Small-wavenumber spectrum with nonzero Saffman integral ($E(k)\sim L{k}^2/(4{\pi }^2)$)

A finite nonzero Saffman integral gives $E(k)=L{k}^2/(4{\pi }^2)+o(k^2)$ in the standard isotropic spectrum normalization. This follows by expanding the radial spectral transform at small wavenumber. A further analytic term requires additional correlation moments.