Vortex shedding flowmeter with mechanically amplifying pressure sensor

This invention discloses a vortex shedding flowmeter comprising a vortex generator-detector constructed into an integrated assembly wherein the vortex shedding frequencies are detected by a pressure detector including at least one panel of extended surface area, which are pivotably or flexibly confined within a planar cavity included in the bluff body that generates a series of vortices shed from the two sides thereof in an alternating pattern at frequencies substantially proportional to the velocity of the fluid stream wherein the bluff body is immersed. The two opposite planar walls of the planar cavity confining a pressure detector panel respectively include a plurality of small holes open to each of the two sides of the bluff body. The fluctuations in the fluid pressure created by the vortices shed from the two sides of the bluff body in an alternating pattern produce alternating pressure differences across the pressure detector panel and, consequently, creates oscillatory pivoting or flexing motions thereof, which are detected by a transducer connected to the pressure detector panel assembly, that may include a single pressure panel of a large surface area or a plurality of pressure panels disposed in a parallel arrangement and connected to a single transducer.

BACKGROUND OF THE INVENTION 
The vortex shedding flowmeters commercially available at the present time 
determine vortex shedding frequencies by measuring the effect of the 
pressure fluctuations occuring in the immediate vicinity of the bluff body 
or by detecting the action of sinuating streamlines in a downstream 
region. In present day technology, the pressure fluctuations accompanying 
vortex shedding are measured by detecting the side-to-side deflection of 
the bluff body resulting from the pressure difference across the two sides 
thereof, or by measuring the deflection of a diaphragm with two sides 
respectively exposed to two pressure holes open to the two sides of the 
bluff body, respectively. The side surface area of the bluff body as well 
as the area of the diaphragm with each side exposed to a single pressure 
hole is generally limited to a small size. As a consequence, the existing 
method of detecting the pressure fluctuations accompanying vortex shedding 
is effective only for the vortices of sizable intensity, which is 
generally proportional to the square of the fluid velocity. The existing 
vortex shedding flowmeters employing the aforementioned pressure detection 
method fail to measure air velocities less than 25 feet per second under 
the standard condition and the water velocities less than 1.5 feet per 
second. The cord length of the wing employed in today's vortex shedding 
flowmeters for measuring the lift force created by the sinuating 
streamlines produced by the vortices cannot be greater than four times the 
bluff body width, as the wave length of the sinuation streamlines is about 
eight times the bluff body width. Consequently, the surface area of the 
wing employed for detecting the effect of the sinuating streamlines is 
generally limited to a small size. The existing vortex shedding flowmeters 
employing a wing fail to measure air velocities less than 20 feet per 
second and water velocities less than 1.0 feet per second. It is well 
established fact that the vortices are shed in regular pattern at 
velocities as low as a few feet per second for air flow under the standard 
condition and a fraction of a foot per second for water flow. There are 
numerous applications in the industries where the measurement of air 
velocities less than 10 feet per second and water velocities less than 1.0 
feet per second is required. The present day vortex shedding flowmeters 
have failed to meet such requirements. 
SUMMARY OF THE INVENTIONS 
The primary object of the present invention is to provide a vortex shedding 
flowmeter with a pressure sensing means for measuring the vortex 
frequencies, which means include a single pressure detector panel of a 
large surface area or a plurality of parallel pressure detector panels 
connected to each other wherein the two sides of each pressure detector 
panel are respectively exposed to the fluctuating pressures at the two 
sides of the bluff body. 
Another object is to provide a vortex shedding flowmeter with a pressure 
sensing means including one or more pressure detector panels respectively 
included in a planar cavity wherein each of the two opposite walls thereof 
include a plurality of pressure holes open to each of the two sides of the 
bluff body. 
A further object is to provide a vortex shedding flowmeter with a pressure 
sensing means wherein the planar cavity confining the pressure detector 
panel is included within the bluff body or within the bluff body and 
downstream extension thereof. 
Yet another object is to provide a vortex shedding flowmeter with a 
pressure sensing means wherein the pressures at the two sides of the bluff 
body communicate through one or more pressure holes connecting the two 
sides of the bluff body at the junction between the bluff body and the 
trailing edge extension thereof. 
Yet a further object is to provide a vortex shedding flowmeter including a 
transducer that detects oscillatory pivoting motions of the pressure 
detector panel or panels about an axis parallel to the lengthwise axis of 
the bluff body. 
