Spectral dynamics of turbulent heat flux in plane Rayleigh–Bénard convection

The spectral budget of the vertical heat flux left angle bracket w theta right angle bracket ⟨ w θ ⟩ wθ is investigated in turbulent Rayleigh–Bénard convection by direct numerical simulation. Eight cases spanning three Rayleigh numbers ( italic Ra equals 1 times 10 Superscript 5 Ra = 1 × 10 5 Ra = 1× 10⁵ , 6 times 10 Superscript 6 6 × 10 6 6× 10⁶ and 4 times 10 Superscript 8 4 × 10 8 4× 10⁸ ) and up to three geometric aspect ratios each are computed at italic probability equals 1 Pr = 1 Pr = 1 . The premultiplied spectra of left angle bracket w theta right angle bracket ⟨ w θ ⟩ wθ reveal a two-peak structure when both italic Ra Ra Ra and upper Gamma <mm