On streamwise vortices in a turbulent wall jet that flows over a convex surface

Abstract

Flow visualization and correlation measurements revealed the existence of large streamwise vortices in a turbulent wall jet that is attached to a circular cylinder. These coherent structures were not to be found near the nozzle, nor were they artificially triggered, thus the vortices could be a product of centrifugal instability. The existence and scale of this large-scale coherent motion were corroborated by stability analysis applied to the measured mean flow.

Large-eddy simulations of a turbulent Coanda jet on a circulation control airfoil

“…According to Likhachev et al 9 and Neuendorf et al, 10 who reported the existence of large-scale, counter-rotating streamwise vortices in a Coanda jet over a circular cylinder ͑and suggested that they were due to centrifugal instability͒, the value of g 33 provides a good way to detect the existence of such counterrotating vortices. Specifically, g 33 shows a negative peak at ⌬z Ϸ z / 2, where z is the average spanwise spacing between adjacent pairs of counter-rotating vortices.…”

“…[8][9][10][11] Carefully designed experiments by Neuendorf and Wygnanski,8 who considered a two-dimensional jet blowing over a circular cylinder as well as over a flat plate, have shown that the spreading rate of the Coanda jet is much higher than that of the plane wall jet ͑in spite of the fact that the normalized, self-similar mean velocity profiles are almost identical between the two jets͒. Likhachev et al 9 further investigated the Coanda jet by performing two-point correlation measurements and a stability analysis to suggest the existence of large-scale, counterrotating streamwise vortices due to centrifugal instability. Neuendorf et al 10 then reported particle image velocimetry ͑PIV͒ measurements of such streamwise vortices in the Coanda jet.…”

Numerical Simulation of Air Jet Attachment to Convex Walls and Application to UAV

“…Wygnanski and co-workers did an experimental study of the curved wall jets [1][2][3][4][5] observing that curved wall jet had greater spreading rate than the plane wall jet. They were observing large stream-wise vortices that increased turbulent momentum exchange which lead to faster spreading rates.…”

Longitudinal Vortices in Turbulent Boundary Layers Subjected to Wall Curvature and Strong Adverse Pressure Gradients: Numerical Investigations Using LES and DNS

“…Indeed, when scrutinizing experimental data from another experiment (turbulent wall-jet over a Coanda cylinder), Wygnanski and coworkers found hard evidence that Gortler-type longitudinal vortices are present in this turbulent flow and that these vortices may significantly contribute to momentum transfer between the outer and inner regions, which helps to keep the flow attached (see Likhachev et al [4]). Also, from these experiments, it was found that the observed size (the wave length X z ) of the Görtler-type vortices scales directly with the (boundary) layer thickness (M = S).…”

“…Also, we believe that their role in turbulent boundary layers may have been downplayed in the past because these vortices could not be reliably detected in the earlier experiments. Unequivocal identification of such vortices is associated with considerable experimental difficulties (see Likhachev et al [4]). In fact, in a more recent, preliminary DNS with a larger spanwise domain, we have found strong evidence that Görtler-type vortices are indeed present in this flow.…”