Still another object is to provide a vortex shedding flowmeter including a 
transducer that detects oscillatory pivoting motions of the pressure 
detector panel or panels about an axis parallel to the direction of the 
fluid flow. 
Still a further object is to provide a vortex shedding flowmeter including 
a transducer that detects oscillatory flexing motions of the pressure 
detector panel or panels. 
These and other objects of the present invention will become clear as the 
description thereof proceeds.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
In FIG. 1 there is illustrated a cross section of an embodiment of the 
combination of a bluff body and a pressure detector panel arranged in 
accordance with the principles of the present invention, which cross 
section is taken along a plane perpendicular to the lengthwise axis of the 
bluff body and parallel to the direction fo the fluid flow. The first 
principal element of the vortex generator-detector included in the vortex 
shedding flowmeter of the present invention comprises bluff body and 
trailing edge extension 1 that is an elongated member disposed in a 
perpendicular angle with respect to the direction of the fluid flow, which 
includes a blunt loading edge side 2 squarely facing the fluid flow and 
the two lateral sides 3 and 4 and a trailing edge extension 5. The 
combination of a bluff body-trailing edge extension 1 includes a planar 
cavity 6 that contains a pressure detector panel 7 which is the second 
principal element. The space between the wall of the cavity 6 and the 
surfaces of the pressure detector panel 7 has to be reasonably small. It 
is generally desirable that the pressure detector panel 7 must be clearly 
separated from at least one side wall of the planar cavity 6. A first set 
of plurality of holes 8 disposed through one side wall of the planar 
cavity 6 emerges from one lateral side 3 of the bluff body in a 
concentrated pattern at a locality intermediate the leading and trailing 
edges of the bluff-body trailing edge extension combination 1. A second 
set of a plurality of holes 9 disposed through the other side wall of the 
planar cavity 6 emerges from the other lateral side 4 of the bluff body in 
a concentrated pattern at a locality intermediate the leading and trailing 
edges of the bluff body-trailing edge extension combination 1. A set of 
blind holes 10 open to one lateral side 3 and another set of blind holes 
11 open to the other lateral side 4 are connected to each others by a 
pressure communicating hole 12 routed through the bluff body around the 
planar cavity 6. The extremity of the planar cavity 6 adjacent to the 
trailing edge may include one or more openings 13 breaking through the 
trailing edge 14 of the bluff body-trailing edge extension combination 1. 
The fluid flowing in the direction from the leading edge 2 to the trailing 
edge 14 of the bluff body-trailing edge extension combination 1 produces 
two rows of vortices 15 and 16 respectively shed from the two lateral 
sides 3 and 4 of the bluff body in an alternating pattern, wherein the 
frequency of the vortex shedding is proportional to the fluid velocity. 
In FIG. 2 there is illustrated another cross section of the combination of 
bluff body-trailing edge extension 1 shown in FIG. 1, which cross section 
is taken along plane 2--2 as shown in FIG. 1. The combination of bluff 
body-trailing edge extension 1 extends from an anchoring or securing 
flange 17 secured to the conduit wall 18, and extends through the conduit 
wall 18 and into the interior of the conduit, wherein it is disposed all 
the way or partially across a cross section of a flow passage provided by 
the conduit. The two sets of blind holes 10 and 11 respectively open to 
the two lateral sides 3 and 4 of the bluff body are connected to each 
others by the pressure communicating holes 12 routed through the bluff 
body around the planar cavity 6. The pressure detecting panel 7 is 
contained within the planar cavity 6. The combination including the bluff 
body-trailing edge extension 1 and the pressure detecting panel 7 enclosed 
within the planar cavity 6 generates vortices and detects the vortex 
shedding and, consequently, this combination will be called the "vortex 
generator-detector" hereafter. When the vortex generator-detector extends 
all the way across a cross section of the flow passage, the extremity 19 
thereof opposite to the anchoring flange 17 should be secured to the 
conduit wall. When the vortex generator-detector extends partially across 
a cross section of the fluid passage, the extremity 19 opposite to the 
anchoring flange 17 should include a flow guide or flow straightener 20 
that prevents the fluid from flowing around the extremity 19. 
