## 5 Results
### Modifying (Mc) Outlet Width
(FC) reverse flow is associated to the alternative appearance of the stagnation pressure points at the (FC) outlets internal vertical walls, as it was observed in Figures 4d and 5e for the smallest inlet width. At high mixing chamber outlet widths, there is no (FC) reverse flow. Regarding the (FC) mass flow amplitude, a decrease of about 32% is observed, when comparing the values of the highest outlet width with the ones obtained at the lowest outlet width. The decrease in feedback channel mass flow amplitude as outlet width increases can be more clearly seen at high Reynolds numbers, in general it can be said that all differences can be seen more clearly at high Reynolds numbers, the dynamic values at several Reynolds numbers are not presented in the present paper. The phase lag between the oscillator output mass flow and the feedback channel mass flow is about 4.4 \(\times\) 10\({}^{-3}\) and 2.4 \(\times\) 10\({}^{-3}\) s, respectively for the lowest and highest outlet widths at Reynolds 16034. It seems high phase lag values are related to high (FO) output mass flow amplitudes. Although not directly presented in the present manuscript, at low (MC) outlet widths, the pressure difference between the upper and lower (FC) channel outlets, was particularly high, a maximum pressure difference of 4200 Pa was measured. For the highest outlet width studied, this maximum pressure difference was of 2500 Pa. The peak to peak stagnation pressure oscillations amplitude at the (MC) converging walls, was specially high at low outlet widths and high Reynolds numbers. From Figure 9b,d, it is observed that for the lowest outlet width studied, the peak to peak net momentum amplitude acting onto the jet entering the (MC), and the peak to peak inlet angle amplitude of the jet at the same point, are respectively of 43% and 30% higher than the respective values obtained when evaluating the highest outlet width. A final relevant point to highlight on the average pressure, is that for most of the cases presented in this paper, and regardless of the modification considered, as Reynolds number increases from 16034 to 32068, the average pressure at the (MC) outlet converging walls, increased by approximately 150%. Yet there are two exceptions, one of them is whenever the highest (MC) outlet width is employed, for this particular case, the same increase of Reynolds number brings an increase of the average pressure of about 12.7%. The second exception appears when the lowest (MC) outlet width is employed, being the increase of average pressure of 316% for the same increase of the Reynolds number. For highest outlet widths, the central core of the main jet flows towards the (EC) without impinging on the (MC) converging walls, just some fluid particles located at the lateral sides of the jet impinge on the (MC) converging walls, therefore explaining why the average spatial pressure on these walls is particularly small. Regardless of the geometry modification evaluated, the stagnation pressure peak to peak amplitude at the (MC) converging walls, increases with the Reynolds number increase. The detailed evaluation of this particular parameter is to be found in the final part of this paper. Figure 9: Dynamic effects of the (MC) outlet width modification on the main flow parameters, Reynolds number 16034. Each graph presents three non-dimensional curves characterizing results from the baseline, the lowest and highest outlet 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. Figures (**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.