Aerodynamics and Design for Ultra-Low Reynolds Number Flight
Aerodynamics and Design for Ultra-Low Reynolds Number Flight
Aerodynamics and Design for Ultra-Low Reynolds Number Flight
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FIGURE 5.14 Near-body grid geometry.<br />
The remaining cells are distributed across three levels of Cartesian off-body grids,<br />
surrounding the near-body grids, with the innermost domain matching the outer cell<br />
Chapter 5<br />
spacing of the near-body volume grids. The total grid size is approximately 5.5 million<br />
cells <strong>and</strong> required approximately 24 hours to run a single operating point using 16<br />
processors of a SGI Origin 2000.<br />
In order to reasonably assume steady-state flow, the hub model had to differ significantly<br />
from the actual part. The as-built rotors employ a 1.0mm high, 2.5mm diameter disk as<br />
a hub. In use, the underside of the hub is effectively faired by the presence of the motor.<br />
The flat upper <strong>and</strong> lower surfaces of the hub, combined with the absence of the motor<br />
body in the computation, would result in large amounts of unsteady, separated flow. This<br />
problem is dealt with by increasing the height of the modeled hub <strong>and</strong> capping both ends<br />
with hemispheres.<br />
Separation is less likely, but the modified hub adds significant wetted area. The skin<br />
friction drag of the hub is not incorporated into the calculation of the global rotor <strong>for</strong>ces,<br />
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