Drag coefficients, fragments

Ajrag Average fragment presented area Cj = Drag coefficient... 

McCleskey, F., Drag Coefficients for Irregular Fragments, Twenty-Second Explosives Safety Seminar, Anaheim, CA, Aug 1986. 

If the above values for typical velocity are substituted into the above equation, a maximum range of 5 X 105 ft is possible. Therefore, it is clearly necessary to include air resistance. To include air resistance, a value of CD, the drag coefficient, must be estimated. The drag coefficient ranges from 0.48 for a sphere to 2 for flow perpendicular to a flat strip, and for most fragments ranges from 1.5 to 2.0. 

The velocity of sound in air is around 0.335 km/s therefore, the Mach number of the fragment is initially (0.898)/(0.335) = 2,7. At the point where it has lost half its velocity its Mach number is 1.35. From Figures 27.16 and 27.18, we see that the drag coefficient in this velocity range is around 1.6. From Eq. (27.21) we can now find the distance at which the initial velocity would be halved. 

Threat models define the fragment initial velocities relative to the point of detonation, masses, area coefficients, materials, drag coefficients, ricochet angles and distribution in angular bands along an axis of rotational symmetiy (Fig. 9.6). CASPER contains a database of predefined weapons that are based on arena fragmentation trials. There is also the facility to enter more threats to suit the particular operational scenario. 

The drag coefficient, Cd is determined from Table 3.10. For a round fragment with its face perpendicular to the direction of travel, Cp = 0.47. 

This is the experted range of the fragments. If the fragments were flatter instead of spherical, then the drag coefficient would be larger and the resulting distance would be less. 

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