A theoretical analysis comparing the fan power and coolant (LN2) flow rates resulting from injection of the LN2 either upstream or downstream of the drive fan of a closed circuit transonic cryogenic tunnel is presented. The analysis is restricted to steady state tunnel operation and to the condition that the tunnel walls are adiabatic. The stagnation pressure and temperature range of the tunnel is from 1.0 to 8.8 atm and from 300 K to liquefaction temperature, respectively. Calculations are made using real gas properties of nitrogen. Results show that the fan power and LN2 flow rates are lower if the LN2 is injected upstream of the fan. The lower fan inlet temperature resulting from injecting upstream of the fan has a greater influence on the power than does the additional mass flow going through the fan

Adcock, J. B.

English

NASA Technical Reports Server

General Disclaimer 
One or more of the Following Statements may affect this Document 
 
 This document has been reproduced from the best copy furnished by the 
organizational source. It is being released in the interest of making available as 
much information as possible. 
 
 This document may contain data, which exceeds the sheet parameters. It was 
furnished in this condition by the organizational source and is the best copy 
available. 
 
 This document may contain tone-on-tone or color graphs, charts and/or pictures, 
which have been reproduced in black and white. 
 
 This document is paginated as submitted by the original source. 
 
 Portions of this document are not fully legible due to the historical nature of some 
of the material. However, it is the best reproduction available from the original 
submission. 
 
 
 
 
 
 
 
Produced by the NASA Center for Aerospace Information (CASI) 
https://ntrs.nasa.gov/search.jsp?R=19770020193 2020-03-22T09:29:00+00:00Z
a
0
st
t«^
tto
ROM
National Aeronautics and
Space Administration
Umoey Asseerch Center
Hampton, Virpinla 23665
s f i77
NAM
RECEIVED
	
