Abstract:
A two-dimensional model of the aerodynamics of rotor blades in
forward flight is proposed in which the motion of the blade is
represented by periodical variations of the freestrearn velocity and
incidence. A novel implicit methodology for the solution of the
compressible Reynolds averaged Navier-Stokes equations and a twoequation
model of turbulence is developed. The spatial discretisation is
based upon Osher's approximate Riernann solver, while time integration
is performed using a Newton-Krylov method.
The method is employed to calculate the steady transonic
aerodynamics of two supercritical aerofoils and the unsteady
aerodynamics of pitching aerofoils. Comparison with experiment and
independent calculations for these test cases is satisfactory. Further
calculations are performed for the self-excited periodic flow around a biconvex
aerofoil. Comparison of quasi-steady and unsteady calculations
suggests that the flow instability responsible for the self-excited flow is
due to the presence of a shock induced separation bubble in the
corresponding steady flow.
Finally the method is used to predict the aerodynamics of aerofoils
performing inplane and combined inplane-pitching motions. Results
show that quasi-steady aerodynamic models are unsuitable at conditions
representative of high-speed forward flight. For shock free flows, the
unsteady effects of freestrearn oscillations can be represented by a
simple phase lag. For transonic flows the influence of unsteadiness on
shock wave dynamics is shown to be complex. Calculations for indicial
motion show that the unsteady behaviour of the flow is related to the
finite time taken by disturbance waves to travel to the shock wave from
the leading and trailing edges of the aerofoil.
