Effects of flow oblique angle on three-dimensional steady streaming at low Keulegan-Carpenter number

This paper concerns the effects of flow oblique angle on steady streaming around a circular cylinder in oscillatory flow. Threedimensional (3D) direct numerical simulations are conducted at Keulegan-Carpenter (KC) number of 2 and frequency parameter (β) of 400. The oblique angle is defined as the angle between the incoming flow direction and the direction perpendicular to the cylinder axis. The calculated steady streaming field is studied by way of vorticity cores and streamlines. For the perpendicular incoming flow under the governing parameters specified, mutually interacting vortices along the cylinder span are observed when looking at instantaneous flow structures. The steady streaming results show well-defined vortices distribution as the three-dimensional instability is mostly smoothed out during the time-averaging. For an oblique incoming flow, the existence of an axial flow component changes the features of steady streaming observed for the perpendicular case. The vortical tubes are shortened and obliquely oriented, and the vorticity field near the cylinder surface suffers a decrease in strength. Both the instantaneous flow development and the timeaveraged steady streaming show that as the magnitude of the axial flow component increases, the resulted steady streaming field experiences a gradually reduction of three-dimensionality and eventually switches to two-dimensional.