scholarly journals Plunging jets from orifices of different geometry

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Giorgio Moscato ◽  
Giovanni Paolo Romano
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
Air Bubbles ◽  
Natural Processes ◽  
Water Jets ◽  
Starting Point ◽  
Air Water Interface ◽  
Plunging Jets ◽  
Small Reynolds Numbers ◽  
Jet Characteristics

Plunging jets are used in many industrial and civil applications, as for example in sewage and water treatment plants, in order to enhance aeration and mass transfer of volatile gases. They are also observed in natural processes as rivers self-purification, waterfalls and weirs. Many investigations dealt with the plunging jets in different configurations, but the dependence on Reynolds number and jet geometry were still not sufficiently addressed. For example, Mishra et al. (2020) studied an oblique submerged water impinging jet at different nozzle-to-plate distances and impingement angles, but only at a rather small Reynolds numbers (2600). On the other hand, different jet geometries have been extensively considered, but not for the plunging jet configuration (Mi, 2000; Hashiehbaf &Romano, 2013). In this work, plunging water jets issuing in air from orifices of different shape are considered. The aim of the work is to detail and compare jet behaviors in terms of velocity fields generated after impacting the air-water interface, as a function of Reynolds number and orifice geometry. However, air bubbles entrainment is mainly avoided in order to study the jet characteristics in a simpler case and use it as a reference starting point for future works.

scholarly journals Thermoelectric Generation with Impinging Nano-Jets

Energies ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 492
Author(s):  
Fatih Selimefendigil ◽  
Hakan F. Oztop ◽  
Mikhail A. Sheremet
Keyword(s):  
Fluid Dynamics ◽  
Power Generation ◽  
Computational Fluid Dynamics ◽  
Reynolds Number ◽  
Conversion Efficiency ◽  
Reynolds Numbers ◽  
Thermoelectric Generation ◽  
Volume Fractions ◽  
Water Jets ◽  
Conversion Efficiencies

In this study, thermoelectric generation with impinging hot and cold nanofluid jets is considered with computational fluid dynamics by using the finite element method. Highly conductive CNT particles are used in the water jets. Impacts of the Reynolds number of nanojet stream combinations (between (Re1, Re2) = (250, 250) to (1000, 1000)), horizontal distance of the jet inlet from the thermoelectric device (between (r1, r2) = (−0.25, −0.25) to (1.5, 1.5)), impinging jet inlet to target surfaces (between w2 and 4w2) and solid nanoparticle volume fraction (between 0 and 2%) on the interface temperature variations, thermoelectric output power generation and conversion efficiencies are numerically assessed. Higher powers and efficiencies are achieved when the jet stream Reynolds numbers and nanoparticle volume fractions are increased. Generated power and efficiency enhancements 81.5% and 23.8% when lowest and highest Reynolds number combinations are compared. However, the power enhancement with nanojets using highly conductive CNT particles is 14% at the highest solid volume fractions as compared to pure water jet. Impacts of horizontal location of jet inlets affect the power generation and conversion efficiency and 43% variation in the generated power is achieved. Lower values of distances between the jet inlets to the target surface resulted in higher power generation while an optimum value for the highest efficiency is obtained at location zh = 2.5ws. There is 18% enhancement in the conversion efficiency when distances at zh = ws and zh = 2.5ws are compared. Finally, polynomial type regression models are obtained for estimation of generated power and conversion efficiencies for water-jets and nanojets considering various values of jet Reynolds numbers. Accurate predictions are obtained with this modeling approach and it is helpful in assisting the high fidelity computational fluid dynamics simulations results.

Force on a Small Particle Attached to a Plane Wall in a Hiemenz Straining Flow

2012 ◽  
Vol 134 (11) ◽  
Author(s):  
A. B. Maynard ◽  
J. S. Marshall
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Reynolds Numbers ◽  
Lower Surface ◽  
Ring Structure ◽  
Plane Wall ◽  
Small Reynolds Numbers ◽  
Particle Force ◽  
Volume Method ◽  
Excellent Accuracy

The force acting on a spherical particle fixed to a wall and immersed in an axisymmetric straining flow is examined for small Reynolds numbers. The steady, incompressible flow field is computed using an axisymmetric finite-volume method over conditions spanning five decades in the Reynolds number. The flow is characterized by the formation of a vortex ring structure in the wedge region formed between the particle lower surface and the plane wall. A power law expression for the dimensionless particle force is obtained as a function of the Reynolds number, which is found to hold with excellent accuracy for Reynolds numbers below about 0.1.

