Rarefaction waves are expanding regions in a fluid where pressure, density, and temperature decrease, typically forming after a shock wave or in response to a sudden drop in pressure. Unlike shock waves—which compress and heat the medium—rarefaction waves spread out the fluid and reduce its density.
These waves travel through the medium as smooth, continuous expansions, allowing the fluid to accelerate and occupy more space. They are most often observed in gases, but can also occur in other compressible media.
Key Characteristics:
- Represent a decompression rather than compression.
- Travel at the local speed of sound in the fluid.
- Are governed by the same equations as shock waves but with opposite effects.
Examples:
- In a shock tube, after the shock wave moves forward, a rarefaction wave propagates backward into the high-pressure section.
- In explosions, rarefaction follows the initial blast wave, creating a temporary vacuum-like region.
- In astrophysics, rarefaction waves occur in supernova remnants and gas jets.
Rarefaction waves are essential in the study of compressible fluid dynamics, as they help explain expansion processes, high-speed flow behavior, and pressure equalization in various scientific and engineering applications.