A fluid velocity measuring device is described which, when placed in a freestream fluid flow, causes vortices to be formed at a frequency proportional to the flow rate of the fluid. Sensors on the device generate electric signals with frequency proportional to the rate of vortex creation and with relative mean amplitudes indicative of fluid flow direction. Electric circuitry translates the electric signals into indications of fluid speed and direction

Thomas, D. F., Jr.

Williams, L. A., Jr.

English

NASA Technical Reports Server

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON. D.C. 20546
REPLY TO
ATTN OF: GP
TO:
FROM:
DEC 2 1 1978
NST-44 •*,
XXIv/Scientific & Technical Information Division
Attn: Miss Winnie M. Morgan
GP/Office of Assistant General
Counsel for Patent Matters
SUBJECT: Announcement of NASA-Owned U.S. Patents in STAR
In accordance with the procedures agreed upon by Code GP and Code
KSI, the attached NASA-owned U.S. Patent is being forwarded for
abstracting and announcement in NASA STAR.
The following information is provided:
U.S. Patent No.
Government or
Corporate Employee
Supplementary Corporate
Source (if applicable)
NASA Patent Case No.
H.
V) i S i & o
NOTE - If this patent covers an invention made by a corporate employee
of a NASA Contractor, the following is applicable:
YES / 7 NO
Pursuant to Section 3°5(a) of the National Aeronautics and. Space Act,
the name of the Administrator of NASA appears on the first page of the
patent; however, the name of the actual inventor (author) appears at
the heading of column No. 1 of the Specification, following the words
"...with respect to an invention of ..."
Bonnie L. .Henderson
Enclosure
(NASA-Case-L-AR-11729-1) FLUID VELOCITY
M E A S U R I N G DEVICE Patent (NASA) 9 p
CSCL 20D
- L.:. 00/34
N79-12359
Uncles
394614
https://ntrs.nasa.gov/search.jsp?R=19790004188 2020-03-20T18:04:01+00:00Z
United States Patent
Thomas, Jr. et al.
[ii] 4,122,712
[45] Oct. 31,1978
[54] FLUID VELOCITY MEASURING DEVICE
[75] Inventors: David F. Thomas, Jr.; Leon A.
Williams, Jr., both of Hampton, Va.
[73] Assignee: The United States of America as
represented by the United States
National Aeronautics and Space
Administration, Washington, D.C.
[21] Appl. No.: 856,461
[22] Filed: NOT. 30, 1977
[51] Int CM G01F 1/32
[52] U.S. Cl 73/189; 73/194 VS
[58] Field of Search 73/189, 194 VS, 194 B
[56] References Cited
U.S. PATENT DOCUMENTS
3,452,594 7/1969 Dale 73/194
3,645,132 2/1972
3,720,104 3/1973
3,785,203 1/1974
3,797,309 3/1974
Rasmussen 73/189
Zanker 73/194
Mull 73/170
Joy et al. 73/194
Primary Examiner—Herbert Goldstein
Attorney, Agent, or Firm—Wallace J. Nelson; Howard J.
Osborn; John R. Manning
[57] ABSTRACT
A fluid velocity measuring device which when placed
in a freestream fluid flow causes vortices to be formed
at a frequency proportional to the flow rate of the fluid.
Sensors on the device generate electric signals with
frequency proportional to the rate of vortex creation
and with relative mean amplitudes indicative of fluid
flow direction. Electric circuitry translates the electric
signals into indications of fluid speed and direction.
7 Claims, 6 Drawing Figures
12
14
14
U.S. Patent Oct. si, 1978 sheet i of 4 4,122,712
FIG. 1
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FIG. 4
U.S. Patent Oct. 31,1978 Sheet 2 of 4 4,122,712
1-15
12
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FIG. 2
-14
U.S. Patent Oct. SI, 1978 Sheet 3 of 4 4,122,712
FIG. 3
7
FIG. 5
U.S. Patent Oct. 31,1978 Sheet 4 of 4 4,122,712
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4,122,712
FLUID VELOCITY MEASURING DEVICE
ORIGIN OF THE INVENTION
The invention described herein was made by employ-
ees of the United States Government and may be manu-
factured and used by or for the government for govern-
mental purposes without payment of any royalties
thereon or therefor.
BACKGROUND OF THE INVENTION
A further object of this invention is a fluid velocity
measuring device which yields the foregoing advan-
tages and which is simply constructed and easy to oper-
ate.
Other objects and advantages of the present invention
will be readily apparent from the following description
and drawings which illustrate a preferred embodiment
of the present invention.
10 SUMMARY OF THE INVENTION
The present invention involves a fluid velocity mea-
This invention relates to a fluid velocity measuring
 suring device, positionable in a freestream of fluid flow
device. More particularly, it relates to a fluid velocity
 to cause vortices to be created at a frequency proper-
measuring device wherein oscillating rotary forces on
 tionai to the rate of floW) utilizing sensors to generate
the device arising from the shedding of vortices created. 15
 signals representative of fluid velocity, the frequencies
by the passing of a freestream of fluid around the device
 of which are proportional to fluid flow speed and the
and translations! drag forces on the device are detected amplitudes of which are indicative of fluid flow direc-
