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Experimental investigation on flow quality in MF-TA1 Wind Tunnel
To cite this article: D E Husaru et al 2018 IOP Conf. Ser.: Mater. Sci. Eng. 444 082006
 
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1234567890 ‘’“”The 8th International Conference on Advanced Concepts in Mechanical Engineering IOP Publishing
IOP Conf. Series: Materials Science and Engineering 444 (2018) 082006 doi:10.1088/1757-899X/444/8/082006

Experimental investigation on flow quality in MF -TA1 Wind
Tunnel
D E Husaru1, Th Popescu2, D Zahariea2, M S Pavăl3
1Mechanical Enginee ring, Mechatronics and Ro botics Department “Gheorghe Asachi”
Technical University of Iasi, Iasi, Romania
2Fluid Mechanics, Fluid Machinery and Fluid Power Systems Department, “Gheorghe Asachi”
Technical University of Iasi, Iasi, Romania
3Mechanical Engineering and Road Automotive Engineering Department, “Gheorghe Asachi”
Technical University of Iasi, Iasi, Romania
E-mail : [anonimizat]
Abstract. This paper presents the results of the first calibration stage of the MF -TA1 wind
tunnel: measurement of velocity distributions in the median plane of the test section using 3D –
Laser Doppler Anemometer. Are presented the main functional and technical featu res of MF –
TA1 wind tunnel and 3D Laser -Doppler Anemometer. For this experiment a 3D Laser Dop pler
Anemometer was positioned at 90 degrees from test section and lenses with focal length at 800
mm was used. The measurement domain is a matrix of 273 points on 500×300 mm. The laser
probe movement in each point was performed with a 3D traverse system. The results are
presented through graphics for velocity distributions , while for mean of velocity components,
dynam ic pressure and mean turbulen ce in the median plane of test section the results are
presented through numerical values .
1. Introduction
In the wind tunnel section is must to obtain high standards for the flow quality in order to accomplish
accurate and rel iable measurement data. Flow quality in the test section of wind tunnels relates mainly
to spatial aspects of the flow. For aeronautical applications is required a spatial uniformity in the entire
empty test section of the wind tunnel. Spatial flow uniformity can be documented by contour plots of
velocity magnitude in one or more cross -sectional planes of the wind tunnel. The flow in test section
of wind tunnel must meet high standards of spatial uniformity. A set of indicators for evalu ation the
flow quality in test section is developed by Moonen [ 1].
Measurements in empty test section of wind tunnel are required that could be used for the
identification and means for suppression of suspected sources of flow disturbances in the test sect ion
and around the wind tunnel circuit, [ 2].
In order to make accurate measurement on a model in a wind tunnel is necessary to determine the flow
parameters. The main flow parameters are : pressure, temperature, Mach number and Reynolds
number. These parameters can be determined from calibration relationships, calculated or measured.
Dynamic pressure can be determinate with a Pit ôt-static probe or a high-quality pressure transducer
connected to a pressure taps in the nozzle before test section of wind tunnel , and from dynamic
pressure, the velocity can be further calculated [3].
On the other hand, velocity is a fundamental parameter in fluid mechanics. One of the most
advanced method for velocity measurement in fluid mechanics is laser velocimetry, that used an
optical technique based on light scattering by tiny particles used as flow tracers , [4], the laser
velocimetry being the preferred technique used to measure instantaneous velocity.

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1234567890 ‘’“”The 8th International Conference on Advanced Concepts in Mechanical Engineering IOP Publishing
IOP Conf. Series: Materials Science and Engineering 444 (2018) 082006 doi:10.1088/1757-899X/444/8/082006

In this paper is presented the measurem ent of velocity distribution in the median plane of the test
section of the MF TA -1 wind tunnel using 3D Laser -Doppler Anemometer. Also, four quality
indicators related to the longitudinal component of the flow and four indicators for turbulence are
presented .

2. MF -TA1 Wind Tunnel description
The MF -TA1 wind tunnel is part of the Aerodynamics and Hydrodynamics Laboratory of the
Department of Fluid Mechanics, Fluid Machinery and Fluid Power Systems. The full modernization of
the MF -TA1a wind tunnel took place in 2014 -2016 through the project POSCCE -A2-O2.2.1 -2009, ID
911, No. 430 / 21.12.2012, SMIS code 13987, "Development of the research platform for efficient and
sustainable energy – ENERED". The aerodynamic and constructive conception and design of the wind
tunnel belongs entirely to the Department of Fluid Mechanics, Fluid Machinery and Fluid Power
Systems . The main features of MF -TA1 wind tunnel are: low-turbulence, closed -circulation,
controlled cooling, continuously adjustable velocity in the range of 0 ÷ 80 m/s, octagonal work area of
0.48 m2, shape factor √2, and contraction ratio 9. Installed power on the wind tunnel is 90 kW. The
tunnel is used for testing aerodynamic profiles, testing experimental body models and experimental
validation of numerical models in aerodynamics.

