Abstract: The Synthetic Jet (SJ) control on the propulsion behavior of a foil in plunge-pitch motion is examined in this work by numerical simulations. An elliptic foil with ratio of 8 performs the plunge and pitch motions synchronously. A pair of SJs with the same frequency and strength is integrated into the upper and lower surfaces of the foil. As a result, the local flow field around the foil could be obviously modified by the SJs. At the Reynolds number of 200, the effects of the inclined angle between the jet direction and the chord line, the phase angle between the SJs and the flapping motion as well as the location of SJ on the propulsion performance are systematically investigated. Compared with the pure plunging and pitching foil, it is indicated that the enhancement of mean thrust and propulsive efficiency can be obtained by the SJs with suitable working parameters. Based on the numerical analysis, it is found that the jet flow on the foil surfaces, which changes the local pressure distribution to increase the pressure difference between upper and lower surfaces, can benefit the propulsion behavior of the flapping foil.

Key words: propulsion behavior, plunge-pitch motion, elliptic foil, synthetic jet