Viscous dark energy accretion activities : sonic speed, angular momentum and Mach number studies Sandip Dutta, Promila Biswas and Ritabrata Biswas Eur. Phys. J. C, 81 4 (2021) 348 Published online: 22 April 2021 DOI: 10.1140/epjc/s10052-021-09124-6