Parametric study and scaling of jet manipulation using an unsteady minijet

A parametric study is conducted for the control of a turbulent jet using a single unsteady minijet. A number of control parameters that influence the decay rate K of the jet centreline mean velocity are investigated, including the mass flow rate ratio Cₘ , excitation frequency ratio fₑ/f₀ and exit diameter ratio $d/D$ of the minijet to main jet, along with the duty cycle ( [STIX]x1D6FC ) of the minijet injection. Extensive hot-wire, particle image velocimetry and flow visualization measurements were performed in the manipulated jet. Various flow structures have been identified, such as the flapping flow, non-flapping flow and that showing a manipulable thrust vector, depending on Cₘ , fₑ/f₀ and [STIX]x1D6FC . Empirical scaling analysis unveils that, prior to the minijet impingement upon the wall of the nozzle and the generation of turbulence, the relationship K=g₁ ( Cₘ , fₑ/f₀ , $d/D$ , [STIX]x1D6FC ) may be reduced to K=g₂ ( [STIX]x1D709 ), where g₁ and g₂ are different functions and the scaling factor [STIX]x1D709=(√MR/[STIX]x1D6FC)(d/D)ⁿ ( √MR≡ Cₘ(D/d) is the momentum ratio and n is a constant that depends on [STIX]x1D6FC ) is physically the effective momentum ratio per pulse or effective penetration depth. Discussion is conducted based on K=g₂ ( [STIX]x1D709 ), which provides important insight into the jet control physics.