'P ?1
INPUT BRAG
NASA TECHNICAL.	 NASA TM X- 74036
MEMORANDUM
(NASA —TM —X-74036) EFFECT OF LN2 INJECTION
STATION LOCATION ON THE DRIVE FAN POWER AND
LN2 BEQUIRERENTS OF A CRYOGENIC WIND TUNNEL
(NASA) 19 p HC A02/11F 101	 CSCL 14B
G3/09
N77-27137
Uaclas
35507
EFFECT OF LN2
 INJECTION STATION LOCATION ON THE DRIVE FAN
POWER AND LN2
 REQUIREMENTS OF A CRYOGENIC WIND TUNNEL
By
JERRY B. ADCOCK
JUNE 1977
#	 This informal documentation medium is used to provide accelerated or
special release of technical information to selected users. The contents
may not most NASA formal editing and publication standards, may be re-
vised, or may be incorporated in another publication.
WFRCT OF LB  IWECTION STATION LOCATION ON THE
DRIYL PAN POW= A39D LN2 R IR OM OP A
CRYOGMC WIND TUNNEL
Jerry B. Adcock
ABSTMUCT
I
This theoretical analysis consists of comparing the fan power and LN2
 flow
rates resulting from the injection of LN2
 either upstream or downstream of the
fan of a closed circuit transonic cryogenic tunnel. The analysis is restricted
to steady-state tunnel operation. The results show that the fan power and
LN2 flow rates are lower if the LN2 is injected upstream of the fan.
SUPMY
The theoretical analysis of this report compares the fan power and
coolant 02 ) flow rates resulting from injection of the LN 2
 either upstream or
downstream of the drive fan of a closed circuit transonic cryogenic tunnel.
The analysis is restricted to steady-state tunnel operation and to the condi-
tion that the tunnel walls are adiabatic. The stagnation pressure and
temperature range of the tunnel is from 1.0 to 8.8 atm and from 300 K to
f
liquefaction temperature, respectively. The calculations are made using the
real-gas properties of nitrogen. The results show that the fan power and
f
LN2 flow rates are lower if the LN 2
 is injected upstream of the fan. The
lowear fan inlet temperature resulting from injecting upstream of the fan has a
greater influence on the power than does the additional mass flow !going
through the fan.
INTRODUCTION
A new transonic wind tunnel that will satisfy the nation's high Reynolds
number test needs is currently being designed at the Langley Research Center
(ref. 1). This tunnel is based on the cryogenic concept that was developed
and demonstrated at Langley (refs. 2, 3). One of the main advantages of
reducing the temperature of the test gas as a means of obtaining the desired
high Reynolds number capability is that a large reduction in tunnel size is
afforded while maintaining acceptable stagnated pressures thereby resulting in
large savings in capital cost.
For this concept, reduction of the test gas temperature and the removal
of the heat generated by the drive fan and the heat conducted through the
walls of the tunnel is accomplished by pumping liquid nitrogen into the circuit
and letting it vaporize. The location in the tunnel circuit for this LN 2
 injec-
tion is being studied in the design of the above mentioned tunnel. Some of
the considerations are; sufficient distance upstream from the test section in
order to insure thorough mining and uniform temperatures at the test section,
excessive thermal stresses and possible material errosion due to LN 2
 droplets
impinging on internal structures, and the effect of the location of the
injection relative to the drive fan on tunnel drive power and 1112 consumption.
The purpose of this paper is to present an analytical comparison of the drive
power and LN2
 requirements associated with LN2
 injection upstream and down.-
strewn of the drive fan.
2
SYMBG :,S
CP	 specific heat at constant pressure, J/(kg•K)
S	 flow of energy, per unit time, J/sec
h	 specific enthalpy, J /kg
m	 mass—flow rate, kg/sec
p	 pressure, atm
r	 fan total pressure ratio, pt,4/pt,3
T	 temperature, K
i+1	 work per unit time or power, J/sec
Y	 ratio of specific heats
P	 density, kg/m3
Subscripts
DN	 downstream of fan
e	 exhaust gas
F	 fan
i	 LN2 injected
3
s	 constant entropy
t	 stagnation condition
UP	 upstream of fan
0,1,2,3,4,5	 tunnel station numbers
ANALYTICAL MODEL AND PROCEDURE
The operational mode of the cryogenic tunnel to be considered in this
analysis is the steady-state mode (i.e., constant stagnation temperature,
stagnation pressure, and test section Mach number). The test conditions to be
considered encompass the envelope of the tunnel that is under design. The
stagnation pressure range is from 1.0 to 8.8 atm and the stagnation temperature
range is from ambiFrt temperatures (300 K) down to liquefaction temperatures
(80-120 K, depending on pressure). The fan pressure ratios necessary to
achieve a given test section Mach number in the closed-circuit fan-driven
tunnel are assumed to be as follows:
Ml r
0.2 1.025
o.b 1.050
0.8 1.075
1.0 1.100
1.2 1.200
a
4
It is further assumed that this Mach number-pressure ratio correspondence is
invariant with stagnation temperature and pressure. In these calculations, the
