Turbulent mixing and transport in a thermally stratified interfacial layer in decaying grid turbulence

1991 ◽  
Vol 3 (5) ◽  
pp. 1143-1155 ◽  
Author(s):  
Jayesh ◽  
Kyunghwan Yoon ◽  
Z. Warhaft
Keyword(s):  
Turbulent Mixing ◽  
Interfacial Layer ◽  
Grid Turbulence ◽  
Mixing And Transport

Fluorescent dye measurements of the mixing and transport of wastewater discharge in the bosphorus

1995 ◽  
Vol 32 (2) ◽  
pp. 61-68 ◽  
Author(s):  
Emin Özsoy ◽  
Mohammed Abdul Latif ◽  
Sükrü T. Besiktepe ◽  
Alexander Gaines
Keyword(s):  
Extreme Events ◽  
Interfacial Layer ◽  
Lower Layer ◽  
Fluorescent Dye ◽  
Longitudinal Dispersion ◽  
Wastewater Discharge ◽  
Exchange Flows ◽  
Background Levels ◽  
Good Agreement ◽  
Mixing And Transport

The performance of the wastewater discharge of Istanbul is evaluated based on fluorescent dye technique, supported by hydrographic and current measurements. Under the normal exchange flows, as well as during extreme events of blocking, the dye essentially remained confined in the lower layer. The maximum upper layer average dye concentration in the Bosphorus was close to the background levels, while the interfacial layer values were larger. Good agreement is found between the observations and simple models of longitudinal dispersion in the lower layer of the Bosphorus.

The effects of unstable stratification and mean shear on the chemical reaction in grid turbulence

2000 ◽  
Vol 408 ◽  
pp. 39-52 ◽  
Author(s):  
KOUJI NAGATA ◽  
SATORU KOMORI
Keyword(s):  
Chemical Reaction ◽  
Turbulent Mixing ◽  
Mixing Layer ◽  
Stratified Flow ◽  
Laser Doppler Velocimeter ◽  
Grid Turbulence ◽  
Unstable Stratification ◽  
Sheared Flow ◽  
Small Scales ◽  
Neutrally Stratified

The effects of unstable thermal stratification and mean shear on chemical reaction and turbulent mixing were experimentally investigated in reacting and non-reacting liquid mixing-layer flows downstream of a turbulence-generating grid. Experiments were carried out under three conditions: unsheared neutrally stratified, unsheared unstably stratified and sheared neutrally stratified. Instantaneous velocity and concentration were simultaneously measured using the combination of a laser-Doppler velocimeter and a laser-induced fluorescence technique. The results show that the turbulent mixing is enhanced at both large and small scales by buoyancy under unstably stratified conditions and therefore the chemical reaction is strongly promoted. The mean shear acts to enhance the turbulent mixing mainly at large scales. However, the chemical reaction rate in the sheared flow is not as large as in the unstably stratified case with the same turbulence level, since the mixing at small scales in the sheared neutrally stratified flow is weaker than that in the unsheared unstably stratified flow. The unstable stratification is regarded as a better tool to attain unsheared mixing since the shearing stress acting on the fluid is much weaker in the unstably stratified flow than in the sheared flow.

The growth of a turbulent patch in a stratified fluid

1988 ◽  
Vol 190 ◽  
pp. 55-70 ◽  
Author(s):  
Harindra J. S. Fernando
Keyword(s):  
Energy Source ◽  
Mixed Layer ◽  
Turbulent Mixing ◽  
Interfacial Layer ◽  
Patch Size ◽  
Stratified Fluid ◽  
Buoyancy Frequency ◽  
External Energy ◽  
External Energy Source ◽  
Vertical Size

The behaviour of a turbulent region generated within a linearly-stratified fluid by an external energy source has been studied experimentally. A monoplanar grid that generated small-amplitude oscillations was used as the energy source. The results show that the mixed layer initially grows rapidly, as in an unstratified fluid, but when its physical vertical size becomes rf ∼ (K1/N)½, at a time tf ≈ 4.0 N−1, where N is the buoyancy frequency and K1 is the ‘action’ of the grid, the buoyancy forces become dominant and drastically reduce further vertical growth of the patch. While the patch size remains at rf, a well-defined density interfacial layer is formed at the entrainment interface. An important feature of the interfacial layer is the presence of internal waves, excited by the mixed-layer turbulence. If the grid oscillations are continuously maintained, the interfacial waves break and cause turbulent mixing, thereby increasing the size of the patch beyond rf at a very slow rate. Theoretical estimates are made for the growth characteristics and are compared with the experimental results.

scholarly journals Turbulent mixing at a shear-free density interface

1988 ◽  
Vol 189 ◽  
pp. 211-234 ◽  
Author(s):  
Imad A. Hannoun ◽  
E. John List
Keyword(s):  
Internal Waves ◽  
Turbulent Mixing ◽  
Interfacial Layer ◽  
Richardson Number ◽  
Laser Doppler Velocimeter ◽  
Dense Layer ◽  
Wave Spectra ◽  
Density Interface ◽  
Photodiode Array ◽  
Diffusive Effects

