Abstract

The velocity of gas flow has been remotely measured using a technique which involves the coherent detection of scattered laser radiation from small particles suspended in the fluid utilizing the doppler effect. Suitable instrumentation for the study of wind tunnel type and atmospheric flows are described. Mainly for reasons of spatial resolution, a function of the laser wavelength, the wind tunnel system utilizes an argon laser operating at 0.5 μ. The relaxed spatial resolution requirement of atmospheric applications allows the use of a carbon dioxide laser, which has superior performance at a wavelength of 10.6 μ, a deduction made from signal-to-noise ratio considerations. Theoretical design considerations are given which consider Mie scattering predictions, two-phase flow effects, photomixing fundamentals, laser selection, spatial resolution, and spectral broadening effects. Preliminary experimental investigations using the instrumentation are detailed. The velocity profile of the flow field generated by a 1.27-cm diam subsonic jet was investigated, and the result compared favorably with a hot wire investigation conducted in the same jet. Measurements of wind velocity at a range of 50 m have also shown the considerable promise of the atmospheric system.

© 1970 Optical Society of America

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References

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  1. S. L. Soo, Fluid Dynamics of Multiphase Systems (Blaisdell Publishing Company, Waltham, Massachusetts, 1967).
  2. A. E. Siegman, Proc. IEEE 54, 1350 (1964).
    [CrossRef]
  3. S. Corrsin, U. Corrsin, S. Mahinder, “Further Experiments on the Flow and Heat Transfer in a Heated Turbulent Air Jet,” NACA Rept. 998 (1950).

1964 (1)

A. E. Siegman, Proc. IEEE 54, 1350 (1964).
[CrossRef]

Corrsin, S.

S. Corrsin, U. Corrsin, S. Mahinder, “Further Experiments on the Flow and Heat Transfer in a Heated Turbulent Air Jet,” NACA Rept. 998 (1950).

Corrsin, U.

S. Corrsin, U. Corrsin, S. Mahinder, “Further Experiments on the Flow and Heat Transfer in a Heated Turbulent Air Jet,” NACA Rept. 998 (1950).

Mahinder, S.

S. Corrsin, U. Corrsin, S. Mahinder, “Further Experiments on the Flow and Heat Transfer in a Heated Turbulent Air Jet,” NACA Rept. 998 (1950).

Siegman, A. E.

A. E. Siegman, Proc. IEEE 54, 1350 (1964).
[CrossRef]

Soo, S. L.

S. L. Soo, Fluid Dynamics of Multiphase Systems (Blaisdell Publishing Company, Waltham, Massachusetts, 1967).

Proc. IEEE (1)

A. E. Siegman, Proc. IEEE 54, 1350 (1964).
[CrossRef]

Other (2)

S. Corrsin, U. Corrsin, S. Mahinder, “Further Experiments on the Flow and Heat Transfer in a Heated Turbulent Air Jet,” NACA Rept. 998 (1950).

S. L. Soo, Fluid Dynamics of Multiphase Systems (Blaisdell Publishing Company, Waltham, Massachusetts, 1967).

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Figures (21)

Fig. 1
Fig. 1

Planar scattering configuration.

Fig. 2
Fig. 2

Three-dimensional laser velocity instrument.

Fig. 3
Fig. 3

Schematic of one component of the three-dimensional LDV instrument.

Fig. 4
Fig. 4

Schematic of laser velocimeter and its alignment relative to the jet.

Fig. 5
Fig. 5

Scattering volume as a function of optic parameters: alpha values.

Fig. 6
Fig. 6

Scattering volume as a function of optic parameters: beta values.

Fig. 7
Fig. 7

Diameter of focal region as a function of f number of lens.

Fig. 8
Fig. 8

Spatial resolution of scattering region.

Fig. 9
Fig. 9

Basic block diagram of frequency tracker.

Fig. 10
Fig. 10

Schematic laser doppler velocimeter system.

Fig. 11
Fig. 11

Particle size distribution for Royco DOP generator at operating pressure of 25 psig.

