In an application of computational fluid dynamics (CFD), flow fields about a slender-bodied finned projectile and the resulting aerodynamic forces and moments on the projectile were computed. The size and shape of the projectile (a blunt-nosed, ogivecylinder body, 316.7 mm long, 23.5 mm in diameter, with four tail fins) are representative of a preliminary design of a future air-defense projectile. The computations are exemplary of those needed for predicting aerodynamic performances in order to optimize designs of advanced projectiles, missiles, and rockets in general.

Surface Pressure Contours on the projectile were computed for a speed of Mach 3.5 and an angle of attack of 2°.
The computations were performed by a commercial parallel-processing CFD code that solves the Reynolds-averaged Navier-Stokes equations of flow of a compressible, viscous fluid on computational grids by means of a finite-volume, implicit numerical integration scheme. The numerical scheme includes unifiedgrid, unified-physics, and unified-computing features. This code was used in conjunction with another commercial code that generated the computational grids about the projectile, based on a computer-aided design (CAD) file representing the projectile surfaces.

Turbulence was represented by a cubic k-ε mathematical model - a member of a class of models, commonly used in CFD, that are so named because they include the time-averaged kineticenergy density (k) associated with the local fluctuating (turbulent) component of flow and the time-averaged rate of dissipation (ε) of this turbulent-kinetic- energy density. A pressure/temperature- based inflow/outflow routine was utilized for the inflow boundary condition, while a characteristics-based inflow/outflow routine was used for the far-field boundary condition. A centroidal extrapolation routine was used for the outflow boundary, and an isothermal wall condition was used on the projectile surfaces. The computations were fully three-dimensional: that is, flow fields were not assumed to be symmetrical. All computations were performed under atmospheric conditions of free-stream pressure = 101,325 Pa and temperature = 298 K. Most of the cases were completed by use of 16 processors. The average central-processing- unit time needed to converge on the solution for each case was about 100 hours.

The cases considered included Mach numbers ranging from 1.5 to 5.0 and angles of attack from 0° to 5° (for example, see figure). Steady-state solutions were obtained for these cases. Force and moment data computed from these solutions were found to be acceptably close approximations to available semi-empirical force and moment data.

This work was done by Karen Heavey and Jubaraj Sahu of the Army Research Laboratory. For more information, download the Technical Support Package (free white paper) at under the Information Sciences category. ARL-0010

This Brief includes a Technical Support Package (TSP).
Application of CFD to a Slender-Bodied, Finned Projectile

(reference ARL-0010) is currently available for download from the TSP library.

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This article first appeared in the April, 2007 issue of Defense Tech Briefs Magazine.

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