Session BE: Biofluids II: General II - Biologically Generated Flows

Experiments on blood-sucking mechanism of a female mosquito

The blood-sucking phenomena of a female mosquito were investigated experimentally At first, the velocity fields of blood-sucking flow inside the proboscis of a female mosquito were measured consecutively using a micro particle image velocimetry (PIV) system The velocity signals of the blood-sucking flow in the proboscis show a periodic pulsatile flow pattern and the spectral analysis of the velocity waveform exhibits a clear peak at 6.1 Hz. The blood flow inside the proboscis has a parabolic profile, similar to that of a Hagen-Poiseuille flow. In addition, the synchrotron X-ray micro-imaging technique was employed to visualize the dynamic movement of the two pumping organs (cibarial pump and pharyngeal pump) inside the head of blood-sucking using iodine solution as a contrast material. The temporal variation of the two pump organs of a female mosquito was found to be superior, compared to that of a male mosquito. In addition, we found the functional relationship of the two pumps operating in a systematic manner with a small phase difference.   

Microscopic filter feeders near boundaries

We show through calculations, simulations, and experiments that the eddies often observed near sessile filter feeders are due to the presence of nearby boundaries. We model the common filter feeder \emph{Vorticella}, which is approx $50~\mu$m across and which feeds by removing bacteria from ocean or pond water that it draws towards itself. We use an analytic stokeslet model and a Brinkman flow approximation with the organism modeled as a cylinder with two different boundary conditions to predict the size of the eddy caused by two parallel no-slip boundaries that represent the slides between which experimental observations are often made. We also use three-dimensional finite-element simulations to fully solve for the flow around a model \emph{Vorticella}. Additionally, we track particles around live feeding \emph{Vorticella} in order to determine the experimental flow field. Our models are in good agreement both with each other and with the experiments. We also show through calculations that filter feeders such as \emph{Vorticella} can greatly enhance their nutrient uptake by feeding at an angle rather than perpendicular to a substrate.   

Modification of boundary layer momentum by the presence and pumping behavior of the bivalve clam, \textit{Mercenaria mercenaria}, in a tidal channel

The presence and activity of biological organisms have the potential to modify turbulent boundary layer characteristics in natural field settings. To determine the effect of the presence and pumping behavior of the bivalve clam\textit{, Mercenaria mercenaria}, on the boundary layer momentum, profiles were collected for flood tides in the tidal rivers adjacent to Wassaw Sound, Georgia, USA. Velocity profiles were collected simultaneously with two adjacent Acoustic Doppler Velocimeters for boundary layer flows above sediments with and without the presence of buried clams. Treatment sites included clams buried in mud sediments, sand sediments, downstream of oyster beds, and downstream of sea grass beds. We hypothesize that the modification of boundary layer momentum is unique to the treatment characteristics. Vertical profiles of mean velocity, turbulent kinetic energy, and Reynolds shear stress are calculated from the collected time records. Preliminary analysis suggests that flows downstream of sea grass and oyster beds are less affected by the presence of clams than flows over sand and mud flats. Clams reduce the horizontal velocity values above mud substrates when compared to adjacent measurements without clams present, particularly close to the substrate. When buried in sand flats, clams tend to increase the horizontal velocity values higher in the water column.   

Experimental Investigation of 3-D flow fields around the mouth of the Dwarf Seahorse during attacks on planktonic prey

Copepods are an important planktonic food source for fish species. High predation has led to the development of effective escape responses with short reaction times (less than 2 ms), maximum escape velocities of over 500 body lengths per second and shear sensitivity as low as 1.5s$^{-1}$. Using high speed digital holography (2 kfps), we measure 3-D distributions of velocity generated by a dwarf seahorse (\textit{Hippocampus zosterae}) during attacks on its copepod prey, \textit{Acartia tonsa}. It is found that successful attacks often produce smaller or even no detectable hydrodynamic disturbances around the strike zone, when compared to unsuccessful attempts. In this paper, we will provide quantitative characterization of this ``low-flow'' zone. Further, to elucidate the role of a possible geometrical advantage of the seahorse's head in minimizing its bow wave, high-speed time resolved PIV measurements are conducted in a low-speed water tunnel. On-going analysis will provide insights and implications in understanding the dynamics of flows around the stagnation point at high Reynolds number flow. Sponsored by NSF.   

A Darwinian mechanism for biogenic ocean mixing

Recent observations of biogenic turbulence in the ocean have led to conflicting ideas regarding the contribution of animal swimming to ocean mixing. Previous measurements indicate elevated turbulent dissipation in the vicinity of large populations of planktonic animals swimming in concert. However, elevated turbulent dissipation is by itself insufficient proof of substantial biogenic mixing. We conducted field measurements of mixing efficiency by individual \textit{Mastigias sp.} (a Palauan jellyfish) using a self-contained underwater velocimetry apparatus. These measurements revealed another mechanism that contributes to animal mixing besides wake turbulence. This mechanism was first described by Sir Charles Galton Darwin and is in fact the dominant mechanism of mixing by swimming animals. The efficiency of Darwin's mechanism (or drift) is dependent on animal shape rather than fluid length scale and, unlike turbulent wake mixing, is enhanced by the fluid viscosity. Therefore, it provides a means of biogenic mixing that can be equally effective in small plankton and large mammals.   