Fig. 12
Fig. 12

Comparison of mean velocities determined by pressure measurements with mean velocities given by the LDV frequency tracker.

Fig. 13
Fig. 13

Distribution of turbulence intensity along the axis of a round free jet.

Fig. 14
Fig. 14

Comparison of mean velocity profile for a round free jet.

Fig. 15
Fig. 15

Comparison of turbulent intensity profile of a round free jet.

Fig. 16
Fig. 16

Comparisons of LDV and hot wire spectral distributions for 1.27-cm diam jet with core velocity of 173 ft/sec (x/D = 2.0); spectral power density in (ft/sec)2/Hz; frequency in Hz.

Fig. 17
Fig. 17

Comparisons of LDV and hot wire spectral distributions with 1.27-cm diam jet with core velocity of 173 ft/sec (x/D = 2.0). Spectral power density in (ft/sec)2/Hz; frequency in Hz.

Fig. 18
Fig. 18

Schematic of velocimeter arrangement for wind velocity measurement.

Fig. 19
Fig. 19

Coaxial focused heterodyne configuration.

Fig. 20
Fig. 20

Nomogram to estimate system spatial resolution.

Fig. 21
Fig. 21

Typical spectrum analyzer displays of velocimeter output.

Tables (3)

Tables Icon

Table I Normalized Mean Square Values of the Relative Velocity of the Particle and Fluid

Tables Icon

Table II System of Equations Relating Doppler Shifts to Velocity Components for the LPV

Tables Icon

Table III Optic Diameters

Equations (21)

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ω D = ( k s c k i ) · V .
ω D = 2 π f D = ( 2 V D / c ) ω i cos ( ϕ / 2 ) ,
1 2 m V 2 ¯ = k 1 2 T ,
d U p d t α β U p = α β U + β d U d t + β ( 3 α π ) 1 2 × t 0 ( d / d τ ) ( U U p ) ( t τ ) 1 2 d τ ,
U R 2 ¯ / U 2 ¯ = 0 Ω R ( 1 ) Ω ( 2 ) f ( ω ) d ω ,
Ω R ( 1 ) = ( 1 β β · ω α ) 2 , Ω ( 2 ) = 1 β 2 ( ω α ) 2 + ( 6 ) 1 2 β ( ω α ) 3 2 + 3 ( ω α ) + ( 6 ) 1 2 ( ω α ) 1 2 + 1.
S / N = 1 4 ( η n σ ¯ λ A / B ) ,
d T 0.64 λ f T / R T , Z T 1.6 ( f T / R T ) 2 λ,
d R 1.22 λ f R / R R , Z R ( f R / R R ) 2 λ .
V = ( d T 3 / 3 sin θ ) · C ,
C = [ 1 + ( d R d T ) 2 ] E ( π 2 , d R d T ) [ 1 ( d R d T ) 2 ] K ( π 2 , d R d T ) ,
α = d R / d T = 2 F R / F T 1 ,
β = d T / d R = F T / 2 F R 1 ,
V = 4.68 × 10 12 D F R 3 cm 3 ,
D = ( 1 + β 2 ) E [ ( π / 2 ) , β ] ( 1 β 2 ) K [ ( π / 2 ) , β ] .
S / N = [ η A / ( π R T 2 ) ( π R R 2 ) σ ] / π L 4 λ 2 B
S / N = 1 4 ( η n σ λ A / π B ) [ π / 2 + tan 1 ( π R t 2 / λ f t ) ] ,
S / N = 1 4 ( η n σ λ A / B ) ,
S N = 1 4 η n σ λ A π B ( tan 1 { λ f t π R t 2 [ ( 1 + π 2 R t 4 λ 2 f t 2 ) n 1 ] } tan 1 × { λ f t π R t 2 [ ( 1 + π 2 R t 4 λ 2 f t 2 ) n 1 ] } ) .
S / N = 1 4 ( n σ λ A / B ) .
S / N = 3.5 × 10 8 / B .

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