# The PIV Measurements of Time-Averaged Parameters of the Synthetic Jet for Different Orifice Shapes
###### Abstract  
In the present study, the flow fields generated by a synthetic jet (S) were investigated with particle image velocimetry (PIV). The \(\mathfrak{S}\mathfrak{I}\) time-averaged parameters, such as velocity, turbulent kinetic energy (TKE), and vorticity, were compared by using the Reynolds number (\(Re=5000\)) and dimensionless stroke length (\(L_{0}=2;10\)). Three different orifice shapes with the same equivalent diameter were used: circle, square, and slot. The flow fields of the investigated parameters were presented and discussed at a distance from the orifice \(x/d\leq 10\), and the difference in radial and axial profiles were compared. The impact of the orifice shape and dimensionless stroke length on the investigated parameters was discussed. ZNMF; vorticity; turbulent; TKE; PIV +
Footnote †: journal: Medical Engineering, 2012  
continuous jet at a far distance from the orifice (\(0<x/d<30\), where \(x\) is the distance from the office (m) and \(d\) is the diameter of the orifice (m)) and pointed to the similarity between the continuous jet and SJ at a high Reynolds number and low Strouhal number or high distance, \(x/d\), respectively. In the next part of the Introduction, we focus on the investigations performed using the PIV method. [PERSON] and [PERSON] [16] investigated the evolution of circular and chevron SJ at a constant Reynolds number (\(Re=5000\)). They described the phenomenon of vortex merging, which results in azimuthal disturbances in the vortex ring, and the phenomenon of the formation of longitudinal pairs of vortex structures in the case of circular SJ. The topology of the chevron SJ was more complicated, and the coherence of the axisymmetric ring was replaced by streamwise flow structures by [PERSON] et al. [17]. [PERSON] et al. [17] showed that the turbulent kinetic energy (TKE) increased near the nozzle in the case of the chevron orifice and the TKE decreased at a distance of \(1.5<x/d<4.5\). [PERSON] and [PERSON] [18] used the slug parameters and proved that SJ can be distinguished by two dimensionless parameters: dimensionless stroke length (\(L_{0}\)) and Reynolds number (\(Re\)). The dimensionless stroke length equal to 1 was determined as an SJ formation criterion, whereas [PERSON] et al. [19] determined the axisymmetric SJ formation criterion to be \(L_{0}=0.5\). [PERSON] and [PERSON] [18] described the evolution of SJ and described the values of the Reynolds number and orifice distance (\(x/d\)) for which the formed vortex ring is laminar, transitional, or turbulent. [PERSON] et al. [20] investigated circular and slot SJ for enhanced heat transfer at low Reynolds numbers (50, 300, and 500). The slot SJ characterized the higher TKE and also the lack of coherent structure of the vortex. For this reason, the slot SJ provides a better cooling performance than the circular SJ, especially at a small distance from the orifice. This observation was also pointed out in [21; 22]. However, [PERSON] et al. [22] found that for a far distance from the orifice (\(x/d>5\)), the square SJ is better than the slot SJ. The visualization of the circular, slot, and square SJ was performed by [PERSON] et al. [12]. The similarity between square and circular SJs was indicated. However, the square SJ had azimuthal deformation in a plane corresponding to the diagonal of the orifice cross-sectional area. [PERSON] et al. [12] did not observe longitudinal stream-wise vortices for the square and circle SJ, which were observed by [PERSON] and [PERSON] [16]. These structures were observed for the slot SJ at an aspect ratio of \(AR=5\) (\(AR=b/a\), where \(a\) is the length of the shorter side of the orifice (m), and \(b\) is the length of the longer side of the orifice (m)). [PERSON] et al. [12] observed the vortex bifurcation at \(AR=5\). The impinging SJ configuration is commonly used in the cooling application, and this is the reason for investigating its flow fields. [PERSON] et al. [23] investigated the slot, impinging SJ. They noted the importance of the Stokes number.