Page 99 - Aeronautical Engineer Data Book

78 Aeronautical Engineer’s Data Book
Also:
∆p dp
K =
=
∆ d
and
�� � � K
p
d
a = =

d
where a = the velocity of propagation of a
pressure wave in the fluid
5.1.5 Fluid statics
Fluid statics is the study of fluids which are at rest
(i.e. not flowing) relative to the vessel containing
it. Pressure has four important characteristics:
• Pressure applied to a fluid in a closed vessel
(such as a hydraulic ram) is transmitted to
all parts of the closed vessel at the same
value (Pascal’s law).
• The magnitude of pressure force acting at
any point in a static fluid is the same,
irrespective of direction.
• Pressure force always acts perpendicular to
the boundary containing it.
• The pressure ‘inside’ a liquid increases in
proportion to its depth.
Other important static pressure equations are:

• Absolute pressure = gauge pressure +
atmospheric pressure.
• Pressure (p) at depth (h) in a liquid is given
by p = gh.
• A general equation for a fluid at rest is
�
dp �
pdA – p + dA – gdAdz = 0
dz
This relates to an infinitesimal vertical
cylinder of fluid.

5.2 Flow equations
Flow of a fluid may be one dimensional (1D),
two dimensional (2D) or three dimensional