Numerical Analysis on Effect of Jet Injection on Vortex Shedding for Flow Over a Circular Cylinder

摘要

Two-dimensional numerical investigations on the flow characteristics past a circular cylinder with a jet injection at the rear stagnation point are performed. Transient, incompressible, laminar, and isothermal flow governing equations are solved with finite volume method. Numerical simulations have been carried out at a Reynolds number of 150 with different injection ratios (IR) ranging from 0.5 to 7. Time evolutions of the coefficients of drag and lift, and streamline patterns are plotted. Three different flow pattern ranges are observed, namely wake dominant (IR0-1.5), transition (IR1.5-2.5) and jet dominant (IR2.5), and they are characterized by the combined effects of vortex shedding, undulation and jet dominant phenomena appearing in the flow downstream. It is also found that Cd decreases slightly with the injection ratio up to 1.5, after that it monotonically increases with the injection ratio. The similar incremental trend is observed in the Strouhal number variation with IR up to 1.5; then, it increases almost linearly till IR4. When IR is greater than 4, there is a sudden drop in the Strouhal number value equal to zero and it remains constant after that for all the IR values considered in this study. The power spectral density of Cl indicates that the dominant frequency is present for the lower IR up to 4 and that no dominant frequency appears in the higher injection ratio range of 5-7 due to a complete suppression of the vortex shedding behind the cylinder by a dominant jet mechanism.