## 5 Results
### Modifying (Mc) Outlet Width  
The second dimensional evaluation undertaken consisted in analyzing the effect of modifying the mixing chamber outlet width. Figure 7, introduces the results obtained for the three Reynolds numbers studied. The first thing to observe, is that, an outlet width increase involves a reduction of the (FO) output frequency and amplitude, such reduction is more relevant as the Reynolds number increases. For example, at Reynolds 8711 and when comparing the values of the maximum and minimum outlet widths evaluated, the maximum decrease in frequency and amplitude was of about 7% and 60% respectively. At Reynolds 32,068, the respective decrease of frequency and amplitude was about 9% and 74%. In other words, the range of frequencies and amplitudes a given fluidic oscillator can produce, when modifying the outlet width, increases with the Reynolds number increase. The variation of the outlet width affects mostly the (FO) outlet amplitude. A point to consider when comparing Figures 3 and 7, is that the increase of the inlet width was bringing an increase in frequency and a decrease in amplitude, while an increase of outlet width generates a decrease in outlet frequency and amplitude. This opposite effect needs to be understood when evaluating the velocity fields under these four extreme conditions, these instantaneous velocity and pressure fields are presented in Figure 8.  
Figure 7: Fluidic oscillator output mass flow frequency (**a**) and peak to peak amplitude (**b**) as a function of the mixing chamber outlet width and for three different Reynolds numbers, 8711, 16034 and 32068. Figure 8a,b, show the velocity vectors magnitude inside the oscillator for the highest and lowest outlet widths evaluated. Notice that when the (MC) outlet width is minimum, the velocity of the jet leaving the external chamber is maximum, more than four times the maximum velocity found for the rest of the cases studied in this paper. The average pressure in the (MC) is about nineteen times higher than for the rest of the cases studied. The fluid is pressurized due to the restriction effect caused by the small outlet width. The fluid stiffness in the (MC) and therefore its dynamic response is particularly high, explaining why high frequencies are linked to small outlet widths. At the (EC) the pressure is particularly low, see Figure 8d, in fact the relative negative pressure is of about 120 KPa, which is physically not possible and in reality shows that for small outlet widths cavitation is likely to appear at the (EC). Under these conditions, at the (FO) outlets, the section used by the flow to leave the oscillator is being reduced, leaving a large part of the outlet section in which reverse flow exists, huge spatial velocity differences are to be seen at the (FO) outlets. As a result, high (FO) outlet mass flow amplitudes are expected. Figure 8c shows, for the highest outlet width studied, there is a low pressure area generated below the jet due to the Coanda effect, it can also be seen that the (FC) located below the (MC) is beginning to be pressurized, a clear stagnation pressure point is observed at the (MC) outlet lower converging wall. The mass flow spatial distribution at the (FO) outlets, appears to be much uniform, the (FO) outlets have a smaller surface through which reverse flow exists, being this directly linked to smaller outlet amplitudes. The (MC) is slightly pressurized, the fluid stiffness is low and so it is the (FO) outlet mass flow oscillating frequency. For the present (FO) and regardless of the dimensional modification, the maximum mass flow amplitudes at the (FO) outlets, are directly linked with the reverse flow existing at the outlets, the bigger the reverse flow the higher the (FO) outlet oscillation amplitude. The outlet width can be effectively used to control the outlet oscillations amplitude.