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Journal of Babylon University/Pure and Applied Sciences/ No.(1)/ Vol.(1)! "#11
Fig (1) Designed and manufactured wind tunnel
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Journal of Babylon University/Pure and Applied Sciences/ No.(1)/ Vol.(1)! "#11
The design conforms to the recommendations given in the references arlow et
al,)444 , oo& , )47*, 8ong + 1ar&inson,)449", given here in , on the state : of art to
find optimum construction ratio, wall profile , wire screen and honeycomb selection
for the settling chamber to have good flow qualities in the test section. The flow
qualities are initiated in the large settling chamber where very low velocities permit
use of multiple wire screens honeycomb without incurring much losses to ma&e flowuniform and reduced turbulence level. The settling chamber cross section is made to
contract considerably to reach test section at a short test possible distance.
Interpretation of results is sensitive to the test section airflow quality, (ousif et
al,)44), design the wind tunnel with crosssection 0.7; m" square and ).;m" long
and contraction ratio ustable test section could used either as the environment,
subsonic or climatic wind tunnel. 2iterature survey indicates acceptable value of mean
velocity variation of about ?0.*= to 0.;=, flow angularity of about ?0.;, turbulence
intensity of 0.;=and power factor for this type of tunnel of about *.; .
@$act solutions have not proved sufficient to predict adverse velocity gradient near
the wall trial and error methods and empirical relationships were deployed wherevernecessary. Also A'#(#)* software is used to chec& the distribution of velocity +
pressure.
esign, construction and testing of a subsonic wind tunnel that the wind tunnel
simulates a high speed stream of air to flow past a model of the ob>ect being
testedB5ig.3"C
ind tunnel is a chamber though which air is forced at controlled velocities in order
to study the effects of aerodynamic flow around airfoils or scale models.
The parts of wind tunnel areD
). A settling chamber to straighten the flow and control turbulence intensity.
*. A contraction !one to ta&es a large volume of low :velocity air and reduces it
to a small volume of high velocity air without creating turbulence.
3. A test section where the test article and sensors are installed.
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$eoretical Analysis of %ind $unnel
&ontraction DesignA$isymmetric steady ideal irrotational flow in cylindrical coordinate system is
considered sufficient for the appro$imation the design Aldruby ,)477".
ontinuity equationD
Irrotationality conditionD
ombining it reduces to sto&e eltrame equationD
ith particular solution of the form
And general solution of the fromD
En substituting general solution equation3" in continuity equation )"
The velocity components becomes (ousif et al ,)44)" D
Indication at $ a$is, r F0,urF0F*f$",vrF0F0 GGGGGGGGGGGG..G.;"
As $H, the boundary condition at the end of contraction should be D
-H*f$"
5or all r GGGGGGGGGGGGGGGG.G.. 6"
/H0
This is possible when f$" H0 as $ HJ suggesting formation of f$" to satisfy the
following two conditions hyperbolic in nature.
hange in a$ial velocity pattern should be in continuity from inlet to outlet ofcontraction.
Airflow at the inlet and outlet of contraction to be uniform therefore, the simplest
form of f$" which satisfies the .. isD
here & ) is constant representing controlling parameter for the accuracy of
contraction, the two constants A and ) can be determine form the ..
Kowever equation 9" has unsatisfaction wall velocity gradients resulting in delayed
wall infle$ion for contraction.
ohen suggested modification as followers (ousif et al, )44)"D
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Journal of Babylon University/Pure and Applied Sciences/ No.(1)/ Vol.(1)! "#11
here constants & ), A and ) are as in eq. 9" and 8 * is a constant of small value
while * can be determine from the ..at $F0.
#ubstituting @q.4" in @q.3", the stream function becomesD
efining the profile of wall contraction in terms of only two variable $ and r.
A, ) and * can be obtained by specifying velocities at the inlet and outlet at $F0. & ) and & * are the geometric aspect ratios of contraction affecting slenderer and the
position of point of contraction.
