SAND DYNAMICS AND RIPPLE DYNAMICS

SAND DYNAMICS

Here we focus on the description and quantification of the dynamics of a single particle moving in a turbulent, wall-bounded, oscillatory flow. In simple words, this is a single sand grain moving in water which is being forced back and forth over a plane and rigid surface by the passage, say, of waves.
Our tool is a spectral-element Navier Stokes solver, with which we perform numerical simulations of the three dimensional situation. This requires the use of computers such as my beowulf cluster and others similar to these which are housed at the MCS division of Argonne National Laboratory.

Two types of experiments are being performed:
1) Fixed particle. In this case the particle is constrained to stay at one location while the fluid moves around it.
2) Moving particle. The particle is allowed to move in response to the flow around it. The particles two degrees of freedom are translation and rotation.

What we are interested in doing is in characterizing in great detail the lift and drag of the particle as a function of the Reynolds number, the gap between the particle and the wall, and a parameter that is related to the frequency of the flow. We do this numerically because this experiment has been mostly inaccessible to wet-lab experimental means in the range of parameters that we are interested in.
  • Some Animations

    This is a collaborative effort with Dr. Paul Fischer and Dr. Gary Leaf, from the MCS Division at Argonne National Laboratory

    Sand Ripples:

    We are using an annular sediment dynamics tank to experimentally probe the generation and stability of sand ripples that are generated by the action of a steady shearing force on a bed of loose sediment. The tank is about 1 meter in diameter and has a width of about 2.5 cm. The shear is provided by a powerful motor, which drives a rotor over the water/sediment-filled tank. The topography along the ring is captured by a sequence of video cameras , which are capable of seeing the whole 360 degrees of the tank at once. The system is driven as well as captured by a computer/controller combination , using labview and pcrunner. The sediment will form patterns under steady or oscillatory shearing.
    Movies that show the sediment in motion will be posted here shortly. For now, you'll have to settle for a low-tech short animation. The rotor is the object moving above, the ripples are entirely made up of sand. The whole thing is in water. The bars precess in the direction of the rotor shear. What is striking, as is evident from the space-time plots is that there are bursts of activity in the bars where the bar locally accelerates in the process losing sediment.

    This is a collaborative effort with Profs. Raymond Goldstein and Adriana Pesci, from the Physics department, University of Arizona.

    Last modified: 9 March 2001