ◽  
Vol 71 (684) ◽  
pp. 858-859
Author(s):  
N. Rajaratnam ◽  
K. Subramanya
Keyword(s):  
Three Dimensional ◽  
Flow Characteristics ◽  
Maximum Velocity ◽  
Potential Core ◽  
Free Jets ◽  
Axisymmetric Jet ◽  
Plane Jets ◽  
Velocity Decay ◽  
Different Shapes ◽  
Semi Empirical

Fairly elegant semi-empirical theories are available for predicting the turbulent diffusion of axisymmetric and plane jets. However, there are relatively few investigations on the non-axisymmetric jets, herein denoted as three-dimensional jets. The extensive investigations conducted at the Polytechnic Institute of Brooklyn on three-dimensional jets have shown that the flow field is characterised by three distinct regions; the potential core, the characteristic decay (CD) region and the axisymmetric decay (AD) region. In the CD region the velocity profiles in the direction of the minor axis are similar but the maximum velocity decay curves are different for different shapes. In the AD region the flow characteristics are similar to that of an axisymmetric jet. Yevdjevich has recently conducted another investigation on rectangular jets.

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.

Modelling of Laminar Canonical Flows: Revisit

2012 ◽  
Author(s):  
Kofi Freeman K. Adane ◽  
Mark F. Tachie
Keyword(s):  
Three Dimensional ◽  
Shear Thinning ◽  
Secondary Flows ◽  
Newtonian Fluids ◽  
Navier Stokes ◽  
Jet Flows ◽  
Wall Jet ◽  
Navier Stokes Equation ◽  
Incompressible Navier Stokes Equation ◽  
Insight Into

Three-dimensional laminar lid-driven and wall jet flows of various shear-thinning non-Newtonian and Newtonian fluids were numerically investigated. The complete nonlinear incompressible Navier-Stokes equation was solved using a collocated finite-volume based in-house CFD code. From the results, velocity profiles at several locations, jet spread rates, secondary flows and vorticity distributions were used to provide insight into the characteristics of three-dimensional laminar canonical flows of shear-thinning non-Newtonian and Newtonian fluids.

The Influence of Aspect Ratio on Incompressible, Turbulent Flows From Rectangular Slots

1980 ◽  
Vol 31 (4) ◽  
pp. 285-305 ◽  
Author(s):  
G.F. Marsters ◽  
J. Fotheringham
Keyword(s):  
Aspect Ratio ◽  
Turbulent Flows ◽  
Turbulence Intensity ◽  
Three Dimensional ◽  
Thin Plates ◽  
Shear Stresses ◽  
Mean Velocity ◽  
Contour Maps ◽  
Velocity Decay ◽  
Spreading Rates

SummaryJets issuing from rectangular slots cut in thin plates exhibit some unusual features, including unequal spreading rates in the spanwise and transverse directions, the appearance of velocity peaks near the “ends” of the jet and changing rates of centreline velocity decay in the downstream direction. This study examines the effects of aspect ratio on such flows. The flow field has been investigated using both total head tubes and hot wire anemometry. The results are presented in the form of three-dimensional plots of total pressure and contour maps of constant velocity, streamwise turbulence intensity and the Reynolds shear stresses. The decay of mean velocity and stream-wise turbulence intensity along the centreline are presented. The rates of spanwise spreading and the location of the velocity peaks at various downstream stations are discussed. If the aspect ratio is small enough, spanwise peaks in the mean velocity distribution are suppressed.

Application of Synthetic Wall Jets for Pressure-Less, Counter-Current Conveyance of Thin Liquid Layers

2014 ◽  
Author(s):  
Thomas Sturz ◽  
Frieda Sandberg ◽  
Peter Walzel
Keyword(s):  
Driving Forces ◽  
Jet Flow ◽  
Narrow Slit ◽  
Wall Jet ◽  
Flow Conditions ◽  
Wall Jets ◽  
Directed Movement ◽  
Oscillation Cycle ◽  
Wall Jet Flow ◽  
Counter Current

