Natural Breakdown of Planar Jets

1972 ◽  
Vol 94 (4) ◽  
pp. 720-728 ◽  
Author(s):  
D. O. Rockwell ◽  
W. O. Niccolls
Keyword(s):  
Reynolds Number ◽  
Nozzle Exit ◽  
Vortex Formation ◽  
Reynolds Numbers ◽  
Mature Stage ◽  
Hydrogen Bubble ◽  
Core Flow ◽  
Transport Velocity ◽  
Hydrogen Bubble Technique

The growth of planar jets is studied using the hydrogen bubble technique of flow visualization. A five-fold range of nozzle exit Reynolds number (1860 to 10,800) is considered. Generation of streaklines and timelines permits characterization of the process of vortex formation and coalescence. Both symmetrical and asymmetrical modes of vortex growth and coalescence, along with the resultant deformation of the jet core flow, are examined. Nascent and mature stage coalescence are defined and portrayed. Vortex axial transport velocity and frequency of formation of the vortices are evaluated for selected Reynolds numbers.

Experimental characterization of three-dimensional corner flows at low Reynolds numbers

2012 ◽  
Vol 707 ◽  
pp. 37-52 ◽  
Author(s):  
J. Sznitman ◽  
L. Guglielmini ◽  
D. Clifton ◽  
D. Scobee ◽  
H. A. Stone ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Channel Cross Section ◽  
Experimental Characterization ◽  
Low Reynolds Numbers ◽  
Low Reynolds

AbstractWe investigate experimentally the characteristics of the flow field that develops at low Reynolds numbers ($\mathit{Re}\ll 1$) around a sharp $9{0}^{\ensuremath{\circ} } $ corner bounded by channel walls. Two-dimensional planar velocity fields are obtained using particle image velocimetry (PIV) conducted in a towing tank filled with a silicone oil of high viscosity. We find that, in the vicinity of the corner, the steady-state flow patterns bear the signature of a three-dimensional secondary flow, characterized by counter-rotating pairs of streamwise vortical structures and identified by the presence of non-vanishing transverse velocities (${u}_{z} $). These results are compared to numerical solutions of the incompressible flow as well as to predictions obtained, for a similar geometry, from an asymptotic expansion solution (Guglielmini et al., J. Fluid Mech., vol. 668, 2011, pp. 33–57). Furthermore, we discuss the influence of both Reynolds number and aspect ratio of the channel cross-section on the resulting secondary flows. This work represents, to the best of our knowledge, the first experimental characterization of the three-dimensional flow features arising in a pressure-driven flow near a corner at low Reynolds number.

Transverse Oscillations of a Jet in a Jet-Splitter System

1972 ◽  
Vol 94 (3) ◽  
pp. 675-681 ◽  
Author(s):  
D. O. Rockwell
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Nozzle Exit ◽  
Reynolds Numbers ◽  
Dimensionless Frequency ◽  
Two Dimensional ◽  
Vena Contracta ◽  
Wide Range ◽  
Jet Behavior ◽  
Transverse Oscillations

The fundamental transverse oscillations of a liquid jet which impinged upon a flow splitter were examined for a wide range of dimensionless splitter distance, nozzle exit Reynolds number, and dimensionless frequency. The results are presented in the form of a design map. The data, taken at low nozzle aspect ratio, reveal that fundamental (stage 1) oscillations can exist for Reynolds numbers up to at least 7000. Up to Reynolds numbers of about 3000, the jet behavior is Reynolds number dependent for all values of splitter distance. Beyond Reynolds number of 3000 the jet behavior is independent of Reynolds number. In general, the Strouhal number, based on nozzle exit-splitter distance, decreases with increasing values of splitter distance. Jets issuing from nozzles with no parallel development sections were considered. Jet nozzle shape influences the dimensionless frequency of oscillation in that the effect of a vena contracta formation outside the nozzle exit is to yield a higher value of dimensionless frequency relative to nozzles which produce parallel flow with small boundary layer thickness at the exit. Similar decreases have been found for two-dimensional jets. Of the above findings, the only comparable results for two-dimensional jets are variations in Strouhal number with nozzle exit-splitter distance.

