Approximate Analysis of Strake Wings at Low Speeds

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HE analysis of strake wings, even at low speeds, is one of great complexity. The separated flow from highly swept leading edges of the strake influences the flow over the basic wing (having a prominent nose radius). While, in recent years, some advancements have been made for the analysis of highly swept wings having separated flow from the leading edges, and a number of well-establis hed methods exist for the analysis of conventional wings having prominent nose radius, there are no suitable methods available for the analysis of strake wings when both types of flow are to exist simultaneously. The main problem seems to be to get the vortex field represented properly as it passes over the main wing. An approximate approach has been presented here. In this approach, slender wing theory is being used for the separated flow on the foward highly swept part (strake) and the upwash field from this (as a two-dimensional field) being fed into lifting surface theory. The separated flow theory, as developed by Brown and Michael,J replaces the spiral vortex sheets from the straight leading edges of a highly swept wing by two concentrated vortices and two feeding vortex sheets connecting the leading edge and the concentrated line vortices. Their theory is applicable to delta wings having straight leading edges. Smith2 extended the theory for delta wings having curved leading edges. The present investigation is restrictd to strakes having straight leading edges; thus, Brown and Michael's theory has been used for the analysis of the separated flow. The lifting surface theory used in the present treatment is the wellestablished vortex lattice theory.3'4 A FORTRAN-IV computer program has been developed to find the vortex strength distribution, chordwise and spanwise load distribution, and the overall characteristics of the wing. For the limited experimental results available, only the overall lift coefficient at different angles of attack have been compared and are shown in Figs. 1-3 for three examples taken from Refs. 5 and 6. The spanwise load distributions are shown in Fig. 4. The results of the present simplified approach appear to be highly convincing.