by piezoelectric sensor crystals which create electric
 tjon
signals from which fluid velocity components of speed
 The device indudes a housi mounted around a
and direction are deduced by an electnc circuit. Previ- 20
 indle fixed at one and to some reference structure.
fieari ;de a low fricdon CQntact and ali t
between ^  housj ^ the mounti indle Sensors
afe mounted betwe* n ^ housj ^/^ mountidle measure rotationa] forcfes caused b vorte*
^ translational drag forces relative to the
.
 c?
reference structure. The sensors generate electric sig-
nals which are translated into indications of fluid flow
ously, the measurement of freestream fluid flow veloc-
ity was accomplished by the utilization of two separate
instruments: one to measure flow speed, e.g. pilot-static
tube, venturi tube, bridled pressure plate; and the other
to measure flow direction, e.g. directional vane (wind 25
vane, weather vane). The present invention measures
freestream flow velocity with a single device.
The utilization of the vortex street phenomenon as an
indication of fluid speed is well known in the prior art.
When a body is placed in a stream of fluid flow with a 30 BRIEF DESCRIPTION OF THE DRAWINGS
Reynolds number between ICPand 103, vortices are shed
alternately from either side of the body at a frequency
proportional to the speed of fluid flow.
The prior art, however, limits the application of the
vortex street phenomenon to flow inside a conduit with 35
the relationship between vortex creation frequency and
fluid speed being dependent upon the conduit diameter.
The present invention imposes no such requirement and
may be mounted in a freestream of fluid such as the air
for measuring wind velocities, or in a wind tunnel for 40
measuring air stream perturbations created by aircraft
wings and fuselages, or in the ocean or river for measur-
ing water current velocities. The present invention
measures vortex creation frequency at the point of cre-
ation whereas prior art devices counted the vortex ere- 45 employed in the present invention and capable of inter-
ation frequency at a remote spot somewhat down- preting electric signals into secondary signals proper-
speed and direction by additional electric circuitry.
FIG. 1 is an elevational sectional view of a fluid ve-
locity measuring device as viewed along the line I—I of
FIG. 2;
FIG. 2 is a plan sectional view taken along the line
II—II of FIG. 1;
FIG. 3 is a plan view similar to FIG. 2 showing the
direction of forces incurred by flow from angle ft on
force sensors;
FIG. 4 is a sectional view taken along line IV—IV of
FIG. 1;
FIG. 5 is a graph of the relative magnitude of the
forces of FIG. 3 as a function of time; and
FIG. 6 is a schematic diagram of the electrical circuit
stream. Downstream counting may lead to unaccept-
able accuracy since extraneous currents may induce
error. Furthermore, downstream counting is impracti-
cal in a freestream since the counter would require 50
repositioning for each change in fluid flow direction.
One known device which utilizes temperature sensors
to determine vortex creation frequency at the point of
creation requires precision aligning and it is impractical
tionai to the fluid velocity components of speed and
direction.
DESCRIPTION OF PREFERRED EMBODIMENT
Referring to FIG. 1, a fluid velocity measuring de-
vice includes a hollow cylindrical housing shell 10 en-
closed on the top by an upper cover 11 and enclosed on
the bottom by a lower cover 12 and positioned concen-
for use in a freestream fluid. Some advantages of the 55 trically about a hollow cylindrical mounting spindle 20
present invention are, firstly, the consolidation of the having threads 26 for fixing to a reference structure and
enclosed on the top by a spindle cover 21. The spindle
20, the shell 10, upper cover 11, lower cover 12, and
spindle cover 21 share a common axis of symmetry 16.
60 A pivot bearing 22 affixed to the upper surface of spin-
dle cover 21 at the axis of symmetry 16 is accommo-
dated by dimple 13 located on the bottom surface of
upper cover 11 at the axis of symmetry 16.
Three point bearings 25 provide a low friction
A further object of this invention is a fluid velocity 65 contact between spindle 20 and lower cover 12.
measuring device which yields the foregoing advan- As shown more particularly in FIG. 4, the three point
tages and which also measures fluid flow speed and bearings 25 of the preferred embodiment are spaced at
direction at the same time and at the same place. 120 degree intervals about spindle 20.
functions of both of these types of instruments into one
simple solid state device with no.moving parts, and
secondly, that both flow speed and flow direction can
be measured at the same time at the same place.
An object of the present invention is a fluid velocity
measuring device adapted to accurately measure frees-
tream fluid flow speed and direction utilizing transla-
tional drag and vortex formation phenomenon.
4,122,712