scholarly journals Formation and Topology of vortices in Couette Flow over open cavities

2020 ◽  
Vol 197 ◽  
pp. 10005
Author(s):  
Cesare Biserni ◽  
Andrea Natale Impiombato ◽  
Aminhossein Jahanbin ◽  
Eugenia Rossi di Schio ◽  
Giovanni Semprini
Keyword(s):  
Reynolds Number ◽  
Couette Flow ◽  
Flow Problem ◽  
Vortex Formation ◽  
Reynolds Numbers ◽  
Single Vortex ◽  
Low Reynolds Numbers ◽  
Natural Systems ◽  
And Topology ◽  
Open Cavities

The present study investigates the planar Couette flow problem for low Reynolds numbers inside a rectangular duct with a morphing cavity serving as a vortex formation promoter. A finite element code implemented in COMSOL Multiphysics is employed to analyze the effects of the cavity aspect ratio and variations of the Reynolds number on formation and topology of the vortices within the embedded cavity. The obtained results indicate that the cavity height is influential in the number of vortices. It is shown by increasing the Reynolds number, a single vortex tends to move towards the outlet. In addition, streamlines demonstrate that small vortices in vicinity of the cavity corner tend to be enlarged with increase of the Reynolds number. The developed numerical model can be extended to the flow structure of natural systems such as an embayment subjected to parallel-to-shore currents.

On vortex strength and drag in bluff-body wakes

1975 ◽  
Vol 69 (4) ◽  
pp. 721-728 ◽  
Author(s):  
Owen M. Griffin ◽  
Steven E. Ramberg
Keyword(s):  
Reynolds Number ◽  
Bluff Body ◽  
Vortex Formation ◽  
Reynolds Numbers ◽  
Vortex Street ◽  
Hot Wire ◽  
Force Measurements ◽  
Experimental Conditions ◽  
Vortex Strength ◽  
The Mean

In a recent paper (Griffin & Ramberg 1974) the authors studied the vortex-street wakes behind forced vibrating rigid cylinders. All experimental conditions were within the regime of wake capture or synchronization between the vibration and vortex frequencies. Both mean and fluctuating velocities in the wake together with the length of the vortex formation region were measured as functions of vibration amplitude and frequency at a Reynolds number of 144. The viscous vortex strength, age and spacing at this Reynolds number were then obtained by matching a model for the vortex street with the mean and r.m.s. velocity profiles obtained from hot-wire measurements. These results are employed here to determine the steady drag force on the vibrating cylinder by means of the von Kármán drag formulation. The drag coefficients determined in this way are in agreement with the recently published direct force measurements of Tanida, Okajima & Watanabe (1973) and Griffin, Skop & Koopmann (1973) at Reynolds numbers of 80, 500-900 and 4000. From these results a direct relation is drawn between the increased drag on resonantly vibrating structures and changes in the vortex strength, spacing and formation in their wakes.

Numerical Simulations of Heat and Fluid Flow in Grooved Channels With Curved Vanes

2003 ◽  
Author(s):  
Matthew McGarry ◽  
Antonio Campo ◽  
Darren L. Hitt
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Heat Exchangers ◽  
System Performance ◽  
Vortex Formation ◽  
Electronics Cooling ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
Heat And Fluid Flow

The use of vanes in grooved channels for heat transfer enhancement has received more attention in the recent years due to applications in heat exchangers and electronics cooling. The current work focuses on characterizing the vortex formation around heated elements in grooved channels with curved vanes. A computational model is developed to examine the effect that the vortices have on heat transfer and system performance for a range of Reynolds numbers of 100 to 800. These vortices explain the previously observed characteristics in system performance for geometries with the use of curved vanes. At a Reynolds number of 400 these vortices inhibit heat transfer and increase pressure drop in the channel, resulting in significant decreases in system performance.