Mass transport under standing waves over a sloping beach

2012 ◽  
Vol 701 ◽  
pp. 460-472 ◽  
Author(s):  
Pietro Scandura ◽  
Enrico Foti ◽  
Carla Faraci
Keyword(s):  
Reynolds Number ◽  
Free Surface ◽  
Mass Transport ◽  
Cell Structure ◽  
Standing Waves ◽  
Reynolds Numbers ◽  
Sea Waves ◽  
Small Reynolds Numbers ◽  
Sloping Beach

AbstractThis paper deals with the mass transport induced by sea waves propagating over a sloping beach and fully reflected from a wall. It is shown that for moderate slopes the classical recirculation cell structure holds for small Reynolds numbers only. When the Reynolds number is large, the cells interact among themselves giving rise to the merging of the negative cells and the confinement of the positive ones near the bottom. Under such circumstances the fluid moves onshore near the bottom and offshore near the free surface. The seaward decrease of the vorticity produced at the bottom appears to be the reason for the merging phenomenon.

The slow motion of a sphere in a rotating, viscous fluid

1964 ◽  
Vol 20 (2) ◽  
pp. 305-314 ◽  
Author(s):  
Stephen Childress
Keyword(s):  
Reynolds Number ◽  
Angular Velocity ◽  
Viscous Fluid ◽  
Classical Problem ◽  
Slow Motion ◽  
Reynolds Numbers ◽  
Constant Angular Velocity ◽  
Axis Of Rotation ◽  
Small Reynolds Numbers ◽  
Analytical Result

The uniform, slow motion of a sphere in a viscous fluid is examined in the case where the undisturbed fluid rotates with constant angular velocity Ω and the axis of rotation is taken to coincide with the line of motion. The various modifications of the classical problem for small Reynolds numbers are discussed. The main analytical result is a correction to Stokes's drag formula, valid for small values of the Reynolds number and Taylor number and tending to the classical Oseen correction as the last parameter tends to zero. The rotation of a free sphere relative to the fluid at infinity is also deduced.

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.

A general theory for the motion of a body through a fluid at low Reynolds number

1990 ◽  
Vol 430 (1878) ◽  
pp. 89-104 ◽  
Keyword(s):  
Reynolds Number ◽  
Angular Velocity ◽  
Stokes Problem ◽  
Low Reynolds Number ◽  
Fluid Motion ◽  
Reynolds Numbers ◽  
Linear Velocity ◽  
Special Cases ◽  
Small Reynolds Numbers ◽  
Low Reynolds

The motion of a body through a viscous fluid at low Reynolds number is considered. The motion is steady relative to axes moving with a linear velocity, U a , and rotating with an angular velocity, Ω a . The fluid motion depends on two (small) Reynolds numbers, R proportional to the linear velocity and T proportional to the angular velocity. The correction to the first approximation (Stokes flow) is a complicated function of R and T ; it is O ( R ) for T ½ ≪ R and O ( T ½ )for T ½ ≫ R . General formulae are derived for the force and couple acting on a body of arbitrary shape. From them all the terms O ( R + T ) or larger can be calculated once the Stokes problem has been solved completely. Some special cases are considered in detail.

Numerical Simulation of Two-Dimensional Drops Suspended in Simple Shear Flow at Nonzero Reynolds Numbers

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
S. Mortazavi ◽  
Y. Afshar ◽  
H. Abbaspour
Keyword(s):  
Reynolds Number ◽  
Shear Flow ◽  
Normal Stress ◽  
Reynolds Numbers ◽  
Normal Stress Difference ◽  
Two Dimensions ◽  
Simple Shear Flow ◽  
Stress Difference ◽  
Areal Fraction ◽  
Small Reynolds Numbers

The motion of deformable drops suspended in a linear shear flow at nonzero Reynolds numbers is studied by numerical simulations in two dimensions. It is found that a deformable drop migrates toward the center of the channel in agreement with experimental findings at small Reynolds numbers. However, at relatively high Reynolds numbers (Re=80) and small deformation, the drop migrates to an equilibrium position off the centerline. Suspension of drops at a moderate areal fraction (φ=0.44) is studied by simulations of 36 drops. The flow is studied as a function of the Reynolds number and a shear thinning behavior is observed. The results for the normal stress difference show oscillations around a mean value at small Reynolds numbers, and it increases as the Reynolds number is raised. Simulations of drops at high areal fraction (φ=0.66) show that if the Capillary number is kept constant, the effective viscosity does not change in the range of considered Reynolds numbers (0.8–80). The normal stress difference is also a weak function of the Reynolds number. It is also found that similar to flows of granular materials, suspension of drops at finite Reynolds numbers shows the same trend for the density and fluctuation energy distribution across the channel.

