The flow past rodlike cylindrical fibers with circular cross section is involved in many industrial and natural processes, such as bubbling fluidized beds, pulp and paper making or the sedimentation of ice crystals in clouds. Despite the large number of studies devoted to the flow past a circular cylinder held perpendicular to the incoming flow in the laminar and transitional regimes, much less is known when the body is arbitrarily inclined or even aligned with this incoming flow. In the first part of this thesis, the flow past a finite-length circular cylinder, the axis of which makes some angle with the uniform incoming flow, is studied numerically from creeping-flow conditions to the first non-stationary regimes. Three dimensionless parameters then govern the problem when the upstream flow is steady and uniform : the aspect ratio ,, the inclination angle which is the angle between the cylinder axis and the incoming velocity, and the Reynolds number. The investigation focuses on the way these parameters affect the flow structure past the body, the transition mechanisms in the wake and the hydrodynamic loads up to Re = 400. In the specific case where the cylinder is aligned with the upstream flow, influence of the aspect ratio and inertial effects in the low-to-moderate Reynolds number regime is examined by comparing numerical results with theoretical predictions provided by the slender-body approximation. When the cylinder is inclined with respect to the incoming flow and inertial effects are dominant, three distinct types of vortex patterns, all preserving a symmetry plane, are observed in the wake past cylinders with aspect ratios in the range 3-7, depending on Re and ,. The wake structure involves a steady pair of counter-rotating streamwise vortices up to Re=330. In this regime, for large enough Re and an open separation region emanating from the leading edge takes place along the upstream part of the lateral surface of the cylinder. This structure has a deep influence on the flow structure in the vicinity of the body and on the surface stress distribution. Beyond Re330, increasing the inclination angle first leads to a regime in which double-sided hairpin-shaped vortices are shedded downstream, while another regime characterized by the shedding of single-sided hairpin vortices takes over for large enough inclinations. Based on the numerical results, drag, lift and torque approximate models valid in the range 20Re400 are built for inclined cylinders of arbitrary aspect ratio. While the force perpendicular to the cylinder axis follows a remarkably linear law, the axial force and the torque are found to exhibit complex dependencies with respect to the three control parameters. In the seond part, we investigate the torque on a finite-length cylinder rotating perpendicularly to its axis of symmetry. The ratio of the length of the cylinder to its diameter varies from 1 to 15. In the creeping flow regime, we find a good agreement with the slender body theory for sufficiently long cylinders. For shorter cylinders, we propose a modification of the theory which matches well the numerical results. In inertia-dominated regimes, a noticeable wake develops, made of two pairs of counter-rotating vortices. We show that, due to symmetry properties, the upstream and downstream disks do not contribute to the shear-induced torque on the body. However, the pressure contribution of the two disks are significant and cannot be neglected particularly for short cylinders. We show that the shear stress on the lateral part of the body varies as the inverse of the square root of the Reynolds number, as predicted by the boundary layer theory. Based on the previous observations, we present an empirical formula for the torque which matches well the numerical results over the entire range of Reynolds number and aspect ratio studied here.