07. Turbulence and Flow Instabilities

Free jets are among the most basic flows used in various engineering devices, and the flow characteristics required for jets depend on the engineering device. For example, in reciprocating combustion engines, greater jet diffusion and entrainment are required to burn fuel more efficiently, whereas in air curtains for outside air-blocking devices, the jet is required to maintain flow velocity further downstream without diffusion. Numerous jet-control methods have been investigated to improve these characteristics. One control method is an intermittent jet, in which the flow is repeatedly ejected and stopped. It is known that vortex rings formed in the flow improve the diffusion, mixing, and entrainment of the jet. In addition, multiple jets flowing in the same direction, such as fuel injection from a multi-hole nozzle in a diesel engine, have been applied in various industrial fields, but the effect of intermittent control on the flow in such multiple jets has not been fully investigated. In this study, we conducted a direct numerical simulation (DNS) to investigate the effect of phase differences on the flow characteristics of a multiple intermittent jet consisting of two intermittent jets with the same intermittent frequency when phase differences of 0 (in-phase), π / 2, and π (anti-phase) were applied to the intermittent control of each jet. We discovered that the in-phase causes a switching phenomenon in the flow, the anti-phase causes the flow to deflect, and a phase difference of π / 2 causes the flow to expand.

Prof.

Mamoru Takahashi