# Fluid Dynamics Videos

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From 2006-2010, the APS Division of Fluid Dynamics "Gallery of Fluid Motion" videos were deposited in eCommons. Videos have also been deposited to arXiv.org, and are now managed by the APS. See the APS Gallery of Fluid Motion (http://gfm.aps.org) for more information.

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Item Numerical simulation of transom-stern wavesHand, Randall E.; Valenciano, Miguel; George, Kevin; Biddlecome, Tom; Walters, Richard; Stephens, Mike; O'Shea, Thomas T.; Brucker, Kyle A.; Dommermuth, Douglas G. (APS DFD Gallery of Fluid Motion, 2010-11-23)The flow field generated by a transom stern hullform is a complex, broad-banded, three-dimensional system marked by a large breaking wave. This unsteady multiphase turbulent flow feature is difficult to study experimentally and simulate numerically. The results of a set of numerical simulations, which use the Numerical Flow Analysis (NFA) code, of the flow around the Model 5673 transom stern at speeds covering both wet- and dry-transom operating conditions are shown in the accompanying fluid dynamics video. The numerical predictions for wet-transom and dry transom conditions are presented to demonstrate the current state of the art in the simulation of ship generated breaking waves. The interested reader is referred to Drazen et al. (2010) for a detailed and comprehensive comparison with experiments conducted at the Naval Surface Warfare Center Carderock Division (NSWCCD) The interested reader is referred to Drazen et al. (2010) for a detailed and comprehensive comparison with experiments conducted at the Naval Surface Warfare Center Carderock Division (NSWCCD).Item Electroworming : The behaviors of Caenorhabditis (C.) elegans in DC and AC electric fieldsChuang, Han-Sheng; Raizen, David; Dabbish, Nooreen; Bau, Haim (2010-10-15)The video showcases how C. elegans worms respond to DC and AC electrical stimulations. Gabel et al (2007) demonstrated that in the presence of DC and low frequency AC fields, worms of stage L2 and larger propel themselves conscientiously and deliberately towards the cathode. Rezai et al (2010) have demonstrated that this phenomenon, dubbed electrotaxis, can be used to control the motion of worms. In the video, we reproduce Rezai's experimental results. Furthermore, we show, for the first time, that worms can be trapped with high frequency, nonuniform electric fields. We studied the effect of the electric field on the nematode as a function of field intensity and frequency and identified a range of electric field intensities and frequencies that trap worms without apparent adverse effect on their viability. Worms tethered by dielectrophoresis (DEP) avoid blue light, indicating that at least some of the nervous system functions remain unimpaired in the presence of the electrical field. DEP is useful to dynamically confine nematodes for observations, sort them according to size, and separate dead worms from live ones.Item Falling Flexible SheetsAlben, Silas (2010-08-04T15:05:22Z)We present a fluid dynamics video showing simulations of flexible bodies falling in an inviscid fluid. Vortex sheets are shed from the trailing edges of the bodies according to the Kutta condition. The basic behavior is a repeated series of accelerations to a critical speed at which the sheet buckles, and rapidly decelerates, shedding large vortices. Examples of persistent circling, quasi-periodic flapping, and more complex trajectories are shown.Item Simulation of flow patterns generated by the hydromedusa Aequorea victoria using an arbitrary Lagrangian–Eulerian formulationMOHSENI, Kamran (Science Direct, 2009-03-31)A new geometrically conservative arbitrary Lagrangian–Eulerian (ALE) formulation is presented for the moving boundary problems in the swirl-free cylindrical coordinates. The governing equations are multiplied with the radial distance and integrated over arbitrary moving Lagrangian–Eulerian quadrilateral elements. Therefore, the continuity and the geometric conservation equations take very simple form similar to those of the Cartesian coordinates. The continuity equation is satisfied exactly within each element and a special attention is given to satisfy the geometric conservation law (GCL) at the discrete level. The equation of motion of a deforming body is solved in addition to the Navier–Stokes equations in a fully-coupled form. The mesh deformation is achieved by solving the linear elasticity equation at each time level while avoiding remeshing in order to enhance numerical robustness. The resulting algebraic linear systems are solved using an ILU(k) preconditioned GMRES method provided by the PETSc library. The present ALE method is validated for the steady and oscillatory flow around a sphere in a cylindrical tube and applied to the investigation of the flow patterns around a free-swimming hydromedusa Aequorea victoria (crystal jellyfish). The calculations for the hydromedusa indicate the shed of the opposite signed vortex rings very close to each other and the formation of large induced velocities along the line of interaction while the ring vortices moving away from the hydromedusa. In addition, the propulsion efficiency of the free-swimming hydromedusa is computed and its value is compared with values from the literature for several other species.Item Nonlinear spin-up of a thermally stratified fluid in cylindrical geometriesPacheco, J. Rafael; Smirnov, Sergey A.; Verzicco, Roberto (2009-10-26T23:05:41Z)This is an entry for the Gallery of Fluid Motion of the 62nd Annual Meeting of the APS-DFD (fluid dynamics videos). This video shows the three-dimensional time-dependent incremental spin-up of a thermally stratified fluid in a cylinder and in an annulus. The rigid bottom/side wall(s) are non-slip, and the upper surface is stress-free. All the surfaces are thermally insulated. The working fluid is water characterized by the kinematic viscosity $\nu$ and thermal diffusivity $\kappa$. Initially, the fluid temperature varies linearly with height and is characterized by a constant buoyancy frequency $N$, which is proportional to the density gradient. The system undergoes an abrupt change in the rotation rate from its initial value $\Omega_i $, when the fluid is in a solid-body rotation state, to the final value $\Omega_f$. Our study reveals a feasibility for transition