Investigations of Supersonic Flow around a Long Axisymmetric Body

One of the most important parameters affecting missiles’ length and diameter is the required space for their apparatus, systems, etc. Increasing this space causes an increase in both the body length and the missile’s fineness ratio, L/d (Fleeman, 2001). For such bodies, the problems of flow separation and boundary layer growth at various flight conditions are very important. Of course, the boundary layer growth and its separation, affect the aerodynamic characteristics, particularly the drag force and the stability criterion. Both of these have important roles in the missile performance and its mission implementations. Also, the performance of various control surfaces (especially those located close to the end of the body) varies with flow separation (Cebeci, 1986). For some rockets and missiles, the after body cross-section changes longitudinally (particularly in space vehicles). Furthermore, due to the lack of sufficient space for arranging the systems (e.g., actuator of controlled fins, avionics, etc.), it is necessary to increase the body cross section near those systems. The lack of space may also appear when controlled fins are installed on the motor surface. Hence, in many occasions the body cross-section needs to be increased (Chin, 1965; Soltani et al., 2002). However, the computation of the flow parameters and their variations for non-zero angles of attack, when bodies are tapered, is not an easy task, e.g., it takes a considerable amount of memory and CPU time to compute the flow over such bodies. In addition, as the angle of attack increases, the flow over a portion of the body may separate, making the flow more complicated. Moreover, experimental data for flow properties along tapered bodies to validate CFD codes are rare (Soltani et al., 2002; Perkins & Jorgensen, 1975). The computational simulation of flow over complex geometries usually requires structured multi-block grids. On the other hand, the geometric complexity requires more blocks and also more grid points. Even though, the computer programming (using multi-block grid for such flows) is very troublesome, it is computationally very efficient and quick. On the other hand, suitable grid generation plays the first and the most important role, when using multiblock grid. Grid generation needs to be consistent with flow solution. In some methods, the discritization error increases due to the inaccurate adoption of the grid boundaries with the real flow boundaries, which could be due to the non-orthogonality of the grid lines, especially near the walls.