ME 130L
17810 – 17895
The University of Texas at Austin
Mechanical Engineering Department
Spring ’10
Dr. Hidrovo
1
ME 130L
Experimental Fluid Mechanics
Background and PreLab #3  Wind Tunnel Measurements and Dimensional Analysis of a
Scaled Down Wind Turbine
I.
Background
All of our measurements in this lab are based on an understanding of the Bernoulli
equation.
This equation and its application to velocity measurement are described below.
1.
The Bernoulli Equation
The Bernoulli equation is one of the most powerful, and most abused, in fluid mechanics.
It states that the total energy of a fluid particle traveling along a streamline between any two
points 1 and 2, shown on Figure 1, is conserved:
()
p +
1
/
2
·
ρ
V
2
+
ρ
gz
1
=
p +
1
/
2
·
ρ
V
2
+
ρ
2
= Constant
p , V
11
p
, V
22
z
1
z
2
reference line
Figure 1: Streamline with reference potential energy line used in the Bernoulli eqn.
This equation is really just a restatement of conservation of mechanical energy.
In
physics you learned that the potential energy (
mgh
) of a body is converted to kinetic energy
(
1
/
2
·
mV
2
) as it falls, but the total energy of the body (the sum of the two terms) is conserved and
remains constant.
The Bernoulli equation can be thought of as the same physical principle
adapted to fluids in two important ways.
The first is that it is converted to a perunitvolume
basis (hence the mass
m
is replaced by the density
ρ
), and the second is that the static pressure
term (
p
) is included.
The Bernoulli equation is
only
valid when the following conditions are satisfied:
1.
The equation is applied along a streamline.
2.
The flow is steady.
3.
The flow is incompressible; i.e.,
≈
constant (true if the Mach number is less than about
0.3).
4.
The flow is inviscid (frictionless).
This preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentME 130L
17810 – 17895
The University of Texas at Austin
Mechanical Engineering Department
Spring ’10
Dr. Hidrovo
2
2.
Nomenclature
p
Static pressure, total pressure,
or
thermodynamic pressure
is the pressure that is
felt when moving with the flow.
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '07
 Koen
 Mechanical Engineering, Fluid Dynamics, Wind turbine, Stagnation pressure, Mechanical Engineering Department

Click to edit the document details