Whistling behavior of periodic systems : corrugated pipes and multiples side branch system

Whistling behavior of two geometrically periodic systems are investigated: corrugated pipes and a multiple side branch system. In both systems frequency (Helmholtz number) is a non-decreasing piecewise constant function of the Mach number, whose increase on average is approximately linear. The plateaus, lock-in frequencies, of this piecewise constant function correspond to the longitudinal acoustic pipe modes. In both systems pressure fluctuation amplitude changes non-monotonically with Mach number with local maxima that correspond to the lock-in frequencies. A characteristic length, equal to cavity width plus upstream edge radius, yields the smallest discrepancy in the measured peak whistling Strouhal number for both corrugated pipes and multiple side branch system. For both systems the upstream edge radius of the cavity has a strong effect on pressure fluctuation amplitudes. Whistling amplitudes increase by a factor of 3–5 upon rounding off the upstream cavity edges. The radius of the downstream edge has a less pronounced effect on the sound amplitude and frequency. The geometric parameters of the multiple side branch system can easily be modified. This makes the multiple side branch system a convenient tool for making experiments on the effects of various geometric parameters. A number of aspects are addressed with the multiple side branch system such as the effect of pipe termination geometry, source localization, side branch depth to diameter ratio, a gradient in depth along the pipe and hysteresis upon change in the acceleration or deceleration of the flow

Experimental validation of a quasi-steady theory for the flow through the glottis

International audienc

Self-sustained aeroacoustic oscillations in multiple side branch pipe systems

Low frequency fl ow excited acoustic resonances have been observed in the pipe network of a compressor station. These pulsations have been identified as aeroacoustic oscillations sustained by the instability of the grazing flow along closed side branches of the pipe system. The investigation of this phenomenon is carried out on a scale model. Since the scale model shows an acoustic behavior similar to the compressor station it is used in order to characterize some of the design parameters that are in uencing the aeroacoustic behavior of the pipe network. These parameters are the shape of the edges at the junction between the side branches and the main pipe, the depth of the side branches and the geometrical symmetry of the system. The resonance modes of the pipe network are predicted by means of a plane wave acoustic model. A model for the evaluation of the global maximum pulsation amplitude from the knowledge of a local maximum pulsation amplitude is then presente