Abstract:
A novel transition model has been developed for use in CFD simulations of helicopter
rotor aerodynamics. The model includes significantly improved physical modelling
of the transition
processes occurring in the steady and unsteady flows found on
helicopter rotors. The model has been coupled with the k-co and k-co SST two
equation turbulence models using a novel adaptation of the technique developed by
Wilcox for the low Reynolds number k-oa model.
The method has been employed to calculate transitional flows occurring in three key
ow
regimes found in helicopter aerodynamics; that around steady and unsteady
aerofoils and that around a hovering helicopter rotor. The performance of the k-co and
the k-w SST turbulence models have been
investigated for transitional flow
simulations and the k-w SST shown to
provide substantial improvements for
transitional flows
containing separations. Dramatic improvements in the computed
pressure and skin friction distributions for several aerofoil flows have been observed
over those computed using a conventional fully turbulent simulation. Corresponding
improvements are observed in the computed lift and drag polars and transition on set is
well predicted for both low and high Reynolds number flows.
A novel structured/unstructured a priori adapted grid generation strategy has been
developed for hovering rotor flows that provides improved rotor solutions for
transitional flow analysis. The method offers vast improvements in the preservation
of vorticity in the solution at greatly reduced computational expense. Tip vortices
have been maintained to a Wake
age of 1170 degrees with just 2 million cells per
blade. The transition model has then been applied to the high quality rotor solutions
and
good agreement obtained between computed and experimental results,
highlighting that three-dimensional effects have a relatively small effect on hovering
rotor transition in-board of the blade tip. I addition, the first known verification of a
Navier-Stokes rotor code against the Fogarty semi-analytical rotating at plate case
was presented and excellent agreement obtained.
