# The PIV Measurements of Time-Averaged Parameters of the Synthetic Jet for Different Orifice Shapes
## 3 Results and Discussion
### The Velocity of the Synthetic Jet  
In Figures 5 and 6, the dimensionless time-averaged velocity fields at \(Re=5000\) and \(L_{0}=2\) and \(10\) were presented, respectively. The velocity fields for the circle and square orifices are similar at the same dimensionless stroke length. In the case of the slot orifice, there are significant differences along the long- and short-axis velocity fields compared to the circle and square orifices. It must be noted that the characteristic velocity, \(U_{e}\), of SJ was the same in each case (Table 1). The change of the dimensionless stroke length, \(L_{0}\), was realized by the change of the SJ operation frequency and the real power of the supply. The velocity component discussed in the present section was the time-averaged velocity in the \(x\)-direction. Figure 5: \(Cont.\)Figure 5: Synthetic jet dimensionless time-averaged velocity field at \(Re=5000\), \(St\) = 0.5, and \(L_{0}\) = 2: (**a**) circle orifice, (**b**) square orifice, (**c**) slot-long side, and (**d**) slot-short side. Figure 6: _Cont._  
In Figures 7 and 8, the axial distributions of the centerline dimensionless time-averaged velocity were presented at \(Re=5000\) and \(L_{0}=2\) and \(10\), respectively, while in Figures 9 and 10, the radial distributions of the centerline dimensionless time-averaged velocity were presented. Figure 8: Centerline dimensionless time-averaged velocity axial distribution at \(L_{0}=10\). Figure 6: Synthetic jet dimensionless time-averaged velocity field at \(Re=5000\), \(St=0.1\), and \(L_{0}=10\): (**a**) circle orifice, (**b**) square orifice, (**c**) slot-long side, and (**d**) slot-short side. Figure 7: Centerline dimensionless time-averaged velocity axial distribution at \(L_{0}=2\). 3.1.1. Impact of the Orifice Shape on the Velocity  
For the circle orifice, the time-averaged dimensionless velocity was the highest in the range of \(1<x/d<3.5\) at \(L_{0}=2\) (Figure 5a), and in the range of \(1<x/d<2.5\) at \(L_{0}=10\) (Figure 6a). The SJ expands at the axial and radial directions, but the rate of expansion was higher for a lower dimensionless stroke length (compare Figures 4 and 5). The time-averaged velocity in the vicinity of the orifice tends toward zero due to the fact that the SJA is called the zero-net-mass-flux; similar results were presented in Refs. [23; 24]. The velocity fields for the circle and square orifice are very similar for both values of dimensionless stroke length. The time-averaged SJ velocity field for the circle orifice for \(x/d<2\) was very similar to the time-averaged velocity field determined for continuous jet by [PERSON] and [PERSON] [34] at \(Re=5181\); the similarity between the continuous jet and the SJ was confirmed many times [3; 35; 36]. The dimensionless time-averaged velocity field for the slot orifice is completely different than it is for the circle and square orifices. In the case of the slot-long axis (Figures 5c and 6c), the SJ velocity field in the radial direction contracts at a distance of \(0.5<x/d<2\). In the case of the slot-short axis (Figures 5d and 6), rapid radial expansion is observed. The same phenomenon for the slot orifice was observed by [PERSON] [37] and [PERSON] et al. [24]. The centerline distributions of the time-averaged velocity were presented in Figures 7 and 8. The SJ velocity value tends toward zero near the orifice area, \(x/d=0\). It can be assumed that the result obtained near the orifice (\(x/d<0.5\)) was burdened with an additional error, due to the proximity of the orifice. This is especially visible for the slot-short side dimensionless time-averaged velocity field (Figures 5d and 6d). In this case, the orifice edge  
Figure 10. Dimensionless time-averaged velocity radial distribution at \(L_{0}=10\). Figure 9. Dimensionless time-averaged velocity radial distribution at \(L_{0}=2\). was the smallest (Table 1, \(a=10\)), and therefore the impact of the orifice on the movement of the particles was the highest.