Dept. of Aerodynamics c-cfd Warsaw University of Technology ESPCI

Flow behind sphere - basic info

In general flow behind the sphere can be divided into few stages. First one starts form rest up to Reynolds number 20 when flow is still attached, then in the next stage called first regime the flow is characterised by toroidal axisymmetrical recirculation zone. This is shown in the Fig. 1.

all regimes
Fig. 1 First, second and third regime seen from the top.

With Re=212 (being precise 200-220 depending on the experiment) the flow undergoes first bifurcation and the thread is mirror symmetrical with two counter-rotating vortices.

Approaching second threshold Reynolds number (~275) the flow becomes unsteady and those two vortices start to oscillate forming some kind of spatial spiral vortices. The third regime is characterized by so called Hairpins vortices, and is non-stationary.