Aerodynamic characteristics of external store configurations at low speeds

Aerodynamic characteristics of external store configurations used on interceptor aircraft were investigated experimentally and computationally. Balance measurements, flow visualization, and static pressure measure- ments were made in a low-speed wind tunnel. The experimental and computational data revealed the global structure of the flow around a basic configuration. Six groups of models were used in the present study. This article discusses the results for the first and second group of models. The incompressible flow over a limited number of models was computed by solving the Navier-Stokes equations. The solution method is based on the Galerkin finite element discretization of space and the fractional step discretization of time. Reasonably good agreement was observed between the experimental and computational static pressure distributions on a basic geometry. The computational data, which revealed details of reverse flow regions, supported and supplemented the experimental data. using the code employed in the present study are presented in Refs. 5-7. The scope of the study was limited to the aero- dynamic characteristics of the isolated carriage, i.e., inter- ference with the aircraft body was not investigated. The experimental and computational data revealed the global structure of the flow around the carriage. Balance measure- ments showed that aerodynamically more suitable forms of the carriage geometry could be obtained by modifying its major drag-producing features. Surface flow visualization in- dicated locations of vortical flow regions whose existence was also supported by contour plots of the measured static pres- sure. Despite differences in the Reynolds numbers of the computed and measured flows, reasonably good agreement was observed between the experimental and computational static pressure distributions on the basic carriage geometry. The computations also exhibited details of reverse flow re- gions and, thus, both supported and supplemented the ex- perimental data that did not include velocity measurements. The geometry of the basic carriage used in the present study is not axisymmetric. There is a lack of data in the literature on studies of external stores that have nonaxisymmetric ge- ometries. References 8 and 9 present data for bodies having square and rectangular cross sections. Studies of the flow around axisymmetric bodies show that there exist four char- acteristic flow regimes10"12: "vortex-free," "symmetric vor- tex," "asymmetric vortex," and "wake-like" flow regimes are observed with increasing angle of attack. Crossflow separation of the boundary layer on an axisymmetric body gives rise to formation of vortices on the lee side. Reference 10 states that the nonlinear lift force due to these vortices can be much larger than the lift predicted by the linear (small perturbation) theory. References 13-15 describe studies that investigate the effect of afterbody modifications on the drag of axisymmetric bodies. Interference between the flowfields of stores and air- craft bodies is investigated by Refs. 1 and 2.