Experimental Fluid Mechanics

Experimental Fluid Mechanics

1. Types of flows

   • Steady/Unsteady flows
   • Laminar/Turbulent flows
     • Intermittency factor
   • Incompressible/Compressible flows
     • Potential flows
       • Vortex flows
         • Counter-part Eddies
   • Invisicid/Viscous flows
     • Shear flows
       • Bounded (wall) flow
         • Boundary layer
       • Free shear flow
         • Mixing layer
         • Wake
         • Jet

2. Flow separation

   • Vortex shedding
     • Karman vortex
     • Strouhal Number
       • Universal = 0.198 or 0.18
       • Relation with Drag

3. Random concepts

   • Brownian motion
     • the erratic random movement of microscopic particles in a fluid, as a result of continuous bombardment from molecules of the surrounding medium.
   • Size of particle
     • Mean free path - the average distance travelled by a gas molecule or other particle between collisions with other particles.
     • Continuum
     • Rarefied
   • Viscosity
     • As a gas is heated, the movement of gas molecules increases and the probability that one gas molecule will collide with another gas molecule increases.  In other words, increasing gas temperature causes the gas molecules to collide more often. This increases the gas viscosity because the transfer of momentum between stationary and moving molecules is what causes gas viscosity. As a liquid is heated, the viscosity decreases ... just the opposite effect as in gases.  Why?  Because liquids have much higher inter-molecular activity and attraction forces that keep the molecules closer together (i.e., that is why they are liquids).  Heating a liquid increases the energy level of the molecules to the point where those inter-molecular forces are weakened and therefore the resistance to flow through the liquid (i.e., the liquid viscosity) decreases.