Challenging bulk viscous unified scenarios with cosmological
  observations
  In a spatially flat Friedmann-Lema\^{i}tre-Robertson-Walker universe, we
investigate a unified cosmic fluid scenario endowed with bulk viscosity in
which the coefficient of the bulk viscosity has a power law evolution. The
power law in the bulk viscous coefficient is a general case in this study which
naturally includes several choices as special cases. Considering such a general
bulk viscous scenario, in the present work we have extracted the observational
constraints using the latest cosmological datasets and examine their behaviour
at the level of both background and perturbations. From the observational
analyses, we find that a non-zero bulk viscous coefficient is always favored
and some of the models in this series are able to weaken the current tension on
$H_0$ for some dataset. However, from the Bayesian evidence analysis,
$\Lambda$CDM is favored over the bulk viscous model.