$est SectionA closed rectangular test section with filleted corners considerably less power than the
open type recommended length of test section should be less than twice the ma$imum
width (ousif et al ,)44) and #hapiro ,)4;3" gives the drop in static pressure asD
here &Fconstant D 0.0)6 to 0.0
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This givers the requires divergence and the test section outlet width.
DiffuserAssuming constant velocity distribution, gives diffuser efficiency asD
here, p) and p* are static pressures at the cross sections at A)diffuser inlet" and
A* diffuser outlet", -) is the mean velocity at A). The low efficiency arises out of
large loss moreover of energy during pressure recovery from flow &inetic energy.
Adverse pressure gradient associated with velocity reduction favoures undesirable
flow separation from the walls. 1arameters efficiency diffuser performance are rate of
e$pansion cross section shape , turbulence level .2. effect and effect of wall shape,
%ecommended Aldruby, )477" values of diffuser divergence is ;N to )0N beyond
which efficiency drops rapid as it depends on the turbulence level and empirical
relationship derived from e$perimental results.
The ratio *O.2 thic&nessPma$. diffuser width" Q0.00; give 40= and deterioratesrapidly as the ratio e$ceeds 0.00;" .2arger diffuser angle can be reduced by .2.
control such as use of deflector vanes and Por introduce spiral flow to energies by
mi$ing high energy core flow with .2. growth improving up to 70= for larger
diffuser angle up to ;3N.
Fan
5an differs from airplane propellers by usage of multi blades to avoid pulsation and
usage of thin blades with pre rotating vanesPaft straightened vans to avoid
rotationality. In open circuit wind tunnel aft fans have little effect on test section
airflow quality and therefore vans may not be required. The parameters affecting fan
efficiency is tip clearance, component of radial flow, blade liftPdrag ratio, number of blade, blades %e. 'o. www.ARA.org ", blade angle and tip compressibility effect
Flow 'uantities
hile uniform and steady airflow is desirable at the test section, in practice
associates with low frequency fluctuations and high frequency turbulence. The state
of art of design to reduce the turbulence level. %eduction of turbulence is achieved
through identifying the sources improve construction the usage of damping screen and
honey comb in the setting chamber considerably improves flow qualities, if the
turbulence intensity is above 0.9=". #creens reduce turbulence level but it has little
effect on removing swirl and lateral mean velocity variation. Koneycomb with cell
length S7O cell diameter, proved to be suitable Abbaspour and #hv>ee,*004" smaller
si!e honey comb diameter could help abatement of turbulence and in some cause may
dispense with the use of screen. #quare and he$agons shaped honey comb give better
result than circular section.
*erimental *art+anufacturing and &alibration te Subsonic %ind tunnel
The specification of test sectionD
ross section F 30cmO30cm
2ength F 60 cm
/elocity≈ 3; mPsec
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Journal of Babylon University/Pure and Applied Sciences/ No.(1)/ Vol.(1)! "#11
Fig!(,) te used Fan
Area ratio-.
Fan-The used fan is shown in 5ig
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$est Section DesignTest suction walls must have minimal .2." growth to avoid static pressure drop on
account of energy losses i.e. avoid a hori!ontal buoyancy,phenomena.
In this study the wor&ing section is construction of clear 1erspe$ with crosssection of
300mmO300mm" and length of 600 mm. 5ig 7" represent schematic + 5ig.9"represented photo of the test section.
Fig() *oto of test section wit s*ecimen Fig () scematic diagram of test section
Diffuser DesignThe iffuser slope angle is )93 degree" to avoid separation of shown in 5ig.4 a,b"
Fig!(3!a) Diffuser Design Fig!(3!b) Diffuser *oto
$e &onstructionThe bell mouth settling chamber, test section, and diffuser were separately constructed
as an unit >oint together by bolt and isolated by cascade which can decreased the
vibration between the element of the device at less the device is hung on a load table
and isolated by cascade too, the part of the fan is support in the diffuser and isolated
from it. 5ig)0" shows the >oining of the parts of wind tunnel .