The interaction of a sharp density interface with oscillating-grid-induced shear-free turbulence was experimentally investigated. A linear photodiode array was used in conjunction with laser-induced fluorescence to measure the concentration of dye that was initially only in the less dense layer. A laser-Doppler velocimeter was used to measure the vertical velocity in and above the density interface at a point where the dye concentration was also measured. Potential refractive-index-fluctuation problems were avoided using solutes that provided a homogeneous optical environment across the density interface. Internal wave spectra, amplitudes and velocities, as well as the vertical mass flux were measured. The results indicate that mixing occurs in intermittent bursts and that the gradient (local) Richardson number remains constant for a certain range of the overall Richardson number Rj, defined in terms of an integral lengthscale, buoyancy jump and turbulence intensity. The spectra of the internal waves decay as f−3 at frequencies below the maximum Brunt-Väisälä frequency. These findings give support to a model for oceanic mixing proposed by Phillips (1977) in which the internal waves are limited in their spectral density by sporadic local instabilities and breakdown to turbulence. The results also indicate that, for a certain Rj range, the thickness of the interfacial layer (normalized by the integral lengthscale of the turbulence) is a decreasing function of Rj. At sufficiently high Rj the interfacial thickness becomes limited by diffusive effects. Finally, we discuss a simple model for entrainment at a density interface in the presence of shear-free turbulence.

A note on the expansion of turbulent wakes

1967 ◽  
Vol 28 (1) ◽  
pp. 183-193 ◽  
Author(s):  
J. F. Keffer
Keyword(s):  
Turbulent Mixing ◽  
Strain Field ◽  
Turbulent Wake ◽  
Geometric Distortion ◽  
Main Stream ◽  
Convective Velocity ◽  
Realistic Approach ◽  
Homogeneous Strain ◽  
Mixing And Transport ◽  
External Strain

An analysis has been made of a two-dimensional turbulent wake which was subjected to a homogeneous strain. This was applied in such a way that the rate of growth of the wake tended to be accelerated but the main stream convective velocity remained constant. An attempt to describe the flow by classical self-preservation techniques was made. However, the results suggested that a detrainment of wake fluid would result. In lieu of this a more realistic approach was sought and it was found that in certain situations where the flow has had an opportunity to develop before the strain is applied, the growth of the wake in the strain field can be described successfully by a simple geometric distortion. It appears likely that in these cases the interaction between the external strain and the turbulent structure within the wake is negligible, the wake remaining essentially passive. Suggestions as to the mechanism of the turbulent mixing and transport under these conditions are made.

scholarly journals Mixing and Entrainment in the Red Sea Outflow Plume. Part I: Plume Structure

2005 ◽  
Vol 35 (5) ◽  
pp. 569-583 ◽  
Author(s):  
Hartmut Peters ◽  
William E. Johns ◽  
Amy S. Bower ◽  
David M. Fratantoni
Keyword(s):  
Red Sea ◽  
Turbulent Mixing ◽  
Interfacial Layer ◽  
Vertical Structure ◽  
Bottom Layer ◽  
Companion Paper ◽  
Gulf Of Aden ◽  
Local Maxima ◽  
Downstream Distance ◽  
Winter Conditions

Abstract When the salty and heavy water of the Red Sea exits from the Strait of Bab el Mandeb, it continues downslope into the Gulf of Aden mainly along two channels. The 130-km-long “Northern Channel” (NC) is topographically confined and is typically only 5 km wide. In it, the Red Sea plume shows unanticipated patterns of vertical structure, turbulent mixing, and entrainment. Above the seafloor a 25–120-m-thick weakly stratified layer shows little dilution along the channel. Hence this bottom layer undergoes only weak entrainment. In contrast, a 35–285-m-thick interfacial layer shows stronger entrainment and is shown in a companion paper to undergo vigorous turbulent mixing. It is thus the interface that exhibits the bulk of entrainment of the Red Sea plume in the NC. The interfacial layer also carries most of the overall plume transport, increasingly so with downstream distance. The “Southern Channel” (SC) is wider than the NC and is accessed from the latter by a sill about 33 m above the floor of the NC. Entrainment into the bottom layer of the SC is diagnosed to be strong near the entry into the SC such that the near-bottom density and salinity are smaller in the SC than in the NC at the same distance from Bab el Mandeb. In comparison with winter conditions, the authors encountered weaker outflow with shallower equilibration depths during the summer cruise. Bulk Froude numbers computed for the whole plume varied within the range 0.2–1. Local maxima occurred in relatively steep channel sections and coincided with locations of significant entrainment.

Direct numerical simulation of turbulent mixing in regular and fractal grid turbulence

2010 ◽  
Vol T142 ◽  
pp. 014065 ◽  
Author(s):  
Hiroki Suzuki ◽  
Kouji Nagata ◽  
Yasuhiko Sakai ◽  
Toshiyuki Hayase
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Turbulent Mixing ◽  
Grid Turbulence
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