| Winkler, J.F. and Bragg, M.B., "Local Flowfield About Large Distributed Roughness in the Initial Ice Accretion Process", Paper No. 96-0868, AIAA 34th Aerospace Sciences Meeting, Reno, NV, January 15-18, 1996. |
| An experimental investigation of the local flowfield about large isolated and distributed roughness placed in a flat-plate laminar boundary has been performed. Large roughness in this sense refers to roughness with a height to boundary-layer thickness greater than unity, k/ d >1. This type of roughness is typical of the type of roughness that occurs during the initial accretion of ice on an aircraft in flight. The roughness elements were hemispherical in shape, and the test conditions were run with a nominal roughness Reynolds number (Re k) of 3900 and with k/d varying from 2.6 to 3.5. Fluorescent oil surface flow visualization was used in conjunction with 2D laser-Doppler velocimeter (LDV) data to examine the flowfield over the clean plate, the isolated roughness, and the distributed roughness. Results showed at least 3 identifiable primary vortices upstream of the distributed roughness. It was shown that the recirculation region behind the isolated roughness was larger and stronger than the recirculation region behind the distributed roughness. Comparison of velocity profiles downstream of the roughness indicated that the distributed roughness flowfield was further developed in the transition process than the isolated roughness flowfield at any given location. |