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As the X-33 nears final construction, the analytical emphasis has been
redirected from generating design data to mitigating flight risk.
Computational simulation of the flow field surrounding deflected elevon
control surfaces has been performed to verify engineering estimates of
the heating levels that the canted fin must be designed to withstand.
This analysis serves to reaffirm design assumptions and reduce
uncertainty, thus decreasing flight risk.
In previous simulations,
surface heating predictions were based on the assumption of a smooth
body. In reality, the body surface has both protuberances, such as
steps and gaps formed between seals or tiles, and control-surface
deflections that divert the flow from its nominal path. These surface
irregularities and control-surface deflections trigger local fluid
mechanical interactions that increase the heat transfer in some zone of
influence on the surface. The thermal protection system is designed to
account for these local effects by applying multiplicative scale
factors, derived through empiricism and theory that augment the
baseline smooth-body heating levels.
To validate the design
correlations, computational fluid dynamics (CFD) techniques have been
used to simulate the flow field around deflected elevon control
surfaces. The geometric model includes the gap between the elevon
control surface and the main body, the gap between the elevon surfaces,
and the abbreviated edge of the elevon at the tip of the canted fin.
Figure 1 shows radiative equilibrium surface temperature contours on
the windward side of the X-33, along with an expanded view of the
deflected elevon surfaces. The flow conditions are Mach 10, an angle of
attack of 30 degrees, an altitude of 180,000 feet, and elevon
control-surface deflection of 25 degrees. Evident in the figure is the
increased heating on the face of the elevon generated by its deflection
into the hypersonic flow field. Also discernible is increased heating
on the sides of the elevon caused by the flow accelerating around the
edges of the control surface. The maximum elevon surface temperature
occurs in the gap region. These results are being used to verify the
suitability of the design.
Point of Contact: D. Kontinos
(650) 604-4283
dkontinos@mail.arc.nasa.gov
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Fig. 1. Computed radiative equilibrium surface temperature contours on the X-33 vehicle with the elevon control surface deflected 25 degrees at
Mach 9, an angle of attack of 30 degrees, and an altitude of 180,000 feet.
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