Measurements of wavenumber-celerity spectrum in plane and axisymmetric jets

The wavenumber-convection velocity spectra W/(k, U) in the near and far fields of plane and axisymmetric free air jets have been computed from digitized hot-wire data. This spectrum was obtained in a 3. 18 multiplied by 140 cm plane jet and in a 2. 54-cm-diam axisymmetric jet. For both jets the exit mean velocity U//e was 30 m/s. The spectra indicate that the jets are characterized by energetic large-scale structures not only in the near field (slightly downstream of the potential core) but also in the self-preserving region. The streamwise length scale of the most energetic eddies increases in proportion with that of the jet width. The streamwise length scale of these eddies is about 3 times the local jet width in the circular jet and 3. 5 times the local jet width in the plane jet. With increasing eddy sizes, the dispersion in the convection velocity U increases as W(k, U) becomes progressively skewed towards U values higher than the local time mean velocity U.