Mixed convection in turbulent particle-laden channel flow at Re _τ = 180

Abstract

A numerical investigation of mixed convection in a turbulent particle-laden channel flow is presented. Using Eulerian-Lagrangian Direct Numerical Simulations (DNSs) within the point-particle approach, the interaction between wall turbulence, particle inertia and thermal inertia, and buoyancy in the two-way coupling regime has been studied. The flow dynamics is controlled by the friction Reynolds number, Richardson number, particle Stokes and thermal Stokes numbers, and the Prandtl number. The effects of particle inertia and buoyancy on fluid and particle statistics are shown for a friction Reynolds number of 180, Stokes numbers ranging from 0.6 to 120, Richardson numbers ranging from 2.72 × 10−4 to 27.2 at a single Prandtl number, 0.71. The results indicate that the effect of particle inertia is significant on particle statistics, but not as pronounced on fluid statistics at the relatively low volume fraction considered. Particle inertia modulates the overall heat flux in a non-monotonic way.

Influence of Coherent Vortex Rolls on Particle Dynamics in Unstably Stratified Turbulent Channel Flows

“…This effect is especially evident for particles with St + = 120 (Figure 9b). As observed in [17], the attenuated turbophoresis can be ascribed to the enhancement of the wall-normal motions induced by increasing buoyancy forces. Consequently, for the case at Ri τ = 27.2, more particles populate the layers more distant from the wall, as evidenced by the bump-shaped concentration profiles for y + ≳ 10 (blue curves in Figure 9b,c).…”

“…The particle feedback on the fluid phase is disregarded, as the primary objective of this investigation is to explore the influence of large-scale coherent structures on particle dynamics, without considering the modulation of fluid variables due to the presence of particles. Moreover, this modulation is expected to be minimal and does not qualitatively modify the flow field, as demonstrated in other works at similar volume fractions [17,43]. Furthermore, within the limit of validity of the one-way coupling regime, the effects of particle collisions are negligible [44] and can be safely disregarded.…”

“…The pre-multiplied spanwise spectral densities of fluid variables at the wall-normal location y + ≃ 20 are presented in Figure 6. For comparison, the spectra for the pure forced convection case at the same Re τ , obtained from the results of Zaza and Iovieno [17], are also shown. At Ri τ = 0.272, the spectra exhibit close alignment with those of the pure forced convection case.…”

“…Several numerical and experimental studies have explored the influence of buoyancy on wall-bounded shear flows, revealing qualitative changes in wall turbulence characteristics and structures under both stable [1][2][3][4][5][6][7][8] and unstable [9][10][11][12][13][14][15][16][17] stratification.…”

“…To date, few works have analyzed the dynamics of a solid dispersed phase in wallbounded flows under thermal unstable stratification [17,31]. The recent numerical investigation by Zaza and Iovieno [31], employing point-particle direct numerical simulations, explored how the interplay between particle inertia, wall turbulence, and heat transfer via both natural and forced convection alters the statistics of both the fluid and the particles in channel flow.…”