An investigation of high-wavenumber temperature and velocity spectra in air

Turbulent temperature and velocity fluctuations in air were measured at a height of 4 m over a tidal mud flat. Particular attention was focused on the high-wavenumber, small-scale region of the spectra of these fluctuations. The measurements of the velocity fluctuations were made with a constant-temperature hot-wire anemometer; the hot wire consisted of a platinum wire 5 μm in diameter and approximately 1 mm in length. Temperature fluctuations were measured with a platinum resistance thermometer which consisted of a platinum wire 0·25 μm in diameter and about 0·30 mm in length. The velocity spectra results agree well with the classical results of Grant, Stewart & Moilliet (1962) and Pond, Stewart & Burling (1963). In addition, they extend the velocity spectrum in air to slightly higher wavenumbers. The one-dimensional Kolmogorov constant K ’ estimated from these data was 0·51. The temperature spectra clearly show the shape of the one-dimensional temperature spectrum in air beyond the -5/3 region. In air temperature and velocity spectra are very similar. The value of the scalar constant K ’ 0 , which appears in the scalar -5/3 law, computed from these data was 0·81. Direct measurement was made of all parameters that enter into the calculation of it.