(a) (b)

(c) (d)

(e)
Figure 1. MF-TA1 Wind tunnel .

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1234567890 ‘’“”The 8th International Conference on Advanced Concepts in Mechanical Engineering IOP Publishing
IOP Conf. Series: Materials Science and Engineering 444 (2018) 082006 doi:10.1088/1757-899X/444/8/082006

The main elements of the MF -TA1 wind tunnel are shown in figure 1, (a) 3D general view ; (b) 3D
test section view ; (c) turbofan; (d) heat exchanger; (e) 2D section view . The components of the wind
tunnel are presented in figure 1 , (e): T1- settling chamber; T2 nozzle; T3 -test section ; T4a, T4b –
diffuser n umber 1; T5-elastic connection; T6, T7 corner number 1 and corner number 2; T8 -upstream
connection; T9 (V) – turbofan ; T10 – downstream connection ; T11 diffuser n umber 2; T12 -heat
exchanger with elliptical tubes; T13, T14 – corner number 3 and n umber 4.
The cross section of the wind tunnel is octagonal, with three exceptions: sections T8, T9 (V) and
T10. The useful overall dimensions of the wind tunnel are: length 13120 mm, variable height
4140/3330 mm and maximum width 2500 mm. For the vibrations not to be transmitted to the test
section , the following measures have been taken: the turbofan and the heat exchanger is framed by
elastic connections, the turbofan is supported and fix ed by six vibration dampers. The VAN 1400 -0 /
50-4-90 turbofan (made by Howden Turbowerke GmbH) is powered by VEM IE3 W41F 280 M4
capacity motor, with 1487 rpm nominal speed, and 90 kW installed power. The motor is powered by a
frequency converter of the type SINAMICS G120 (Siemens). Accuracy of engine speed modification
(real speed deviation from prescribed s peed) is 0.015 rpm .

3. Laser Doppler Anemometer description and components
The Laser Doppler Anemometer uses the non -intrusive principle in the measurement procedure. This
equipment is recommended for reversible flow applications, chemical reactive or high temperature
media, where the physical sensors are difficult or impossible to be used. For measurements, the fluid
flow should be filled with tracer particle . The main advantages of th e laser velocimetry method are:
non-intrusive measurement , spatial and temporal resolution , no calibration is required at each use and
reverse flow measurement ability , [5].
The main component of Laser Doppler Anemometer is Flow Lite System . This system allows
several measurement configurations to be carried out: measurement of a single velocity component –
module 1D, figure 2, (a); measurement of two velocity components – module 2D, figure 2, (b), and
measuring the three components of the velocity by combining 1D and 2D modules aligned under a
certain angle so that the volume of measurement coincides. For this experiment the Flow Lite 2D
system was used , [6].
The Flow Lite system is the continuous laser beam generation equipment, including beam splitter,
optical receiver, interference filter, photodetector, and focusing lenses. The laser probe is part of the
Flow Lite system structure and represents the element that comes in direct contact with the test
section . The laser probe is mounted on the 3D Traverse System and is moved to each measurement
point . For signal processing and analysis of experimental data, the Flow Lite system is connected to
the BSA -F60 signal processor.

(a) (b)

(c) (d)
Figure 2. Laser Doppler Anemometer components.

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1234567890 ‘’“”The 8th International Conference on Advanced Concepts in Mechanical Engineering IOP Publishing
IOP Conf. Series: Materials Science and Engineering 444 (2018) 082006 doi:10.1088/1757-899X/444/8/082006

The signal processor, receives information from the photo -detector which converts the fluctuating
light intensity received to the laser probe to an electrical signal. Information are filtered and amplified
in the signal processor, by frequency analysis using the robust Fast Fourier Transform algorithm, [ 5,6].
The laser probe is moved in each measurement point by a computerized 3D traverse system. All 3
working axis of the traverse system have a length of 1010 mm and a pitch of 0.1 mm, being moved by
stepper motors, figure 2, (c). The control equipment of traver se system, figure 2, (d), is connected to
the process computer by a RS 232 port, [ 7].

4. Experiment setup
To perform the measurements , the Flow Lite 2D module with two laser beams with wavelengths of
532 and respectively 561 nm was used . The laser probe is equipped with a lens with a focal length of
800 mm. The laser beam is oriented perpendicular to the wind tunnel test section axis. An array of
measurement points has been created in the median plane of the test section .
The area covered by the array is 500×300 mm and the pitch on both axes is 25 mm, resulting 21
points on the y axis and 13 in the z axis; the reporting being made to the xyz system of the traverse
system, figure 3. In front of the test section , the significance of the axes is: x-longitudinal axis, y-
transverse axis, z- vertical axis.
In this experiment , only two components of velocity are determined :
u(longitudinal velocity) and
w
(transversal velocity) , which represent the mean of each particle velocity on the measurement
volume for every point .
The laser beam remains positioned at each measuring point until one of these two conditions is
accomplished: a measuring time of 60 seconds , or 10000 particles pass ing through the measurement
volume. The results obtain ed for each point are mediated by the signal processor.

