Wontae Hwang

Homogeneous and isotropic turbulence modulation by small heavy (St ∼ 50) particles

(Received 9 March 2005 and in revised form 7 March 2006) The interaction of a dilute dispersion of small heavy particles with homogeneous and isotropic air turbulence has been investigated. Stationary turbulence (at Taylor micro-scale Reynolds number of 230) with small mean flow was created in a nearly spherical sealed chamber by means of eight synthetic jet actuators. Two-dimensional particle image velocimetry was used to measure global turbulence statistics in the presence of spherical glass particles that had a diameter of 165 µm, which was similar to the Kolmogorov length scale of the flow. Experiments were conducted at two different turbulence levels and particle mass loadings up to 0.3. The particles attenuated the fluid turbulence kinetic energy and viscous dissipation rate with increasing mass loadings. Attenuation levels reached 35–40 % for the kinetic energy (which was significantly greater than previous numerical studies) and 40–50 % for the dissipation rate at the highest mass loadings. The main source of fluid turbulence kinetic energy production in the chamber was the speakers, but the loss of potential energy of the settling particles also resulted in a significant amount of production of extra energy. The sink of fluid energy in the chamber was due to the ordinary viscous dissipation and extra dissipation caused by particles. The extra dissipation was greatly underestimated by conventional models.

A Combined CFD/MRV Study of Flow Through a Pin Bank

RANS and time averaged URANS simulations of a pin bank are compared quantitatively and qualitatively to full 3D mean velocity field data obtained using magnetic resonance velocimetry (MRV). The ability of the CFD to match MRV velocity profiles through the pin bank is evaluated using the SST turbulence model. Quantitative comparisons of the velocity profiles showed an overprediction of peak velocity by the CFD at the first pin rows, and a smaller oscillatory error that diminishes as it moves through the pins, resulting in better matching towards the exit.Copyright