Experimental Evidence of the Kraichnan Scalar Spectrum at High Reynolds Numbers

Measurements of horizontal temperature gradient spectra were carried out in a 25 m × 12 m × 3 m freshwater well mixed swimming pool. The associated flow Reynolds number was found to vary from 4 × 103 to 6 × 103. In all analyzed cases, at large wavenumbers k, the temperature gradient spectra exhibited behavior consistent with the Kraichnan spectral form: ~exp[−(6qk)1/2k] with constant . The measurements are in agreement with direct numerical simulations of a passive scalar flow with of Bogucki et al. and with recent experimental observations of Sanchez et al.