Reynolds number dependence of velocity structure functions in a turbulent pipe flow

Low-order moments of the increments delta u and delta v where u and v are the axial and radial velocity fluctuations respectively, have been obtained using single and X-hot wires mainly on the axis of a fully developed pipe flow for different values of the Taylor microscale Reynolds number R-lambda. The mean energy dissipation rate <epsilon > was inferred from the u spectrum after the latter was corrected for the spatial resolution of the hot-wire probes. The corrected Kolmogorov-normalized second-order structure functions show a continuous evolution with R-lambda. In particular, the scaling exponent zeta(v), corresponding to the v structure function, continues to increase with R-lambda in contrast to the nearly unchanged value of zeta(u). The Kolmogorov constant for delta u shows a smaller rate of increase with R-lambda than that for delta v. The level of agreement with local isotropy is examined in the context of the competing influences of R-lambda and the mean shear. There is close but not perfect agreement between the present results on the pipe axis and those on the centreline of a fully developed channel flow.