# FLUID MECHANICS LAB 1

Μηχανική

24 Οκτ 2013 (πριν από 4 χρόνια και 7 μήνες)

76 εμφανίσεις

FLUID MECHANICS LAB 1

Purpose
: a.) To provide a variety of experiences with fluids which will serve as a basis

for future study and future analysis.

b.) To provide practice in carefu
l observation as related to good experimental

methods.

Procedure
:

STATIONS

1. Straws.

In this section we used our mouths as pumps and various straws as the piping
system. Keeping the pressure from the pumps pretty much constant, we
experimente
d with many different straws to see what effect they would have on
the flowrate of the system. What was observed in this station was that the only
factor that seemed to have an effect on the flowrate was the diameter of the straw.
As we increased the dia
meter of the straws, the flowrate would also increase. The
overall length of the piping system didn’t seem to have any significant effect on
the flowrate. For example, compare a straw that has numerous bends making its
true undeformed length considerably

large, but with the same diameter as a straw
that is undeformed but with less overall length. The two straws both seem to have
the same flowrate.

One factor that was overlooked in the experiment, but would seem to have an
effect on the flowrate is the ch
ange in height of the straw. The height difference
from one opening of the straw to the other would seem to effect the time it takes
for a fluid to pass through the entire straw. This was unnoticed in the experiment
because there weren’t any significant
differences in the height changes of each of
the straws. This is one thing I would like to confirm later in the course.

2.

Vortex Gun (container with hole).

This station involved created a vortex by tapping on the backside of a can with a
hole centered abou
t the opposite side. With each tap, a vortex was created
through and hole and moved in a linear manner until it died out. Although the
vortex was not visible, it was confirmed by blowing out a lighted candle some
distance away. The distance the vortex t
raveled was found by increasing the
distance between the can and the flame, while still being able to extinguish the
flame.

How the vortex forms is still not clear to me. I can only guess by knowing the
overall shape of a vortex and observing the shape of

the hole cut out of the can.
This is yet another thing I look forward to learning later in the course.

3.

Vortex Gun (dye in water).

Now that I am writing up the report I realize stations 2 & 3 might only be counted
as one. I apologize for this. Although

ignorance is not an excuse, had I been
aware I would have easily performed another experiment.

The dye visualization was a great way to observe and shape and movement of a
vortex. We observed the vortices move through the water until they die out at the
surface or until they reach the container wall. When they reached a wall, the
vortices seemed to be increasing in size. This was explained as a reaction of a
vortex seeing a mirror image of itself reflecting off the wall. This is another
phenomenon I lo
ok forward to working with in the future.

4.

Diving Tony.

Playing with Diving Tony was something I remember doing as a kid, but never
bothered to figure out how it worked. It was observed that as we put pressure on
the walls of the 2
-
liter, Tony would begin

to dive down into the water. The harder
we squeezed, the farther he would go. We removed Tony from his natural
environment and noticed a small pocket on the bottom of him. We concluded that
this pocket trapped and stored air while Tony was inside the 2
-
liter. As we
squeezed the container, we were increasing the pressure inside the container.
Because the volume of a liquid is held pretty much constant, the bubble of air
underneath Tony had to decrease in size. Since the volume of this air is
decreasin
g and the mass is held constant, the density of it had to be increasing.
The density of this air increases until it reaches a certain value, in which Tony
begins is descent to the bottom of the container. If this density is brought to some
value and held

constant, it can be observed that Tony will stay at some resulting
height. Also, the faster the container is squeezed, the quicker Tony will dive to
the bottom of his home.

5.

Airplanes.

For this experiment, the large Styrofoam glider was used. The glider

was
assembled and brought to an indoor location with sufficient throwing area. As the
glider was passed back and forth, we quickly learned what adjustments had to be
made in order for the glider to have a successful flight. When the flaps on the
back of

the plane were tipped downward, the plane would fly downward. And
conversely, when the tips were aimed upward, the plane would fly up. Also, the
greater upward the tips were positioned, the quicker the plane would fly up. If
ailable, the plane would create a loop after it was
released.

6.

Rockets.

For this station we used the same rocket and pump for all trials. All variables
were held constant as we varied only the number of pumps. This included
maintaining a constant angle o
f projection and a constant amount of water in the
missile. The projection angle as an impact on the how far the missile will travel.
An angle of 45 deg. yields the maximum travel with the missile and was the angle
used in the experiment. Also, the amou
nt of water used for each trial is
significant. The projectile soars in a somewhat smooth fashion until all the water
is drained from the missile. At this time, the projectile tends to dwindle away and
fall to the ground. The following formula is for ca
lculating the thrust of the
projectile.

Thrust =

A V
2

where

is the density of the water used, A is the flow area, and V is the volume
of the water in the missile. Since the density and flow area remained constant, the
thrust varies only with the volum
e of the water. The volume of water inside the
missile is highest prior to launching, so the thrust is at a maximum when it is first
released and decreases as the volume of water decreases. Since the thrust depends
on the square of the volume, I wouldn’t

expect the position graph of the projectile
versus time to be linear. Also, the equations of motion learned in physics class
wouldn’t work for this application since the thrust of the projectile varies over
time and is not like the standard throwing of a

baseball with only an initial
velocity. I would expect, however, the graph of the position of the missile versus
the number of pumps to be linear.