L. Djamil  , 
    Numerical Study of the Instability Patterns Between Counter Rotating Disks,
    Journal of Engineering and Applied Sciences,
    Volume 3,Issue 1,
    2008,
    Pages 1-6,
    ISSN 1816-949x,
    jeasci.2008.1.6,
    (https://makhillpublications.co/view-article.php?doi=jeasci.2008.1.6)
    Abstract: The flow between counter-rotating disks for aspect ratio R/h = 7, is investigated numerically. This flow gives rise to a new instability pattern, a circular chain of vortices connected to the boundary layers trough spiral arms. The physical mechanism for this instability is elucidated: the balance between the centrifugal effects of each rotating disk results in the detachment of the boundary layer over the slower rotating disk, leading to a free shear layer in the bulk of the flow, witch becomes unstable via a Kelvin-helmholtz-type instability.
    Keywords: Rotating flows;flow between disks;shear instability;pentagonal patterns