Simulation of the turbulent axisymmetric bluff body wake with pulsed jet forcing

The turbulent axisymmetric bluff body wake is studied with a large eddy simulation (LES). The effect of pulsed jet forcing on the wake is investigated. For completeness, the pulsed jet actuator is included in the computational domain. Spectral proper orthogonal decomposition (SPOD) is applied to analyze the wake and the effect of pulsed jet forcing. The numerical results show good agreement with the experimental results and successfully reproduce the dominant modes of the axisymmetric wake. SPOD identifies the axisymmetric bubble pumping mode (${\mathrm{St}}_D=0.06)$, axisymmetric-breaking vortex shedding mode $({\mathrm{St}}_D=0.22)$, and an axisymmetric-breaking mode close to the subharmonic of the shedding mode $({\mathrm{St}}_D=0.1)$. When the high-frequency pulsed jet $({\mathrm{St}}_{\theta }=0.107)$ is applied to the wake, the pressure fluctuation on the base and the azimuthal modes are globally weakened without any mode selection. The mean flow properties show that the inlet flow is driven towards the wake centerline by the high-frequency jet, and the shear layer deviates, forming a concave separation streamline. The entrainment in the wake is suppressed, and the wake is narrowed, leading to a global pressure rise. The high-frequency pulsed jet is concentric and greatly enhances the entrainment in the vicinity of the separation point. A low-pressure region is generated there, which drives the inlet flow towards the wake. Low-frequency forcing $({\mathrm{St}}_{\theta }=0.029$) generates a diffusive pulsed jet which enhances the mixing and entrainment in its trajectory. Low-frequency forcing reduces the wake length and accelerates recirculating flow near the base, leading to a reduction in base pressure, and the vortex shedding mode $({\mathrm{St}}_D=0.2)$ is amplified.