Bi-stability Detection in the Flow Around a Sphere by Means of Experiments and Lattice Boltzmann Simulations

Abstract

With the aim to detect bi-stability in the highly separated flow around a sphere mounted on a cross-stream rod, wind tunnel measurements and numerical simulations with a Lattice Boltzmann method (LBM) are performed and compared. In both, LBM simulation and experiment, a bi-stable flow behaviour is detected at a Reynolds number of Re=105 based on the sphere diameter, the inflow velocity and the kinematic viscosity, whereas such behaviour is absent at Reynolds numbers as high as Re=3×105. The bi-stable behaviour detected in the time series of the aerodynamic side force acting on the sphere for Re=105 is reflected by a bi-modal probability density function. For Re=3×105, on the contrary, the probability density function is nearly Gaussian. Further, in agreement with the experiment, two counter-rotating vortex tubes originating from the intersection of the leeward and cross-stream rod-ward side of the sphere are generated.