HART Missile and Launch Lug
AeroCFD Analysis, Mach = 0.5
**
AeroCFD** is
classified as an axisymmetric 3-D and planar 2-D
Computational Fluid Dynamics (CFD) computer program.
However, AeroCFD solutions are not limited to bodies of
revolution even though AeroCFD's bodies of revolution
can be very complex. Results of an AeroCFD analysis is
presented that determines the forces and pressure
distribution acting on a typical launch lug and superimposes
these effects on the main body of the **
HART
Missile**. The analysis involves first solving
the flow field acting on a rocket and its fins in 3-D axisymmetric form. Then, in a separate
analysis performing a 2-D analysis of the launch
lug using the **Import Shape**
geometry defined in figure-1. The Import Shape of the
launch lug is 2-D, however AeroCFD has the capability to
define launch lug thickness in the Z
direction where for this example the thickness is
defined to be 0.188. This approximation allows the
analyst to define a launch lug as a 3-D body for the
purpose of determining the axial force (FX) and normal
force (FY) acting on a 3-D body. Flow field interference
between airframe and launch lug is a consideration.
However, a good "engineering" approximation for the
forces acting on a launch lug and its contribution to
total force acting on a rocket can be made using the
principal of superposition. This useful "engineering"
approximation is especially good in regions where flow
field interference of the airframe, fins and launch lug
is minimal. For example, launch lugs, or most objects
located on the airframe, are located ahead and midway
between the fins of a typical model or high power
rocket. This approximation is especially good for Mach 0.5 flight as illustrated in Figure-3
because the background flow field of the inserted launch
lug closely matches the pressure contours of the **
HART
Missile**
by itself. This condition indicates minimal
airframe-launch-lug interference and says that
superposition is a good estimate for Mach 0.5
flight of the **HART
Missile**. For the Mach 1.2 flight condition,
airframe-launch-lug interference is increased but the
aerodynamic forces acting on the launch lug can still be
successfully modeled using this technique. However, this "engineering"
approximation is less
accurate as Mach number is increased well above Mach 1 due to
interference with the nose cone induced shock layer as
illustrated in Figure-5. In conclusion, this analysis
demonstrates that AeroCFD solutions are not limited to
bodies of revolution and with a little imagination AeroCFD
can be applied to attached objects like launch lugs if
flow interference is not severe but is very cost
effective. The true cost to perform the
same analysis in full 3-D using a commercially available CFD program involves taking weeks to
generate a 3-D CAD model, performing complex meshing around fins and launch lug and then
spending hours of expensive computation time on a supercomputer. For
example, this analysis took only two hours from initial set-up to
final solution using AeroCFD. |