Self-Preserving Properties of Unsteady Round Buoyant Turbulent Plumes and Thermals in Still Fluids

2003 ◽  
Vol 125 (5) ◽  
pp. 821-830 ◽  
Author(s):  
F. J. Diez ◽  
R. Sangras ◽  
G. M. Faeth ◽  
O. C. Kwon
Keyword(s):  
Turbulent Flows ◽  
Salt Water ◽  
Ccd Camera ◽  
Reynolds Numbers ◽  
The Self ◽  
Experimental Conditions ◽  
Cross Sectional ◽  
Time Resolved ◽  
Density Ratios ◽  
Source Fluid

The self-preserving properties of round buoyant turbulent starting plumes and starting jets in unstratified environments. The experiments involved dye-containing salt water sources injected vertically downward into still fresh water within a windowed tank. Time-resolved images of the flows were obtained using a CCD camera. Experimental conditions were as follows: source diameters of 3.2 and 6.4 mm, source/ambient density ratios of 1.070 and 1.150, source Reynolds numbers of 4,000–11,000, source Froude numbers of 10–82, volume of source fluid for thermals comprising cylinders having the same cross-sectional areas as the source exit and lengths of 50–382 source diameters, and streamwise flow penetration lengths up to 110 source diameters and 5.05 Morton length scales from the source. Near-source flow properties varied significantly with source properties but the flows generally became turbulent and then became self-preserving within 5 and 20–30 source diameters from the source, respectively. Within the self-preserving region, both normalized streamwise penetration distances and normalized maximum radial penetration distances as functions of time were in agreement with the scaling relationships for the behavior of self-preserving round buoyant turbulent flows to the following powers: time to the 3/4 power for starting plumes and to the 1/2 power for thermals. Finally, the virtual origins of thermals were independent of source fluid volume for the present test conditions.

Round Turbulent Thermals, Puffs, Starting Plumes and Starting Jets in Uniform Crossflow

2003 ◽  
Author(s):  
F. J. Diez ◽  
L. P. Bernal ◽  
G. M. Faeth
Keyword(s):  
Fresh Water ◽  
Salt Water ◽  
Water Channel ◽  
Reynolds Numbers ◽  
Ccd Cameras ◽  
Experimental Conditions ◽  
Time Resolved ◽  
Buoyant Flows ◽  
Video Images ◽  
Density Ratios

The self-preserving properties of round turbulent thermals, puffs, starting plumes and starting jets, in unstratified and uniform crossflow, were investigated experimentally. The experiments involved dye-containing fresh water (for nonbuoyant flows) and salt water (for buoyant flows) sources injected vertically downward into crossflowing fresh water within a water channel. Time-resolved video images of the flows were obtained using CCD cameras. Experimental conditions were as follows: source exit diameters of 3.2 and 6.4 mm, source Reynolds numbers of 2,500–16,000, source/ambient velocity ratios of 4–35, source/ambient density ratios (for buoyant flows) of 1.073 and 1.150, volumes of injected source fluid (for thermals and puffs) comprising 16–318 source diameters, streamwise (vertical) penetration distances of 0–200 source diameters and 0–13 Morton length scales (for buoyant flows) and crosstream (horizontal) penetration distances of 0–620 source diameters. Near-source behavior varied significantly with source properties but the flows generally became turbulent for streamwise distances within 5 source diameters from the source and became self-preserving for streamwise distances from the source greater than 40–50 source diameters. Crosstream motion satisfied the no-slip convection approximation. Streamwise motion for self-preserving conditions satisfied the behavior of corresponding self-preserving flows in still fluids: round thermals and puffs in still fluids for round thermals and puffs in crossflow and two-dimensional line thermals and puffs in still fluids for round starting plumes and jets in crossflow. The no-slip convection approximation for crossflow motion combined with self-preserving approximations for streamwise motion was also effective for predicting flow trajectories at self-preserving conditions for steady round turbulent plumes and jets in crossflow.

