# THIS IS A UK MIRROR OF: http://www.swcp.com/itsc/movies/

## ITSC Fluids Movie Archive

#### Computational Fluid Dynamics (CFD) and Thermal Analysis.

Scientific visualization and animation is becoming indispensable in modern engineering analysis where enormous amounts of data must be processed in order to better understand the output of typical CFD codes. Many engineering analysis require complex fluid dynamic calculations to resolve pressures, temperatures, densities and other field variables. In this page are several animation's that demonstrate the wide variety of fluid flow problems that ITS Corporation can address. The animation's chosen are those that are encountered in classic fluid dynamics problems, as well as situations that are familiar to many people.

Example 1a (150K) A heated plate with a thick initial  thermal boundary layer is suddenly accelerated to 5 m/s in air. The thermal boundary layer is swept downstream and rolls up into a pair of shed vorticies. Temperature contours are shown in the movie making the flow visible. The Reynolds number of the flow is 200,000, well beyond the critical Reynolds number of 40 where vortex shedding begins. Thus the wake region is unstable and breaks up into a Von Karman vortex street. Vortex shedding from a rectangular bar is demonstrated in Example 1b (75k). The periodic nature of the Von-Karman vortex street is best illustrated in Example 1c (63K) which shows the vortex street created by a flat plate. This movie only includes a single cycle of the phenomenon, therefore configure your (MPEG) viewer to play the movie in a continuous loop.

Example 2a (84K) A fire showing the formation of semi - periodic eddies.  This animation shows the location of hot spots and the cooler vapor dome overlaying a pool of hydrocarbon fuel.  In example 2b (187K) a solid object moves horizontally across the fire. The calculation demonstrates the effect of moving structure in a flow calculation. In example 2c (132K) the object is oriented vertically demonstrating the phenomenon of a flame holder, where a wake behind an object, created by the large indraft of air, captures and holds a flame. Example 2d (536K) This calculation is identical to example 2-a except that the structure is moving down to the base of the flame. At the base the flame attaches itself completely to the object.  Example 2E (321K) demonstrates a vortex shedding fire-object interaction. The fire oscilliates about a cylinder due to the vortex shedding phenomenon demonstrated in examples 1a-c.  Example 2F shows a rectagular object in an engulfing fire with a crosswind.

Example 3a (350K) The classic Raleigh-Taylor instability is illustrated in this calculation. When a high density fluid is placed over a low density fluid an unstable condition exists. The instability causes the two fluids to exchange places. In this example an initial perturbation is placed in the center in order to initiate the instability. The size of the box is quite large so that the exchange of fluids takes place in a fairly turbulent manner. An asymetric fluid exchange occurs when a step in fluid level is used as an initial condition, as shown in example 3b (321K).  The large difference in the fluid behavior contrasted in examples 3a and 3b demonstrates the high sensitivity to initial conditions for this type of instability. The effect of fluid viscosity is demonstrated in example 3c (266K). The same parameters of size, initial perturbation, and density difference, but a much higher viscosity was used. The high viscosity serves to damp out the high degree of turbulence found in the previous examples allowing the large wavelength instabilities to dominate the flow behavior.

The Kelvin-Helmholtz is another classic flow instability. This instability is characterised by waves that appear between two superposed fluids of differing densities and velocities. A familiar example are the ripples that form when wind flows over a pool of water. Example 4a (44K) demonstrates the Kelvin instabiliy wherein two stably stratified fluids are flowing from left to right with the uppermost low density fluid traveling 3.5 times faster than the lower heavy fluid. Another example of the Kelvin-Helmholtz instability are waves that grow on jets of high or low density fluid, such as the hot bouyant jet of gas shown in example 4b (132K).

When a layer of fluid is heated from below and cooled from above the resulting convection patterns are often called the Benard instability. The next example (104K) illustrates the transition to convection of an initially quiescent layer of fluid that has a vertically unstable temperature gradient. The fluid is low Prandtl number (Pr = 0.0125 = high thermal conductivity). Another example (120K) shows the tempmerature contours from a slightly higher Prandtl number fluid (Pr = 2.25 low thermal conductivity)

Compressible flow calculations usually involve shock wave dynamics. In this set of examples shock wave diffraction and interaction with solid objects will be demonstrated. Example 5a (81K) shows the density contours that result as a shock wave passes by a cylinder. Example 5b (139K) shows the density contours that result when shock wave passes over a wedge. A third example 5c (468K) shows the density contours resulting from the propagation of a shock wave though a structure with partitions (such as a muffler). The far right partition contains a combustible mixture with an ignition point at the beginning of the calculation .This example demonstrates shock induced flame propagation, explosive chemical reaction, in addition to reflection, refraction, and dissipation of shock waves.

Gravity wave phenomena is a familiar process to virtually everyone. The most common example is water waves at the beach. A less familiar example are gravity waves in a fluid with a stable density stratification such a two gas layers at different temperatures. Example 6a(248K) shows sloshing gravity waves in a tank with a sloping sidewall. Another gravitational instability is the slumping of a high density fluid into a low density fluid. Example 6b (357K) is very similar to the Raleigh-Taylor instability examples except that the initial condition is a vertical slab of cold dense gas surrounded by slabs of warmer low desity gas.

Material transport involves the simultaeous solution of the Navier Stokes equations along with a material transport equation. Debris transport from a through a complex geometry is shown in this example (531K)