In FIG. 3 there is illustrated a further cross section of the vortex 
generator-detector shown in FIGS. 1 and 2, which cross section is taken 
along plane 3--3 as shown in FIG. 1. In this cross section view, the 
plurality of through holes 8 extending from one side wall of the planar 
cavity 6 to one lateral side 3 of the bluff body as well as the plurality 
of blind hole 10 connected to the pressure communicating hole 12 are 
clearly illustrated. One extremity 21 of the pressure detector panel 7 is 
secured to the corresponding extremity of the bluff body-trailing edge 
extension combination 1, wherein the former may be fixedly secured to the 
latter as shown in the illustrated embodiment or it may be simply or 
pivotably secured instead of the fixed securement. The other extremity 22 
of the pressure detecting panel 7 is connected to a transducer 23 such as 
a piezo electric transducer that converts the oscillatory lateral 
deflections of the pressure detector panel 7 to alternating electromotive 
forces. The electronic signal processor 24 analyzes the output from the 
transducer 23 and provides data related to the vortex shedding frequency 
or the fluid velocity obtained therefrom, which data may be displayed by a 
data display means 25 or transmitted out by an output means 26. In the 
illustrated embodiment the other extremity 22 of the pressure detector 
panel 7 is connected to the transducer assembly 23 by means a swivel joint 
or pivoting joint including a ball joint 27 engaging a socket 28. 
In FIG. 4 there is illustrated a cross section of the transducer 23 taken 
along a plane including the central axis thereof and perpendicular to the 
chord line of the pressure detector panel 7. The pivotable joint 
comprising the ball 27-socket 28 is connected to a rib member 29 extending 
from a thin flange 30 that is under a pressurized contact with a pair of 
piezo electric crystals 31 and 32, which are disposed in a mirror image to 
one another with respect to a plane including the central plane of the rib 
member 29 and that of the pressure detector panel 7. The pair of piezo 
electric crystals 31 and 32 are contained in a cavity 34 included in a 
transducer vessel 35 wherein the cavity 34 is sealed by a threaded plug 36 
that compresses the two piezo electric crystals 31 and 32 onto the thin 
flange 30. The pair of electrical wires 37 and 38 respectively connected 
to the two piezo electric crystals 31 and 32 are routed through a hole 
disposed through the threaded plug 36. As shown in FIG. 3, the transducer 
vessel 35 is rigidly secured to the holder or flange structure supporting 
the vortex generator-detector combination comprising the bluff body and 
the pressure detector panel. 
The vortex shedding flowmeter or the vortex generator-detector illustrated 
in and described in conjunction with FIGS. 1, 2, 3 and 4 operates on the 
following principles : The two rows of vortices 15 and 16 respectively 
being shed from the two lateral sides 3 and 4 of the bluff body in an 
alternating pattern raises and lowers the fluid pressure at the two 
lateral sides 3 and 4 in the same alternating pattern. The alternately 
rising and falling fluid pressures on the two lateral sides 3 and 4 in 180 
degree phase difference are transmitted to the two sides of the pressure 
detector panel 7 and, consequently, the pressure detector panel 7 
experiences alternating lateral loadings thereon that result in 
alternating lateral flexing motions thereof. Such alternating lateral 
flexing motions of the pressure detector panel 7 produce alternating 
pivoting motions of the rib 29 about an axis coinciding with the line of 
intersection between the rib 29 and the thin flange 30, which alternating 
pivoting motions alternatively increase and decrease the pressure on the 
two piezo electric crystals that generate alternating electromotive forces 
directly related to the lateral flexing motions of the pressure detector 
panel 7. As a consequence, the frequencies of the alternating 
electromotive forces induced between the two piezo electric cyrstals 31 
and 32 are the same as the vortex shedding frequencies, that is 
proportional to the fluid velocity in a wide Reynolds number range that 
includes practically all ranges of the fluid velocity measurements 
required in the industries. The electronic processor 24 receiving the 
signals from the transducer 23 through the two conducting wires 37 and 38 
filters the noises and amplifies the vortex signals, which are then 
analyzed and converted to vortex shedding frequencies, or fluid 
velocities, or volume or mass flow rates. 
The first novelty or ingenuity included in the present invention is the 
"large surface area" of the pressure detector panel that is exposed to the 
fluid pressure transmitted through the "plurality of pressure transmitting 
holes" originating in a "concentrated pattern" from a "linear locality" 
intermediate the bluff body and the trailing edge extension thereof. The 
large surface of the pressure detector panel cannot be exposed directly to 
the fluid stream because the pressure fluctuations take place in different 
phase relations in the time structure at different localities and, 
consequently, the pressure fluctuations at different localities cancel 
each other rather than build up when the large surface area of the 
pressure detector panel is exposed to pressures at different localities. 