Round Turbulent Thermals, Puffs, Starting Plumes and Starting Jets in Uniform Crossflow

2003 ◽  
Vol 125 (6) ◽  
pp. 1046-1057 ◽  
Author(s):  
F. J. Diez ◽  
L. P. Bernal ◽  
G. M. Faeth
Keyword(s):  
Fresh Water ◽  
Salt Water ◽  
Water Channel ◽  
Reynolds Numbers ◽  
Ccd Cameras ◽  
Experimental Conditions ◽  
Time Resolved ◽  
Buoyant Flows ◽  
Video Images ◽  
Density Ratios

The self-preserving properties of round turbulent thermals, puffs, starting plumes and starting jets, in unstratified and uniform crossflow, were investigated experimentally. The experiments involved dye-containing fresh water (for nonbuoyant flows) and salt water (for buoyant flows) sources injected vertically downward into crossflowing fresh water within a water channel. Time-resolved video images of the flows were obtained using CCD cameras. Experimental conditions were as follows: source exit diameters of 3.2 and 6.4 mm, source Reynolds numbers of 2,500–16,000, source/ambient velocity ratios of 4–35, source/ambient density ratios (for buoyant flows) of 1.073 and 1.150, volumes of injected source fluid (for thermals and puffs) comprising 16–318 source diameters, streamwise (vertical) penetration distances of 0–200 source diameters and 0–13 Morton length scales (for buoyant flows) and crosstream (horizontal) penetration distances of 0–620 source diameters. Near-source behavior varied significantly with source properties and distance from the source but the flows generally became turbulent for streamwise distances within 5 source diameters from the source and became self-preserving for streamwise distances from the source greater than 40–50 source diameters. Crosstream motion satisfied the no-slip convection approximation. Streamwise motion for self-preserving conditions satisfied the behavior of corresponding self-preserving flows in still fluids: round thermals and puffs in still fluids for round thermals and puffs in crossflow and two-dimensional line thermals and puffs in still fluids for round starting plumes and jets in crossflow. The no-slip convection approximation for crossflow motion combined with self-preserving approximations for streamwise motion were also effective for predicting flow trajectories at self-preserving conditions for steady round turbulent plumes and jets in crossflow.

Self-Preserving Properties of Unsteady Round Nonbuoyant Turbulent Starting Jets and Puffs in Still Fluids

2002 ◽  
Vol 124 (3) ◽  
pp. 460-469 ◽  
Author(s):  
R. Sangras ◽  
O. C. Kwon ◽  
G. M. Faeth
Keyword(s):  
Fresh Water ◽  
Turbulent Flows ◽  
Ccd Camera ◽  
Maximum Flow ◽  
Fluid Volume ◽  
The Self ◽  
Experimental Conditions ◽  
Time Resolved ◽  
Virtual Origin ◽  
Jet Behavior

The self-preserving properties of round nonbuoyant turbulent starting jets, puffs, and interrupted jets were investigated both experimentally and theoretically for flows in still and unstratified environments. The experiments involved dye-containing fresh water sources injected into still fresh water within a large windowed tank. Time-resolved video images of the flows were obtained using a CCD camera. Experimental conditions were as follows: jet exit diameters of 3.2 and 6.4 mm, jet exit Reynolds numbers of 3000–12,000, jet passage lengths in excess of 50 injector passage diameters, volume of injected fluid for puffs and interrupted jets up to 191 source diameters, and streamwise penetration lengths up to 140 source diameters. Near-source behavior varied significantly with source properties but the flows generally became turbulent within 5 source diameters from the source and self-preserving behavior was generally observed at distances greater than 20–30 source diameters from the source. Within the self-preserving region, both the normalized streamwise penetration distance and the normalized maximum flow radius varied as functions of time in agreement with estimates for self-preserving turbulent flows to the following powers: 1/2 for starting nonbuoyant jets and 1/4 for nonbuoyant puffs and interrupted jets. Effects of injected fluid quantity for self-preserving puffs and interrupted jets could be handled by correlating the location of the virtual origin as a function of the volume of the injected fluid represented by the number of passage lengths of injected fluid. In particular, the virtual origin for puffs was independent of injected fluid volume for injected passage lengths less than 120 but became proportional to the injected fluid volume thereafter, defining a boundary between puff and interrupted-jet behavior.

