Simulation of Cryogenics Cavitation

gapingthingsΠολεοδομικά Έργα

15 Νοε 2013 (πριν από 3 χρόνια και 4 μήνες)

88 εμφανίσεις


Simulation of C
ryogenics
Cavitation


Sean Kelly
1

and Corin Segal
2

University of Florida, Gainesville, Florida, 32611, USA

Cavitation in turbopumps is a major concern to the performance
and longevity of this equipment
since it leads to v
ibration, unst
eady flow and
potentially
destructive erosion

of

the surfaces.
Unlike
conventional substances such as water, cryogenics undergo a large temperature deficit that occurs
under

vaporization

and therefore cavitation in water is
quite
different than in cryogeni
cs
1
.
Therefore,

cavitation
simulation in water is limited. Hence, the study

detailed below employs a thermosensitive fluid to
simulate cryogenic cavitation.
The onset and formation of vapor b
ubbles and cloud cavitation

is

studied
here
under various
cavitation
conditions
using a

NACA 0015 hydrofoil as a generic surface.

The
experienced

conditions include changes in fluid velocity and cavitation number.


C
ryogenic
s

are

simulated
with perfluorinated ketone 2
-
trifluoromethyl
-
1, 1, 1, 2, 4, 4, 5, 5,
5
-
non
afluoro
-
3
-
pentanone as the working fluid at temperatures
between
25 and 70 degrees C.
2

The angle of attack of the airfoil
is

varied
from 0 to 7 degrees

and the freestream fluid velocity
is

in the range of
6

to 10 m/s.
Strouhal numbers vary between 0.07 to 0.5 and Reynolds numbers of
the flow occur between
780
,000 and 2
,120
,000.

The hydrofoil has a chord length of 50.8mm and



1

Graduate Research Assistant, MAE University of Florida, Gainesville FL 32611.

2

Associate Professor, MAE University of Florida, Gainesville FL 32611, Associate Fellow AIAA.

the flow has a dynamic viscosity ranging from 3.53 x10
-
4
to 6.26x10
-
4

kg/m*s.
Cavitation
number
,

defined as



















is
achieved in these experiments
in a
range from

2.11 at 6 m/s and 25 degrees C
to almost zero

at 10 m/s and 48 degrees C
, thus a broad range of cavitation conditions
can

be simulated
.

The fluid was chosen for its
large temperature change during evaporation

and hence
the
local effect on the cavitation characteristics is significant
. It appears
as

T


which is found from

* 0.7 0.2
Pr Re
T T
    

The flow being studied has

a thermodynamic effect on the
same order of magnitude as

liquid
hydrogen
, whereas water ranges on the order of magnitude of 0.01
.
This thermodynamic effect is defined
as

*
,
vap
v
p l
H
T
C



 

.

Figure 1
a

shows the
facility
, which has a 10
0
x 10
0mm
test section capable of 10

m/s

maximum

flow and has optical access from the top and front via glass windows and laser access
through the hydrofoil. It is equipped with stagnation and settling chambers
and a 7.5kW
submersion
heater. The hydrofoil can be pos
itioned with an angle of attack from
-
10 to 10
degrees.
Figure 1b shows
selected results of
cavitation on the hydrofoil. At the bottom of the
image filaments of incipient cavitation appear on the hydrofoil and at the top there appears the
onset of cloud ca
vitation.

Figure 2 shows
selected results of well
-
developed

cloud cavitation over the entire span of
th
e hydrofoil when the

cavitation number
was set to

0.7. This type of cavitation is
turbulent and
increases the

heat transfer to the surface
, a

potentially
significant

loss in flow rate
for a pump,
and an increase in vibration and
high differential
pressure
fluctuations across the suction and

pressure sides
.

Figure
2a

is a top view with the leading and trailing edge identified in the image.
Figure

2b
is a side view with the hydrofoil suction side evident.
It

can be seen

from figure
2

that
cavitation extends beyond the trailing edge of the hydrofoil

and although the initial conditions
and geometry are 2
-
D,

cavitation is

3 dimensional

and unsteady
.
These two images were taken in
different experiments and indicate a large degree of unsteadiness is present.



a)







b)


Fig. 1

a) layout of the
facility

used in the experiments
.

This facility has a test section measuring 102x 102 mm

capable of
9.6 m/s with optical access from the top and side via glass windows and via laser sheet from the rear.

b)
Top view of
NACA0015 hydrofoil
under incipient cavitation

in f
louroketone at ambient pressure and temperatures
of 1atm and 25°C, respectively. Flow is

from left to right at 6.7 m/s., angle of attack is 5.1 degrees.




a)






b)

Fig. 2

a) Top view of cavitation at 35 degrees C and 8.64 m/s. This corresponds to a cavitation number of 0.7. Flow
from left to right. Superimposed vertical lines i
ndicate leading and trailing edge of the hydrofoil. b) Side view of
flow
at 40 degrees C and 7,16 m/s
. Flow is from left to right. Vertical lines indicate leading and trailing edge of the
hydrofoil.




References


1.

Cervone, A., Bramanti, C., Rapposelli, E., d’Agostino, L., “Thermal Cavitation Experiments on a
NACA 0015 Hydrofoil”.
Transactions of the ASME
,
128

(3), p. 326
-
331, 2006.

2.

Gustavsson, J. P. R., Denning, K., Segal, C.,

Experimental study of Cryogenic Cavita
tion Using
Fluoroketone

, AIAA 2008
-
0576,
46
th

AIAA Aerospace Sciences Meeting and Exhibit
, Reno, NV,
Jan 7
-
10, 2008