from an axisymmetric initial circulation to non-axisymmetric flow patterns at late spin-up times.Item Nonlinear spin-up of a thermally stratified fluid in cylindrical geometriesPacheco, J. Rafael; Smirnov, Sergey A.; Verzicco, Roberto (2009-10-25T20:02:06Z)This is an entry for the Gallery of Fluid Motion of the 62nd Annual Meeting of the APS-DFD (fluid dynamics videos). This video shows the three-dimensional time-de\-pen\-dent incremental spin-up of a thermally stratified fluid in a cylinder and in an annulus. The rigid bottom/side wall(s) are non-slip, and the upper surface is stress-free. All the surfaces are thermally insulated. The working fluid is water characterized by the kinematic viscosity $\nu$ and thermal diffusivity $\kappa$. Initially, the fluid temperature varies linearly with height and is characterized by a constant buoyancy frequency $N$, which is proportional to the density gradient. The system undergoes an abrupt change in the rotation rate from its initial value $\Omega_i $, when the fluid is in a solid-body rotation state, to the final value $\Omega_f$. Our study reveals a feasibility for transition from an axisymmetric initial circulation to non-axisymmetric flow patterns at late spin-up times.Item Primary Atomization of a Liquid Jet in CrossflowRana, Sandeep; Herrmann, Marcus (2009-10-23T17:43:39Z)We present a visualization of the primary atomization of a turbulent liquid jet injected into a turbulent gaseous cross-stream. Detailed numerical simulation results were obtained using the Refined Level Set Grid (RLSG) method, coupled to a finite volume, balanced force, incompressible LES/DNS flow solver (M. Herrmann, J. Comput. Phys., 227, 2008). The liquid jet is injected into a Re=740,000 compressed air cross stream with momentum flux ratio 6.6, Weber number 330, Reynolds number 14,000, and density ratio 10. The simulation takes the details of the injector geometry (C. Brown & V. McDonell, ILASS Americas, 2006) into account. Grid resolution in the primary atomization region is a constant 32 grid points per injector diameter in the flow solver, and 64 grid points per injector diameter in the level set solver, resulting in grid sizes of 21 million control volumes for the flow solver and a theoretical maximum of 840 million nodes for the level set solver. We employ a hybrid Eulerian/Lagrangian approach for the liquid in that broken off, small, nearly spherical liquid drops tracked by the Eulerian level set approach are transferred into Lagrangian point particles to capture the evolution of the liquid spray downstream of the primary atomization region (M. Herrmann, J. Comput. Phys., 2010). The simulation results clearly show the simultaneous presence of two distinct breakup modes. While the main column of the jet is subject to a wavy instability mode, resulting in the formation of bags that break under the influence of the cross stream flow at the end of the liquid core, ligaments are formed on the sides of the jet near the injector exit that stretch and break. The flow in the wake of the bending liquid jet is characterized by strong turbulence. Comparison of the simulation results to experimental data show that mean jet penetration is in excellent agreement to experimental correlations and drop size distributions converge under grid refinement (M. Herrmann, J. Eng. Gas Turb. Power, 132(2), 2010).Item Hydrothermal waves in evaporating sessile drops (APS 2009)BRUTIN, David; RIGOLLET, Fabrice; LE NILIOT, Christophe (2009-10-23T16:17:16Z)This fluid dynamics video was submitted to the Gallery of Fluid Motion for the 2009 APS Division of Fluid Dynamics Meeting in Minneapolis, Minnesota. Drop evaporation is a simple phenomena but still unclear concerning the mechanisms of evaporation. A common agreement of the scientific community based on experimental and numerical work evidences that most of the evaporation occurs at the triple line. However, the rate of evaporation is still empirically predicted due to the lack of knowledge on the convection cells which develop inside the drop under evaporation. The evaporation of sessile drop is more complicated than it appears due to the coupling by conduction with the heating substrate, the convection and conduction inside the drop and the convection and diffusion with the vapour phase. The coupling of heat transfer in the three phases induces complicated cases to solve even for numerical simulations. We present recent experimental fluid dynamics videos obtained using a FLIR SC-6000 coupled with a microscopic lens of 10 µm of resolution to observe the evaporation of sessile drops in infrared wavelengths. The range of 3 to 5 µm is adapted to the fluids observed which are ethanol, methanol and FC-72 since they are all half-transparent to the infrared.Item Infrared video of a warm water surface in the presence and absence of surfactant monolayersBower, S. M.; Saylor, J. R. (2009-10-19T22:38:44Z)Infrared (IR) videos are presented which show a warm water surface undergoing convective processes. These fluid dynamics videos show the water surface with: 1) no surfactant monolayer material present, 2) a liquid-phase monolayer of oleyl alcohol, and 3) a solid-phase monolayer of cetyl alcohol.Item Geometry of elastic hydrofracturing by injection of an over pressured non-Newtonian FluidJ Chavez-Alvarez, E Soto; B Barrientos, C Mares; M Cerca (2009-10-19T21:13:32Z)The nucleation and propagation of hydrofractures by injection of over pressured fluids in an elastic and isotropic medium are studied experimentally. Non-Newtonian fluids are injected inside a gelatine whose mechanical properties are assumed isotropic at the experimental strain rates. Linear elastic theory predicts that plastic deformation associated to breakage of gelatin bonds is limited to a small zone ahead of the tip of the propagating fracture and that propagation will be maintained while the fluid pressure exceeds the normal stress to the fracture walls (Ch\'avez-\'Alvarez,2008) (i.e., the minimum compressive stress), resulting in a single mode I fracture geometry. However, we observed the propagation of fractures type II and III as well as nucleation of secondary fractures, with oblique to perpendicular trajectories with respect to the initial fracture. Experimental evidence shows that the fracture shape depends on the viscoelastic properties of gelatine coupled with the strain rate achieved by fracture propagtion.