Reynolds Number Effects on the Characteristics of Twin Jets Interacting With a Free Surface

2016 ◽  
Author(s):  
M. S. Rahman ◽  
E. M. Nabess ◽  
M. F. Tachie
Keyword(s):  
Reynolds Number ◽  
Free Surface ◽  
Maximum Velocity ◽  
Mean Velocity ◽  
Free Jet ◽  
Turbulent Characteristics ◽  
Reynolds Number Effects ◽  
Velocity Decay ◽  
Twin Jets ◽  
Velocity Measuring

The effects of Reynolds number on the turbulent characteristics of surface attaching twin jet were investigated experimentally. Particle image velocimetry was used as the velocity measuring technique. Twin jets were produced using square orifice nozzle pair. The Reynolds numbers based on the jet exit velocity and the nozzle width were varied from 2620 to 7900. The offset height ratio was fixed at 2 during the experiments. The jet reattached to the free surface and the reattachment length decreased with increase of Reynolds number. Free surface showed significant effect on the maximum velocity decay, jet spread, streamwise mean velocity distribution, Reynolds shear and normal stresses in the upper jet. The decay and spread rate of the lower jet was comparable to free jet due to less confinement effect. The mean and turbulent quantities reported herein were nearly independent of Reynolds number. Proper orthogonal decomposition was performed to reveal the dynamic role of the energetic structures embedded within the flow.

Effects of Reynolds Number on Turbulent Characteristics of Surface Jet

2016 ◽  
Author(s):  
M. S. Rahman ◽  
M. F. Tachie
Keyword(s):  
Reynolds Number ◽  
Reynolds Shear Stress ◽  
Maximum Velocity ◽  
Reynolds Numbers ◽  
Mean Velocity ◽  
Potential Core ◽  
Turbulent Characteristics ◽  
Reynolds Number Effects ◽  
Surface Jet ◽  
Jet Characteristics

Experimental study was carried out to investigate the Reynolds number effects on surface jet characteristics. The surface jet was produced using orifice nozzle with offset height ratio of 2. Six different Reynolds numbers ranging from 2300 to 11900 were investigated. Potential core region of the jet decreased with Reynolds number up to the Reynolds number of 5500. Reattachment point was sensitive to Reynolds number within the range of the present study. The maximum velocity decay and jet spread were nearly independent of Reynolds number. The streamwise mean velocity, streamwise turbulence intensity and Reynolds shear stress distribution along surface-normal direction were affected by the free surface and showed Reynolds number independency at the Reynolds numbers beyond 5500.

Characteristics of Twin Jets in the Vicinity of a Free Surface

2016 ◽  
Author(s):  
M. S. Rahman ◽  
E. M. Nabess ◽  
M. F. Tachie
Keyword(s):  
Free Surface ◽  
Reynolds Shear Stress ◽  
Mean Velocity ◽  
Mixing Performance ◽  
Separation Ratio ◽  
Turbulent Characteristics ◽  
Velocity Decay ◽  
Twin Jets ◽  
Proper Orthogonal

Investigation of turbulent characteristics of twin jet near the free surface was carried out experimentally at four offset height ratios of 1, 2, 3 and 4. The experiments were conducted using square orifice nozzle pair with separation ratio of 2.6 at Reynolds number of 3890. The effect of the free surface as well as the effect of the offset height ratio on the streamwise mean velocity, streamwise turbulence intensity and Reynolds shear stress were discussed. The velocity decay and jet spread were quantified in order to characterize the effect of offset height on entrainment and mixing performance. The flow dynamics at the free surface was characterized by observing the variation of streamwise mean velocity and turbulence intensities at the free surface. Proper orthogonal decomposition was performed and the role of the energetic structures in the surface attaching twin jet was discussed both qualitatively and quantitatively.

