New and less-known results in the theory of oscillatory and wave
phenomena in fluid flows are presented. A unified approach, based
on physical intuition mixed with simple analytical models,
is used for waves of different physical origins. It allows a
quantitative analysis in terms of physics, which complements significantly
the traditional formal mathematical approach.

Some physical concepts such as wave energy and momentum in a
moving fluid are analyzed taking into account induced mean flows.
The physical mechanisms that are responsible for hydrodynamic
instability of shear flows are considered within the concept of
negative energy waves. A variety of phenomena for waves of different types
is analysed, based on the phenomenon of wave over-reflection.
A number of well-known theorems of hydrodynamic theory of stability
are interpreted in terms of
the interaction of waves having different energy signs. Great
attention is drawn to the plasma-hydrodynamic analogy which is a
powerful tool for physical analyses of general mechanisms of wave
amplification and absorption in flows. A lot of hydrodynamical,
acoustical and geophysical phenomena may be classified on the
basis of this analogy. Various wave-flow interaction problems are
considered, for instance, wave generation in whistlers, wave
scattering and amplification by vortices, methods of wave remote
sounding, some nonlinear dynamical phenomena, etc.

The book is intended for researchers specialized in wave theory,
aero-acoustics, geophysical and astrophysical fluid dynamics, and
related fields.