Direct Numerical Simulations (DNS) based on MAC Method are performed at different Reynolds numbers and blockage ratios. DNS helps in predicting flow field, variation of drag coefficient, non-dimensional frequency called Strouhal number at different values of Reynolds number and blockage ratios. The study is performed at different blockage ratios (β), ranging from 0.1 to 0.9, to study the effect of blockage ratios on fluid flow stability and critical Reynolds number. Also, linear stability analysis is used to understand the fluid dynamics observed. A set of partial differential equations governing the perturbed fluid flow are solved numerically and attempt is made to calculate the precise values of Reynolds number and blockage ratio at which different bifurcations in fluid flow are observed. © Springer India 2017.