Unsteady pressure results

The unsteady pressure fluctuations are measured along the bump and the corresponding unsteady pressure coefficient and phase leads towards bump motion are deduced for five chosen pressure taps. The amplitudes of the unsteady pressures fluctuations shift significantly at the reduced frequency k=0.221 for the pressure taps located 20% upstream and downstream of the

200 400 600 800 10OO

200 400 600 800 10OO

1 (Hz) 1 — 200Hz

600 lOOO 1500 2000

f – 200Hz

500 lOOO 1500 2000

f — 200Hz

500 10OO 1500 2000

f (Hz)

Figure 6. Time-variant and power spectra of static pressure, shock wave movement and bump top motion at 10Hz, 75Hz and 200Hz perturbation frequencies

bump axial chord as shown in Figure 8. Moreover the unsteady pressure co­efficients remain stable and range between 2 and 4 for the three pressure taps located within 40% to 80% of the bump axial chord. The phase lead towards bump motion of the static pressure flictuations range between 90Deg. and 180Deg. for the pressure taps located before the bump max height, and be­tween -180Deg. and 90Deg. for the pressure taps located after the max bump height. At the pressure tap located close to the shock wave mean location (67% of the bump chord) and at y/H=0.25, the phase leads towards bump motion follow the same decreasing trend. In comparison with the shock wave motion phase variation, a global decrease in phase close to 270Deg. is observed for the pressure taps located after the shock wave.

3. Conclusion

Phase relations among oscillatory bump motion, shock wave movement and unsteady pressure fluctuations are investigated in the case of a flexible generic model controlled-oscillated in bending mode shapes at an inlet Mach number of 0.63, over a range of reduced frequencies from 0.015 to 0.294. The follow­ing conclusions are drawn:

• The mode shapes of such a fhxible bump strongly depends on the exci­tation frequency of the generic model.

Figure 8. Chord wise static pressure flictuations at reduced frequencies from k=0 to k=0.294 at MiSOi = 0.63

The phase of shock wave movement towards bump local motion shows a decreasing trend for the third bending mode shapes at reduced frequency higher than k=0.074.

At the pressure tap located after the shock wave formation (67% of the bump chord), the phase of pressure flictuations towards bump local mo­tion presents the same decreasing trend as for the shock wave movement analysis.

For those same pressure taps, lower and stable pressure coefficients are also observed.

Acknowledgements