To maintain incompressible turbulence, the incormpressible Navier Stokes equations
∂ui∂xi=0
∂ui∂t+uj∂ui∂xj=−∂p∂xi+ν0∂2ui∂xj∂xj
have to be suplemented by some kind of an energy source acting at large scales. Often, a Gaussian, white in time forcing is assumed such that its two-point correlator is given by
⟨ˆfi(ˆk)ˆfj(ˆk′)⟩=2D(k)(2π)d+1δ(ˆk+ˆk′)
How can I generally prove that assuming a power law for the energy input spectrum of the forcing D(k) leads to a scale invariant turbulent energy spectrum? Is assuming a power law like this sufficient and necessary to guarantee scale invariance?