Figure 3. Measurement points .

5. Experimental r esults
The variation of longitudinal velocity component , and transversal velocity component in the median
plane of test section are presented in figure 4, respectively in figure 5 by surface plots 3D.
The
u velocity component values are in range of 9.506
 9.605 m/s and the mean velocity is
u
=9.593 m/s . The mean velocity of
w component velocity is
w =-0.0217 m/s and range of the
w
velocity component is -0.142
 0.121 m/s. These values were obtained at 200 rpm nominal speed of
the VAN 1400 -0 / 50 -4-90 turbofan.

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1234567890 ‘’“”The 8th International Conference on Advanced Concepts in Mechanical Engineering IOP Publishing
IOP Conf. Series: Materials Science and Engineering 444 (2018) 082006 doi:10.1088/1757-899X/444/8/082006

Figure 4. Longitudinal velocity component .

Figure 5. Transversal velocity component .

The value of s tandard deviation for both velocity component was calculated with the formula:

()1/2
2
11N
Vi
iσ V VN==− (1)
where
N is number of measurement points,
iV is the
iu or
iw values of velocity component s in each
measurement point while
iV are the mean value for
iu velocity component, respectively for
iw
velocity component. The values for standard deviation are
uσ =0.0318 m/s and
wσ =0.0409 m/s.
Further , we will calculate four quality indicators related to the longitudinal (streamwise)
component of the flow. The indicators related to the residual cross -flow component
()_u
sym yIz ,
()_u
sym zIy
,
()_u
antisym yIz ,
()_u
antisym zIy have similar definitions presented hereunder in equations 2 -5.
The indicators
()_u
sym yIz and
()_u
sym zIy are describing the lateral flow uniformity of the streamwise
component , while indicators
()_u
antisym yIz and
()_u
antisym zIy are measuring the skewness of the
streamwise component of the flow :

()()
()max
min
max
min2
_
_
2,
,y
sym y
y u
sym y y
yu y z dy
Iz
v y z dy=
 (2)

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1234567890 ‘’“”The 8th International Conference on Advanced Concepts in Mechanical Engineering IOP Publishing
IOP Conf. Series: Materials Science and Engineering 444 (2018) 082006 doi:10.1088/1757-899X/444/8/082006

()()
()max
min
max
min2
_
_
2,
,y
antisym y
y u
antisym y y
yu y z dy
Iz
v y z dy=
 (3)

()()
()max
min
max
min2
_
_
2,
,z
sym z
z u
sym z z
zu y z dz
Iy
v y z dz=
 (4)

()()
()max
min
max
min2
_
2,
,antisym zz
z u
antisym z z
zu y z dz
Iy
v y z dz−
=
 (4)
where
()_ ,sym yu y z and
(),sym zu y z− are the symmetric parts of
u velocity, while
()_ ,antisym yu y z
(),antisym zu y z−
are the antisymmetric parts of
u velocity component along
y axis and respectively
z
axis. Variation of the four quality indicators for streamwise component of the flow are presented in
figures 6-9 on longitudinal direction and transversal direction. The uniformity ind icators
()_u
sym yIz
and
()_u
sym zIy are near to 1, and skewness ind icators
_u
antisym yI and
_u
antisym zI are near to 0, what it
indicates the very good lateral symmetry velocity distribution in median plane o f test section on
longitudinal direction, respectively on transversal direction for
u velocity component .

Figure 6. Index of uniformity along z axis
_u
sym yI .

Figure 7. Skewness index along z axis
_u
antisym yI .

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1234567890 ‘’“”The 8th International Conference on Advanced Concepts in Mechanical Engineering IOP Publishing
IOP Conf. Series: Materials Science and Engineering 444 (2018) 082006 doi:10.1088/1757-899X/444/8/082006

Figure 8. Index of uniformity along y axis
_u
sym zI .

Figure 9. Skewness index along y axis
_u
antisym zI .
Further, statistical analysis on flow quality is developed . In figure 10-13 are presented turbulent
stress
xxσ , turbulent stress
zzσ , root mean square velocity
rmsU and respectively cross moment
''uw
by surface plots 3D .

Figure 1 0. Turbulent stress
xxσ.

