Field notes from a compressible multiphase CFD researcher
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[Paper Review] A water-air interface in uniform flow produced an 8×10⁸ Pa pressure spike — the non-disturbance condition in a pressure-based BN model
Reproducing the non-disturbance condition from Re and Abgrall's 2022 pressure-based Baer–Nunziato model: if volume fraction and phase mass don't share one flux, interface pressure jumps by hundreds of MPa.
A Steady-State Preconditioner Inside a Dual-Time Loop Took 19× More Inner Iterations — A Low-Mach Acoustic Pulse Test
Put a Weiss–Smith preconditioner into physical time and the acoustic pulse freezes in place. Put it inside dual time and the answer returns, but inner iterations jump from 16 to 305.
A Ball Thrown at 5 m/s Passed Through a 20 mm Wall — Penalty Contact vs. the IPC Log Barrier
In the same implicit Euler step, penalty contact skips over a thin wall while the IPC log barrier with a CCD-filtered line search stops micrometers short. A 1D experiment shows why.
Velocity came out one sixth at τ=0.6 — dropping the half-force F/2 from Guo forcing
Keep the Guo source term but drop F/2 from the LBM velocity and the effective body force shrinks by (1−1/2τ). On Kolmogorov flow at τ=0.6 the amplitude is 0.166 of exact.
A Small Wobble in Mixture Fraction Drops the Mean Flame Temperature by 964 K — Presumed β-PDF and the Infinity at Z=0
At stoichiometric mean Z, the β-PDF mean temperature sits 964 K below T(Z̄). When a<1, a 100-cell uniform-grid integral also overshoots by 115 K. Here is why, with code.
A Two-Cell Interface Loses 39% of Its Surface Tension — The Anisotropy of the Korteweg Stress
Across a flat liquid–vapor interface the normal pressure stays constant and only the tangential pressure dips. That dip is surface tension, and a dz=1 lattice loses up to 39% of it.
[Paper Review] MSTACS with Slope 3 Blew Up After 255 Steps at Co=0.5 — Compressive Differencing and the Courant Limit
We ran the compressive scheme of MSTACS eq. (18) on a 1D slab. Without redistribution it diverges above Co=0.44. The culprit is the product of the NVD slope k and the Courant number.
[Paper Review] Raising β to 2 froze the interface at 14 cells and made a sine worse than first-order upwind — Tallois's compressive limiter
With a β=2 compressive limiter on the volume fraction, a slab interface stays 14 cells wide after five periods. The same limiter gives a sine wave a larger L1 error than first-order upwind.
Changing only τ changed the density of a gas at rest — the (τ−½)² stress of Shan–Chen velocity-shift forcing
Apply the same force to a resting D1Q3 gas column and only Shan–Chen forcing gives a τ-dependent density. The shifted equilibrium velocity leaves a fake (τ−½)²F²/ρ stress.
Dividing the Reverse Rate by Kp Split 99.6% of AlO at 2500 K — The (p°/RT)^Δn Hidden in the Equilibrium Constant
Plugging Kp into kr = kf/K skews the equilibrium of any reaction with Δn≠0 by (p°/RT)^Δn. An AlO dissociation reactor reproduces the SI and CGS versions of the mistake.
Halving the Grid Spacing Tripled the Error — What an Increment-Based Stopping Rule Hides in Jacobi Iteration
Stop Jacobi when the update drops below a tolerance and the error left behind grows as 1/(1-ρ) on finer grids. A 2D heat-conduction plate compares Jacobi, SOR and optimal ω.
Adding a v Term to a v² Term Got Both Ends Right and Missed the Middle by 42% — Prony's Two-Term Drag Law and Re = 60
Bossut measured drag growing with v², Du Buat with v. Prony's sum a·v²+b·v hands over control at Re = 60 and overpredicts settling speed by up to 42% right there.
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