A Lagrangian approach to identifying vortex pinch-off

There exists a physical limit to the size of an axisymmetric vortex ring beyond which it rejects further vorticity flux, and a trailing jet forms behind it. This process is termed ``vortex pinch-off,'' and it has been correlated with maximally efficient fluid transport in pulsed jets\footnote{Krueger and Gharib, Phys.~Fluids, {\bf 15}, p. 1271, 2003.}. The established method for identifying vortex pinch-off consists of measuring the circulation of the vortex ring after it has separated from its trailing shear layer, and comparing it to the total circulation to determine the instant when the vortex ring ceased to accept vorticity\footnote{Gharib \emph{et al.}, J.~Fluid~Mech., {\bf 360}, p. 121, 1998.}. However, this method relies heavily on the vorticity field, which breaks down due to viscous diffusion in low Reynolds number and unsteady biological flows. We introduce a criterion for identifying pinch-off based on the Lagrangian coherent structures (LCS) in the flow, which is found to be in good agreement with the established criterion based on circulation. The Lagrangian criterion is frame-invariant and does not rely on the vorticity field, and so is a useful tool in the study of complex biological vortex-shedding flows.   

A paradox of hovering insects in two-dimensional space

A paradox concerning the flight of insects in two-dimensional space is identified: insects maintaining their bodies in a particular position (hovering) cannot, on average, generate hydrodynamic force if the induced flow is temporally periodic and converges to rest at infinity. This paradox is derived by using the far-field representation of periodic flow and the generalized Blasius formula, an exact formula for a force that acts on a moving body, based on the incompressible Navier-Stokes equations. This paradox provides insight into the effect of the singular behavior of the flow around hovering insects: the far-field wake covers the whole space.\\[4pt] Reference:\\[0pt] M. Iima, {\it J. Fluid Mech.}, (2008), {\bf 617}, 207--229.   

Butterfly proboscis as a biomicrofluidic system

It looks amazing how butterflies and moths with their thin feeding trunk are being able to sip very thick liquids like nectar or animal extractions. Their sucking ability goes beyond that: one can observe butterflies and moths probing liquids from porous materials like fruit flesh or wet soils. This suggests that the suction pressure produced by these insects is sufficiently high. The estimates based on engineering hydraulic formulas show that the pressure can be greater than one atmosphere, i.e. it can be greater than that any vacuum pump could supply. In this experimental study, the principles of interfacial flows are used to carefully analyze the feeding mechanism of butterflies and moths. We document the feeding rates and proboscis behavior of Monarch butterflies (Danaus plexippus) in different situations: when butterfly feeds from droplets, from vials modeling floral cavities, and from porous materials modeling fruits, wet soils, or dung. Using high speed imaging and simple models, we propose a scenario of butterfly feeding which is based on capillary action. According to the proposed mechanism, the trunk of butterflies and moths works like a fountain pen where the air bubbles play a significant role in controlling fluid flow.   

Implicit Large Eddy Simulation of Flow over a Corrugated Dragonfly Wing Using High-Order Spectral Difference Method

Implicit large eddy simulations of flow over a corrugated dragonfly wing at a Reynolds number of 34,000 at high angles of attack have been investigated with a high-order unstructured spectral difference Navier-Stokes solver. The computational results are compared with a recent experimental study by Hu et al. Both 2D and 3D simulations are carried out to assess how realistic and reliable the 2D simulations are in comparison with 3D simulations. At the angle of attack of 16 degrees, the 2D simulation failed to predict the stall observed in the experiment, while the 3D simulation correctly predicted the stall. In addition, the 3D simulation predicted a mean lift coefficient within 5{\%} of the experimental data. We plan to compute at least another angle of attack and compare with the experimental data. The numerical simulations demonstrated the potential of the high-order SD method in large eddy simulation of physically complex problems.   

Effect of flexibility of wing on aerodynamic performance in plunge motion

The improvement of aerodynamic performance in plunge motion is investigated through a flexibility of chordwise and spanwise directions by applied a prescribed deformation on a airfoil at Reynolds number of 30000. The aerodynamic performance of flapping motion can be evaluated through a thrust force, a input power and a propulsive efficiency which is a ratio of propulsive power which generate from thrust force to input power. Unsteady viscous flows over NACA 0012 airfoils in plunge motions are computed by using a time-accurate preconditioned Navier-Stokes solver coupled with a volume grid deformation code. For spanwise or chordwise flexibility, there is a optimal phase angle for maximum thrust force and propulsive efficiency. Especially, a combination of spanwise and chordwise flexibility can improve aerodynamic performance higher than that of adding increment from each of flexibility. Compared with rigid motion, 10{\%} deformation in chordwise and spanwise directions with zero phase angle can enhance the thrust force coefficient from 0.22 to 0.38 and 0.54 respectively, while thrust force coefficient is 0.8 by combination of spanwise and chordwise flexibility.