# Novel Fluidic Oscillator Evaluation Considering Dimensional Modifications
## 6 Results
### Feedback Channel Dimensional Modifications (2D-CFD)
Focusing on the FC mass flow, it can clearly be seen that for the FC1 case, there is no reverse flow; a small amount of fluid is always flowing from the feedback channels towards the mixing chamber; notice as well the small associated peak-to-peak amplitude. As the FC width increases to FC2, there is an almost negligible FC reverse flow, with the peak-to-peak amplitude being slightly higher than in the FC1 case. A further increase in the FC width to FC3 and FC4 generates a drastic increase in the feedback channel reverse flow as well as its peak-to-peak amplitude, with the FC reverse mass flow maximum value being higher than the direct FC value. When observing the variations in the FO outlet mass flow (Figure 18a), it is seen that the oscillation amplitude keeps growingwith FC width. In fact, the oscillation amplitude considerably grows when comparing the FC1 and FC2 cases, but a further increase in the FC width, to FC3 = STD, slightly reduces the amplitude. The FO outlet mass flow's peak-to-peak amplitude remains rather similar for the FC4 and FC3 cases, yet the randomness associated with the oscillations for the FC4 case (maximum FC width studied) is considerably higher than for the rest of the FC widths studied. Note that a higher FO outlet mass flow peak-to-peak amplitude involves a higher swept angle of the jet at the oscillator outlet. Regarding the FO outlet mass flow's oscillating frequency (Figure 18b), the frequency tends to decrease with FC width increases. Yet, for the maximum FC width studied, FC4, there is a sudden increase in frequency; note that for this particular case the FO outlet mass flow's peak-to-peak amplitude shows a decrease while increasing its randomness, very likely due to the large number of degrees of freedom associated with the jet inside the MC. Figure 15: Instantaneous velocity and pressure fields along a full oscillation period divided into 4 equidistant time steps. Minimum feedback channel width, FC1. Figure 16: Instantaneous velocity and pressure fields along a full oscillation period divided into 4 equidistant time steps. Maximum feedback channel width, FC4. At this point it is interesting to recall the work of [14; 26; 35], among others, in which they emphasized the effect on the FO outlet frequency of variations in the MC entrance and outlet widths as well as the FO outlet width. In fact, in [35] they highlighted the ratios FO outlet width/MC entrance width and MC entrance width/FO power nozzle as two of the relations that had a particularly relevant effect on the FO's dynamic performance. Based on the 2D-CFD simulations presented in Section 6.3, we studied the FO outlet mass flow frequency, in Hz, as a function of FO outlet width/MC entrance width \(=(FOo/MCe)\). The relation was \(f(Hz)=26.9845\times(FOo/MCe)^{2}-62.945\times(FOo/MCe)+64.3368\); the coefficient of determination was \(R^{2}=0.9194\); the equation shows a small decrease in frequency as a function of the FOo/MCe ratio increase. We also studied the FO outlet mass flow frequency (Hz) as a function of MC entrance width/FO power nozzle \(=(MCe/FOpw)\), obtaining the relation \(f(Hz)=7.0742\times(MCe/FOpw)^{2}-14.2213\times(MCe/FOpw)+34.8239\)), with the coefficient of determination \(R^{2}=0.9564\). This shows that the FO outlet frequency tends to increase with the \(MCe/FOpw\) ratio. In order to find an equation which summarizes the FO outlet mass flow frequency as a function of the dimensional modifications presented in Sections 6.3 and 6.4, we decided to link the FO's frequency with the time-averaged reverse FC outlet mass flow. We noticed that the trend is the same as that observed for different MC internal angles and it is also the same as observed when comparing the 3D with the 2D simulations. That is, as the time-averaged FC reverse flow increases, the FO outlet frequency decreases.