Investigation of Turbulent Mixing in a Macro-Scale Multi-Inlet Vortex Nanoprecipitation Reactor by Stereoscopic-PIV

2014 ◽  
Author(s):  
Zhenping Liu ◽  
James C. Hill ◽  
Rodney O. Fox ◽  
Michael G. Olsen
Keyword(s):  
Reynolds Number ◽  
Turbulent Mixing ◽  
Three Dimensional ◽  
Stereoscopic Particle Image Velocimetry ◽  
Vortex Center ◽  
Mean Velocity ◽  
Vortex Model ◽  
Functional Nanoparticles ◽  
Turbulent Characteristics ◽  
Macro Scale

Flash Nanoprecipitation (FNP) is a technique to produce monodisperse functional nanoparticles through rapidly mixing a saturated solution and a non-solvent. Multi-inlet vortex reactors (MIVR) have been effectively applied to FNP due to their ability to provide both rapid mixing and the flexibility of inlet flow conditions. Until recently, only micro-scale MIVRs have been demonstrated to be effective in FNP. A scaled-up MIVR could potentially generate large quantities of functional nanoparticles, giving FNP wider applicability in the industry. In the present research, turbulent mixing inside a scaled-up, macro-scale MIVR was measured by stereoscopic particle image velocimetry (SPIV). Reynolds number of this reactor is defined based on the bulk inlet velocity, ranging from 3290 to 8225. It is the first time that the three-dimensional velocity field of a MIVR was experimentally measured. The influence of Reynolds number on mean velocity becomes more linear as Reynolds number increases. An analytical vortex model was proposed to well describe the mean velocity profile. The turbulent characteristics such as turbulent kinematic energy and Reynolds stress are also presented. The wandering motion of vortex center was found to have a significant contribution to the turbulent kinetic energy of flow near the center area.

Modulations on turbulent characteristics by dispersed particles in gas–solid jets

2005 ◽  
Vol 461 (2062) ◽  
pp. 3279-3295 ◽  
Author(s):  
Kun Luo ◽  
Jianren Fan ◽  
Kefa Cen
Keyword(s):  
Large Scale ◽  
Stokes Number ◽  
Vortex Structures ◽  
Half Width ◽  
Mean Velocity ◽  
Turbulent Characteristics ◽  
Velocity Decay ◽  
Large Scale Vortex ◽  
High Reynolds ◽  
The One

A direct numerical simulation technique combined with a two-way coupling method was developed to study a gas–solid turbulent jet with a moderately high Reynolds number. The flow was weakly compressible and spatially developing. A high-resolution solver was performed for the gas phase flow-field and the Lagrangian method was used to trace particles. The modulations on flow structures and other turbulent characteristics by particles at different Stokes numbers were investigated. It is found that the particles at Stokes numbers of 0.01 and 50 can advance the development of the large-scale vortex structures and make the turbulence intensity profiles wider and lower, but the particles at a Stokes number of 1 delay the evolution of the large-scale vortex structures and decrease the turbulence intensities. The jet velocity half-width and the decay of the streamwise mean velocity in the jet centreline are reduced by all particles, in which particles at a Stokes number of 0.01 result in a larger reduction of the velocity half-width and particles at a Stokes number of 1 lead to a larger reduction of the streamwise mean velocity decay. All particles decrease the vorticity thickness, but increase the fluid momentum thickness. In addition, the two-way coupled particle distribution is more uniform than that of the one-way coupled case.

Experimental Study of Reynolds Number Effects on Three-Dimensional Offset Jets

2014 ◽  
Author(s):  
Zacharie M. J. Durand ◽  
Shawn P. Clark ◽  
Mark F. Tachie ◽  
Jarrod Malenchak ◽  
Getnet Muluye
Keyword(s):  
Experimental Study ◽  
Reynolds Number ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Reynolds Shear Stress ◽  
Three Dimensional ◽  
Shear Stresses ◽  
Mean Velocity ◽  
Flow Measurements ◽  
Reynolds Number Effects

The effect of Reynolds number on three-dimensional offset jets was investigated in this study. An acoustic Doppler velocimeter simultaneously measured all three components of velocity, U, V and W, and turbulence intensity, urms, vrms, and wrms, and all three Reynolds shear stresses, uv, uw, and vw. Turbulent kinetic energy, k, was calculated with all three values of turbulence intensities. Flow measurements were performed at Reynolds numbers of 34,000, 53,000 and 86,000. Results of this experimental study indicate the wall-normal location of maximum mean velocity and jet spread to be independent of Reynolds number. The effects on maximum mean velocity decay are reduced with increasing Reynolds number. Profiles of mean velocities, U, V and W, turbulence intensities, urms, vrms, and wrms, and turbulent kinetic energy, k, show independence of Reynolds number. Reynolds shear stress uv was independent of Reynolds number while the magnitude of uw was reduced at higher Reynolds number.