Vortex Formation for Different Geometry of Cavities Using High Reynolds Number

2014 ◽  
Vol 699 ◽  
pp. 416-421
Author(s):  
Mohd Noor Asril Saadun ◽  
Muhammad Zulhakim Sharudin ◽  
Nor Azwadi Che Sidik ◽  
Mohd Hafidzal Mohd Hanafi
Keyword(s):  
Reynolds Number ◽  
High Reynolds Number ◽  
Stokes Equations ◽  
Vortex Formation ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Contaminant Removal ◽  
Navier Stokes Equations ◽  
High Reynolds

A preliminary study of Computational Fluid Dynamics (CFD) on the effect of high Reynolds numbers in the cavity has been carried out. Two dimensional model analysis of the flow characteristics were conducted using the numerical solution of Navier-Stokes equations based on the finite difference method. The flow characteristics in the cavity and the driven flow were modeled via turbulence equation modelling. This paper focuses on the effects of different high Reynolds number on the flow pattern of contaminant removal in the cavity. Different types of geometry and aspect ratio of the geometry were used as the parameters of the cavity in this study. Based on visualization of flows between each model with the different parameters used, the results of a comparison analysis focusing on the behavior of the flow were reported.

The Effect of Reynolds Number on Microfan Performance

2004 ◽  
Author(s):  
David Quin ◽  
Ronan Grimes ◽  
Ed Walsh ◽  
Mark Davies ◽  
Stefan Kunz
Keyword(s):  
Reynolds Number ◽  
Heat Dissipation ◽  
Axial Flow ◽  
Reynolds Numbers ◽  
Electronic Systems ◽  
Piv Measurements ◽  
Flow Characterization ◽  
Image Velocimetry ◽  
Macro Scale

Miniaturisation of modern electronics means that future compact electronic systems are likely to be too hot to be held in the users hand. Simultaneous increases in heat dissipation will also require the development of novel compact cooling technologies. In systems such as mobile phones and palmtop computers, macro scale fans cannot be used to overcome this problem, as they are too large. As a solution, the implementation of micro fan technology is proposed. Previous investigators have shown that reduction of the Reynolds number of turbomachinery results in reduced efficiency. To experimentally investigate this predicted phenomenon, a series of geometrically similar axial flow fans have been fabricated. These range in size from the macro to the micro scale with the Reynolds numbers varying linearly with fan dimensions. Through detailed Particle Image Velocimetry (PIV) measurements and pressure flow characterization of these fans, this investigation aims to quantify the reduction in efficiency, which occurs as the Reynolds number is reduced. This paper concludes that the extent to which fan efficiency is reduced by Reynolds number is in surprisingly good agreement with relatively simple predictions developed by the authors in previous investigations. Reduced Reynolds number was also seen to alter the velocity distribution at the fan outlet. This is an important point as it indicates a change in the physics of the flow with reducing scale.

Measurements of Velocity and Turbulence in Vertical Axisymmetric Isothermal and Buoyant Jets

1992 ◽  
Vol 114 (1) ◽  
pp. 135-142 ◽  
Author(s):  
J. Peterson ◽  
Y. Bayazitoglu
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Transition Region ◽  
Nozzle Exit ◽  
Low Reynolds Number ◽  
Reynolds Numbers ◽  
Buoyant Jets ◽  
Velocity Fluctuations ◽  
Curve Fit ◽  
Low Reynolds

The current study examines the transition region of axisymmetric isothermal and buoyant jets of low Reynolds number, directed vertically upward into a stagnant, unstratified ambient. The region in which measurements were obtained allows examination of two types of transition occurring in the jet: from nozzle exit dominated to fully developed, and from momentum to buoyancy-dominated flow. Isothermal velocity data were acquired using a two-channel laser-Doppler anemometer for Reynolds numbers ranging from 850 to 7405. The buoyant cases studied had Froude numbers ranging from 12 to 6425 and Reynolds numbers from 525 to 6500. In each case data were taken from 5 to 44 nozzle diameters downstream. Curve fit approximations of the data were developed by assuming polynomial similarity profiles for the measured quantities. Each profile was individually curve fit because in the transition region under consideration the flow field is not necessarily similar. Profile constants were then curve fit to determine profile variation as a function of nozzle exit parameters and downstream location. These allow prediction of the downstream velocity flow field and turbulent flow field as a function of the Reynolds number, Froude number, and density ratio at the nozzle exit. Profile width and entrainment increased at low Reynolds number. Axial and radial velocity fluctuations were found to increase at low Reynolds number. The buoyant cases studied were found to have lower velocity fluctuations and significantly lower Reynolds stresses than isothermal cases of similar Reynolds number.