real gas properties of nitrogen as given by J'acobsen's equation of state
(ref. 4) will be utilized.
A sketch of the analytical model tunnel is shown in figure 1. There is a
supply reservoir where LN2 is stored at 1.0 atm and the corresponding vapor
temperature. From this reservoir LN 2 is pumped into the tunnel at either the
upstream injection station (2) or the downstream injection station (4). This
pumping is assumed to be isentropic and it is further assumed that the liquid
must be pumped to the stagnation pressure at the injection location. In
actuality, the liquid would probably have to be pumped to a pressure higher
than the stagnation pressure, but that additional pumping has a nF?,:i;ible
effect on the energy of the liquid nitrogen going into the tunnel. When the
LN2 is injected at the upstream station, it is assumed that the cooling process
is complete prior to the flow Ming compressed at the fan. In order to
achieve steady-state conditions, gaseous nitrogen is exhausted from the
settling chamber of the tunnel at the same mass flow rate that LN2 is added.
The following general assumptions apply to this analytical tunnel irregard-
less of where the LN2 is being injected. First, the tunnel is assumed to be
perfectly insulated (i.e., adiabatic). In actuality, there would be some heat
conducted through the walls, but even at low Mach numbers where the fan power
is low, this heat energy is only about 10 percent of the fan energy. Second,
all of the tunnel stagnation pressure losses due to friction and separation
occur between the test section and the upstream injection station. Third, the
fan compression is isentropic.
4
5
Application of the first law of thermodynamics is now made to this
analytic tunnel. The energies that cross the system boundaries (tunnel walls)
are the energy of the LN 2 being injected, the work being done on the flow by
the fan, and the energy of the gaseous nitrogen that is exhausted. The energy
equation for the system in rate form is
W + Ei - Ee	 (1)
With the assumptions that have been made, the stagnation conditions at the
various stations in the tunnel are sufficiently known so that the terms of
this equation can be evaluated. These stagnation conditions are given in the
following tabulation. Note that the stagnation pressures around the circuit
are independent of where +he injection occurs.
Station pt T 
Upstream Downstream
Injection injection
1 pt.1 Tt,i Tt,i
2 Pt,2 ^ pt
.l fr
Tt'? :_ Tt'1 Tt,2 = Ttsi
3 pt.3 ` Pt,2 m,•3 = Tt,l
4 Pt,4 = pt,l Tt,4 = T-,1
5 Pt, 5 ' Pt,1 -L.5 - 7t:i Tt,5 - Tt'1
U
First, consider the solution of the energy equation for the upstream injec-
tion case. The rate that energy is being injected is given as
Si = mihi
The enthalpy of the injected liquid is
hi = ho +f Pt,2 ( 
R)d
po
The second term is the isentropic pumping of the liquid to the stagnation pres-
sure at the injection station. The density of the liquid is essentially
constant for the pressure range of this study and is evaluated at storage con-
ditions. The rate that energy is being exhausted from the tunnel is
$e ehe ii he
The exhaust enthalpy, he , is evaluated at the stagnation conditions at the
exhaust station. The remaining energy term is the isentropic compression vork
at t:r fan and is given as
1	 •	 /
With the stagnation conditions doaastream of the fan and the stagnation pressure
upstream of the fan known, the remaining stagnation conditions upstream of the
fan can be determined by the real-gas procedures outlined in reference 5. The
Z
i
test section mass	 rate, ml, is also calculated using the procedure of
reference 5.
WOMM these three energy terms are inserted into the energy equation, an
expression for the L82 flow rate results.
i
11
;iAhtF)Ai i hi ^ he Aht'F!
With the L82 flog rate known, the fan work rate or power is calculated from
equation 2.
Nov consider the case of injection downstream of the fan. The energy of
the Lg2 being injected is calculated using the same formula as before with the
only difference being the stagnation pressure to which the LN2
 has to be pumped.
Ei = mihi = mi ho + pt ,4 ) dp
.f
po
The energy of the exhausting gaseous nitrogen is calculated in the same manner
as before and the power of the fan is
W : Il 
tit ,F) s
	 l^!
For this case, the stagnation conditions upstream of the fan are known along with
the stagnation pressure downstream of the fan. By working along a line of con-
stant entropy the remaining stagnation conditions do—astream can be determined.
8
Since the injected LN2 does not go through the fan, the fan power can be
determined prior to the determination of the LN2 flow rate. The LN2 flow rate
is again determined by substituting the energy terms into the energy equation.
mitAh.
m.i = he - hi
4
For the analysis, a given set of tunnel conditions (Pt 'l- jt,l' M. , r)
are chosen, then the fan power and LN2
 flow rates are determined for both the
...vstream and downstream injection cases.
