Scalar interactions between parallel jets measured using a two-channel PLIF technique

2015

J. Fluid Mech.

Mixing and reaction between two scalars initially separated by scalar-free ambient fluid is important in problems ranging from ecology to engineering. Using a two-channel planar laser-induced fluorescence (PLIF) system the instantaneous spatial structure of two independent scalars emitted from parallel jets into a slow coflow is quantified. Of particular interest is the scalar covariance used to define the correlation coefficient. Joint probability distribution functions (JPDFs) and instantaneous images of the scalar fields demonstrate that initially the flow mainly consists of incursions of fluid from one jet into the other, and vice versa, before scalars have time to assemble in attracting regions of the flow and coalesce due to diffusive flux. Decomposing the joint probability distribution exhibits the effect these events have on scaler overlap and scalar covariance. Along the centreline near where the mean profiles of the jets meet, the scalar covariance is negative; however, the covariance becomes positive as the scalars converge in shared structure and diffusive flux bridges a reduced barrier of ambient fluid. The mixing path between scalar filaments can be probabilistically observed through the conditional diffusion of the two scalars at various points in the flow.

Section: Experimental Approachmentioning

confidence: 99%

Joint probabilities and mixing of isolated scalars emitted from parallel jets

Soltys

2015

J. Fluid Mech.

“…1) has been used to quantify the spatial and temporal dispersion and coalescence of two initially distant scalars released in the flume. The 2C-PLIF system used in the present study is identical to that used and described in Soltys and Crimaldi (2011), and the reader is referred to that work for additional details about the system design, calibration, and validation.…”

Section: Two-channel Planar Laser-induced Fluorescencementioning

confidence: 98%

“…Fig. 1 Schematic of two-channel planar laser Induced fluorescence system as detailed in Soltys and Crimaldi (2011) …”

Section: Cylinder Wake Mixing Experimentsmentioning

confidence: 99%

See 1 more Smart Citation

Effect of instantaneous stirring process on mixing between initially distant scalars in turbulent obstacle wakes

Shoaei

2017

Exp Fluids

Self Cite

and experimentally (Soltys and Crimaldi 2015). This scalar coalescence occurs even for passive scalars where the dynamics of each scalar field evolves independently of the other; the structure of the shared velocity field is responsible for the coalescence. If the initial separation distance between the two scalars is smaller than the largest coherent length scales of the local flow, the two scalar fields develop similar instantaneous spatial distributions. While it is easier to envision these processes in simple flows, recent numerical simulations (Pratt et al. 2015) have shown that in more complex 2D flows involving multiple interacting vortices, initially distant scalars coalesce in regions of intense mixing and attracting Lagrangian coherent structures.In aquatic ecosystems, structured flows can facilitate stirring and diffusion to enhance reactions or population growth by bringing together species and nutrients (e.g., Richards and Brentnall 2006). Structured flows stir any introduced scalars into thin filament shells (Garrett 1983), enhancing local scalar gradients, increasing the interfacial area of the scalar through chaotic stretching and folding (Hinch 1999), leading finally to increased mixing by molecular diffusion.Structured flow can also contribute directly to the colocation of conspecifics or species competing for a resource (e.g., Károlyi et al. 2000). The presence of benthic aquatic fauna can itself lead to structured flow in wakes downstream of the organisms. Flow structure is also modified by benthic topology such as sea-mounts, and can be dominated by a vortex wake that produces mixing (Richards 1990). As a specific example, these stirring mechanisms may enhance fertilization rates for reproduction by benthic marine invertebrates, which reproduce by broadcast spawning: plumes of egg and sperm are released, at separate locations, into Abstract A two-channel planar laser-induced fluorescence technique is used to study mixing and reactions between two initially distant scalars in the turbulent wake of a cylindrical obstacle. The scalars are released continuously and isokinetically upstream of the cylinder, with a lateral separation that initially impedes mixing between them. The effect of the turbulent wake on mixing and reaction enhancement is determined by measuring the segregation parameter for cases with and without the cylinder obstruction. Results indicate that scalar mixing and reaction rates (in the low-Damkohler limit) increase significantly in the presence of the cylinder wake. The study also shows that the dominant contribution of total reaction derives from the scalar covariance associated with instantaneous flow processes, and depends strongly on streamwise location within the wake. The results have broad implications for mixing processes in engineering and ecology.

“…Laboratory experiments in a water flume of a similar wake geometry are shown in Fig.5, where a two-color planar laserinduced fluorescence system (Soltys and Crimaldi, 2010) is used to visualize quantify the scalar fields. Fluorescent dyes are used as high-Schmidt-number surrogates for egg (red) and sperm (blue).…”

mentioning

confidence: 99%

The role of structured stirring and mixing on gamete dispersal and aggregation in broadcast spawning

Journal of Experimental Biology

2012

SummaryBroadcast-spawning benthic invertebrates synchronously release sperm and eggs from separate locations into the surrounding flow, whereupon the process depends on structured stirring by the flow field (at large scales), and sperm motility and taxis (at small scales) to bring the gametes together. The details of the relevant physical and biological aspects of the problem that result in successful and efficient fertilization are not well understood. This review paper includes relevant work from both the physical and biological communities to synthesize a more complete understanding of the processes that govern fertilization success; the focus is on the role of structured stirring on the dispersal and aggregation of gametes. The review also includes a summary of current trends and approaches for numerical and experimental simulations of broadcast spawning.