
CENG
lOlA
 2009
SAMPLE PROBLEMS
D.M1LLER
During the last week
of
class, on Tues and Wed, we will review the course material and go over sample problems. Please bring
your texts to class. I have sketched some problems below which are typical
of
the type which may appear on the fmal. Please
come to class prepared to answer a few
of
these,
of
your choice,
if
you are called upon. We will only have time to outline the
approach you would take in most cases, i.e. indicate the method and which equation you would use, not to do the details with
numbers. You may assume you would be given appropriate dimensions, properties, empirical CD, and equations
or
that the
final is open book.
Example Questions
I. Answer
Briefly~
•
Since a rough surface increases friction and a turbulent flow has a larger effective viscosity than a laminar flow, which
should also increase friction shear forces, discuss briefly why dimpled
golfballs
have less drag and therefore go farther
than smooth balls
of
the same size and weight.
•
Why does streamlining a body sometimes reduce and sometimes increase the drag?
2. Answer Briefly:
•
List the assumptions necessary to obtain the NavierStokes equations
•
What
is
the difference between an Eulerian and a Lagrangian description
of
fluid mechanics, and what
is
the difference
between a control system and a control volume.
•
What
is
the buoyancy force due to?
•
From what Law is the extended Bernoulli equation derived? When
is
it valid only along a streamline?
3. Answer Briefly:
•
Discuss why does the water
jet
goes much
fwther
when you place your thumb over the garden hose exit and decrease the
exit area?
•
What are the Reynold's stresses, where do they come from, and when are they important.
4. Estimate the fluid velocity for transition from laminar to turbulent flow
if
the pipe diameter
is
I cm and the fluid
is:
(a)
water;
(b)
air . Does the result depend on whether the pipe is vertical
or
horizontal?
5. Derive a relation between the absolute pressure at any altitude h and the absolute pressure at sea
level,
given as P
=
Po
at y
=
0 . Assume air
is
an ideal gas P
=
pRT , and assume the atmosphere
is
isothermal
(RT
=
constant).
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 Fall '08
 staff
 Fluid Dynamics, Shear Stress, pipe, velocity field

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