Particle Scale Numerical Simulation on Momentum and Heat Transfer of Two Tandem Spheroids:an IB-LBM Study

The cold fluid flowing over two hot spheroids placed in a tandem arrangement was numerically studied via a GPU-based immersed boundary-lattice Boltzmann method(IB-LBM)model.The drag coefficient and average Nusselt number of both the two spheroids were obtained with the main influencing factors investigated.To validate the IB-LBM model,several numerical case studies containing one and two spheres were firstly conducted to reach the good agreement with the previously reported data.Then,a number of simulations were further carried out which were designed by changing the particle aspect ratio(1.0≤Ar≤4.0)and inter particle distance(1.5≤ι≤7.0,whereι=L/D,D stands for the volume-equivalent sphere diameter)as well as the Reynolds number(10≤Re≤200).Their influence on the momentum and heat transfer characteristics between the solid and fluid phases was fully discussed.Numerical results show that,for all the considered Reynolds numbers and aspect ratios,the individual and total drag coefficients and average Nusselt number increase with the inter particle distance.The inter particle distance has greater influence on the drag coefficient and average Nusselt number of the trailing particle than the leading one.The drag coefficient and average Nusselt number of the trailing particle are far less than the leading one under the same working conditions.The prediction correlations for the drag coefficient and average Nusselt number of both the two spheroids were established with low deviations.At last,the influence of the relative incidence angles between the two tandem spheroids on the momentum and heat transfer was studied.It is shown that the relative incidence angles play significant roles due to the change of the frontal area of the leading spheroid with these angles.

Natural Convection in a Concentric Annulus:A Lattice Boltzmann Method Study with Boundary Condition-Enforced Immersed Boundary Method

In this paper,a boundary condition-enforced IBM is introduced into the LBMin order to satisfy the non-slip and temperature boundary conditions,and natural convections in a concentric isothermal annulus between a square outer cylinder and a circular inner cylinder are simulated.The obtained results show that the boundary condition-enforced method gives a better solution for the flow field and the complicated physics of the natural convections in the selected case is correctly captured.The calculated average Nusselt numbers agree well with the previous studies.