Quantitative Visualization of a Submerged Pseudoplastic Jet Using Particle Image Velocimetry

1995 ◽  
Vol 117 (3) ◽  
pp. 369-373 ◽  
Author(s):  
A. Shekarriz ◽  
J. R. Phillips ◽  
T. D. Weir
Keyword(s):  
Reynolds Number ◽  
Particle Image Velocimetry ◽  
Nozzle Exit ◽  
Particle Image ◽  
Reynolds Numbers ◽  
Streamwise Velocity ◽  
Image Velocimetry ◽  
Close Observation ◽  
Quantitative Visualization ◽  
Nozzle Exit Velocity

A preliminary experimental study of a pseudoplastic jet flow is reported in this paper. The velocity field was measured using Particle Image Velocimetry. Unlike a Newtonian jet, the pseudoplastic jet was observed to experience a sudden drop in its velocity at a reproducible position downstream of the nozzle for the range of velocities examined. This position moved downstream with an increase in the nozzle exit velocity. The center-line streamwise velocity decayed as X–15 to X–30 within the terminating region of the jet for three different nozzle exit velocities of 2.43, 3.17, and 5.42 m/s. This decay is in contrast to X–1 decay for a turbulent or laminar Newtonian jet. The location of the terminating region did not appear to scale with Reynolds number, Plasticity number, or Hedstrom number. At Reynolds numbers of 3000 and 6400, the instantaneous streamwise velocity maps indicated that the flow was fairly laminar, with a sinuous instability appearing at the higher Reynolds number condition. Close observation of the jet indicated that local turbulence could exist within regions of high shear rate. Further detailed study is required to confirm this observation.

scholarly journals Simulation of Lid-Driven Cavity Flow with Internal Circular Obstacles

2020 ◽  
Vol 10 (13) ◽  
pp. 4583 ◽  
Author(s):  
Tingting Huang ◽  
Hee-Chang Lim
Keyword(s):  
Reynolds Number ◽  
Solid Wall ◽  
Vortex Formation ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Time Model ◽  
Cross Sectional ◽  
Driven Cavity ◽  
Secondary Vortices ◽  
Boltzmann Method

The Lattice Boltzmann method (LBM) has been applied for the simulation of lid-driven flows inside cavities with internal two-dimensional circular obstacles of various diameters under Reynolds numbers ranging from 100 to 5000. With the LBM, a simplified square cross-sectional cavity was used and a single relaxation time model was employed to simulate complex fluid flow around the obstacles inside the cavity. In order to made better convergence, well-posed boundary conditions should be defined in the domain, such as no-slip conditions on the side and bottom solid-wall surfaces as well as the surface of obstacles and uniform horizontal velocity at the top of the cavity. This study focused on the flow inside a square cavity with internal obstacles with the objective of observing the effect of the Reynolds number and size of the internal obstacles on the flow characteristics and primary/secondary vortex formation. The current LBM has been successfully used to precisely simulate and visualize the primary and secondary vortices inside the cavity. In order to validate the results of this study, the results were compared with existing data. In the case of a cavity without any obstacles, as the Reynolds number increases, the primary vortices move toward the center of the cavity, and the secondary vortices at the bottom corners increase in size. In the case of the cavity with internal obstacles, as the Reynolds number increases, the secondary vortices close to the internal obstacle become smaller owing to the strong primary vortices. In contrast, depending on the sizes of the obstacles ( R / L = 1/16, 1/6, 1/4, and 2/5), secondary vortices are induced at each corner of the cavity and remain stationary, but the secondary vortices close to the top of the obstacle become larger as the size of the obstacle increases.

Sign in / Sign up

Export Citation Format

Share Document