Moving sphere simulations using the chimera grid approach

Steady and unsteady cases with moving spheres were computed using the Chimera Grid Approach and OVERFLOW, a compressible Reynolds Averaged Navier-Stokes flow solver. The cases modeled situations encountered with agricultural seeding machines. Central differencing with scalar TLNS3D dissipation for spatial terms and implicit Euler time advancement were used. First, a sphere moving with a constant velocity away from a suction orifice was computed and the resulting forces were compared with experimental values. Second, one sphere was dropped and allowed to move under the influence of aerodynamic and gravitational forces with six degrees of freedom. Third, two spheres were dropped similar to the second case this time taking collisions between the two spheres into account. The force data compared with experimental data averaged an 8% error for 3.5 kPa suction out of the orifice, and 13% for 1.75 kPa suction out of the orifice, and 4% error for a 3.5 kPa suction case with second order dual time stepping. For the sphere drop cases, the desired behavior was known by experimentalists, and was achieved with minimal error. Testing on 8 to 96 processors with a 6.616 million grid point mesh demonstrated nearly linear speedup. Through the investigation, it was shown that the Chimera Grid Approach used with OVERFLOW is a valid choice for moving mesh applications.