Circular flow around a turning point in an annular area between two coaxial porous cylinders Médard Marcus Nganbe, Jacques Hona, Elisabeth Ngo Nyobe and Elkana Pemha Eur. Phys. J. Plus, 134 5 (2019) 236 Published online: 28 May 2019 DOI: 10.1140/epjp/i2019-12593-2