Vortical motion contributions to stress transport in turbulent boundary layers

Abstract

Four-wire hot-wire probe measurements are used to examine the relationships between the motions bearing spanwise vorticity, ωz, and the mechanisms responsible for turbulent stress transport. The measurements were carried out in thick zero pressure gradient turbulent boundary layers over the Reynolds number range, 1010<Rθ<4850. Because 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 the terms in the balance equation for 〈u2〉, except the pressure strain correlation, to be directly measured. Regarding wall region vorticity dynamics, velocity–vorticity correlation measurements are used to investigate ωz motion contributions to the gradients of the turbulent stresses. In particular, the measured positive correlation between v and ωz for y+<15 is shown to be consistent with the large ∂〈−uv〉/∂y gradient in this region, and physically, with the outward motion of sublayer streaks. Relationships between the motions bearing ωz and the sweep and ejection bursting events are examined, and the results are discussed in connection with the turbulent diffusion term in the budget for 〈u2〉. The present results indicate that in the near-wall region (but outside the sublayer) approximately two-thirds of the contributions to the turbulent diffusion term come from the correlation between the uv shear product and ωz fluctuations. The overall results are discussed relative to coherent motion interactions and the known properties of the inner region vorticity field.

Experimental study on the role of spanwise vorticity and vortex filaments in the outer region of open-channel flow

“…Later, Klewicki et al (1994) found that features of the velocity-vorticity correlations coincide well with the vortex models proposed by Falco (1991) and Smith et al (1991) in the near wall region. Recently, by measuring the spectra of velocity, vorticity and their co-spectra, Priyadarshana et al (2007) further established that the velocity-vorticity interactions responsible for the "scale selection" feature of the co-spectra could be interpreted properly by the hairpin vortex packets proposed by Adrian et al (2000b).…”

Velocity–vorticity correlation structure in turbulent channel flow

“…This topological change illustrates an important difference between the near-wall region CS and loglayer CS; the latter is characterized by two cigar-like elongated structures shown in figure 11(c). Although more extensive study is needed to confirm this observation in the future, let us note a consistent experimental observation of Klewicki, Murray & Falco (1994): one +ω 3 eddy above the probe and another −ω 3 one below the probe. Note that the NWCS 13 always exists, even for y + r > 100, indicating that u 1 over the whole domain affects ∂u 1 /∂y near the wall.…”

“…The authors found a +ω3 eddy above the probe and a −ω3 eddy below the probe (Klewicki et al 1994). The inclination angle for the upstream envelope of the composite vortical packet is 10…”

Characteristics of the Lamb Vector in the Outer Region of a Turbulent Boundary Layer

“…They concluded that the velocity signature is consistent with the presence of internal shear layers, inclined to the wall. Klewicki et al 18 investigated the u 2 ω 3 term in the near wall region and concluded that the existence of positive spanwise vorticity for x 2 + > 12 is consistent with the presence of a ring-like eddy.…”