VORTICAL MOTION CONTRIBUTIONS TO STRESS TRANSPORT IN TURBULENT BOUNDARY-LAYERS

Four-wire hot-wire probe measurements are used to examine the relation ships between the motions bearing spanwise vorticity, omega(z), and th e mechanisms responsible for turbulent stress transport. The measureme nts were carried out in thick zero pressure gradient turbulent boundar y layers over the Reynolds number range, 1010 < R(theta) < 4850. Becau se of the scale of the flow, the spatial resolution of the probe was, in general, very good. The capabilities of the probe allowed all of th e terms in the balance equation for [u2], except the pressure strain c orrelation, to be directly measured. Regarding wall region vorticity d ynamics, velocity-vorticity correlation measurements are used to inves tigate omega(z) motion contributions to the gradients of the turbulent stresses. In particular, the measured positive correlation between v and omega(z) for y+ < 15 is shown to be consistent with the large part ial derivative[-uv]/partial derivative y gradient in this region, and physically, with the outward motion of sublayer streaks. Relationships between the motions bearing omega(z) and the sweep and ejection burst ing events are examined, and the results are discussed in connection w ith the turbulent diffusion term in the budget for [u2]. The present r esults indicate that in the near-wall region (but outside the sublayer ) approximately two-thirds of the contributions to the turbulent diffu sion term come from the correlation between the uv shear product and o mega(z) fluctuations. The overall results are discussed relative to co herent motion interactions and the known properties of the inner regio n vorticity field.