Characteristics of the near wake region behind a cylinder at critical and super-critical Reynolds numbers

Large-eddy simulations (LES) of the flow past a circular cylinder are used to investigate the characteristics of the near wake region at Reynolds numbers Re = 2.5 x 10(5) - 8.5 x 10(5). This range encompasses both the critical and super-critical regimes. Wake characteristic lengths are measured and compared between the different Reynolds numbers. It is shown that the super-critical regime is characterised by a plateau in the drag coefficient at about C-D approximate to 0.22, and a quasi-stable wake which has a width of d(w)/D approximate to 0.4. Power spectra of the lift fluctuations are computed. Wake vortex shedding is found to occur for both regimes investigated, although a jump in frequencies is observed when the flow enters the super-critical regime. The analysis also shows a steep decrease in the fluctuating lift when entering the super-critical regime. Furthermore, the analysis of the turbulent statistics shows that after the changes occurring at critical Reynolds numbers, the wake enters a regime where its dynamics is quite similar regardless of the Reynolds number.