## 1 Introduction  
The synthetic jet (S)) is generated by the expulsion and injection of fluid into a closed cavity through an orifice or a nozzle. Firstly, the fluid is sucked into the cavity, and then expulsed as a jet. The jet is not being sucked to the actuator but moved away from the orifice and the vortices are formed at its edge. In this way, nonzero mass flow is synthesized at some distance from the orifice. However, because the time-mean mass flow in the orifice is zero, the SJ is called zero-net-mass-flux (ZNMF). The schematic way of SJ generation was presented in Figure 1. The synthetic jet actuator (SJA) can move the fluid using a loudspeaker [1], piezoelectric transducer [2], piston [3], or plasma [4]. The SJ has many applications and can be used in electronic cooling [1, 3], mixing enhancement [4, 5], flow control [6, 7, 8], or underwater propulsion systems [9, 10]. Especially the first area of the SJ application is now developed and new types of actuators [11, 12] are still developed to increase the efficiency of the cooling system. However, the use of the SJA in a cooling system is limited by the sound pressure level (SPL) specified in standards e.g., in EN ISO 9241-6:2002 [13]. The negative effect of noise on physical and psychological well-being was proven many times [14, 15], and the noise level is included during the design of the work environment [16]. The SPL generated by the SJA is quite high and can be equal even to over 90 dB [17]. However, the noise is usually not so high and fluctuates close to 60 dB [18, 19]. It makes that the way to reduce the SPL is sought, and the use of the chevron orifice is one of them. The chevron nozzles are used mainly in aircraft to create the secondary jet crossed with primal jet. The cutouts in a nozzle wall induce stream vortices and that enhancement mixing between adjacent streams and in that way reduce the velocity gradient and as a result the noise [20]. The impact of the chevron edge of the nozzle on the flow structure and noise reduction was confirmed numerically [21, 22] and experimentally [23]. The turbulent structure of the jet flow through the chevron nozzle makes that it can be used to heat transfer enhancement in impinging continuous jet, and also in impinging SJ [24, 25]. The SJA with the chevron nozzle was investigated by [PERSON] et al. (2018, 2019, 2020). They investigated mainly the difference in flow organization in the case of SJ generated by the actuator with the circular nozzle and the chevron nozzle. The cutouts in the chevron office generate the streamwise vortices that alter the shape of the vortex ring (2018). It made that the vortex ring is not circular but more complex, but dissipate faster than vortices in the case of the circular nozzle. [PERSON] and [PERSON] (2019) showed that the time-average centerline velocity is the same for chevron and circular SJ in a distance \(x/d=6\), where \(x\) is an axial distance from the orifice and \(d\) is an orifice diameter. During, the centerline momentum velocity was the same, regardless of the type of orifice. The other flow organization impact also on the time-averaged turbulent kinetic energy distribution. The chevron SJ topology affects the distribution of the Nusselt number on the cooling plate in the case of impinging SJ application. In effect, the chevron synthetic jet shows better heat transfer characteristics than the circular synthetic jet (2019). The impact of the chevron orifice on the heat transfer enhancement was also confirmed by [PERSON] et al. (2019). [PERSON] et al. (2019) showed that except for the noncircular vortex ring the chevron SJA generated also the counter-rotating streamwise vortices in cutouts of the orifice. These structures have a significant impact on heat transfer enhancement. [PERSON] and [PERSON] (2019) investigated the SPL of SJA with a chevron orifice. The orifice had the same number of chevrons but differed in the height of cutouts. Depending on the actuator power, the chevron orifice can decrease the noise generated by the actuator.