[Paper Review] Half Water, Half Air, and Sound Crawls at 24 m/s — The K∇·u Term in the Murrone–Guillard Five-Equation Model
·8 min read
A 50% air–water mix carries sound at 23.6 m/s, slower than either phase. Dropping K∇·u from the five-equation model makes the same pulse run at 745 m/s.
The Kinked String Was Fine, the Cut String Overshot by 9% — How the 1747 Wave-Equation Fight Ended Numerically
·6 min read
d'Alembert's traveling waves and Bernoulli's sines agree until the series is cut. A jump keeps a 9% overshoot; a smooth bell is already exact by 32 modes.
The Outlet Is Open, Yet the Wave Comes Back — NSCBC and the Price of σ
·9 min read
At σ = 0 a duct reflects 0% and keeps a +0.30 pressure offset; at σ = 0.25 the reflection is 1.9% and the offset drops to 0.0007.
[Paper Review] A Droplet Sends Almost Every Sound Wave Back — Acoustic Impedance and a Sharp-Interface Two-Phase Solver
·7 min read
Air-water reflection returns 99.889% of the acoustic energy. A 1% gas fraction drops Wood's sound speed from 1500 m/s to 120.5 m/s.
Supersonic Flow Can't See Upstream — Characteristics and Sound Waves in the Euler Equations
·6 min read
At 220 m/s in air the speeds are -118.06, 220, and 558.06 m/s. Past Mach 1 the left-going sound wave no longer reaches upstream.