mechanism of vortices appearance in the taylor-couette flow system

This work is devoted to study the taylor-couette flow at the early structuring stages. it is aimed to gain insight on the taylor and ekman vortices genesis mechanism since the first hints of presence detected at ta=10^-4. simulations are carried out using ansys fluent software package. the basic system geometry is characterized bya height h= 150mm, ratio of inner to outer cylinder radii η= 0.9, radial gap δ= 0.11 and an aspect ratio corresponding to system height reported togap length, г= h/δ = 15. ekman and taylor cells are tackled since the taylor number ta=10^-4 to the first (tvf) and second (wvf) instabilities settlement at tac1= 43.8 and tac2= 54, respectively. it is sought to shed light on the underlying mechanism responsible for flow genesis and to identify all the intermediate successive steps from ex-nihilo when the system is at rest up to complete vortices formation. the obtained results show that presence of ekman cells is already perceptible since a taylor number as low as ta= 10^-4. in fact, localized overpressure zones are detected on system inner endcaps surfaces regularly distributed according to a π/2 phase lag. these overpressure zones azimuthally propagate to meet and cover the entire gap circumference when ta~10^-2 to10^-1.