**5.4 Computational grid**

The body oriented grids are generated using a homotopy scheme. The stretched grids are generated in an orderly manner. The grid-stretching factor is selected as 5,


#### **Table 5.**

*Trajectory points and initial conditions.*

**125**

**Figure 7.**

*Numerical Simulation of Base Pressure and Drag of Space Reentry Capsules at High Speed*

and the outer boundary of the computational domain is maintained as 1.5–2.5 times maximum diameter *D* of the reentry module. In the downstream direction, the computational boundary is about 6–9 times the diameter of the module; *D*. **Figure 6** shows enlarged view of grid over the Soyuz, the MUSES-C and the OREX vehicle. The grid arrangement is found to yield a relative difference of about ±5% in the computation of fore-body aerodynamic drag coefficient. The convergence criterion is based on the difference in density values at any of the grid points, between two successive

algorithm is described in detail in Refs. [24, 25] and validated with many test cases.

**Figure 7** depicts the velocity vector plots over the Apollo, the Apollo-II, the OREX and the MUSES-C space vehicles. It can be visualized from the vector plots that all the significant flowfield features such as a bow shock wave, rapid expansion fans at the shoulder, recirculation region with a converging free-shear layer and formation of the vortex flow in the base-shell region are well captured for *M∞* = 5.0. The wake flowfield immediately behind the space vehicle base exhibits complex flow characteristics. The formation of the bow shock wave on the fore-body

*Close-up views of velocity vector plots (a) Apollo; (b) ARD; (c) OREX and (d) MUSES-C at M∞ = 5.0.*

where *n* is time-step counter. The present numerical

*DOI: http://dx.doi.org/10.5772/intechopen.83651*

│ ≤ 10<sup>−</sup><sup>5</sup>

iterations │*ρ<sup>n</sup>* + 1 − *ρ<sup>n</sup>*

**6. Flowfield characteristics**

**Figure 6.** *Enlarged view of computational grid; (a) Soyuz; (b) MUSES-C; and (c) OREX.*

*Numerical Simulation of Base Pressure and Drag of Space Reentry Capsules at High Speed DOI: http://dx.doi.org/10.5772/intechopen.83651*

and the outer boundary of the computational domain is maintained as 1.5–2.5 times maximum diameter *D* of the reentry module. In the downstream direction, the computational boundary is about 6–9 times the diameter of the module; *D*. **Figure 6** shows enlarged view of grid over the Soyuz, the MUSES-C and the OREX vehicle. The grid arrangement is found to yield a relative difference of about ±5% in the computation of fore-body aerodynamic drag coefficient. The convergence criterion is based on the difference in density values at any of the grid points, between two successive iterations │*ρ<sup>n</sup>* + 1 − *ρ<sup>n</sup>* │ ≤ 10<sup>−</sup><sup>5</sup> where *n* is time-step counter. The present numerical algorithm is described in detail in Refs. [24, 25] and validated with many test cases.
