Transient three-dimensional flow structures of oblique jet impingement on a circular cylinder

A large eddy simulation (LES) was conducted to visualize the three-dimensional (3D) flow structures of a round jet impinging onto a circular cylinder with an inclination angle of 45°. The Reynolds number of the round jet is 11,800, and the distance from the nozzle exit to cylinder surface is four times the jet diameter. To verify the LES results, planar particle image velocimetry (PIV) measurements were obtained using the same flow conditions. After the impingement, the jet becomes a 3D curved wall jet and is attached to the cylinder wall far downstream due to the Coanda effect. The time-averaged pressure field indicates that the jet attachment is caused by the strong suction pressure after the impingement. However, the instantaneous pressure field reveals that positive and negative pressure bands repeatedly appear with 3D vortex structures near the impinging point. Ring-like rollup structures expand in the circumference direction over time, and weakened vortices are sustained longer in the limited spanwise boundary. The most notable feature is that a clockwise rotational vortex moves down to the wall when the counter-clockwise rotational vortex moves up from the surface, followed by a sign change of the instantaneous wall pressure. The ensemble-averaged velocity fields show good agreement between the LES and PIV results.