'Substituting equations (3) and (4) into equations (9)
and (10) : •
F., + Fc = FTDa -
or,
(11)
and,
or,
= FT
10
(12) 15
Substituting equations (1) and (2) into equations (11)
and (12) respectively,
Fa+Fc=2F rDcos0 (13) 20
Fb+ Fj=2FTDsin0 . : (14)
Dividing equation (14) by equation (13),
25
Fb+ 2FTDsin
Fa+ Fc ~ 2FTDcos0
or,
30
= tan/3 (15)Fa + F, cos
Taking the arc tangent of both sides of equation (IS)
(16)
0 = arc tan
The direction, /3, of freestream flow 15 is given by
equation (17) in terms of the measurable quantities V0,
Vfc Vp and Vrf. The fluid speed S is proportional to the
vortex creation frequency, / and is determined by the
simple relationship
= kf
35
40
And, for identical crystals 34a, 346, 34c, and 34rf
which generate voltages Va, V^, Vp and Vrf, respec-
tively, equally proportional to force thereon, equation
(16) can be rewritten 45
(17)
50
55
(18)
where k is a constant (zO.19).
FIG. 6 is a schematic of a simple electric circuit for
performing equations (17) and (18). The force induced 6°
crystal voltage signals are first filtered, eliminating all
frequencies above 200 cycles per second, to preclude
the passage of structural material resonance frequency
signals. Fluid speed, S, is calculated by taking any one
of the filtered signals (Va is used for purpose of illustra- 65
tion of FIG. 6), feeding it into a frequency counter and
multiplying the resulting frequency signal by a constant,
k, to obtain the fluid speed, S = kf. The calculated
speed signal is at this point fed to a speed readout.
The fluid direction equation (17) is calculated in the
remainder of the circuit of FIG. 6. Vais added to Vcand
V6is added to Vd. Thus (V6+V(/)/(V0+Vc) is taken to
find /?. Since the arc tangent function only yields values
from +90° to —90° an additional test must be per-
formed to determine if a correction must be made to
obtain the true angle /3. If (V0+Vc) > 0, angle of inci-
dence /3 is left as calculated, but if (VD+VC) > 0°, 180"
is added to /J. The true angle ft has been determined at
this point. However, it will have a value from — 90° to
270° and since it is preferable to have values between 0°
and 360°, ft is now tested and corrected by adding 360°
thereto. The fluid flow direction signal is at this point
fed to a direction readout.
The above described fluid velocity measuring device
is constructed primarily of metallic material. However,
the shell 10, upper cover 11, and lower cover 12 are
plastic for the purpose of minimizing material resonance
frequency signals in the electric circuit. The use of these
materials in the preferred embodiment is not intended to
limit the present invention thereto, and any suitable
material may be used alternatively.
The above described fluid velocity measuring devices
utilizes piezoelectric sensor crystals to sense vortex
creation frequency and translational drag force in a
freestream of fluid flow. It is understood that other
electric sensing devices capable of generating signals
having frequency proportional to vortex creation fre-
quency and amplitudes representative of fluid flow
direction, including strain gauges and induction coils
but not excluding others, may also be employed.
The above description and drawings are only illustra-
tive of one embodiment which achieves the objects,
features, and advantages of the present invention, and it
is not intended that the present invention be limited
thereto. All modifications of the present invention
which come within the spirit and scope of the following
claims are considered part of the present invention.
What is claimed as new and desired to be secured by
Letters Patent of the United States is:
1. A fluid velocity measuring device positionable in a
freestream of fluid flow to cause vortices to be shedded
therefrom at a frequency proportional to fluid flow
speed, said device comprising:
a housing mounted on a spindle;
said housing being capable of oscillatory rotary mo-
tion about said spindle induced by, and at a fre-
quency indicative of, the periodic shedding of vor-
tices therefrom; said housing being further capable
of translational motion relative to said spindle in-
duced by, and indicative of the direction of, said
freestream fluid flow;
said spindle fixable at one end to a reference structure
and extending into said housing;
bearing means providing low friction contact and
alignment of said housing with said spindle;
force sensing means attached between said housing
and said spindle capable of generating an electric
signal indicative of said vortex creation frequency
and indicative of the direction of translational drag
force on said housing by said fluid flow; and
electric circuitry for translating said electric signal
into a readout of fluid speed and direction.
2. A fluid velocity measuring device as in claim 1
wherein said force sensing means includes four sensors
positioned at 90° intervals around said spindle.


Fluid velocity measuring device

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