Abstract:
A combined experimental and theoretical study is described of the low speed flow over a
highly swept and cambered wing that simulates the flow features of a transonic manoeuvre
condition. The thesis is divided into two parts:
Part I examines the research objectives from a customer perspective, with background
information on the project history and funding sources. Since the research is aimed at
improving the aerodynamic performance of low observable configurations, stealth
technologies are discussed and their implications for combat aircraft wing flows. The
management chapter of the thesis then discusses the influences affecting the decision making
process for the acquisition of weapon systems in the UK.
Part II describes the design of a highly swept and cambered wing that generates strong adverse
pressure gradients near the trailing edge, leading to three-dimensional separations in this
region. Using surface flow visualisation the nature of these flows is defined, indicating how the
position of a separated streamline moves forward with increasing angle of incidence. These
observations are confirmed by flow predictions using the SAUNA Computational Fluid
Dynamics (CFD) method that solves the Reynolds Averaged Navier-Stokes equations,
employing a two-equation turbulence model. The mechanism of the flow separation is also
predicted using CFD, indicating that a separated stream surface reattaches at the wing trailing
edge, forming a ‘tunnel’ of separated flow. To the authors knowledge this represents the first
time that the main physical features of such a complex three-dimensional separated flow has
been modelled using a CFD method. From an evaluation of the CFD methods employed, a
design process has been proposed by which a wing designer can determine if wing flows over
similar configurations remain attached.
Additionally, the velocity magnitudes within parts of the separated shear layers and the wake
are obtained using an optical non-intrusive measurement technique and give good agreement
with the theory. -