An experimental investigation into the influence of trailing-edge separation on an aerofoil's dynamic stall performance

Niven, Andrew James (1988) An experimental investigation into the influence of trailing-edge separation on an aerofoil's dynamic stall performance. PhD thesis, University of Glasgow.

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Abstract

The influence of trailing-edge separation on the dynamic stall
characteristics of a typical rotor section is at present
unclear. Although previous research has given a fundamental
understanding of the unsteady stall process, the variety of
aerofoils tested has made it difficult to isolate the effect
of trailing-edge separation. Further investigation into this
field may be carried out by testing two similar aerofoils
which differ only in their trailing-edge separation
characteristics. The early part of the work concentrated on
the development of a numerical method whereby the theoretical
pressure gradient over the trailing-edge upper surface of a
given aerofoil may be modified to either enhance or reduce
such separation. Since previous work at the University of
Glasgow had included a detailed unsteady aerodynamic study of
a NACA 23012 aerofoil, this was the appropriate profile for
modification. The above technique was applied to this aerofoil
with the objective of modifying the geometry in such a manner
that would retain the leading-edge pressure distribution
whilst forcing an earlier and more gradual trailing-edge
separation growth. The subsequently designed aerofoil,
designated the NACA 23012(A), was shown to display an
enhancement of the trailing-edge separation characteristics
via both boundary-layer calculations and oil-flow
visualisation tests.
On comparison with unsteady data previously collected for the
NACA 23012, several systematic methods of estimating the effects of trailing-edge separation on the dynamic stall
process are presented. During oscillatory tests the NACA
23012(A) displayed a more stable damping characteristic which
was attributed to the enhanced trailing-edge separation
producing an earlier pitching-moment break. Based on the
analysis of pressure-time histories obtained during ramp
tests, it was deduced that a consequence of significant
trailing-edge separation was to delay the initiation of the
dynamic stall vortex. Detailed analysis of hot-film data led
to the conclusion that aerofoils which display a tendency to
stall in steady conditions, via separation growth from the
trailing-edge, will experience vortex initiation by the
breakdown of a thin layer of reversed flow travelling upstream
beneath a stable shear layer which remains in close proximity
to the aerofoil's surface contour.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Subjects: T Technology > TL Motor vehicles. Aeronautics. Astronautics
Colleges/Schools: College of Science and Engineering > School of Engineering > Aerospace Sciences
Supervisor's Name: Galbraith, Dr. R.A. McD.
Date of Award: 1988
Depositing User: Ms Dawn Pike
Unique ID: glathesis:1988-5380
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 10 Jul 2014 15:48
Last Modified: 10 Jul 2014 15:48
URI: http://theses.gla.ac.uk/id/eprint/5380

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