Structure and Mixing Properties of Unsteady Round Nonbuoyant Turbulent Jets and Puffs in Still Gases

2000 ◽  
Author(s):  
R. Sangras ◽  
G. M. Faeth
Keyword(s):  
Fresh Water ◽  
Turbulent Flows ◽  
Ccd Camera ◽  
Maximum Flow ◽  
Turbulent Jets ◽  
Reynolds Numbers ◽  
Time Resolved ◽  
Mixing Properties ◽  
Video Images ◽  
Test Conditions

Abstract A theoretical and experimental study of the temporal development of unsteady round nonbuoyant turbulent jets (starting jets) and puffs (interrupted jets) is described, limited to sources in still and unstratified environments. The experiments involved dye-containing fresh water sources injected vertically downward into fresh water within a large windowed tank with injector passage length/diameter ratios of 50. Time-resolved video images of the flows were obtained using a CCD camera. Test conditions were as follows: jet exit diameters of 3.2–12.7 mm, jet exit Reynolds numbers of 1450–11700, volume of injected fluid for puffs up to 80 passage diameters long, and penetration lengths up to 100 source diameters. Near-source behavior varied significantly with source properties but the flows generally became turbulent near the jet exit with self-preserving behavior observed at distances greater than 20–30 source diameters from the source. Within the self-preserving region, both the normalized streamwise penetration distance and the normalized maximum flow radius varied as functions of time to the following powers, in agreement with estimates for self-preserving turbulent flows: 1/2 for starting nonbuoyant jets and 1/4 for nonbuoyant puffs.

Self-Preserving Mixing Properties of Steady Round Buoyant Turbulent Plumes in Uniform Crossflows

2006 ◽  
Vol 128 (10) ◽  
pp. 1001-1011
Author(s):  
F. J. Diez ◽  
L. P. Bernal ◽  
G. M. Faeth
Keyword(s):  
Salt Water ◽  
Velocity Ratio ◽  
Vertical Direction ◽  
The Self ◽  
Scaling Analysis ◽  
Vortex System ◽  
Direction Parallel ◽  
Mixing Properties ◽  
Source Flow ◽  
Source Fluid

The self-preserving mixing properties of steady round buoyant turbulent plumes in uniform crossflows were investigated experimentally. The experiments involved salt water sources injected into fresh water crossflows within the windowed test section of a water channel. Mean and fluctuating concentrations of source fluid were measured over cross sections of the flow using planar-laser-induced fluorescence which involved seeding the source fluid with Rhodamine 6G dye and adding small concentrations of ethanol to the crossflowing fluid in order to match the refractive indices of the source flow and the crossflow. The self-preserving penetration properties of the flow were correlated successfully based on the scaling analysis of Diez, Bernal, and Faeth (2003, ASME J. Heat Transfer, 125, pp. 1046–1057) whereas the self-preserving structure properties of the flow were correlated successfully based on the scaling analysis of Fischer et al. (1979, Mixing in Inland and Coastal Waters, Academic Press, New York, pp. 315–389); both approaches involved assumptions of no-slip convection in the cross stream (horizontal) direction (parallel to the crossflow) and a self-preserving line thermal having a conserved source specific buoyancy flux per unit length that moves in the streamwise (vertical) direction (parallel to the direction of both the initial source flow and the gravity vector). The resulting self-preserving structure consisted of two counter-rotating vortices having their axes nearly aligned with the crossflow direction that move away from the source in the streamwise (vertical) direction due to the action of buoyancy. Present measurements extended up to 202 and 620 source diameters from the source in the streamwise and cross stream directions, respectively. The onset of self-preserving behavior required that the axes of the counter-rotating vortex system be nearly aligned with the crossflow direction. This alignment, in turn, was a strong function of the source/crossflow velocity ratio, uo∕v∞. The net result was that the onset of self-preserving behavior was observed at streamwise distances of 10–20 source diameters from the source for uo∕v∞=4 (the smallest value of uo∕v∞ considered), increasing to streamwise distances of 160–170 source diameters from the source for uo∕v∞=100 (the largest value of uo∕v∞ considered). Finally, the counter-rotating vortex system was responsible for substantial increases in the rate of mixing of the source fluid with the ambient fluid compared to axisymmetric round buoyant turbulent plumes in still environments, e.g., transverse dimensions in the presence of the self-preserving counter-rotating vortex system were 2–3 times larger than the transverse dimensions of self-preserving axisymmetric plumes at similar streamwise distances from the source.