The pressures loading the pressure detector panel of large surface area 
have to originate from a linear locality a certain distance away from the 
leading edge side of the bluff body. The pressure detector panel of large 
surface area of the present invention mechanically amplifies the pressure 
signal transmitted from the desired localities in much the same way as the 
diaphragm of large surface area employed in the stethoscope. The 
stethoscope enables one to listen to sounds that cannot be heard 
otherwise. The vortex generator-detector of the present invention enables 
one to detect the vortices generated in the low velocity flows, which 
cannot be detected with the existing vortex flowmeter technology. 
The second novelty or ingenuity of the present invention is the use of the 
pressure communicating holes that allow the pressures at the two lateral 
sides of the bluff body to communicate therebetween. The phenomenon of 
fluid dynamic instability that causes the vortices to shed from the two 
lateral sides of the bluff body is closely related to the interaction of 
the fluid pressures at the two lateral sides, as the peak and valley of 
the pressure wave have to shift back and forth between the two lateral 
sides of the bluff body in order to generate and shed vortices in a 
regular pattern. The pressure transmitting holes open to the pressure 
detector panel may be located downstream of the pressure communicating 
holes as in the case of the illustrated embodiment or the former may be 
located intermediate the leading edge face of the bluff body and the 
latter. 
In FIG. 5 there is illustrated a cross section of another embodiment of the 
vortex generator-detector, which cross section is equivalent to that shown 
in FIG. 3, having essentially the same construction as the combination 
shown in FIGS. 1, 2, 3 and 4 with one exception being that one extremity 
39 of the pressure detector panel 40 is simply supported by a pivoting or 
swivel joint, while the other extremity 41 is connected to a transducer 42 
by a swivel or pivoting joint 43. It should be understood that the one 
extremity of the pressure detector sensor may be connected to the bluff 
body or structure supporting thereof by a simple or fixed or semifixed 
manner, while the other extremity may be connected to the transducer by a 
swivel or pivoting joint or by a fixed or rigid joint. 
In FIG. 6 there is illustrated a cross section of a further embodiment of 
the vortex generator-detector having essentially the same construction as 
the combination shown in FIGS. 1, 2 and 3 with a few exceptions, which 
cross section is taken along a plane perpendicular to the lengthwise axis 
of the bluff body and parallel to the direction of the fluid flow. The 
combination of the bluff body 44 and the trailing edge extension 45 
includes two sets of pressure communicating holes 46 and 47 and two sets 
of pressure transmitting holes 48 and 49 open to the planar cavity 50 that 
are open to the trailing edge 51 of the combination of the bluff body 44 
and the trailing edge extension 45. The planar cavity or planar slot 50 
receives the pressure detector panel 52 that is pivotably supported about 
a pivoting axis 53. It should be mentioned that the two sets of pressure 
transmitting holes 48 and 49 may be located intermediate the leading edge 
of the bluff body 44 and the two sets of the pressure communicating holes 
46 and 47, respectively. 
In FIG. 7 there is illustrated another cross section of the vortex 
generator-detector shown in FIG. 6, which cross section is taken along 
plane 7--7 as shown in FIG. 6. The pressure detector panel 52 engaging the 
open planar cavity or planar slot 50 with clearance is pivotably supported 
by a pair of pivoting hines or pivotable supports 54 and 55 respectively 
included in the two extremities of the pressure detector panel 52 adjacent 
one edge thereof. Therefore, the two relative pressure loadings of 
opposite signs respectively exerted on the two sides of the pressure 
detector panel 52 produce oscillatory pivoting motions of the pressure 
detector panel 52 about the pivoting axis passing through the pivoting 
hinges 54 and 55. Such oscillatory motions of the pressure detector panel 
52 are transmitted to the transducer 56 having the same construction as 
that illustrated in FIG. 7. The transmitter arm 57 mechanically couples 
the pressure detector panel 52 to the rib 58 extending from the thin 
flange 59, which is disposed on a plane including the pivoting axis 
passing through pivoting hinges 54 and 55 and perpendicular to the 
direction of the fluid flow. The pair of piezo electric crystals are 
disposed in a mirror image to one another about a plane including the 
pivoting axis passing through the pivoting hinges 54 and 55 and parallel 
to the direction of the fluid flow. The vortex generator-detector 
extending from an anchoring or securing flange 60 secured to the wall 61 
of the pipe or conduit providing the flow passage, extends through the 
pipe wall and into the fluid passage. The extremity 62 of the vortex 
generator-detector may be anchored or secured to the pipe wall or 
terminated in the fluid stream. In the latter case, it is necessary to 
include a flow guide or flow straightener 63 that prevents the fluid from 
flowing around the free standing extremity of the vortex 
generator-detector. The transducer arranged in conjunction with the 
pivoting pressure detector panel 52 is more immune to the noise created by 
the pipe vibration compared with the transducer arranged in conjunction 
with the flexing pressure detector panel shown in FIG. 3, as the former is 
susceptive to the axial vibration of the pipe while the latter is 
susceptive to the lateral vibration of the pipe which is much more 
pronounced than the axial vibratoin in most industrial applications. 