Fig! (14) 5oining te wind tunnel
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Journal of Babylon University/Pure and Applied Sciences/ No.(1)/ Vol.(1)! "#11
The fan caused vibration which is sha&e the device tightly . uring final assembly, care was
ta&en to align center lines of each section to be in one straight hori!ontal line. The >oints were
sealed to give smoothness of flow and oil was coated to reduce .2.
The final step is to commission the new tunnel into operation and to measure flow quantities .
+odel of $urbine 6lade
The models mounting device is built and support in the test section by /" shapeshown in 5igs. ))"+)*".
Fig(11) $e mounted of te s*ecimen
Fig (12) Scematic diagram of blade turbine
Final AssemblyThe wind tunnel is assembly from the mentioned parts, and the final apparatus is
shown in 5igs)3"+)
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Fig (1") Scematic of wind tunnel sown te *itot tube *osition
Fig (1,)$e final assembly of wind tunnel
7umerical SimulationA'#(#)* is a finite element analysis A'#(#)* help, *004" , have the capability to
analy!e a wide range of different problems. There are two ways to use the A'#(#)*
interactively through the graphical userD
). interface -I".
*. used batch file and A'#(# commands.
The main complete flowchart and A12 Ansys 1arametric esign 2anguage" for the
numerical simulation 'a&asone ,*006" is shown in 5ig.);".
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Pprep9
@t,),fluid)
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Journal of Babylon University/Pure and Applied Sciences/ No.(1)/ Vol.(1)! "#11
Fig! (1/)- Flow cart and A#D8 for numerical Simulation
The used element in this analysis is 52-I)
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flow show good agreement with the A'#(# results of blade geometry. 5ig.)4"
#hown the shadow capture of the turbine blade at Rach no. F 0.097.
Fig!(1) Static *ressure distribution on te u**er surface
Fig! (13) Sadow ca*ture of turbine blade at +ac no!4!4
5igs.*0" and *)" are shown the velocity distribution and velocity vector, and 5ig.
**" shows the pressure distribution and 5ig.*3" shows the stream line in thedesigns wind tunnel with turbine blade by A'#(#)* software.
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Journal of Babylon University/Pure and Applied Sciences/ No.(1)/ Vol.(1)! "#11
Fig!(24) 9elocity distribution
Fig!(21) 9elocity 9ector
Fig!(22) #ressure distribution
Fig!(2") Stream line distribution
&onclusions
)In our research , the wind tunnel is manufactured and calibrated for subsonic flow .* ood agreement is observed for testing turbine blade specimen with comple$
geometry.
3 The present e$perimental results show good agreement with A'#(#)* results .
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Aldruby R. I. , )477 Y1rinciple of a!dynamicY, *nd edition.
A'#(#)* online help, A'#(# Ranuals, *004.
Asher K. #hapiro /ol. )+ /ol. *, )4;3Y The ynamics and Thermodynamics of
ompressible 5luid 5lowY, %eference Kand boo&".
arlow X. ., %ea .K and 1ope A. )444. Y2ow: #peed ind Tunnel TestingZ , Xohn
iley Inc.ien&iewic! . )446 ['ew Tools in ind @ngineeringY X. ind. @ng. Aerod., 6;3
)", *94300.
oo& .'.X,)47* [#imulation Technique for #hort Test : #ection ind TunnelM
%oughness , arrier , and Ri$ing evice RethodY , ambridge -niversity
1ress,)*6)36.
8ong 2. + 1ar&inson ./. , )449. [A 3 Tolerant ind Tunnel for eneral ind
@ngineering TestY , 1roceeding of the 3rd International olloquium on luff ody
Aerodynamics and Applications , X. wind @ng. Ind. Aerod. , 649),49;47;.
'a&asone (. and (oshimoto #. and #tolars&i T.A. , *006 Y@ngineering Analysis with
A'#(# #oftwareY, )st published.
(ousif A. K. ,Tlib. #. Xawad + X. A. 8adihm , )44)Yesign #tudy of a 2ow #peedind TunnelY , Xournal of Rilitary @ng. ollage, 'o.6, p.)7