Self-Preserving Mixing Properties of Steady Round Buoyant Turbulent Plumes in Uniform Crossflows

2005 ◽  
Author(s):  
F. J. Diez ◽  
L. P. Bernal ◽  
G. M. Faeth
Keyword(s):  
Salt Water ◽  
Velocity Ratio ◽  
Vertical Direction ◽  
The Self ◽  
Scaling Analysis ◽  
Vortex System ◽  
Direction Parallel ◽  
Mixing Properties ◽  
Source Flow ◽  
Source Fluid

The self-preserving mixing properties of steady round buoyant turbulent plumes in uniform crossflows were investigated experimentally. The experiments involved salt water sources injected into fresh water crossflows within the windowed test section of a water channel. Mean and fluctuating concentrations of source fluid were measured over cross sections of the flow using Planar-Laser-Induced-Fluorescence (PLIF) which involved seeding the source fluid with Rhodamine 6G dye and adding small concentrations of ethanol to the crossflowing fluid in order to match the refractive indices of the source flow and the crossflow. The self-preserving penetration properties of the flow were correlated successfully based on the scaling analysis of Diez et al. (2003) whereas the self-preserving structure properties of the flow were correlated successfully based on the scaling analysis of Fischer et al. (1979); both approaches involved assumptions of no-slip convection in the cross stream (horizontal) direction (parallel to the crossflow) and a self-preserving line thermal having a conserved source specific buoyancy flux per unit length that moves in the streamwise (vertical) direction (parallel to the direction of both the initial source flow and the gravity vector). The resulting self-preserving structure consisted of two counter-rotating vortices having their axes nearly aligned with the crossflow direction that move away from the source in the streamwise (vertical) direction due to the action of buoyancy. Present measurements extended up to 202 and 620 source diameters from the source in the streamwise and cross stream directions, respectively. The onset of self-preserving behavior required that the axes of the counter-rotating vortex system be nearly aligned with the crossflow direction. This alignment, in turn, was a strong function of the source/crossflow velocity ratio, uo/v∞. The net result was that the onset of self-preserving behavior was observed at streamwise distances of 10–20 source diameters from the source for uo/v∞ = 4 (the smallest value of uo/v∞ considered), increasing to streamwise distances of 160–170 source diameters from the source for uo/v∞ = 100 (the largest value of uo/v∞ considered). Finally, the counter-rotating vortex system was responsible for substantial increases in the rate of mixing of the source fluid with the ambient fluid compared to axisymmetric round buoyant turbulent plumes in still environments, e.g., transverse dimensions in the presence of the self-preserving counter-rotating vortex system were 2–3 times larger than the transverse dimensions of self-preserving axisymmetric plumes at similar streamwise distances from the source.

scholarly journals Experimental evidence for a new instability of a vertical columnar vortex pair in a strongly stratified fluid

2000 ◽  
Vol 418 ◽  
pp. 167-188 ◽  
Author(s):  
PAUL BILLANT ◽  
JEAN-MARC CHOMAZ
Keyword(s):  
Turbulent Flows ◽  
Three Dimensional ◽  
Vortex Pair ◽  
Reynolds Numbers ◽  
Stratified Fluid ◽  
Viscous Effects ◽  
Homogeneous Fluid ◽  
Cross Sectional ◽  
Columnar Vortex ◽  
New Type

