Experimental Studies on the Spectrum of Isotropic Turbulence behind Two Grids

As a continuation of the previous work (Journ. Phys. Soc. Japan 10 (1955) 578), hot-wire measurements were made to determine the energy spectrum and decay of spectral components of turbulence behind two grids, the upstream grid having a larger mesh length than the downstream one, with a view to studying the characteristics of isotropic turbulence produced under various initial conditions and at high Reynolds numbers. Similarity of the energy spectrum holds only for high-wave-number range, while the low-wave-number characteristics of turbulence depend on the initial conditions and exhibit no similarity. On the other hand, similarity of the spectrum of vorticity is observed over almost entire wave-number region for the turbulence either behind single or double grids unless high-wave-number disturbances are superposed. Therefore, Lin's decay law, \(\overline{u^{2}}{\sim}[x^{-1}+\textit{const.}]\), is expected to be valid for the turrblence either behind a single grid or with superposed disturbances of low wa...