Upstream velocity fields induced by frontal jet injection in a square cylinder.

The flow characteristics around the frontal face of a square cylinder with a frontal jet injection were experimentally studied in a closed-loop wind tunnel using the PIV technique. Four characteristic flow modes were identified based on the injection ratio: swinging jet, deflected oscillating jet, deflection jet, and <italic>penetrating jet</italic>. At low injection ratio, the flow mode denoted as the <italic>swinging jet</italic> is characterised by two recirculation regions and a four-way saddle point. At moderate injection ratio, the flow mode termed <italic>deflected oscillating jet</italic> is characterised by a recirculation region and a counterclockwise rotating vortex within the recirculation region. At moderately high injection ratio, the flow mode is denoted as <italic>deflection jet</italic>, where a clockwise rotating vortex appears in the flow field. At high injection ratio, the flow mode is termed as <italic>penetrating jet</italic>, with no vortex formation in the flow field. The strength of the turbulence intensities increases considerably with high injection ratios. The time histories of instantaneous velocity for non-injection case, <italic>swinging jet</italic>, and <italic>deflected oscillating jet</italic> modes show periodic oscillations, whereas those of <italic>deflection jet</italic> and <italic>penetrating jet</italic> modes do not show periodic oscillations. The study presents and discusses the time-averaged velocity vectors, and streamlines, vorticity contours, velocity properties, velocity time histories, and power spectral density function under different flow modes. [ABSTRACT FROM AUTHOR]