Unsteady flow past a finite square cylinder mounted on a wall at low Reynolds number

The flow past a finite length square cylinder resembles flow across a short protrusion or a pin fin in a flow device. Direct numerical simulation (DNS) past a finite length square cylinder has been performed at a Reynolds number of 250. The flow field has been explored by solving three-dimensional unsteady Navier-Stokes equations using second order spatial and temporal discretizations. Four different cylinder height-to-width or aspect ratios (2, 3, 4 and 5) have been used to quantify its effect on the flow field and integral parameters. The cylinder aspect ratio is found to have significant effect on the instantaneous as well as time-averaged flow characteristics. The evolution of various flow structures associated with finite length cylinder such as wakes, tip vortices, base vortices and horse-shoe vortices are discussed. The non-dimensional frequency or Strouhal number and drag coefficient is found to increase with increase in cylinder aspect ratio.