Direct particle–fluid simulation of spherical and ellipsoidal particles in turbulent pipe-free-jet flow

Abstract

The dynamics of spherical and ellipsoidal particles in coupled turbulent pipe-free-jet flow at Reynolds number $R{e}_D=15546$ is analyzed by direct particle–fluid simulation. The jet is laden with spherical and ellipsoidal particles with aspect ratios in the range $1\le \beta \le 8$ with a volume loading of $6.67\times 10^{-4}$ supplied by turbulent periodic pipe flow. The flow field is predicted using a finite-volume formulation on an adaptively refined Cartesian mesh. Each particle is fully resolved by a cut-cell method. The method guarantees the conservation of mass, momentum, and energy at the fluid–particle interfaces. To ensure physically correct particle distributions and flow field characteristics, a slicing technique is used to determine the instantaneous solution of a simultaneously computed particle–laden fully-developed turbulent pipe flow that defines the inflow boundary distribution of the jet. The fluid and particle statistics within fully-developed turbulent pipe and free jet flow are investigated independent from each other. Preferential particle distributions, orientations, and time-averaged energy exchange rates are analyzed with emphasis on the impact of the varying particle aspect ratios. The ellipsoidal particles tend to align closer to the particle center than spherical particles in the turbulent pipe. Furthermore, the energy exchange rates and the particle-induced dissipation tend to differ such that the anisotropic particles exchange more energy with the fluid close to the pipe wall. The impact of the particles on the pipe flow influences the turbulent free jet flow for which it serves as inflow condition. Overall, the spreading rate of the particle–laden turbulent free jet is reduced due to the increased fluid dissipation rate. Furthermore, due to the non-spherical particles the kinetic energy of the fluid is lowered by 9% and the turbulence intensity is decreased by approx. 20% at the end of the near field.