In this project, the vectoring behaviour of a pair of parallel synthetic jets is investigated using particle image velocimetry. The synthetic jets are vectored using a phase difference between the driving signals. Using a fixed phase difference, the vectoring behavior can be controlled by changing the Strouhal number (St = f d/u, with f the frequency, u the mean blowing velocity and d the orifice width).

Time-averaged flow fields of the normalized velocity magnitude are shown below. These flow fields show merged and bifurcated jets in multiple directions. Differences are investigated using phase-locked vorticity distributions. The tracking of vortices shows that the vectoring behaviour for a fixed phase difference depends on the pinch-off time of the vortices, which is a function of the Strouhal number. The physical mechanisms that explain the diversity in vectoring behaviour are observed based on the vortex trajectories.

The included angle between the branches of each jet and the momentum flux contained in these branches are analysed. It is shown that the included angle decreases linearly with Strouhal number for the results shown below. The normalized momentum flux increases with Strouhal number for low Strouhal numbers and then decreases towards the synthetic jet formation criterion (St = 1/π).

​These relations to the Strouhal number enable control of the included angle and momentum flux, based solely on the Strouhal number. This can be used in flow control applications. One such application is a forward facing step, illustrated below. The flow over a forward facing step typically creates a separation bubble in front of step, as well as on top of the step. By placing a bifurcated synthetic jet in front of the step, and controlling the included angle and momentum flux, both separation regions might be controlled. The use of the described synthetic jets in a flow control application is the goal of future research.

PhD Student: Tim Berk

Supervisor: Prof. Ganapathisubramani

​Vectoring of parallel synthetic jets