The steady motion of a particle of arbitrary shape at small Reynolds numbers

1965 ◽  
Vol 23 (4) ◽  
pp. 625-643 ◽  
Author(s):  
R. G. Cox
Keyword(s):  
Reynolds Number ◽  
Arbitrary Shape ◽  
Fluid Motion ◽  
Steady Motion ◽  
Reynolds Numbers ◽  
The Body ◽  
Oseen Equations ◽  
Shaped Body ◽  
Symmetry Properties ◽  
Small Reynolds Numbers

The results given by Brenner & Cox (1963) for the resistance of a particle of arbitrary shape in translation at small Reynolds numbers are generalized. Thus we consider here a single particle of arbitrary shape moving with both translation and rotation in an infinite fluid, the Reynolds number R of the fluid motion being assumed small. With the additional assumption that the motion is steady with respect to some inertial frame of reference, we calculate both the force and couple on the body as an expansion in the Reynolds number to O(R2 In R). This force and couple are expressed entirely in terms of various Stokes flows for the given body in rotation or translation.A discussion is given of the form taken by the formulae for the force and couple for cases in which the body possesses symmetry properties. Quantitative results are obtained for both a spheroid and a dumb-bell-shaped body in pure translation and also for a translating rotating sphere and for a dumb-bell-shaped body in pure rotation.The application of the general results to ‘quasi-steady’ problems is considered, with particular reference to a freely falling spheroid (of small eccentricity) which is shown to orientate itself so that it is broad-side on to its direction of motion.Finally the general results are compared with those that would be obtained by the use of the Oseen equations. By consideration of a particular example it is shown that the Oseen equations do not in general give the correct value of the force on the body to O(R).

Flow Field Study in Louvered Fin and Round Tube Heat Exchangers

2010 ◽  
Author(s):  
Henk Huisseune ◽  
Christophe T’Joen ◽  
Peter De Jaeger ◽  
Michel De Paepe
Keyword(s):  
Reynolds Number ◽  
Heat Exchanger ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Recirculation Region ◽  
Louvered Fin ◽  
Horseshoe Vortices ◽  
Small Reynolds Numbers ◽  
Visualization Experiments ◽  
Fin Spacing

Three-dimensional flow structures influence the heat exchanger’s performance. In this study flow visualization experiments were performed in six scaled-up models of a louvered fin heat exchanger with round tubes. The models have a staggered tube layout and differ only in their fin spacing and louver angle. A water tunnel was designed and built and the flow visualizations were carried out using dye injection. For small Reynolds numbers no horseshoe vortices are developed in front of the tubes and the recirculation regions downstream the tubes are small. As the Reynolds number is increased, the horseshoe vortices become larger and stronger. The recirculation bubbles grow until they cover the entire back of the tube. When the Reynolds number is further increased, the recirculation region becomes unsteady. At the same Reynolds number the vortex strength and the number of vortices in the second tube row is larger than in the first tube row. Reducing the fin pitch suppresses the vortex and wake development. Further it was found that the first unsteady flow patterns appear in the wake of the heat exchanger and these instabilities move upstream with increasing Reynolds number. The onset of unsteadiness is postponed to higher Reynolds numbers when the fin pitch or louver angle is reduced.

Low Pressure Turbine Secondary Vortices: Reynolds Lapse

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Matthias Kuerner ◽  
Georg A. Reichstein ◽  
Daniel Schrack ◽  
Martin G. Rose ◽  
Stephan Staudacher ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Numerical Model ◽  
Reynolds Numbers ◽  
Test Facility ◽  
Low Pressure Turbine ◽  
Small Reynolds Numbers ◽  
Unsteady Simulation ◽  
Aero Engines ◽  
Secondary Vortices ◽  
The Impact

A two-stage turbine is tested in a cooperation between the Institute of Aircraft Propulsion Systems (ILA) and MTU Aero Engines GmbH (MTU). The experimental results taken in the Altitude Test Facility (ATF) are used to assess the impact of cavity flow and leakage on vortex structures. The analysis focuses on a range of small Reynolds numbers, from as low as 35,000 up to 88,000. The five hole probe area traverse data is compared to steady multistage CFD predictions behind the second vane. The numerical model compares computations without and with cavities modeled. The simulation with cavities is superior to the approach without cavities. The vortex induced blockage is found to be inversely proportional to the Reynolds number. The circulation of the vortices is dependent on the Reynolds number showing a reversing trend to the smallest Reynolds numbers. The steady numerical model as of yet is unsuitable to predict these trends. A first unsteady simulation suggests major improvements.

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