1. INTERACTION OF A SLOT-TONE WITH A PIPE
Alexis Billon, Vincent Valeau
and Anas Sakout
L.E.P.T.A.B., University of La Rochelle, France

2. Summary Experimental apparatus
Overview of the operating range of the self-sustained tones
Evolution of the slot-tone with the jet velocity and the system geometry
Identification of the amplified instability
Comparison of the acoustic fields within and outside the pipe
Conclusion

3. Experimental apparatus
Length parameter:
Fundamental frequency of the tones

4. Overview of the self-sustained tones
Typical pressure spectrum f0
2f0
f0/2
f0+f0/2
Operating range of the self-sustained tones:
Velocity : from Re0=2400
Geometric : 1.1<L/H<7.5
S.P.L.max = 115 dB

5. Influence of the plate distance (Re0=11.104)

6. Calculation of the shear-layer natural frequency
Michalke’s formula :
Where :
fn = 1350 Hz
Calculated frequency :
Conclusion : same order of magnitude than the self-sustained tones

7. Influence of the jet velocity (L/H=3.0)

8. Comparison of the radiated acoustic field with the acoustic field inside the duct
Coherence
Radiated acoustic field

9. Comparison of the radiated acoustic field with the acoustic field inside the duct
Coherence
Radiated acoustic field

10. Conclusion
Strong self-sustained tones occur over Re0=2400 and 1.1<L/H<7.5
The self-sustained tones are the result of the shear-layer instabilities
Below Re0~7000, the inner and the outer acoustic fields of the duct are weackly coupled. The hydrodynamic feedback is dominant.
Above Re0~7000, the pipe acoustic field reinforces and controls the self-sustained tones. The acoustic feedback is dominant.