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Experimental results
2.1 Description of the operating condition
In these experiments, inlet and outlet time averaged isentropic Mach numbers are set and a time averaged "lambda" shock wave is generated over the generic model surface at 67% (+/-1%) of the bump chord. Figure 3 shows a typical shape of the shock wave created during those experiments. To define this operating condition, the stagnation pressure and the stagnation temperature of the fbw are measured (Pt = 159kPa at Tt = 305K) at ten chords upstream and the corresponding isentropic inlet Mach number is calculated (Misoi = 0.63). The downstream static pressure is measured on the ground wall and allows calculation of a downstream isentropic Mach number MiSo2 = 0.61 at two chords after the generic model. Figure 4 shows the chord wise distribution of local static pressures for the same operating condition. The generic model acts as a contraction of the channel. Miso2 decreases until 10% of the chord and then increases until 50% of the chord where the fbw speed is maximal. Then Miso2 decreases through the shock wave formation. Because of the manufacturing method, the pressure taps are not exactly perpendicular to the surface and thus do not measure the exact static pressure profile as well as the unsteady pressure ffictuations.
Figure 4 describes the way the generic model is oscillating. A regular repartition of the amplitudes along the bump half chords shows a maximal deformation at x/cax = 0.47. Due to its fbxible nature, a first bending mode shape
Schlieren picture of the shock wave created in the test section (Miso1 = 0.63, 0.61) and isentropic Mach number profile at upper and lower bump positions
at k=0.015 changes in a second bending mode shape at k=0.074, and reaches a third bending mode shape at higher reduced frequencies. At the mean shock wave location x/cax = 0.67, the local geometry presents a phase towards bump top motion. This phase is 20Deg. at k=0.015, 45Deg. at k=0.037, 120Deg. at k=0.074, -180Deg. fromk=0.11 to k=0.147, -45Deg. at k=0.221 and -90Deg. at k=0.294.
