Fig. (10) Frequency spectra of v at z = 1.3 and Re = 600, for T = 3.0 ~ 6.0. Wavenumber components of (1) 70, (3) 80 and (5) 90 are filtered out in the wider domain case (2π/10), while wavenumber components of (2) 70, (4) 80, and (6) 90 are filtered out in the narrower domain cases (2π/70, 2π/80, 2π/90), respectively.