# Novel Fluidic Oscillator Evaluation Considering Dimensional Modifications
## 6 Results
### Assessment of Forces Acting on the Jet at the Mixing Chamber Entrance  
To illustrate the effect of the forces acting on the jet as it enters the mixing chamber, two cases were chosen: The minimum FC width case, FC1; and the entrance 1 case, where the angle was \(\delta_{1}=\delta_{STD}+15\). These two particular cases were chosen because they properly clarify the variations in the unsteady force curves when there is no FC reverse flow and when there is a large FC reverse flow. For the smallest FC width, FC1, Figure 20 introduces, for over half an oscillation cycle, the unsteady forces acting on the feedback channels' outlets. Figure 19: All graphs introduce the variations for the four feedback channel widths studied. Unsteady stagnation pressure measured at the mixing chamber lower inclined wall (**a**), time-averaged values and peak-to-peak amplitudes (**b**). Pressure momentum terms measured at the FC lower outlet (**c**) and their respective average values and peak-to-peak amplitudes (**d**). Dynamic mass flow momentum terms measured at the FC lower outlet (**e**), and their respective average values and peak-to-peak amplitudes (**f**). Instantaneous net momentum obtained when considering pressure and mass flow momentum terms at both FC outlets (**g**), average values, and the peak-to-peak amplitudes (**h**). The upper graph represents the mass flow forces acting over the jet on each FC outlet. The central graph characterizes the pressure forces acting on the same FC outlets; for convenience the pressure force acting on the upper FC outlet is represented as positive. The lower graph introduces the overall forces acting on the jet as it enters the MC. The same information, but for the entrance 1 case, characterized by \(\delta_{1}=\delta_{\mathrm{STD}}+15\), is presented in Figure 21.  
Regardless of the case studied, the mass flow forces at the lower FC outlet always push the jet upwards; these forces always push the jet downwards on the upper FC outlet. The mass flow forces for the entrance 1 case, due to the larger FC mass flow associated, are about five times larger than those observed in the FC1 case. When comparing the pressure forces from Figures 20 and 21, it is seen that for the FC1 case the curves oscillate rather smoothly, while the periodic-like oscillation observed in the entrance 1 case has an associated ripple superimposed on the pressure curves. This pressure ripple is observed in all cases where large FC reverse flow exists. As a consequence, this pressure ripple is also observed in the total net force curve presented at the bottom of Figure 21; note that this curve is rather smooth in Figure 20. Note as well that pressure forces are always several orders of magnitude higher than mass flow forces, thus indicating that smaller variations in pressure fields generate large forces on the jet. To understand the origin of the pressure ripple it is necessary to compare the velocity and pressure fields in the FO (see Figures 22 and 23), with the pressure forces acting on the jet. At a time of 1.357 s, Figure 23a,b, the lower FC is pressurized, the jet is being pushed upwards, the pressure forces on the lower FC outlet are higher than those on the upper one, as shown in Figure 21. At this instant, a large FC reverse flow is observed at the upper FC. A few milliseconds later, at about 1.36 s (see Figure 21), the upper FC reverse flow meets the MC central jet at the MC's upper converging wall (upper FC inlet); at this instant the pressure oscillations are particularly large and keep decreasing as the MC jet reaches its upper-most position and starts moving downwards; see, for example, Figure 23c,d and the corresponding pressure force curves in Figure 21 at a time of around 1.37 s. In fact, from this time and until around 1.405 s, the pressure force at the upper FC outlet is pushing the jet downwards; see the stagnation point at the upper MC's converging wall (Figure 23d) and the pressurization of the upper FC in Figure 23f.