Related papers: Slow sound laser in lined flow ducts
We consider the acoustic propagation in lined flow duct with a purely reactive impedance at the wall. This reacting liner has the capability to reduce the speed of sound, and thus to enhance the interaction between the acoustic propagation…
We present a thin subwavelength material that can be flush mounted to a duct and which gives a large wide band attenuation at remarkably low frequencies in air flow channels. To decrease the material thickness, the sound is slowed in the…
An experimental investigation of the acoustical behaviour of a liner in a rectangu- lar channel with grazing flow has been conducted. The liner consists of a ceramic structure of parallel square channels: 1mm by 1 mm in cross section, 65 mm…
The effect of viscosity and thermal conduction on the acoustics in a shear layer above an impedance wall is investigated numerically and asymptotically by solving the compressible linearised Navier-Stokes equations. It is found that…
In this paper the propagation of acoustic plane waves in turbulent, fully developed flow is studied by means of an experimental investigation carried out in a straight, smooth-walled duct.The presence of a coherent perturbation, such as an…
Acoustic cloaking for the suppression of backscattering inside ducts is proposed in the audible range where plane waves are curved around the object using the surface modes of the liner. It is numerically shown that a slowly varying…
We propose a new system suitable for studying analogue gravity effects, consisting of a gas flowing in a duct with a compliant wall. Effective transonic flows are obtained from uniform, low Mach number flows through the reduction of the…
With flow, the acoustical effect of a lined wall cannot be described by a single quantity like the wall impedance. At least two quantities are required. In addition to the impedance, the unsteady tangential force exerted by the wall on the…
In the past decades, many efforts have been devoted to the temporal manipulation of waves, especially focusing on slowing down their propagation. In electromagnetism, from microwave to optics, as well as in acoustics or for elastic waves,…
We analyze the peculiar infrared instability that characterizes stationary inhomogeneous flows when their velocity crosses the sound speed by decreasing values. For definiteness, we work in the context of one dimensional atomic Bose…
We have preformed experiments on a liquid curtain falling from a horizontal, wetted, tube and lateraly constrained by two vertical wires. The fluid motion nearly reduces to a free-fall, with a very low detachment velocity below the tube.…
Local phonon motion underneath a surface interacting with a flow may cause the flow to passively stabilize, or destabilize, as desired within the region adjacent to the subsurface motion. This mechanism has been extensively analyzed over…
The linear stability of stratified two-phase flows in rectangular ducts is studied numerically. The linear stability analysis takes into account all possible infinitesimal three-dimensional disturbances and is carried out by solution of the…
Optimal impedance for each mode is an important concept in an infinitely long duct lined with uniform absorption material. However it is not valid for finite length linings. This is because that the modes in lined ducts are not…
The superflow in a superfluid is bounded from above by Landau's critical velocity. Within a microscopic bosonic model, I show that below this critical velocity there is a dynamical instability that manifests itself in an imaginary sound…
We show that the instability leading to the decay of the one-dimensional superfluid flow through a penetrable barrier are due to the black-hole lasing effect. This dynamical instability is triggered by modes resonating in an effective…
Slow waves and tunneling waves can meet at the cutoff wavelengths and/or transmission band edges of optical and quantum mechanical waveguides. The experimental investigation of this phenomenon, previously performed using various optical…
We investigate the sound propagation in an air-filled tube periodically loaded with Helmholtz resonators. By tuning the Helmholtz with the Bragg resonance, we study the efficiency of slow sound propagation in the presence of the intrinsic…
High-fidelity lattice-Boltzmann very-large-eddy simulations are performed to describe the noise dissipation mechanisms in a single cavity acoustic liner subjected to grazing turbulent flow at a centreline Mach number of 0.3 and plane…
We have investigated the effects of permeable walls, modeled by linear acoustic impedance with zero reactance, on compressible channel flow via linear stability analysis (LSA). Base flow profiles are taken from impermeable isothermal-wall…