Absolute instability of the boundary-layer flows due to rotating a spheroid S. Khan, A. Samad, Department of Mathematics, University of Peshawar
This paper explores local absolute instability in the boundary layer flow over two distinct families of rotating
spheroids (prolate and oblate). While convective instability was established in earlier work by Samad and
Garrett [1], this study delves into the potential occurrence of local absolute instability. Some results of local
convective instability under the assumption of stationary vortices are reproduced for a more comprehensive
investigation. The analysis considers viscous and streamline curvature effects, demonstrating that the localized
mean flow within the boundary layer over either family of the rotating spheroid is absolutely unstable for each
fixed value of the eccentricity parameter ???? ∈ [0, 0.8]. For certain combinations of Reynolds number ???????? and
azimuthal wave number ????, a third branch (Branch 3) of the dispersion relation intersects Branch 1 at a pinch
point, indicating absolute instability. Neutral curves depict regions that are absolutely unstable, while below
critical Reynolds numbers, the region is either convectively unstable or stable. The paper also illustrates the
effect of increasing eccentricity on spatial branches within both convectively and absolutely unstable regions.
From lower to moderate latitudes, the stabilizing effect of ???? on the onset of absolute instability is robust for
the prolate family and almost negligible for the oblate family. At high latitudes of the prolate spheroid, the
stabilizing effect of ???? is fainter but persists until close to the equator. Conversely, at high latitudes of the oblate
spheroid, the stabilizing effect of ???? is more pronounced. The paper discusses the implications of the parallel
flow assumption employed in the analyses.