Vortex structure model in the turbulent boundary layr interacted with longitudinal vortex arrays (1996)

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The interaction between a turbulent boundary layr and longitudinal vortex arrays introduced in the free stream has been investigated experimentally in order to clarify the effect of this interaction on the structure of the vortices and the boundary layr, respectivly. The spanwise periodic longitudinal vortex arrays are artificially generated in a free stream. One of the parameters, spanwise periodicity of longitudinal vortices L/S (L denotes the spanwise distance between neighboring airfoils, S the airfoil span), rules both magnitude an streamwise path of secondary vortices caused within the turbulent boundary layr. Intermittency factor profiles revealed the effect of pairs of counterrotating secondary flows which showed the downwash flow for the midspan of the airfoil, and conversely, the upwash flow for the center slice of neighboring airfoils. Intermittency factors are strongly affected by the spacing between neighboring airfoils. The value of the intermittency factor decreases in t … More he inner layr with increasing L/S at the midspan of the airfoil. The estimation of the longitudinal component of vorticity vector brings new information about the longitudinal vortex characteristics, like path and strength. A further analysis of the other two remaining components of vorticity vector confirm the fact that, in the case of L/S<1, the vortices interact with each other leading to an abrupt loss of vortex strength but the interaction with the boundary is very weak. On the other hand, in the case of L/S*1, the vortex axis changing occurs. The next stage considered was the vorticity transport equation integrated over a control volume in order to find the vorticity flux. The control volume has been chosen so that at any streamwise location only one vortex should be found inside. The small spanwise period leads to high variations of the vorticity flux. The large spanwise period, on the other hand, leads to a steadily decreasing vorticity flux except for a slight variation that is produced by the effect of the vortices axis changing at the rebounding points. Less