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1234567890 ‘’“”The 8th International Conference on Advanced Concepts in Mechanical Engineering IOP Publishing
IOP Conf. Series: Materials Science and Engineering 444 (2018) 082006 doi:10.1088/1757-899X/444/8/082006

Figure 1 1. Turbulent stress
zzσ.

Figure 12. Root mean square velocity
rmsU .

Figure 1 3. Cross -moments
''uw .
Minimum and maximum values for all eight quality indicators for streamwise component of the
flow are presented in table 1.

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1234567890 ‘’“”The 8th International Conference on Advanced Concepts in Mechanical Engineering IOP Publishing
IOP Conf. Series: Materials Science and Engineering 444 (2018) 082006 doi:10.1088/1757-899X/444/8/082006

Table 1. Quality indicators.
Quality indicator Minimum value Maximum value
()_u
sym yIz
0.999962151 0.999990223
()_u
antisym yIz
2.21826709e -06 1.00808413e -05
()_u
sym zIy
0.999992740 0.999997456
()_u
antisym zIy
5.21050824e -07 1.81014937e -05
xxσ
-5.8339244e -03 -1.42812634e -02
zzσ
-2.2368217e -03 -1.22176050e -02
rmsU
6.90100520e -02 1.079730270e -01
''uw
-9.6060000e -04 8.3190000 0e-04

6. Discussion and conclusion
The flow quality of MF TA -1 wind tunnel was investigated via Laser Doppler Anemometer
measurements. There are presented four uniformity indicators, and four turbulence indicators.
Quality indicators
()_u
sym yIz and
()_u
sym zIy shows an excell ent transversal symmetry for
streamwise component of velocity. For MF TA -1 wind tunnel both indicators have values greater than
0.9999. For the wind tunnel investigated by Moonen [1], the minimum values for uniformity
indicators is 0.98 in the best case.
Quality indicators
()_u
antisym yIz and
()_u
antisym zIy shows the lack of angularity for MF TA -a wind
tunnel. The maximum value for
()_u
antisym yIz is 1.00808413e -05. The maximum value for
()_u
antisym zIy
is 1.81014937e -05. For the wind tunnel investigated by Moonen [1], the values of angularity
indicators are in the range 0.01 -0.2 in the best case.
The turbulence indicators show a very good statistical quality. The turbulence stresses
xxσ and
zzσ
have very low values, which indicates low values for rms velocity components. The values streamwise
rms component
rmsU are in range 0.006901 -0.107973 [m/s] . For comparison, Ghorbanian [ 8] reported
for
rmsU value of 0.24 [m/s] in clean condition and 0.14 [m/s] in trip condition. The range for
correlation
''uw shows actually an isotropic turbulence.
MF TA -1 wind tunnel have a n excellent flow quality in the central zone of test section and very
good flow quality in the peripheral zone of test section, all proved by the eight considered indicators.
There will be performed more detailed measurement in the peripheral flow field in o rder to improve
the quality in this zone.
7. References
[1] Moonen P Blocked B Carmeliet J 2007 Indicators for the evaluation of wind tunnel test section
flow quality and application to a numerical closed -circuit wind tunnel Journal of Wind
Engineering and Industrial Aerodynamics 95 pp 1289 -1314
[2] Owen F K Owen A K 2008 Measurement and assessment of wind tunnel flow quality Progress
in Aerospace Sciences 44 pp 315 – 348
[3] Richard G J 2015 Model test of wind turbine in wind tunnels Technical transactions Civil
Engineering 2-B
[4] Boutier A 2012 Laser Velocimetry in Fluid Mechanics London: Wiley –Interscience
[5] https://www.dantecdynamics.com/measurement -principles -of-lda accessed 14.01.2018
[6] DANTEC Dynamics 2010 High Power FlowLite 1D and 2D Instalation and User ’s Guide
Denmark

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1234567890 ‘’“”The 8th International Conference on Advanced Concepts in Mechanical Engineering IOP Publishing
IOP Conf. Series: Materials Science and Engineering 444 (2018) 082006 doi:10.1088/1757-899X/444/8/082006

[7] DANTEC Dynamics 2011 3D Traversing Mechanism Instalation and User’s Guide Denmark
[8] Ghorbanian K Soltani M R Manshadi M D 2010 Experimental investigation on turbulence
intensity reduction in subsonic wind tunnels Aerospace Science and Technology 15 pp 137 –
147

Acknowledgments
The authors would like to acknowledge the technical resources offered by the Laboratory of
Aerodynamics and Hydrodynamics, from the Department of Fluid Mechanics, Fluid Machinery and
Fluid Power Systems, “Gheorghe Asachi” Technical University of Iasi, Roma nia. The Laboratory of
Aerodynamics and Hydrodynamics has been equipped with technical resources with the financial
support of the grant ENERED, POSCCE -A2-O2.2.1 -2009 -4, ID 911.