Interface-resolved Direct Numerical Simulation Of Unconventional Particulate Turbulent Flows

Particulate flows commonly exist in nature and industry.The understanding of the mechanism of particulate flows is helpful to provide theoretical guidance for the related industries.So far,there have been a variety of the DNS works on general particulate flows.However,there have been only limited works on the DNS of the unconventional particulate turbulent flow coupled with non-spherical particles and non-Newtonian fluid.The fictitious domain(FD)method is used to perform the mechanism of the unconventional particulate turbulent flow.The contents of the present thesis are below:The Bingham fluid model and the double-dispersed model are incorporated into the parallel FD method code.For the spheroidal particles and horizontal turbulent channel flows,the effects of the aspect ratio of the spheroidal particles on the turbulence modulation are studied.Our results show that the flow friction decreases as the prolate particles become more slender or the oblate particles become more flatter.Both effects of the low particle volume fraction in the near-wall region and the relatively small Reynolds stress are important to the occurrences of the drag-reduction by the non-spherical particles.In the near-wall region,the ellipsoidal particles tend to align their major axes parallel to the flow direction with a small positive inclination.For the spheroidal particles and vertical turbulent channel flows,the effects of the spheroidal particles with gravity on the turbulence modulation are investigated at two weak settling effects.The Saffman lift force is important to the particle concentration distribution across the channel.At strong settling effect,the flow friction of the spherical case is the smallest because the large-scale vortices are hindered most.In the vertical channel cases,the orientation of the spheroidal particles show similar orientation results in the neutrally buoyant cases in the near wall region.However,in the core region of the channel,long axis of the spheroidal particles will be perpendicular to the flow direction.For the vertical channel turbulent flow filled with a Bingham fluid,the Bingham number based on the mean velocity and the half channel width is 0.0,0.54 and 3.0,respectively.Our results indi-cate that the yield stess of Bingham fluids has drag-reduction effects by weakening the turbulence and the addition of the particles enhances the flow friction.When the fluid plasticity is strong,the single-phase flow has strong temporal and spatial intermittency.The addition of the particles suppresses such the enormous intermittency and turn the flow into 'turbulence.For the horizontal turbulent channel flows of mono-disperse and bi-dispersed suspensions of finite spheroidal particles,the effects of the particle size and shape are studied.For all bi-dispersed cases,both particle concentration and orientation statistics are similar with respect to those of the mono-disperse cases.