TURBULENCE WAVE-NUMBER SPECTRA IN FULLY-DEVELOPED SMOOTH PIPE-FLOW

The structure of fully-developed turbulence in a smooth pipe has been studied via wavenumber spectra for various friction velocities, namely, u(tau) = 0.61 and 1.2 m/s (the corresponding Reynolds numbers based on centerline velocity and pipe radius being respectively 134,000 and 268,000) at various distances from the wall, namely y+ = 70, 200, 400 and 1,000. For each distance from the wall, correlations of the longitudinal component of turbulence were obtained simultaneously in seven narrow frequency bands by using an automated data acquisition system which jointly varied the longitudinal (x) and transverse (z) separations of two hot-wire probes. The centre frequencies of the bandpass filters used correspond to a range of nondimensional frequencies-omega+ from 0.005 to 0.21. By taking Fourier transforms of these correlations, three-dimensional power spectral density functions and hence wavenumber spectra have been obtained at each y+ with nondimensional frequency-omega+ and non-dimensional longitudinal and transverse wavenumbers k(x)+ and k(z)+ as the independent variables. The data presented in this form show the distribution of turbulence intensity among waves of different size and inclination. The data reported here cover a wave size range of over 100, spanning a range of wave angles from 2-degrees to 84-degrees. The effects of friction velocity and Reynolds number on the distribution of waves, their lifetimes and convection velocities are also discussed.