## 3 Parametric Investigation
### Varying the TE Noise Source Location and/or Frequency
Figure 9), some of which extend up to the top and bottom walls, thereby explaining the peculiarities of Figure 7.  
In addition to its sole location, the impact of the TE noise source frequency is also explored. To this end, the previous assessment of the airfoil incidence effect onto the  
Figure 8: Low frequency (\(St=0.294\)) noise radiation from the trailing edge of an airfoil set at low incidence (\(\alpha=5^{\circ}\)). Top: Instantaneous pressure field recorded within the vein after 10 source periods, depicted as incident (**a**) and total (**b**) components. Bottom: corresponding RMS pressure field, with incident (**c**) and total (**d**) components. For visualization purposes, all pressure fields are normalized by \(A_{max}\) and depicted using 60-iso contours distributed over an amplitude range of \([-1;1]\) (**a**,**b**) and \([0;2]\) (**c**,**d**). Figure 9: Low frequency (\(St=0.294\)) noise radiation from the trailing edge of an airfoil set at low incidence (\(\alpha=5^{\circ}\)). Deltas (in dB) between the incident and total RMS pressure fields. low-frequency TE noise (\(St=0.294\), cf. Figure 8) is repeated for three different frequencies (\(St=0.882\), \(1.47\), \(2.94\)). For each case, Figure 10 depicts the deltas between the incident and total RMS pressure fields, as recorded along either the top or the bottom walls. At first sight, the patterns appear to be rather conservative throughout all frequencies. In particular, in its upstream (resp. downstream) part, the top (resp. bottom) wall is systematically impacted by the +60 dB delta peaks, which emerge for the same higher incidences (\(\alpha=15^{\circ}\), \(20^{\circ}\), \(25^{\circ}\)). This is coherent with the fact that this peak originates from the incident field' shadow zone, whose location depends solely on the dipole inclination, whatever the frequency is. Oppositely, the negative delta peaks see their number as well as their respective amplitudes and locations varying importantly with the frequency. This is in line with the fact that these peaks rather relate to the interference effects, which were shown to depend on both the source location and frequency (cf. Section 2.3.2). In particular, more and more of these negative peaks emerge as the source frequency increases, due to the many more noise waves (of shorter wavelengths) and, thus, subsequent interference effects. Consequently, at higher frequencies, the resulting deltas (i.e., installation effects) undergo much quicker variations along both the top and bottom walls. This may complexify the identification of those particular wall locations where to better position a flush-mounted microphone, should in situ noise measurements be conducted. To explore that point, the variability of the wall-recorded deltas towards the source frequency is investigated in a more systematic manner. For all given incidences (\(\alpha=0^{\circ},5^{\circ}\), \(10^{\circ}\), \(15^{\circ}\), \(20^{\circ}\), \(25^{\circ}\)), Figure 11 depicts the top and bottom walls' respective RMS delta as a function of the source frequency (\(St=0.0147\) to \(2.94\), with \(\Delta St=0.03675\)). First, one can see again that whatever the frequency is, the +60 dB delta peaks emerge when the incidence is high enough (\(\alpha>10^{\circ}\)), whereas moving towards the airfoil as it further increases. One can then observe again that whatever this incidence is, the deltas alternate from positive to negative values as the observer moves along each wall, with such alternance occurring more quickly as the frequency increases. Finally, one can see that, whatever the frequency and incidence are, these deltas are less important on the top (resp. bottom) wall region such that \(x/c\in[0,\ 2.5]\) (resp. \(x/c\in[-2.5,\ 0]\)). From this, one can conclude that these two areas are the optimal zones where to position a flush-mounted microphone, should in situ noise measurements be conducted.