interaction fluid-fluid

INTERACTION OF A MONOCHROMATIC PLANE WAVE WITH AN INTERFACE FLUID/FLUID

Animations

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here: Catherine Potel (Université du Maine - France) and Philippe Gatignol (Université de Technologie de Compiègne - France)

See the slides associated to chapter 4 of the fluid acoustic course

	The interaction of an oblique plane wave with an interface separating two fluid media causes a reflected wave in the medium 1 and a transmitted wave in the medium 2. The whole field in the medium 1, which is the summation of the incident and reflected fields, has always a stationary character in the direction perpendicular to the interface (following y), and a propagative character in the direction of the interface dans la direction de l'interface (following x).
When the propagation velocities c₁ and c₂ of the waves in media 1 and 2 are such that c₁ < c₂, there exists a value for the incident angle ₁, denoted _c, and called critical angle for the given interface, such that sin _c = c₁/c₂, from which the transmitted wave in the medium 2 becomes evanescent. The modulus of the reflection coefficient in the medium 1 thus becomes equal to 1 (total reflection), but there is still presence of acoustic energy in the medium 2. The evanescent transmitted wave propagates in a direction parallel to the interface, while its amplitude has an exponential decreasing with the depth (when y increases), in a direction perpendicular to the interface.
The cartographies below represent the amplitude of the real part of the acoustic pressure; color level (red = maximum, blue = minimum). The oblique black lines represent incident, reflected and transmitted rays, as they are predicted by Snell-Descartes' laws: when the transmitted wave is propagative (<_c), it propagates in the direction of its transmitted ray, this direction being perpendicular to the wave planes.
Incident angle inferior to the critical angle _c .	Incident angle superior to the critical _c .
Incident angle equal to the critical angle _c .