Optimal Injection Condition of a Single Pulsed Vortex Generator Jet to Promote the Cross-Stream Mixing

The Flow Structure Produced by Pulsed-jet Vortex Generators in a Turbulent Boundary Layer in an Adverse Pressure Gradient

“…It is not surprising then, that increasing the velocity ratio of pulsed jets also increases the circulation of the generated streamwise vortices [29]. In addition, a higher velocity ratio means that the vortex generated by a jet pulse can propagate further into the boundary layer towards higher-velocity fluid, where momentum transfer is more effective [13,27]. Peaks in wall shear stress are also observed to strengthen with increasing velocity ratio [10].…”

“…The flow structure and momentum transfer process between continuous and pulsed jets are observed to be very similar shortly after activating the pulse [22,27]. During this period, the pulsed jet can be thought of as being quasi-steady and increasing the duty cycle merely increases the length of this period.…”

“…This in effect varied the duty cycle which produced amplitude-modulated variations in the streamwise velocity of the boundary layer. Suzuki et al [27] observed the development of a stable period of jet output in between the start and end of the pulse cycle. The jet output in this period was comparable to that of a continuous jet at the same conditions.…”

“…Studies on boundary layers have failed to find any strong dependence of wall shear stress, or the strength of streamwise vortices on pulsation frequency [1,27,29]. However, Johari and Mc Manus [13] showed that jet penetration can depend on the jet pulsation frequency.…”

Numerical Investigation and Feasibility Study of a PZT-driven Micro-valve Pulsed-jet Actuator

“…In accordance with this estimate it was considered that in order to function satisfactorily as a vortex generator the orifice exit speed for the pulsed jet actuator would need to be at least 100 m/s. This is because velocity ratios between orifice exit and mainstream flow of the order of one to two have been found to produce effective vortexgenerator control with pulsed jets [12,13], although higher values are often used. We have used 100 m/s as the target exit velocity where appropriate in the illustrative calculations presented later.…”