Effect of Transitions on Flow past a Square Cylinder at Low Reynolds Number

Numerical simulations have been performed for three-dimensional flow past a square cylinder. The cylinders are placed normal to the incoming uniform flow. The results are based on higher order spatial and temporal discretization. The computations are carried out for a range of Reynolds number (100-325). The flow is found to be two-dimensional at R=160 while it becomes three-dimensional at R=163.5. Both Mode-A and Mode-A(*) are observed to be quite prominent and distinct at R=175 though they are present in a range of Reynolds number. The spanwise wavelength for Mode-A is higher than at R=250 where finer-scale structures are observed called Mode-B. The decay rate for primary vortices in Mode-A(*) is the fastest and it is the lowest for Mode-B. The magnitude of secondary vortices of Mode-A(*) is quite high compared to Mode-A, but of comparable magnitude to Mode-B. The effect of transitions on the instantaneous flow and root mean square fluctuations are quite significant while the time-averaged flow does not show any noticeable variation.