  In this work, a numerical scheme based on a level-set immersed boundary
method is employed for the numerical simulation of the flow around two tandem
circular cylinders in the subcritical flow regimes. Three different spacing
ratios $\ell/\mathcal{D}$ (where $\ell$ is the center-to-center distance
between the two cylinders with $\mathcal{D}$ being the diameter of the
cylinders) from $2$ to $4$ is considered. The instantaneous flow structures,
pressure distributions and hydrodynamic forces on two tandem cylinders are
analyzed at a Reynolds number of $\mathcal{R}\mathfrak{e}=2.2\times 10^4$. The
strategy is based on a combination of a narrow-band accurate conservative level
set method and ghost-fluid framework. In this strategy, the interface is
defined as the isocontour of a hyperbolic tangent function, which is advected
by the fluid, and then periodically reshaped to enforce the degraded level set
function being a signed distance function using a reinitialization equation
based on an improved form. The latter approach takes advantage of a mapping
onto a classical distance level set while much better preserving the interface
shape.
