A TECHNIQUE FOR FLUID VELOCITY MEASUREMENTS IN THE PARTICLELAGRANGIAN REFERENCE FRAME

摘要

The goal of this paper is to present a technique formeasuring fluid velocities in the reference frame of a solidparticle in air and to compare data obtained using this techniqueto existing data. The particles are assumed to have muchgreater density than the surrounding fluid and the flow aroundthe particle is Stokesian. The modeling of the particles requiresthat the fluid turbulence statistics are measured in the referenceframe of the moving particle (particle-Lagrangian referenceframe). In this investigation, the path of a solid particle isemulated by mounting a two component laser velocimeter (LV)system to a two-dimensional traverse system. The fluid velocityin two components is measured by the LV and then sent to thecomputer. The instantaneous acceleration that a real particlewould undergo in each direction is calculated using themeasured fluid velocity and the Stokes transport equation.When, the traverse has reached its new desired velocity (5 ms),the fluid velocity is measured and the sequence repeats. Thisprocess is repeated 100 times per second compared to anestimated Kolmogorov time scale of 200 msec. The probevolume of the LV system is therefore continually at the locationof the “emulated” particle. The attainable Reynolds numberbased on channel half-width and centerline velocity ranges from1800 to 12,000. Results were compared to direct numericalsimulation results. Fluid velocity autocorrelation coefficientsare shown for both the Eulerian and particle-Lagrangianreference frames.