Remote sensing tool reliably measures statistical properties of supersonic turbulence. Tool neither affects nor is adversely affected by flow field. Device determines characteristics of supersonic flow with optical system and provides method and apparatus for separating translational and rotational motions of turbulent structures in supersonic flow

Funk, B. H.

English

NASA Technical Reports Server

before a photodetector. Because the edge is rotatable, 
both translational and rotational motions of turbulent-
flow structures may be determined. The signals from 
the photodetector are correlated by computer, and the 
correlated data signal is fed into an oscilloscope 
or comparable display apparatus. 
Thus, the device (I) determines the characteristics 
of supersonic flow with an optical system, and (2) 
(continued i°erIeui) 
NEW
two laser beams being converted into readable elec-
trical signals. The tool neither affects nor is adversely 
affected by the flow field. 
Two laser beams are directed through the super-
sonic boundary layer in the test section of a wind 
tunnel. If the layer is two dimensional, the beams 
may be placed parallel to each other; otherwise they 
are positioned so that the volume of flow under
August 1971	 Brief 71-10252 
NASA TECH BRIEF 
Marshall Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Optical ProHng of Supersonic Flows with Statistical Correlation 
A remote sensing tool reliably measures the statis-
tical properties of supersonic turbulence. The charac-
teristics of supersonic flow are determined by an 
optical system with deflections (Schlieren effects) in 
Airflow
examination is restricted to that volume common 
to both beams. 
The turbulence crossing both beams may be more 
easily correlated statistically by using a knife-edge 
Oscilloscope 
Photodetector-A 
Window  
 Low- & High- () Laser-A Amplifier	
_
 
Pass Filters 
Window [A	 B 
Laser-B Lf JJowig - 
/Beam-B ter i 
Knife-Edge-B	 Photodetector-B 
Wind 
Tunnel Thin-Plate Model L Oscilloscope 
Camera Time Delay
Analog 
Correlator 
-	 / 
-
--
B
o 
Integral Data 
Correlated Data Storage 
Apparatus with Two-Dimensional Wind Flow; Schematic
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately ownedrights.
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provides a method and apparatus for separating the 
translational and rotational motions of turbulent struc-
tures in supersonic flow. 
The figure shows a schematic of a wind tunnel 
test section having two opposed windows and hous-
ing a thin-plate model to cause substantially two-di-
mensional airflow turbulence. A collimated.beam from 
Laser-A crosses the airflow upstream, and in the super-
sonic turbulent boundary layer; beam-A is then re- 
ceived by photodetector-A (a photometer). Rotatable 
knife-edge-A is positioned before photodetector-A 
in such a way that approximately 50% of the light 
is blocked from the photodetector. The collimated 
beam from Laser-B crosses the airflow downstream 
of beam-A; beam-13 is then received by photode-
tector-B. Rotatable knife-edge-B is positioned before 
its photodetector such that approximately 50% of 
the light is kept from the detector. 
Signals from the two photodetectors, reflecting dis-
turbances of the two laser beams by disturbances 
in the airflow, pass through separate amplifiers and 
filters to an analog correlator. The correlated data 
are then fed to an oscilloscope, where a camera 
photographs the display. The amplified and filtered 
raw data from the detectors are viewed in a second 
oscilloscope. 
Many modifications and variations of the system 
are possible, including replacing the two lasers with 
a single laser, beam splitter, and mirrors.
Note: 
The following documentation may be obtained 
from:
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95) 
Reference: 
NASA-TM-X-53870 (N70-12209), A Direct 
Measurement of the Most Probable Pre-
ferred Angular Velocity of Turbulent Struc-
tures by Optical Correlation of Laser Schlieren 
Signals 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to: 
Patent Counsel 
Mail Code A&TS-PAT 
George C. Marshall Space Flight Center 
Marshall Space Flight Center, Alabama 35812 
Source: B. H. Funk

Marshall Space Flight Center 
(M F S-20642)
. 
. 
Brief 7 1-10252	 Category 03


Optical probing of supersonic flows with statistical correlation

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