cfd model of a spinning pipe gas lens
TRANSCRIPT
CFD MODEL OF A SPINNING PIPE GAS LENS
SAIP
Dr Andrew Forbes
July 2006
G Snedden1, A Forbes2, C Mahlase1, C Mafusire3 and MM Michaelis4
1CSIR DPSS, PO Box 395, Pretoria
2CSIR National Laser Centre, PO Box 395, Pretoria
3University of Zimbabwe, Mount Pleasant, Harare
4University of Kwazulu-Natal, Durban
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Spinning Pipe Gas Lens
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Focal Length
78 C:f = 94.655w-1.1388
104 C:f = 138.94w-1.4796
125 C:f = 79.151w-1.3439
152 C:f = 197.55w-1.7476
0
1
2
3
4
5
6
7
8
9
6 8 10 12 14 16 18 20Pipe Speed,w (Hz)
Foc
al L
engt
h, f
(m
)
T=78 C
T=104 C
T=125 C
T=152 C
Power (T=78 C)
Power (T=104 C)
Power (T=125 C)
Power (T=152 C)
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Refractive Index
1.0002
1.00021
1.00022
1.00023
1.00024
1.00025
1.00026
1.00027
1.00028
1.00029
1.0003
1.00031
-20 -15 -10 -5 0 5 10 15 20Radial Distance, r(mm)
Ref
ract
ive
Inde
x, n
(r)
78 C 104 C
125 C 153 C
Poly. (78 C) Poly. (104 C)
Poly. (125 C) Poly. (153 C)
Gas Dynamics
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Cold Air
WarmAir
Cold Air
WarmAir
WarmAir
Tube Rotation
Heater tape
WarmAir Opposing Vortices
Guess at the gas dynamics
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Density Profile
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Density Profile
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Flow Profile
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Rosby Waves
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Rayleigh–Taylor Instabilities
Future Work
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Instabilities near the boundary
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3/5
0
2
= rDNnmnmσ
)6/23()6/17()6/5()3/14()1()1(15337.0
2 +ΓΓ−ΓΓ+−=
−
nnn
Nmn
nm
∑∑∞
= =
+=Φ0 0
)],(),([),(n
n
m
mn
mn
mn
mn VBUA θρθρθρ
∫ ∫ Φ+=π
θρρθρθρπ
2
0
1
0),(),(
1)( ddUn
mKA mn
mn
∑−
=
−−+ −−
−−=2
0
2
22 )!()!(!)!()1(
)(
mn
k
kn
mnmn
kmn kkk
knR ρρ
3/5
220
max
min
)(423.0
−
= ∫
h
hn dhhCkr
3/112033.0)( −= κκφ nC
Wavefront Measurement & Control
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Adaptive optics for turbulence correction
• SLM acts as an adaptive optic• Measure wavefront distortion,• Feed result back into SLM to create conjugate
phase,• Propagate conjugate phased beam through
medium.
Control Loop
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Conclusion
• CFD model of gas lens• Shows Rosby waves and Rayleigh–Taylor instabilities
• Propagation model in preparation• Full Fresnel propagation through GRIN system
• Future work• Adaptive optics theory and experiment
Questions