Numerical and experimental investigation of the flowfield near a wrap-around fin.

摘要

A wall-mounted semi-cylindrical model fitted with a single wrap-around fin (WAF) has been investigated both numerically and experimentally, with the objective of characterizing the mean and turbulent flowfield in the vicinity of the fin. Numerical and experimental results are used to determine the nature of the flowfield and quantify the effects of fin curvature on the character of the flow near WAFs. This research has been motivated by the need to identify possible sources of a rolling moment reversal observed at high speeds in sub-scale flight tests.; Detailed mean flow and turbulence measurements were obtained in the AFIT Mach 3 wind tunnel using conventional probes and cross-wire hot-film anemometry at a series of stations upstream of and aft of the fin shock/boundary layer interaction. Hot-film anemometry results showed the turbulence intensity in the fuselage boundary layer to be far greater on the concave side of the fin than on the convex side. Similarly, the Reynolds shear stress rises dramatically on the concave side of the fin and is reduced on the convex side. These results are consistent with the stabilizing and destabilizing effects of pressure gradient distortion on supersonic boundary layers. Mean flow was also obtained in the AFIT Mach 5 wind tunnel using conventional pressure probes. Shadowgraph and schlieren photography were used for flow visualization in both wind tunnels.; Numerical results were obtained at Mach numbers of 2.8 and 4.9 (Re/{dollar}ell=18times10sp6{lcub}rm m{rcub}sp{lcub}-1{rcub}{dollar} and {dollar}rm50{lcub}-{rcub}75times10sp6msp{lcub}-1{rcub}){dollar} employing the algebraic eddy viscosity model of Baldwin and Lomas. Correlation with experimental data suggests that the calculations have captured the flow physics involved in this complicated flowfield. The calculations, corroborated by experimental results, indicate that a vortex exists in the fin/body juncture region on the convex side of the fin. This juncture vortex, not predicted in previous inviscid simulations, can greatly influence the pressure loading on the fin near the root. Changes in this vortex structure may contribute to the rolling moment reversal observed at high supersonic speeds in recent flight test experiments.