This paper shows that a long vertical columnar vortex pair created by a double flap apparatus in a strongly stratified fluid is subjected to an instability distinct from the Crow and short-wavelength instabilities known to occur in homogeneous fluid. This new instability, which we name zigzag instability, is antisymmetric with respect to the plane separating the vortices. It is characterized by a vertically modulated twisting and bending of the whole vortex pair with almost no change of the dipole's cross- sectional structure. No saturation is observed and, ultimately, the vortex pair is sliced into thin horizontal layers of independent pancake dipoles. For the largest Brunt–Väisälä frequency N = 1.75 rad s−1 that may be achieved in the experiments, the zigzag instability is observed only in the range of Froude numbers: 0.13 < Fh0 < 0.21 (Fh0 = U0/NR, where U0 and R are the initial dipole travelling velocity and radius). When Fh0 > 0.21, the elliptic instability develops resulting in three-dimensional motions which eventually collapse into a relaminarized vortex pair. Irregular zigzags are then also observed to grow. The threshold for the inhibition of the elliptic instability Fh0 = 0.2±0.01 is independent of N and in good agreement with the theoretical study of Miyazaki & Fukumoto (1992). Complete stabilization for Fh0 < 0.13 is probably due to viscous effects since the associated Reynolds number is low, Re0 < 260. In geophysical flows characterized by low Froude numbers and large Reynolds numbers, we conjecture that this viscous stabilization will occur at much lower Froude number.It is tentatively argued that this new type of instability may explain the layering widely observed in stratified turbulent flows.

STEREOTYPE THREAT AND STEREOTYPE LIFT: THE CASE OF 10 YEAR OLD GIRLS AND BOYS

2016 ◽  
Vol 12 (4) ◽  
pp. 21-32
Author(s):  
Anna Kwiatkowska ◽  
Małgorzata Mróz
Keyword(s):  
Stereotype Threat ◽  
Cognitive Performance ◽  
Significant Interaction ◽  
Self Esteem ◽  
The Self ◽  
Experimental Conditions ◽  
Significant Interaction Effect ◽  
Significant Drop ◽  
Stereotype Lift ◽  
And Performance

The aim of this study was to examine the effects of stereotypical and counter-stereotypicalinformation on the self-esteem and cognitive performance of 10-year-old children. Our sampleconsisted of 37 girls and 37 boys. Children were presented with 10 “mathematical” puzzles in threeexperimental conditions: stereotypical (boys are better), counter-stereotypical (girls are better), andthe control condition (no particular information). Self-esteem was measured using a non-verbaltask. The results showed a significant interaction effect of “condition x sex” on self-esteem andperformance. Girls revealed no significant differences between control and experimental conditions,while boys showed a significant drop in self-esteem and performance in the counter-stereotypicalcondition as compared to the control condition and a significant lift in self-esteem and performancein the stereotypical condition as compared to the control condition.

A Time-Resolved Low-Angle Light Scattering Apparatus. Application to Phase Separation Problems in Polymer Systems

2001 ◽  
Vol 66 (6) ◽  
pp. 973-982 ◽  
Author(s):  
Čestmír Koňák ◽  
Jaroslav Holoubek ◽  
Petr Štěpánek
Keyword(s):  
Phase Separation ◽  
Light Scattering ◽  
Signal To Noise Ratio ◽  
Scattered Light ◽  
Ccd Camera ◽  
Time Resolved ◽  
Polymer Systems ◽  
Software Analysis ◽  
Phase Separation Kinetics ◽  
Small Angle Light Scattering

A time-resolved small-angle light scattering apparatus equipped with azimuthal integration by means of a conical lens or software analysis of scattering patterns detected with a CCD camera was developed. Averaging allows a significant reduction of the signal-to-noise ratio of scattered light and makes this technique suitable for investigation of phase separation kinetics. Examples of applications to time evolution of phase separation in concentrated statistical copolymer solutions and dissolution of phase-separated domains in polymer blends are given.

Sign in / Sign up

Export Citation Format

Share Document