Tripathi, Manish and Misra, A and M S, Mahesh
(2018)
Effect of Rectangular and Airfoil Planar Member
Cross-section on Cascade Fin Aerodynamics.
In: 2018 AIAA Atmospheric Flight Mechanics Conference, 8–12 January 2018, Kissimmee, Florida.
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Abstract
Grid fins are unconventional control and lifting surfaces consisting of an outer frame
supporting an inner grid of small chord intersecting planar surfaces. These have been
credited for their enhanced lifting characteristics at high angles of attack and high Mach
numbers, miniscule hinge moments with a marginal increase in drag. These have been
used on missiles, reusable launch vehicles etc. Cascade fins, with removal of all the cross
members are a simplified variant of grid fins. In the present study, a sequence of viscous
computational fluid dynamic simulations were performed at low subsonic velocity and high
angles of attack to explicitly study the impact of planar member cross-sectional shape on
the flow characteristics of a cascade fin. Investigations were carried out to elucidate the
effect of NACA0012 airfoil cross-section instead of rectangular flat plate cross-section for
the horizontal members of a cascade fin. Additional simulations to decipher the effect of
varying minimum gap between the airfoil plates was carried out and compared against
results obtained for varying gap between plates for the rectangular flat plate cascade. The
solver has been validated for numerical accuracy by comparing drag and lift coefficient data
available in the literature. The results are indicative of the reduced drag levels leading
to an enhanced aerodynamic efficiency (0
°
- 30
°
) due to airfoil cross-section. Similar or
enhanced lifting characteristics are obtained for airfoil cascade compared to rectangular
cascade before stalling. Albeit, it also leads to hastened and steeper stalling compared
to that of the rectangular plate cascade. Thus, rectangular cascades perform better at
higher angles. Static stability remains the same below the stalling region. Moreover,
inferences related to comparison between the two cross-sections for varying gaps has also
been discussed. The underlying physics associated to change in aerodynamics for respective
variation has been carried out using pressure distribution plots, velocity-pressure contours
and velocity vector based flow visualization plots. Thus, optimized selection of airfoil
as cross-section based on aerodynamic efficiency enhancement, reduced operable angle of
attack region and the higher cost of manufacturing compared to rectangular cascades with
a viable gap selection can be carried out using this analysis
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