# Synthetic Jet Actuators with the Same Cross-Sectional Area Orifices-Flow and Acoustic Aspects
## 2 Materials and Methods  
In the paper, three different orifice shapes were investigated-circular, square, and slot (the most often studied shapes of orifices). The cross-section area of orifices was similar, and the geometric parameters were presented in Table 1. Although it is customary to compare orifices with the same hydraulics diameters [16; 18; 36], the authors of this paper believe that it is the cross-sectional area and not the hydraulic diameter that may have a decisive influence on the flow parameters. The SJ is a quick-changing phenomenon and the viscous forces between the fluid and the orifice walls may be less important than flow damping due to a changes in cross-section. The orifice height was equal to a diameter in the case of the circular orifice, as a side length in the case of the square orifice, and as a width in the case of slot orifice. Most often, the orifice height is less than the orifice diameter, and this case can be treated as borderline between the short and long orifices. The orifices were printed from PETG (polyethylene terephthalate glycol-modified) using 3D technology. The thickness of the wall of the orifice was 2 mm. The actuator body was made of PMMA and loudspeaker STX M.18.200.8.MCX was used. The diameter of the actuator cavity was 150 mm, and the height was 20 mm. The SJA was supplied with a sinusoidal signal generator by a Rigol GD4162 and amplified by an AUNA CD-708 amplifier. The current and voltage drops were measured with Keithley 2701 instruments (6.5 digits, 22-bits) with a 7706 all-in-one I/O module. The current was measured as a voltage drop on a reference resistor (1 \(\Omega\), \(\pm\)0.01%). The velocity was measured with a hot-wire anemometer (HWA). The two-wire constant temperature anemometer (CTA) probe connected to the ATU 08 bridge was used. The first wire used for velocity measurements was calibrated in the range of 0.3-49 m/s and the second wire was used for the temperature measurements. The CTA probe was mounted on a 3D manipulator with \(\pm\)0.02 mm positioning accuracy. The sampling rate was 2000 samples per one SJA operation period. The velocity was calculated based on 100 cycles for each single measurement. For example, for a SJA fed with a frequency 40 Hz the sampling frequency was 80,000 S/s and the total number of samples was 8,000,000. The energetic efficiency, Reynolds number, and stroke length were calculated using the method proposed by [PERSON] [25; 37] and [PERSON] [26]. For this reason, the time-mean reaction force of SJA was measured with precision balance RADWAG WTC2000. The resolution of this device was 0.01 g and the range was 2000 g.  
The SPL measurements were made with a Testo 816-1 equipped with a 1/2\" microphone. The equipment was compiled with the requirements of the IEC 61672-1 Class 2 standard. Its measuring range was 35-100 dB (A) in a frequency of 20-8000 Hz. The back-ground SPL of the environment was confirmed to be at least 10 dB lower than the SPL generated by the SJA. Type A frequency weighting was applied to the SPL measurements (SPL (A)). The SPL measurements performed according to the ISO 3746:2010 [38]. A Honeywell HPB200W2 DA-B barometer was used for the atmospheric pressure measurement. The accuracy of measurement was \(\pm\)40 Pa. The air temperature during measurements was in the range of 19-21.5 \({}^{\circ}\)C.  
LabVIEW software with the NI-USB-6211 card was used to all devices control. The photo of some part of the measurement stand and its scheme was presented in Figure 1 and the accuracy of measured values is presented in Table 2.