Small scale intermittency in a rough wall turbulent boundary layer

Relatively good quality isotropy is observed in the central region of a turbulent boundary layer developing over a mesh screen rough wall. Spectra of velocity and, more especially, vorticity fluctuations satisfy isotropy over a significant wavenumber range. Inertial range scaling exponents zeta(u1)(p) and zeta(u3)(p) of moments of order p(less than or equal to 8) of increments of the transverse velocity fluctuations u(2) and u(3) are significantly smaller than the exponents zeta(u1)(p) of increments of the longitudinal velocity fluctuation u(1). Exponents inferred from the locally averaged values of squared transverse vorticity fluctuations are only slightly smaller than zeta(u1)(p). The difference between zeta(u1)(p) and zeta(u2)(p) [or zeta(u3)(p)] more likely reflects the departure from isotropy of inertial range scales. There is evidence to suggest that the difference decreases with an increase in the Reynolds number and/or a decrease in the magnitude of the mean shear.