Project Title:

A Simplified Vorticity-Enhanced Potential Flow Method for Early

Nielsen Engineering & Research, Inc.
526 Clyde Avenue
Mountain View, CA 94043-2212

93-1 02.05 9457A

A Simplified Vorticity-Enhanced Potential Flow Method for Early
Design and Analysis of Maneuvering Aircraft at High Angles of
Attack

Abstract:

Maneuvering aircraft at high angles of attack experience severe
unsteady loading.  This loading, when unanticipated at the design
stage, can cause fatigue problems and, possibly, structural
failure.  Such instances have occurred in the past, for example
on the twin vertical tail section of aircraft such as the F-15
and F-18, and may be anticipated with the F-22.  The costs
associated with retrofitting such aircraft are substantial.  If
the aerodynamic problems and/or fluid/structure interactions are
caught early in the design cycle, much of those costs can be
avoided.  Preliminary design of high performance highly agile
flight vehicles requires efficient aerodynamic analysis tools. 
These tools must be capable of capturing the key physics which
are the cause of these adverse interactions.  For high angles of
attack and/or unsteady maneuver, the flowfield is complex and the
aerodynamic loads can no longer be characterized by simplified,
quasi-linear, methods such as aerodynamic derivatives.  The
research work proposed herein is to develop a viable alternative
to existing methods by enhancing a well-tested three-dimensional
unsteady full potential code to include high angle of attack
vortical effects.

The proposed project is of considerable benefit to the Federal
Government and to the aerospace industry because the completed
Phase II project will deliver an engineering methodology and a
prediction tool to help designers to ensure that the fatigue
problems occurring on twin-tail tactical fighters do not arise in
future aircraft designs.  The completed project provides the
basis for commercial software that will be licensed to the
aircraft and missile production companies to help their design
process.

Unsteady Aerodynamics, Unsteady Flow Separation, Vortex
Breakdown, Buffeting, Mathematical Modeling, High Angle of
Attack, Potential Flow, Computational Fluid Dynamics