PFR - Aerospace Engineering Sciences Senior Design Projects ...

Project Final Report – CUDBF April 30 th , 2009
ASEN 4028: Aerospace Senior Projects
As shown in the preceding paragraphs, stability for the designed aircraft configuration will not
be an issue and therefore will not be an obstacle in accomplishing the mission goals.
8.1.6 Drag Analysis
With payloads that don’t seem very aerodynamic such as the water bottle, it is necessary to
ensure that there is enough available thrust to overcome the drag predicted. The drag analysis
was performed in a program called PowerFLOW [15] . PowerFLOW is a computational fluid
dynamics tool used to aid in the analysis and visualization of internal and external flows using
the Lattice-Boltzmann Method (LBM). External 3-dimensional, incompressible flow was used
for the simulations for drag estimates obtained from this tool. PowerFLOW consists of two
modules used to set up a simulation and one used to analyze flow results. The module used to
setup the simulation case is called PowerCASE [16] and the module used to visualize the flow
results is called PowerVIZ [17] .
The drag on the airplane was predicted for the case with four rockets on the airplane, the bottle
on the airplane, the bottle, the rocket, and the airplane without payloads. The drag results from
the bottle and the rocket in a simulation volume were compared to hand calculations to
determine if the results produced by PowerFLOW were reasonable. The results from the drag on
the payload alone as predicted by the software and as calculated by hand are shown in Table 13:
Table 13: Drag Prediction on the Payload Calculated by Hand and in PowerFLOW
Payload Drag (By Hand) Re C D Drag (PowerFLOW)
Rocket 0.082 lb 527473 0.75 0.081 lb
Bottle 1.64 lb 998681 0.85 0.531 lb
As seen in the preceding table, it is clear that the drag estimate was very close for the rocket but
for the bottle, the hand calculation was predicted to be much larger than the result from
PowerFLOW. The purpose of calculating drag by hand was to verify the results from
PowerFLOW and evaluate the discrepancy, if any. The reason that the hand calculation for the
drag on the rocket was so similar to the result obtained from PowerFLOW is because the drag
coefficient for the exact rocket being used was found to be 0.75 [18] .
On the other hand, for the bottle, the drag coefficient was estimated as a cylinder from Horener
[19] . The bottle being used on the airplane is not a perfect cylinder. This is responsible for the
difference in drag estimates for the bottle. Because the drag prediction for the rocket done by
hand was accurate (since the correct drag coefficient was used) and this value was different from
PowerFLOW by 0.001 lb, it is valid to assume that the predictions from PowerFLOW are
accurate with the caveat that the cases were set up correctly.
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