CFD of Flow Dynamic and Heat Transfer Characteristics of Dual Step Cylinders at Re = 2100

Three-dimensional flowfields over a uniform and dual step cylinder with an aspect ratio and diameter ratio of 2 at Reynolds number of 2100 are computed numerically. A new configuration of dual step cylinder with a diameter ratio of 0.5 is also considered in the investigation. Diameter ratio of 2 and 0.5 is referred to as step-up and step-down cylinders, respectively. Heat transfer rate predictions for the three configurations for surface temperature of 273 K, 473 K and 673 K are performed. Reynolds averaged Navier Stokes equations are solved, and turbulent stresses are computed using k-ω SST model. The effect of step discontinuity on the flowfield, drag coefficient, coefficient of pressure and heat transfer rate is investigated. The structure of the flow in the wake is significantly different for step-up cylinder compared to that of the uniform and step-down cylinders. The velocity deficiency in the wake of step-up cylinder is high and leads to formation of locally high-pressure region. This high-pressure region induces strong vortices in the span-wise direction. Such vortices in the spanwise direction are not noticed for step down and uniform cylinders. In the wake region, coefficient of pressure is highest for step-up cylinder, and step-down cylinder has lowest value. Temperature distribution in the wake of step-up cylinder is found to be more uniform compared to rest of the two configurations. Heat transfer rate of step-up cylinder at the nose stagnation point of mid-plane is 27% lower compared to that of uniform cylinder. In the wake region, uniform cylinder found to have 34% higher heat transfer rate. The effect of step discontinuity on the drag coefficient found to be minimum.