Flow Characteristics of Flapping Motion of a Plane Water Jet Impinging onto Free Surface

2013 ◽  
Vol 5 (06) ◽  
pp. 846-856 ◽  
Author(s):  
Liqing Zhao ◽  
Jianhong Sun
Keyword(s):  
Free Surface ◽  
Large Scale ◽  
Flow Characteristics ◽  
Mean Velocity ◽  
Flapping Motion ◽  
Eddy Simulation ◽  
Plane Jets ◽  
Velocity Decay ◽  
Turbulent Plane ◽  
Induced Velocity

AbstractA submerged turbulent plane jet in shallow water impinging vertically onto the free surface will produce a large-scale flapping motion when the jet exit velocity is larger than a critical one. The flapping phenomenon is verified in this paper through a large eddy simulation where the free surface is modeled by volume of fluid approach. The quantitative results for flapping jet are found to be in good agreement with available experimental data in terms of mean velocity, flapping-induced velocity and turbulence intensity. Results show that the flapping motion is a new flow pattern with characteristic flapping frequency for submerged turbulent plane jets, the mean centerline velocity decay is considerably faster than that of the stable impinging jet without flapping motion, and the flapping-induced velocities are as important as the turbulent fluctuations.

The Effect of the Nozzle Top Lip Thickness on a Two-Dimensional Wall Jet

2018 ◽  
Vol 141 (5) ◽  
Author(s):  
Rory McIntyre ◽  
Eric Savory ◽  
Hao Wu ◽  
David S.-K. Ting
Keyword(s):  
Reynolds Number ◽  
Maximum Velocity ◽  
Decay Rates ◽  
Wall Jet ◽  
Two Dimensional ◽  
Hot Wire ◽  
Nozzle Height ◽  
Flow Profiles ◽  
Velocity Decay ◽  
Jet Nozzle

The effect of the nozzle top lip thickness on a two-dimensional wall jet was examined experimentally in a wind tunnel using hot-wire anemometry. Lip thicknesses of 0.125b, 0.5b, 1b, and 2b, where b is the jet nozzle height, were considered at a Reynolds number of 30,700 based on the jet nozzle height and jet velocity. Noticeable differences in the flow profiles were observed at the jet outlet, but by 10b downstream these differences became insignificant. Different lip thicknesses resulted in different maximum velocity decay rates. The spread of the wall jet was found to be insensitive to the lip thickness.

On the Development of Incompressible Round and Equilateral Triangular Jets Due to Reynolds Number Variation

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Seyed Sobhan Aleyasin ◽  
Nima Fathi ◽  
Mark Francis Tachie ◽  
Peter Vorobieff ◽  
Mikhail Koupriyanov
Keyword(s):  
Reynolds Number ◽  
Near Field ◽  
Reynolds Stresses ◽  
Turbulent Structures ◽  
Potential Core ◽  
Round Jets ◽  
Flat Side ◽  
Reynolds Number Effects ◽  
Velocity Decay ◽  
Number Variation

The aim of this study is to examine the effects of Reynolds number (Re = 6000–20,000) on mean and turbulent quantities as well as turbulent structures in the near and intermediate regions of equilateral triangular and round sharp contraction jets. The results show shorter potential core length, faster growth of turbulence intensity, and faster diffusion of turbulent structures to the centerline of the triangular jets, implying enhanced mixing in the near field of these jets. On the other hand, the velocity decay and jet spread rates are higher in the round jets. The obtained data in the round jets show that the jet at Re = 6000 has the most effective mixing, while an increase in Reynolds number reduces the mixing performance. In the triangular jets, however, no Reynolds number effects were observed on the measured quantities including the length of the potential core, the decay and spread rates, the axis-switching locations, and the value of the Reynolds number. In addition, the asymptotic values of the relative turbulence intensities on the jet centerline are almost independent of the Reynolds number and geometry. The ratios of transverse and spanwise Reynolds stresses are unity except close to the jet exit where the flow pattern in the major plane of the triangular jet deflects toward the flat side. Proper orthogonal decomposition (POD) analysis revealed that turbulent structures in minor and major planes have identical fractional kinetic energy. The integral length scales increased linearly with the streamwise distance with identical slope for all the test cases.

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