Numerical study of circular synthetic jet formation and comparison with other jet pulsation patterns at Low Reynolds numbers

In this paper, circular synthetic jets at low Reynolds numbers issued into quiescent flows are numerically studied. A 2D axis-symmetrical numerical model is developed in a CFD solver FLUENT and particularly a species model is used to virtually exhibit the jet formation/development. The model is validated by comparing the numerical results with reported PIV data and dye visualisation. It is found that the jet formation criterion (the dimensionless Stokes length L > 0.5) proposed by Holman et al. [16] is not sufficient and the Stoke number (S) and Reynolds number (ReUo) also play an important role in the jet formation. Hence, two parameter maps regarding S versus L and S versus ReUo are depicted, which is of crucial importance to optimize synthetic jet operational conditions and/or predict desired synthetic jet structures. It is shown that a jet train is formed as long as S > 2 and L > 0.5. In addition, as ReUo > 70, the synthetic jet with rollup is formed, while as ReUo 2, no jet train can be formed. Moreover, the flow behaviour of the synthetic jet is compared with other jet pulsation patterns including continuous, intermittent and pulsating jets at low Reynolds numbers. It is observed that the intermittent jet generates a similar flow structure with the synthetic jet, where the pulsating jet as the superimposition of continuous and synthetic jets demonstrates a significant improvement on the jet penetration and enhancement of heat and mass transfer.