A turbulent round jet is experimentally manipulated using a pulsed periodic radial minijet placed near the nozzle exit. The actuation is characterized by the frequency $f_a$, duty cycle α, and mass-flow ratio $C_m$. The flow is measured at a Reynolds number of 8000, based on jet exit velocity and diameter, using the techniques of hot wire, flow visualization. and particle image velocimetry. Following Zhou et al. [J. Fluid Mech. 897, A27 (2020)], the jet decay rate of the centerline mean velocity $K$ is employed as a surrogate for jet mixing. The optimum $f_a$ corresponding to the maximum $K$ is observed to be one-half of the preferred mode frequency $f_0$ of main jet, i.e., $f_a/f_0=0.5$. Measurements indicate that $K$ depends on $C_m$ and α given $f_a/f_0=0.5$. It is found that once $K$, ${\mathrm{C}}_m$, and α are corrected and replaced by their “true values” $K^c$, $C_m^c$, and ${\alpha }^c$, $K=g_1\left(C_m,\alpha \right)$ may be reduced to $K^c=g_2\left({\xi }^c\right)$, where $g_1$ and $g_2$ are different functions and the scaling factor ${\xi }^c=C_m^c/{\alpha }^c$, which represents physically the effective penetration depth of the minijet and, unlike previous report, determines uniquely $K^c$. The manipulated jet is further classified into five typical flow structures, i.e., monomodal I, deflection I, bifurcation, monomodal II, and deflection II, which are uniquely determined by ${\xi }^c$. These representative flow structures are connected to the initial interactions between the minijet and the main jet.

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• Turbulence
• Wakes & jets