The entrainment by pulsed or rather so-called synthetic wall jets can be used to sustain a pressure-less transport of thin liquid layers along ducts. These jets exhibit zero-net-mass-flow conditions and lead to a break of symmetry in the flow pattern during one oscillation cycle. Therefore, only a net impulse is transferred in jet direction and induces a directed movement of the ambient liquid by entrainment according to the jet direction. The aim is to investigate the applicability of the principle to counter-current contactors as an alternative to pressure drop or gravity as driving forces typically applied e.g. in counter-current liquid-liquid contactors. Experiments are performed with an apparatus containing wall-jet flow drives with a multitude of narrow slit-openings (slit-width s = 190 μm) along a channel for synthetic wall jet generation. Firstly, one single wall-jet flow drive is investigated regarding its conveying performance at different related oscillation amplitudes (eslit/s = 7–25) and frequencies (f = 1–5 Hz). Subsequently, the apparatus is extended by a second identical device, arranged in parallel but above and oriented in the opposite conveying direction. This is to demonstrate the applicability of synthetic wall jets for counter-current operations.

Experimental Study of Three-Dimensional Laminar Wall Jets of Non-Newtonian Fluid

2009 ◽  
Author(s):  
Kofi K. Adane ◽  
Mark F. Tachie
Keyword(s):  
Newtonian Fluid ◽  
Open Channel ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Jet Flows ◽  
Wall Jet ◽  
Particle Image Velocimetry Technique ◽  
Piv Measurements ◽  
Image Velocimetry ◽  
Shear Thinning Fluid

A particle image velocimetry technique was employed to study three-dimensional laminar wall jet flows of a non-Newtonian shear-thinning fluid. 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 250 to 800. The PIV measurements were performed in various streamwise-transverse and streamwise-spanwise planes. From these measurements, the velocity profiles, jet growth rate and spread rates were obtained to study the characteristics of three-dimensional wall jet flows of a non-Newtonian fluid.

An Experimental Study of the Forcing Effect on the Flow and Heat Transfer in a Turbulent Wall Jet

2015 ◽  
Author(s):  
Johnny Issa ◽  
Alfonso Ortega
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Stream Flow ◽  
Free Stream ◽  
Maximum Velocity ◽  
Local Maximum ◽  
Jet Flow ◽  
Wall Jet ◽  
Wall Jet Flow ◽  
Turbulent Wall

The effect of the exit wall jet flow excitation on the flow and thermal behaviors of the turbulent wall jet is experimentally investigated. Various forcing amplitudes and frequencies are used in the presence and absence of a free stream flow. Forcing the flow showed to have a major impact on the fluid mechanics of the turbulent wall jet which was clearly shown in the velocity fields and the associated time-averaged quantities such as the wall jet spread and the maximum velocity decay. The normal direction at which the local maximum velocity occurs, also known as the wall jet spreading, is shown to move further away from the wall and is increased by more than 20% under some forcing conditions. The local maximum velocity decay with the downstream direction is reduced by more than 2.5% at further downstream locations. At a given location, the increase in the wall jet spreading together with the reduction in the mean velocity results in a decrease in the wall skin friction calculated using the slope of the mean velocity in the viscous sublayer, a behavior consistent with the literature. Due to its importance in enhancing heat transfer phenomena, the effect of the forcing on the streamwise velocity fluctuations is also investigated under the various forcing conditions. The profiles of the fluctuating component of the velocity, u’, are measured at various downstream locations since they are essential in understanding the growth of the disturbances. Forcing the wall jet increased u’ in the inner and outer regions and revealed the two peaks corresponding to the inner and outer shear layers respectively. This phenomenon is attributed to the added disturbance at the jet exit in addition to the disturbance growth with the downstream direction. The introduction of wall jet flow forcing at various amplitudes and frequencies showed a significant effect on the thermal behavior of the wall jet and was more pronounced in the absence of a free stream flow, a fact related to the evolution of the mixing layer with the downstream direction. In the absence of a free stream flow, Nusselt number decreases with increasing forcing amplitude and frequency in the region close to the jet exit. The decay of Nusselt number in the downstream direction showed an inflection point at further downstream locations which leads to a larger Nusselt number value than the one observed in the unforced case. This behavior is related to the enhanced mixing between the wall jet flow and the free stream due to forcing, which results in a reduction in the wall skin friction and consequently a decrease in the heat transfer rate from the wall.

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