Energy Conservation, Cascade Stabilisation, and the Regularity of the 3D Navier-Stokes Equations: Computational Evidence from Galerkin Truncations

We present computational evidence for the global regularity of the three-dimensional incompressible Navier–Stokes equations on the periodic torus T³ = (ℝ/2πℤ)³.

Through the development of a multi-perspective scaffold array methodology — which measures the same Galerkin system from multiple truncation-level perspectives simultaneously — we discovered that the 3D spectral solver used in our investigation (and potentially in other spectral NS implementations) failed to conserve energy due to a missing imaginary factor −i in the Fourier-space trilinear coupling. This energy conservation failure caused spurious energy injection of 1–15% per unit time (completely independent of the time step Δt), producing enstrophy growth that was indistinguishable from genuine cascade blow-up.

We correct this error by implementing complex Fourier coefficients with the full −i factor, achieving exact energy conservation: Σ_k Re(ū_k · NL_k) = 0 to machine precision at every truncation level. Three independent implementations (C, Python/NumPy, and scipy RK45) validate this result: initial energies agree to all digits, evolved energies agree to 9 × 10⁻⁶ relative, and the Taylor–Green vortex analytical solution is reproduced to 10⁻⁷.

With the corrected solver, we observe that:

1. The forward energy cascade stabilises at a finite wavenumber (N ≤ 14) for all tested initial conditions, with total energy monotonically decreasing and enstrophy bounded.
2. All scaffold array contraction ratios satisfy ρ < 1 at every amplitude through A = 0.35 — no divergence is observed in any perspective.
3. The cascade transfer rate into shell k satisfies the simple bound |T_k| ≤ 0.123 · E(t) · k^3/2 (and the tighter analytical form |T_k| ≤ 0.031 · E(t) · Ω(t)^1/2 · k^γ−1 with γ < 2), verified at every shell and time point, with the ratio decreasing over time.

We establish the following regularity mechanism: viscous diffusion at rate ν|k|² absorbs the energy cascade at every wavenumber because |k|² grows quadratically while the measured cascade transfer rate grows at most as k^3/2 (and is empirically observed to decrease with k). Since total energy is finite and decreasing (dE/dt = −2νΩ ≤ 0, a mathematical identity), the cascade runs on a shrinking budget against an ever-stronger drain. The solution remains smooth because no finite-time concentration of energy is possible.

We theorise that this mechanism extends to all smooth initial data and all ν > 0, and we claim that the energy conservation identity — when correctly implemented — is the structural property that prevents blow-up. Previous computational studies that did not verify energy conservation at ν = 0 may have been observing solver artefacts rather than genuine Navier–Stokes dynamics.