In FIG. 8 there is illustrated a cross section of yet another embodiment of 
the vortex generator-detector of the present invention having essentially 
the same construction as that described in conjunction with FIGS. 6 and 7, 
which cross section shows a view equivalent to that shown in FIG. 6. This 
embodiment includes a series of sets of pressure communicating holes 64, 
65, 66, etc., which are distributed over the entire length of the trailing 
edge extension 67 downstream of the bluff body 68. The embodiment 
described in conjunction with FIGS. 1, 2 and 3 may include a plurality of 
sets of pressure communicating holes instead of one set, as exemplified by 
the embodiment shown in FIG. 8. 
In FIG. 9 there is illustrated a cross section of a vortex 
generatordetector, which cross section is taken along a plane 
perpendicular to the lengthwise axis thereof and parallel to the direction 
of the fluid flow. This embodiment of the vortex generator-detector does 
not include a trailing edge extension such as those elements 5 and 45 
respectively shown in FIGS. 1 and 6. The bluff body 69 includes a pair of 
planar slots 70 and 71 disposed in a side-by-side arrangement parallel to 
the lengthwise axis thereof and parallel to the direction of the fluid 
flow. A pair of pressure detector panels 72 and 73 connected to one 
another at the trailing edge thereof engage the two planar slots 70 and 
71, respectively. The first sides of the pressure detector panels 72 and 
73 facing the first lateral side 74 of the bluff body 69 are exposed to 
the fluctuating fluid pressure on the first lateral side 74 by means of 
the two sets of the plurality of pressure transmitting holes 75 and 76, 
respectively, which pressure transmitting holes are disposed through the 
one side wall of the planar slots 70 and 71 and break through the first 
lateral side 74 of the bluff body 69. The second sides of the pressure 
detector panels 72 and 73 facing the second lateral side 77 of the bluff 
body 69 are exposed to the fluctuating fluid pressure on the second 
lateral side 77 by means of the two sets of pluralities of pressure 
transmitting holes 78 and 79, respectively, which pressure transmitting 
holes are disposed through the other walls of the planar slots 70 and 71 
and break through the second lateral side 77 of the bluff body 69. The 
plurality of pressure transmitting holes 76 open to the planar slot 71 are 
connected to the second plurality of holes 80 breaking through the first 
lateral side 74 of the bluff body 69 by a hole 81 disposed through the 
bluff body and around the first planar slot 70, while the plurality of the 
pressure transmitting holes 79 open to the first planar slot 70 are 
connected to the plurality of holes 82 breaking through the second lateral 
side 77 of the bluff body 69 by a hole 83 disposed through the bluff body 
and around the second planar slot 76. It should be mentioned that the 
holes breaking through the lateral sides of the bluff body should be 
concentrated at a linear locality of an optimum distance measured from the 
leading edge face of the bluff body where the pressure fluctuations 
created by the vortex shedding are maximum. 
In FIG. 10 there is illustrated another cross section of the vortex 
generator-detector shown in FIG. 9, which cross section is taken along 
plane 10--10 as shown in FIG. 9. The combination of the bluff body and 
pressure detector panel assembly extending from an anchoring or securing 
flange 84 that is secured to the wall 85 of the pipe or conduit, extends 
through the pipe wall and into the flow passage. The extremity of the 
vortex generator-detector opposite to the anchoring flange 84 may extend 
all the way to the pipe wall and be secured thereto, or it may terminate 
amid the fluid passage as illustrated in FIG. 2. The plurality of pressure 
transmitting holes 75 extend from the first lateral side 74 of the bluff 
body 69 to the first planar slot 70, while the plurality of the pressure 
transmitting holes 78 extend from the second lateral side 77 of the bluff 
body to the second planar slot 71. The plurality of the blind holes 80 
open to the first lateral side 74 of the bluff body are connected to the 
plurality of the blind holes 76 open to the second planar slot 71 by the 
hole 81 disposed through the bluff body around the first planar slot 70. 
