李苏克
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【电子书】Theoretical and Applied Aerodynamics - and Related Numerical Methods 1th 2015
Preface
The purpose of this book is to expose students to the classical theories of aerodynamics
to enable them to apply the results to a wide range of projects, from
aircraft to wind turbines and propellers. Most of the tools are analytical, but
computer codes are also available and are used by the students to carry out seven to
eight projects during the course of a quarter. These computer tools can be found at
http://mae.ucdavis.edu/chattot/EAE127/ along with the project statements.
The main focus is on aircraft and the theories and codes that help in estimating
the forces and moments acting on profiles, wings, wing-tail and fuselage configurations,
appropriate to the flow regime, i.e., subsonic, transonic, supersonic, viscous
or inviscid, depending on the Mach number and Reynolds number.
The book culminates with a study of the longitudinal equilibrium of a glider and
its static stability, a topic that is not usually found in an aerodynamics but in a
stability and controls book. This chapter reflects the expertise of one of the authors
(JJC), who has been involved for several years in the SAE Aero Design West
competition, as faculty advisor for a student team, (http://students.sae.org/
competitions/aerodesign/west/) and has developed the tools and capabilities
enabling students to develop their own designs and perform well in the competition.
As all airplane modelers know, placing the center of gravity in the correct location
is critical to the viability of an aircraft, and a statically stable remote controlled
model is a requirement for human piloting.
The material is presented in a progressive way, starting with plane, twodimensional
flow past cylinders of various cross sections and then by mid-quarter,
moving to three-dimensional flows past finite wings and slender bodies. In a similar
fashion, inviscid incompressible flow is followed by compressible flow and transonic
flow, the latter requiring the numerical solution of the nonlinear transonic
small disturbance equation (TSD). Viscous effects are discussed and also, due to
nonlinear governing equations, numerical simulation is emphasized.
A set of problems with solutions is placed in Part III. It corresponds to final
examinations given over the last 10 years or so that the students have 2 hours to
complete.
Finally, the reader is assumed to have the basic knowledge in fluid mechanics
that can be found in standard textbooks on this topic, in particular as concerns the
physical properties of fluids (density, pressure, temperature, equation of state,
viscosity, etc.) and the conservation theorems using control volumes. The reader is
also assumed to master undergraduate mathematics (calculus of single variables,
vector calculus, linear algebra, and differential equations). Three appendices are
included in the book, summarizing the material relevant to the subject of interest.
Aerodynamics has a long history and it has reached a mature status during the
last century. There are at least 20 books written on aerodynamics in the last 20 years
(see references). Some of these are excellent textbooks and some are outdated or out
of print. All of the existing texts are based, however, on small disturbance theories.
These theories are essential to gain understanding of the physical phenomena
involved and the corresponding structure of the flow fields. They also provide good
approximations for some simple cases. For practical problems, however, there is a
demand for accurate solutions using modern computer simulation. Small disturbance
theories can still provide special solutions to test the computer codes. More
important perhaps, they can provide a guideline to construct accurate and efficient
algorithms for practical flow simulations. They are also used to develop the far field
behavior required for the numerical solution of the boundary value problems. In
general, the linearized boundary conditions and the restriction to Cartesian grids are
no longer sufficient. Grid generation algorithms for complete airplanes, although
still a major task in a simulation, are nowadays used routinely in industry. Hence,
small disturbance approximations are no longer necessary and indeed full nonlinear
potential flow codes, developed over the last two decades, are available everywhere.
While it is argued that the corrections to potential flow solutions due to vorticity
generated at the shocks can be ignored for cruising speed at design conditions, the
viscous effects are definitely important to assess. Again, boundary layer approximations
can be useful as a guideline to construct effective viscous/inviscid interaction
procedures.
In the book we adopt this view in contrast to a complete CFD approach based on
the solution of the Navier-Stokes equations everywhere in the field for more than
one reason: it is more attractive, from an educational viewpoint, to use potential
flow model and viscous correction. It is also more practical, since Euler and hence
Navier-Stokes codes are more expensive and subject to errors due to artificial
viscosity as a result of the discrete approximations. A simple example is the
accurate capturing of the wake of a wing and the calculation of induced drag, still a
challenge today; for the same reasons, the simulations of propellers and helicopter
rotor flows are in continuing development, let alone, the problem of turbulence.
In the text, the formulation and the numerics are developed progressively to
allow for both small disturbances and full nonlinear potential flows with viscous/
inviscid interactions. Only a few existing books (two or three) address these issues
and we hope to cover this material in a thorough and simple manner.