Measurement of fluid turbulence along the path of a heavy particle in a backward-facing step flow

To accurately model the motion of a solid particle in a turbulent air flow, characteristics of the fluid turbulence in the particle-Lagrangian reference frame must be known. This paper describes a quasi-numerical technique that uses a laser Doppler anemometer (LDA) probe mounted on a two-dimensional traverse to track the path of an emulated particle through a turbulent backward-facing step flow. Fluid velocity measurements (from the LDA) are inputs to a control loop that accelerates the LDA probe as if it were a particle allowing for particle-Lagrangian fluid statistics to be measured. Particles with time constants from 0.1 to 10 s were run through a backward-facing step flow with Reynolds number 10,000 based on step height and inlet velocity. Digital particle image velocimetry (DPIV) was used to estimate the fluid vorticity along the particle path. The results show that the particle behavior is a strong function of particle path. Particles entering the shear layer see a larger range of turbulence and therefore are more affected by the flow than those that stay outside the shear layer.