Streamwise vorticity decay downstream of a three dimensional protuberance

Streamwise vortices generated in boundary layers are known to persist for hundreds of boundary-layer thicknesses. This remarkable property is the main topic of this report. The particular case of the flow field generated by a three-dimensional protuberance immersed in a flat plate boundary layer is studied using numerical modeling. Experimental measurements in a downstream crossflow plane are used to construct initial data for a marching calculation using the boundary-layer and boundary-region approximations; the latter includes crossflow diffusion terms. The former fails to predict the flow field, but results from the latter agree qualitatively in aspects of the flow field determined from the measurements of Tani, et al., and are also in fair quantitative agreement.