# Novel Fluidic Oscillator Evaluation Considering Dimensional Modifications
## 1 Introduction  
Despite the fact that fluidic oscillators (FOs) are commonly used to activate the boundary layer in active flow control (AFC) applications [1; 2; 3; 4; 5; 6], their use as heat transfer enhancers [7; 8; 9; 10; 11], mixing enhancers [12; 13; 14; 15], or as acoustic biosensors [16; 17], among other applications, can be considered. One of the main advantages of FOs versus other active flow control (AFC) methodologies like constant blowing or sucking, resides in the fact that they generate pulsating flow, which reduces the energy required to interact with the boundary layer dynamics and delay its separation in any bluff body [18; 19; 20]. When comparing the different devices capable of generating pulsating flow, there are zero-net-mass-flux actuators (ZNMFAs) and fluidic oscillators (FOs), with the latter having the advantage of not having moving parts, which maximizes their reliability. At present, there are few canonical shapes of FOs and a typical characteristic of all of them is the direct relation between the output frequency and the incoming mass flow. Yet, for a given canonical shape, the dynamic performance depends on the internal configuration as well as the FO scaling [21; 22; 23; 24; 10; 25; 26]. Initial recommendations of how to modify the output frequency of an FO via modifying the inlet width were reported by [PERSON] et al. [27]. A comparison between thesharp corners configuration, initially studied by [27], versus the rounded corners one was undertaken by [PERSON] et al. [28]. It was concluded that the sharp corners configuration generated a more uniform velocity distribution than that from the rounded corners FO. In a further investigation, using the rounded corners configuration previously assessed by [28], [PERSON] et al. [29] observed that when increasing the mixing chamber inlet width, the output frequency tended to raise. It was also noted that rounding the feedback channels decreased separation bubble formation along them. Three-dimensional numerical simulations using the \(k-\omega\) SST turbulence model were conducted by [PERSON] and [PERSON] [30] to study the effect of the mixing chamber (MC) inlet and outlet widths. The MC inlet width considerably changed the feedback channel (FC) flow, unlike what happened when modifying the outlet width. The impact of modifying the mixing chamber and feedback channel lengths on the FO outlet jet frequency and amplitude was numerically evaluated by [PERSON] et al. [31]. Increasing the length of the MC resulted in a considerable decrease in the FO's frequency. No significant variations in the outlet frequency when elongating the FC length were observed. The same observation was noted by [32], but in both studies the flow was considered as incompressible, which is likely to explain the outcome. In a further numerical study performed by [PERSON] and [PERSON] [33], the effect of the feedback channel's (FC's) dimensions was evaluated. Fluid was considered as turbulent and compressible and the 2D-URANS \(k-\omega\) SST turbulence model was used for their study. The FO output frequency increased with an increase in the FC height up to a certain threshold; beyond it, the frequency remained constant. A frequency decrease was observed with an increase in the FC width. The frequency response as a function of the FC length was numerically and experimentally analyzed by [PERSON] et al. [34], who concluded that the FO output frequency decreased as the FC length increased. The same conclusion was obtained by [PERSON] et al. [24] using direct numerical simulations (DNSs) and considering the flow as compressible. It was observed that as the feedback channel length increased, the jet's main oscillation amplitude kept reducing and tended to disappear: the jet was simply tending to fluctuate at high frequencies; when the FC length exceeded a certain length, the main jet oscillations stopped.