RESULTS
A comparison of the fan power and T14  flow rates for a fan pressure ratio
and Mach number of 1.2 is presented in figure 2. The fan power for upstream
injection is always less than that for downstream injection with tLis difference
becoming greater as stagnation temperature is reduced. At the maximum pressure
(8.8 atm) and minimum operating temperatures, this difference is approximately
5.0 percent. As the pressure is reduced to 1 atm, the difference drops to
about 3.0 percent. For an explanation of why the fan powers for upstream
injection are lower, it is instructive to look at an ideal gas form of
equation 2.
'	
W = (11 + 1i) (CP T  , 3 (r Y y 1 - 1}
The term in brackets represents the energy per unit mass ,required for the com-
pression. This term is reduced for reduced fan inlet temperatures, 
Tt,3 as
is the case for upstream injection. Counter to this effect is the increased
9
=as flowing through the fan. The first effect dominates however. For example
at maximum pressure and minimum temperature, the energ y per unit mass for
upstream infection is about T•5 percent lower than for downstream injection
while the LN2 flow rate is about 2.3 percent of the test section flow rate.
This results in a power decrease of 5.2 percent.
For a given set of stagnation conditions, the ratio of LN 2 flow rates is	 A
almost identical to the power ratio. The reason for this is not obvious by
looking at the LN2 flow rate equations (3 and 5). Intuitively though this is
the expected result, because the only energy that has to be counteracted by the
cooling capacity of the LN2
 is the work being done by the drive fan. This of
course assumes that the cooling capacity is not appreciably affected by changes
in injection location. Since the LN2
 flow rate ratio is essentially equal to
the power ratio in subsequent figures only the power ratio will be presented.
For the same fan pressure ratio — Mach number combination, figure 3 shows
the power ratio as a function of stagnation pressure for constant values of
stagnation temperature. The benefits of upstream injection decrease linearly
with stagnation pressure except at the lowest stagnation temperature.
The effect of fan pressure ratio on the power ratio is shown in figure 4.
These particular fan pressure ratios are typical of the various test section
Mach numbers as outlined previously. It turns out that these power curves are
only a function of the fan pressure ratio. Any other Mach number assigned to
the same fan pressure ratio results in the same power ratio curve. These
curves show that as the tunnel pressure losses are reduced (low fan pressure 	
.
ratio), the benefits from upstream injection are reduced accordingly.
10
One of the assumptions that Was made for the analytical model tunnel was
that all of the tunnel total pressure losses occurred prior to the upstream
infection station. A brief stu4y vas made with the total pressure losses dis-
tributed around the tunnel similar to what is expected for the tunnel presently
being designed (ref. 6). The distributed losses had a negligible effect on the
fan paver and LN2 flow rate curves.
CONCLUDING REKAM
This theoretical analysis has consisted of comgmring the fan power and
LN2 flow rates resulting from the infection of LN2 either upstream or downstream
of the fan of a closed circuit transonic cryogenic tunnel. The analysis has
been restricted to steady--state tunnel operation. The results show that the
fan power and LN2 flow rates are lover if the LN2 is injected upstream of the
fan. The reason for this is that the reduction in fan inlet temperature due to
infecting upstream of the fan has a greater influence on the power than does
the increased mass flow going through the fan.
11
REFERENCES
1. Jarrell, R. R.; and McKinney, L. W.: The U.S. 2.5-meter Cryogenic High
Reynolds Number Tunnel. Presented at the 10th Congress of the
International Council of the Aeronautical Sciences (ICAS), Ottawa,
Canada, October 3-9, 1976.
2. Kilgore, R. A.: The Cryogenic Wind Tunnel for High Reynolds Number
Testing. Thesis presented to the Faculty of Engineering and Applied
Science, Department of Aeronautics ex d Astronautics, The University of
Southampton, in partial fulfillment of the requirements for the Degree of
Doctor of Philosophy, Feb. 1974. NASA TM X-70207.
3. Ray, E. J.; Kilgore, R. A.; Adcock, J. B.; and Dnv`nport, E. E.: Analysis
of Validation Tests of the Langley Pilot Tran ,,onfL Cryogenic Tunnel.
NASA TN D-7828, February 1975.
k. Jacobsen, Richard T.: The Thermodynamic Properties of Nitrogen From 65
to 2000 K Wit% Pressures to 10,000 Atmospheres. PhD Thesis, Washington
State Univ., 1972. (Available as NASA CR-128526.)
deoek, J. B.; and Ogburn, M. E.: Power Calculations for Isentropic
Compressions of Cryogenic Nitrogen. NASA TN D-8389, March 1977.
12
•1
4LM
Ll-
4A
a
06EZ)06C14
z-j
0
Zivev
V:
-vice e[-e Z9e )oH 4
1 (YQ'^
..
fill
4-
t 1
t
1-t
E
3
	
