## 5 Results
### Modifying the (Mc) Inlet Width
Figure 5: Dynamic effects of the (MC) inlet width modification on the main flow parameters, Reynolds number 16034. Each graph presents three non-dimensional curves characterizing results from the baseline, the lowest inlet width and the highest inlet width cases, and as a function of the dimensional time. In figure (**a**) the mass flow across the upper oscillator outlet is presented. Figure (**b**) introduces the temporal variation of the (MC) inlet inclination angle. Figure (**c**) presents the pressure at the (MC) lower inclined wall. The net momentum acting on the lateral sides of the main jet is presented in figure (**d**). Figure (**e**) characterizes the mass flow at the lower feedback channel outlet. When observing the effects of the inlet width on the (FC's), Figure 5e, it is seen that, at small inlet widths the average mass flow is about zero, the flow inside the (FC's) is moving in both directions, yet the mass flow entering the (FC) outlet, reverse or negative flow, appears to be higher than the flow leaving such surface. If the inlet width would be further decreased, the reversed flow would keep increasing, eventually stopping the oscillation. As the inlet width increases, the mass flow inside the (FC's), although periodic, has a positive average value, meaning, there is a net mass flow moving from the feedback channels inlet to the outlet, at high inlet widths there is no reverse flow in the (FC's). The reason why at small inlet widths there is reverse flow in the (FC's), is the small stagnation pressure points generated alternatively at the (FC's) outlet internal vertical walls. It is also relevant to highlight that, the peak to peak amplitude of the net momentum driving the jet oscillations inside the mixing chamber, is particularly small when the lowest inlet width is employed, Figure 5d, the jet is prone to fluctuate under these conditions, therefore a small pressure difference at the (FC's) outlets is sufficient to flip the jet. The jet oscillation amplitude inside the (MC) appears not to be affected by this fact, then the amplitude is higher than the one appearing at highest inlet widths. In other words, small inlet widths require small net momentums to flip the jet and the jet oscillation amplitude inside the mixing chamber is maximum. The (MC) incoming jet inclination angle, Figure 5b, suffers a reduction in the peak to peak amplitude of about 4.6% when comparing the maximum and minimum inlet widths, for the same conditions, the variation of the outlet mass flow amplitude, is about 16%. It appears the oscillation inside the (MC) is delimited by the (MC) upper and lower internal horizontal walls. To properly understand the forces acting on the main jet lateral sides, the pressure and the mass flow terms of the net momentum acting on the main jet lateral sides are compared for the lowest, baseline and highest inlet widths, see Figure 6. Regardless of the inlet width studied, the pressure term of the net-momentum is much larger than the net-momentum mass flow term, indicating that the (FO) is pressure driven. Based on their observations and studying two different configurations of (FO), wu et al. [18] reached the same conclusion, although they could not bring a clear prove of it. From Figure 6, it is also important to realize that at low inlet widths, the pressure term of the net momentum is particularly scattered, as previously explained under these conditions in any of the feedback channels there is reverse flow and pressure waves travel in opposite directions. Figure 6: Comparison of the pressure and mass flow terms of the net-momentum and for three characteristic inlet widths, Reynolds number 16034. From the dimensional temporal pressure plots at the (FC's) outlets, not presented in Figure 5, and when comparing the highest and smallest inlet widths studied, it was observed that the average static pressure at both (FC) outlets, decreased about 3000 Pa when the highest inlet width was used.