Generator can produce sinusoidal pressures at frequencies from 300 to 5000 Hz and peak-to-peak amplitudes up to 5.6 lbs/sq in. Amplitude and phase-angle measurements made at various frequencies are compared with measurements from a piezoelectric transducer mounted flush with the resonant tube wall

Englund, R., Jr.

Gebben, V. D.

Myland, T. W.

English

NASA Technical Reports Server

.NASA TECH BRIEF U! INASAI 
Rrsonitor	 Reference 
Nozzle 
Air Supply Tube
August 1970	 Brief 70-10352 
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 Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT; Washington, D.C. 20546. 
Sinusoidal-Pressure Generator for Testing Dynamic Pressure Probes 
Schematic Diagram of Pressure Generator 
A simple sinusoidal-pressure generator (see fig.) 
measures the frequency response of small pressure-
measuring probes. It can produce sinusoidal pressures 
at frequencies from 300 to 5000 Hz and peak-to-peak 
amplitudes up to 5.6 lb/in 2. The design is based on the 
Galton tube, a resonant tube driven by an annular 
air jet (organ-pipe principle). Both amplitude and 
phase-angle measurements are made for test pressure 
probes at various frequencies; these data are com-
pared with measurements from a small piezoelectric 
transducer mounted flush with the tube's wall. The 
generator may also find use in testing of fluidic devices 
for frequency response. 
Measurement of the frequency response of pressure 
probes has generally been limited to frequencies lower 
than a few hundred Hertz. Periodic pressure signals 
have been generated with rotating valves and flow 
modulators, siren-tuned cavities, and piston-driven 
devices which, however, are generally large, com-
plicated, and expensive and do not produce clean 
sinusoidal-pressure waves at high frequencies as does 
the new generator. A clean sinusoidal-pressure wave 
shape is a primary requisite for determination of the 
response of probes unless harmonic analysis of the 
measured signals is undertaken. There are various 
techniques for such analyses, but there is considerable 
complexity in both performance of the analysis and 
reduction of the recorded transient signal to a form 
suitable for analysis. 
The resonator (see fig.) is made of a 12-in, length 
of tubing 1-in, in outer diameter and 0.065-in, in wall 
thickness. The open end of the tube is tapered at 30° 
relative to the tube's axis to effect a sharp edge. The 
resonant frequency is adjusted by movement of the 
tuning piston. The nozzle is made of tubing of the 
same diameter as that used in the resonator; a plug 
fitted within the tube is machined so as to provide 
an annular passage for air flow; the annulus is 0.03-in. 
(continued overleaf) 
This document was prepared under the sponsorship of the National
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Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
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thick. Both the position of the tuning piston and the 
nozzle-to-resonator spacings are varied by electric 
motors. 
In operation, air flows through the nozzle and im-
pinges on the sharp edge of the resonator. The re-
sultant turbulence causes the air column within the 
resonator to oscillate, generating a standing wave in 
the resonator tube. Depending on supply pressure and 
nozzle-to-resonator spacing, either quarter-wave 
length modes or odd multiples of the quarter-wave 
length mode can be stably maintained in the resonator. 
Wave-shape distortion is no greater than 3% at high 
pressures; less than 1% at 0.7 lb/in 2 peak to peak. 
Four sets of pressure ports, each consisting of three 
ports; are located along the resonator tube; ports at 
more than one axial position are required for coverage 
of the frequency range. A pressure node is always 
located at the nozzle end; a pressure antinode, at the 
piston end. As the oscillation mode changes, other 
pressure nodes and antinodes appear within the re-
sonator tube; thus the position of the four sets of 
pressure-measuring ports is dictated by the require-
ment that a set of ports be available in the vicinity of 
an antinode for any frequency and oscillatory mode 
used. The axial positions of the four sets of ports were 
determined so that, with the generator operating in 
the first mode, a pressure tap is available where the 
pressure is within 75% of maximum. One of the three 
ports at each axial station is for the test probe, one 
is for the reference transducer, and the third is a spare.
Notes: 
1. This information may interest persons concerned 
with design, manufacture, and use of instruments, 
especially for measurement of pressure. 
2. The following documentation may be obtained 
from:
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.65) 
Reference: 
NASA-TM-X-1981 (N70-23106), A Sys-
tem for Testing Dynamic Pressure Probes 
Utilizing a Sinusoidal Pressure 
Generator 
Technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B70-10352 
Patent status: 
No patent action is contemplated by NASA. 
Source: T.W. Myland, V.D. Gebben, and 
Dr. R. Englund, Jr. 
Lewis Research Center 
(LEW-1 1094) 
Brief 70-10352	 Category 06


Sinusoidal-pressure generator for testing dynamic pressure probes

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