Comment on "Water Tunnel Flow Visualization: Insight into Complex Three-Dimensional Flow Fields"

Abstract

T are two comments which need to be made with regard to the subject paper (Ref. 1). The first is that extreme care must be exercised in establishing vortex breakdown from inflections in the lift curve slope for strakewing configurations. This can be illustrated by the fact that when the vortex lift theory solutions incorporating all of the trigonometric terms (Polhamus' Suction Analogy—Ref. 2) are used, there is a naturally occurring inflection in the lift curve, i.e., a reduction in the lift curve slope, commencing about a= 16 deg (Ref. 3) and it is unassociated with vortex breakdown. The second comment is that regarding the correlation of wind tunnel force data with water tunnel flow photographs, it must be kept in mind that discrepancies do exist between the vortex breakdown angles observed on strake-wing configurations in the wind tunnel and low Reynolds number water tunnel. (See Ref. 4, for example.) So although the water tunnel appears to provide useful qualitative configuration effect information, it may be questioned from a quantitative standpoint. In view of the preceding comments, one should use extreme caution in applying the vortex breakdown analysis method outlined in the subject paper to strake-wing configurations.