Abstract
In the isotropic turbulent field, energy spectrum was observed by an improved equipment. The measurements were made in a closed channel which was added to the exit cone of an open-type wind-tunnel. A voltage integrator was used to read the fluctuating output of low-frequency components. Low-cut filter attached to the input terminal increased the accuracy at high-frequency region.
Measured spetrum curves are nearly the same as previously reported. The decay of spectral components is severer at high wave-number throughout decay process. The energy transition is estimated from the measurements above mentioned. The wave-number of zero transition decreases as the turbulence decays. Finally, the gradient of spectrum curve is determined by differentiating the spectrum with respect to wind-speed. At medium wave-number region the power index is about -5/3. Three dimensional spectrum is also obtained by this method.