0
On
.
	
LL
Cm
L L
	
J
I
r
1
f;t^ r
1
	
1
	
}1
^
,r
1 ♦
^!J-.
lY-
I
-
-
?I-TT-1
.
.
.1
A
T
-
-
.
"
-i
	
l
-
r^l
.y a
m .
^
 1 ^
^
.
y
	
^
^
._
:.+
-
	
-
-
+A
^
al
^
I
1-,..rl
I
!
,
'
^
'
l
,
 
^
.
F
T
f
f
H
-
.
F
P
}La
is
ly
	
11
^
'
+
 O
O
_
Y
f
t
,
	
-
	
r
r
l
,
{
1
C
o
Ir
.
^
I.
t
i
t^
	
1
	
1 1
^
^
-^
1
	
.
-
-+
 i
y .
}
	
^
	
-
c
N
EIvwNQ.C0CUCN
C
D
C:)
—
J
CINJ
0NCL)
N
L
r-+
O
^i
C
r,
oa
.
 ^
c
^o
o
E
Ofv
Nc
S
aE
o
0
C)
NOLL
•
	
Y
'
	
lI
R
i
l
a
 
I
0
0
fl—
L
^
^
O•
	
O`
I
.
^
N
4}
N
ri
00
	
.
-
NnLO3oc
-
ro
w
I
a
u
E
rnro
-
-
WL
8
r
`
	
^O
	
•t7
0
,
	
p
^
	
O
%
	
O
`
	
C
,
	
O
'
	
a
	
Z
=D
	
LM
•
 3:
	
s
6
L
-
	
-
 
-
-
	
-
	
-
-
 
-
_
 
-
 
-
 
-
	
-
	
-
 
-
-
-
 
-
 3
7DccoEmLdLOOLN30Q-C: 
E
w
a
^
Go
Y
op
C
"
"
	
^
O
 
NZ
^
^
 O
C
o
 
c
—
L
 
o
c
n
 
U
^
	
O
.7
L 
C
a
 
•
-
C
 C
r
o
 
r
o
L
o ^-
U
 
C
n
>
 
3o
w
 
^
vL
u5R
NF
I
	
,
0RS
f Ift"
	
ti
ii 1-1
L—
 
tttH
0
C^
a
l
 
o
G6
F
W
S
J
r
•9109 W
E
 Iv
s
 3
1
9
1
, Q
g
^
 
^
 
L
pP
.
	
P
	
P
	
P
7
 ^
•
•r
	r,
!
r
a;
r
t
it_
^
^
^
^
 •
+
	
^
 '
-
^
.
-E
L
I
-
-
I
i
+?^
r
r
1
r^
+
 p+
r
	
I
	
r
r•-
t
i
+
I
_
^
"
ITI	:
•_i:t
1
	1
	
F
tt r
1
l.y
-
r
I *
1r
F
!
r ^-
.^ i ^
} r-
t+^ r
^
``
_
`I
.
.
-
1
^
•
	
I
_
?-7^
	
^^
	
1
+
`
.
m
ot.
—
^^.
-;^
r
1^
`
' I
 
^
1
I
4
%
'
^
1
	
,I;
	
(
r
1
4
+
it
Y
}
^1
t-1
H
,
i'
	
'^}
1
:.
^
.G
	
^
	
+`1
	
^
1
r
	
:•
	
I'
,
	
^
+fir
::
.
.
t
ONS0
a
>
t
i
_
E
u
Y
O
r-;
o
va
^
Piz
00NO
I.
s1	 Report No
NASA 111 X 74036
2. Government Acc4sion No 3	 Rec.p.ent's Catalog No
4	 Tale and Subt,tle 5	 Rewrt Date
EFFECT OF LN 2 	INJECTION STATION LOCATION ON THE DRIVE FAN .)line	 1077 _
6	 Performing Orgrmtahon Code
POWER AND LN 2 REQUIREMENTS OF A CRYOGENIC WIND TUNNFL
7	 Author(sl 8	 Performinq Orgamtation Report No
Jerry B. Adcock
10 Work Uno No
9	 Performing 0r9anuat,on Name and Addrea
Langley Research Center 11. Contract or Grant No
Hampton, VA 23665
13	 Tvpe of Report and Period covered —^
12	 Sponsoring Agency Name and Address Technical flemorandum
National	 Aeronautics and Space Administration -----
Washington, DC	 20546 14	 s{,onsornq Agency (ode 
15	 Supplementa ry Notes
16	 Abstract
This theoretical	 analysis consists of comparing the fan power and LN 2 flow rates
resulting from the injection of LN 2 either upstream or downstream of the fan of a
closed circuit transonic cryogenic tunnel. 	 The analysis	 is	 restricted to steady-state
tunnel	 operation.	 The results show that the fan power and LN 2 flow rates are lower if
the LN 2 	is	 injected upstream of the fan.
17	 Key Words (Suggested by Author($)) 18	 Distribution Statement
Cryogenic Wind Tunnels Unclassified -	 Unlirnited
LN 2	Injection
- Star Category	 09
Fan Drive Power
19	 security	 clanif. Iof this report) 20	 Secuwy Classif	 (of this page) 21. No. of Pages 22. Price"	
—
Unclassified Unclassified
117 $3.50
For sale b y the National Technical Information Service Springfield. Virginia 22161


Effect of LN2 injection station location on the drive fan power and LN2 requirements of a cryogenic wind tunnel

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server