# Synthetic Jet Actuators with the Same Cross-Sectional Area Orifices-Flow and Acoustic Aspects
## 3 Results and Discussion
### Differences from Other Studies  
The equivalent diameter is used also in other papers [51]. However, there are a few differences between this article and the most common approach to SJ investigation. Firstly, as a characteristic diameter of SJA, the equivalent diameter was used. Similar to diameter in the case of the circular orifice or the width in the case of slot orifice, it is a dimension parameter. The dimensionless parameter, which is not mentioned in the paper but could be used as a characteristic parameter, is the aspect ratio. However, the aspect ratio for circular and square orifices is equal to \(AR=1\), and in the case of the slot orifice is \(AR=0.25\). As such, this parameter, and the others mentioned, also prevents the tested nozzles from being considered similar.  
Secondly, the orifice height is different for each orifice and is equal to the diameter/side/width in the case of the circular/square/slot orifice. Normally the orifice height is the same for each actuator. It is also a characteristic parameter and affects the parameters of the generated SJ, as for example the Reynolds number, the SJ velocity and the SJA efficiency [47,52], or the SPL [51]. However, these dependencies were not found during this research. This is probably due to the fact that the orifice was short--not higher than the characteristic dimension of the orifice shape.  
The different shape of the orifice makes the topology of generated SJ significantly different [17,53,54]. For this reason, depending on the application, the selected nozzle may perform better or worse. For example, the square and rectangular nozzle are more favorable in cooling applications [16] or in some applications of active flow control [13].  
Despite these three fundamental differences, which seem to preclude comparison of these orifices, the obtained results were surprisingly similar. However, keep in mind that these orifices have the same cross-section area and the ratio of the basic design dimension to the orifice height is an equal one. The use of equivalent diameter allowed for the unification of the results and made the results independent of the orifice shape. This can allow better investigation into how other actuator dimensions affect the SJ parameters or how the SJ topology affects, for example, heat exchange. This idea could also be applied to the measurements performed and published, as it fits in with the geometric parameters used in articles. Of course, the presented data do not include the impact of the SJ topology, which has a significant impact on the application of SJA, for example, in the heat transfer [16, 17, 18,36].  
The consistency of results in the case of the SPL measurements is also worth emphasizing. However, this stability may not be maintained for a larger range of real power, as in [29]. These results are also difficult to compare to others because of the differences that have already been mentioned and the small number of articles dealing with the study of noise generated by the SJA. Performing the tests in accordance with the standard [38] will enable the comparison of results in the future.