Laser velocimeter results were compared and found to be consistent with those obtained with conventional measurement techniques and existing compressible boundary layer theory. Turbulence information at supersonic speed has been successfully obtained in compressible boundary layer with laser system

Johnson, D. A.

English

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July 1975	 B75-10141 
NASA TECH BRIEF 
.
	
Ames Research Center 
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Laser Velocimeter Measurements of
High-Speed Compressible Flows 
.
The laser velocimeter appears to be especially well 
suited for the measurement of turbulence transport 
properties in compressible flows because of its non-
disturbing characteristic, sole velocity sensitivity, and 
instantaneous velocity capability. However, there has 
been some question as to whether the velocimeter can 
provide accurate turbulence measurements in the 
compressible boundary layers of a high-velocity gas 
stream. Results of a study of a turbulent boundary 
layer in a supersonic wind tunnel have demonstrated 
that the streamwise mean velocity, the turbulence in-
tensity in the streamwise direction, and the velocity
stream unit Reynolds number of 5.7 x 107/m. The 
region of interest was the turbulent unseeded bound-
ary layer on the nearly adiabatic upper nozzle wall 
for which a detailed flow-field survey had previously 
been made by pitot and static pressure measurements. 
A schematic representation of the laser velocimeter 
system employed in the study is shown in the diagram. 
The optical arrangement was of the standard "dual 
scatter" or "fringe mode" type with forward-scatter 
light collection. The velocity component that is sensed 
with this system lies in the plane formed by the two 
INTERFERENCE 
3-D POSITIONING	 FRINGE PATTERN I PLATFORM 
TEST SECTION 
20.32 cmX20.32 cm TUBE 
SUPERSONIC WIND 
TUNNEL \
	
\ hj'_–RECEIVING LENS
SIDE WALLS 
	
13.5'	
i1	
j4 WATT ARGON LASER 
TRANSMITTING LENS
MIRROR #1 
SPLITTER CUBE 
ON ROTATABLE 
HOLDER	
_______ 
— MIRROR #2 
	
MIRROR #4 -
	
"3-D POSITIONING 
PLATFORM 
correlation uY can be measured in high-speed com-
pressible flows by laser velocimetry. 
The study was conducted in a 20- x 20-cm super-
sonic blowdown wind tunnel at a free-stream Mach 
number of 2.9, a stagnation pressure and temperature 
of 6.8 atm and 291 °K, respectively, and a free-
incident laser beams and is perpendicular to their 
bisector. Thus, by simply rotating the splitter cube, 
various sensitivities to u and v with the attendant 
insensitivity to the w components can be obtained 
(u=velocity component parallel to free stream veloc-
ity, v=velocity component normal to upper wind 
1]	 (continued overleaf) 
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tunnel wall, w=transverse velocity component). The 
Reynolds stress term, liv, was determined by taking 
measurements with the laser beams oriented at +450 
and _450 with respect to the streamwise direction. 
Single-particle, time-domain signal processing was 
employed which enabled the measurements to be 
made at the very low particle concentrations naturally 
present in the flow (estimated to be submicron in 
size). For each measurement station and laser beam 
orientation, several hundred instantaneous velocity 
measurements were obtained from which the turbu-
lence quantities of interest were calculated by statisti-
cal methods. 
The laser velocimeter results were compared and 
found to be consistent with those obtained with con-
ventional measurement techniques and existing com-
pressible boundary layer theory. Hence, for the first 
time, turbulence information at supersonic speeds, 
including the IIV correlation, has been successfully 
obtained in a compressible boundary layer with a 
laser system.
Reference: 
Johnson, D. A.: Laser Velocimeter Mean and 
Fluctuation Velocity Measurements of a Mach 2.9 
Wind Tunnel Wall Turbulent Boundary Layer. 
A.I.A.A Journal, vol. 12, no. 5, May 1974. 
Note: 
No additional documentation is available. Specfic 
questions, however, may be directed to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference B75-10141 
Patent status: 
- NASA has decided not to apply for a patent. 
Source: Dennis A. Johnson

Ames Research Center 
(ARC-10781)
[I 
B75-10141	 Category 03


Laser velocimeter measurements of high-speed compressible flows

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