Measuring and testing – Fluid flow direction – With velocity determination
Reexamination Certificate
2002-05-16
2003-08-05
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Fluid flow direction
With velocity determination
C073S170130, C073S861180, C073S861130, C073S861260
Reexamination Certificate
active
06601447
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates in general to anemometers, and, in particular, to sonic (acoustic) anemometers.
There exist acoustic anemometers, also called sonic anemometers, that measure the temperature and velocity vector components of the wind in the lower atmosphere. In all cases, the anemometers are relatively large, and data is acquired at low rates. The fundamental principle behind the operation of these existing acoustic anemometers is based on the transit time for an acoustic signal to travel along a fixed path from an acoustic transmitter to a receiver.
FIG. 1A
shows a prior art anemometer
10
.
FIG. 1B
illustrates the effect of wind velocity vector U on the sound ray vectors for the single axis, dual path configuration shown in FIG.
1
A. If t
1
and t
2
are the transit times for an acoustic signal to leave transmitters
12
and
14
and arrive at the receivers
16
and
18
,
t
1
=d
/(
m
cos &agr;−
U
&xgr;
),
t
2
=d
/(
m
cos &agr;+
U
&xgr;
),
where U
&xgr;
is the wind vector component parallel to the fixed path
20
, d is the path length, m is the local speed of sound in air, and &agr;=sin
−1
(U
&phgr;
/m) is the angle of projection of m onto U
&phgr;
, the wind vector component normal to U
&xgr;
.
Two methods can be used to at least determine U
&xgr;
. If the transmitters produce a simultaneous acoustic signal, then the difference between the transit times can be used,
U
ξ
≈
m
2
(
t
2
-
t
1
)
2
d
.
This reduction is an approximation since it is assumed that U
&xgr;
<<m. A second method of reduction uses the transit time reciprocal, such that
U
ξ
≈
d
2
(
1
t
1
-
1
t
2
)
.
The second method is exact, and is not dependent on m. Therefore, the local ambient temperature need not be determined.
The local ambient temperature can be determined from the transit times and the normal component of the velocity vector,
m
2
=
d
2
4
(
1
t
1
+
1
t
2
)
2
+
U
ϕ
2
,
=
γ
RT
,
were &ggr; is the ratio of specific heats for air, typically &ggr;=1.4, R is the gas constant for air, and T is the local ambient absolute temperature.
This method of reducing transit times into wind vector components limits the efforts in miniaturizing the measuring apparatus. A trade-off between transit time difference measurement and data acquisition rates is present. The distance d must be sufficiently long to allow high resolution of the transit time differences. Conversely, increasing the length of d requires a decrease in the tone frequency from the acoustic transmitters
12
,
14
, thereby limiting the highest sample rate possible with a digital data acquisition system.
Commercially available acoustic anemometers usually have d ranging between 10 to 20 cm, and the tone frequency from the transmitters at about 20 kHz. The configuration of several acoustic anemometers established in an array can simultaneously determine the three vector components of the wind, as well as the local ambient temperature. With typical dimensions, the smallest apparatus will have a sensing volume diameter of about 40 cm.
SUMMARY OF THE INVENTION
The present invention is an acoustic anemometer capable of instantly measuring all three components of the local wind velocity vector. In one embodiment the local temperature is also measured acoustically. The purpose of the anemometer is to measure the local wind velocity vector components and temperature to sufficiently high resolution such that all velocity and temperature turbulence scales are captured.
REFERENCES:
patent: 4031756 (1977-06-01), Rotier et al.
patent: 4038870 (1977-08-01), Rotier
patent: 4221128 (1980-09-01), Lawson et al.
patent: 5218865 (1993-06-01), Djorup
patent: 5357795 (1994-10-01), Djorup
Ellington Alandra
Lefkowitz Edward
Stolarun Edward L.
The United States of America as represented by the Secretary of
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