The plurality of the blind holes 82 open to the second lateral side 77 of 
the bluff body are connected to the plurality of blind holes 79 open to 
the first planar slot 70 by the hole 83 disposed through the bluff body 
aroudn the second planar slot 71. In the cross sectional view shown in 
FIG. 10, the portion of the hole 83 manifolded to the blind holes 79 is 
located behind the hole 81 manifolded to the blind holes 76. 
In FIG. 11 there is illustrated a further cross section of the vortex 
generator-detector shown in FIG. 9, which cross section is taken along 
plane 11--11 as shown in FIG. 9. The assembly 84 of the pressure detector 
panels 72 and 73 is pivotably supported by the structure belonging to the 
bluff body 69 by a pair of pivoting supports 85 and 86, wherein the 
pivoting axis 87 passing through the two pivoting supports 85 and 86 is 
disposed adjacent to the trailing edge of the bluff body 69 in a parallel 
relationship with respect to the lengthwise axis of the bluff body 69. The 
oscillatory pivoting motions of the pressure detector panel assembly 84 
are detected by the transducer 89 having the same elements and 
arrangements as that described in conjunction with FIG. 7. 
In FIG. 12 there is illustrated a cross section of another embodiment of 
the vortex generator-detector, which cross section is equivalent to that 
shown in FIG. 11. Ths vortex generator-detector has the same construction 
and arrangement as that shown in FIGS. 9, 10 and 11 with one exception 
being that the transducer 90 having the same elements and arrangement as 
that described in conjunction with FIG. 3, detects the oscillatory lateral 
deflections of the pressure detector assembly 91 instead of the 
oscillatory pivoting motions. The first extremity of the pressure detector 
panel assembly 91 is connected to the transducer 90 by a swivel or 
pivoting joint 93 as described in conjunction with FIG. 3, while the 
second extremity 94 is fixedly, simply or semifixedly secured to the 
structure belonging to the bluff body 95. 
In FIG. 13 there is illustrated a cross section of a further embodiment of 
the vortex generator-detector of the present invention which has 
construction and arrangement similar to the vortex generator-detector 
illustrated in FIGS. 9, 10 and 11 or FIG. 12. The bluff body 96 includes 
three planar cavities or planar slots respectively engaged by three 
pressure detector panels belonging to the pressure detector panel assembly 
97. The first sides of the three detector panels facing the first lateral 
side 98 of the bluff body 96 are exposed to the fluctuating pressure of 
the fluid adjacent to the first lateral side 98 of the bluff body by first 
sets of pluralities of pressure transmitting holes, while the second sides 
of the three pressure detector panels facing the second lateral side 99 of 
the bluff body 96 are exposed to the fluctuating pressure of the fluid 
adjacent to the second lateral side 99 of the bluff body 96 by second sets 
of pluralities of pressure transmitting holes, which pressure transmitting 
holes are disposed through the bluff body 96 in an arrangement similar to 
the pressure transmitting holes illustrated in FIGS. 9 and 10. It is clear 
that any number of pressure detector panels may be included in the type of 
vortex generator-detector shown in FIGS. 9 and 13, depending on the 
availability of the space within the bluff body for the inclusion of as 
many planar cavities as possible. In general, the greater the number of 
pressure detector panels, the lower the fluid velocity measurable by the 
vortex shedding flowmeter becomes, as the amplitude of the oscillatory 
pivoting motions or oscillatory lateral deflections of the pressure 
detector panel assembly produced by a given magnitude of the pressure 
fluctuations accompanying the vortex shedding becomes greater in 
proportion to the number of the pressure detector panels included in the 
assembly thereof. In order to measure the vortex shedding frequencies from 
the signals generated by the transducer, the amplitude of the vortex 
signals has to be greater than that of the noise signals generated by the 
pipeline vibration. The teachings of the present invention provide one of 
the most effective means for mechanically amplifying the vortex signals 
without amplifying the noise signals. 
In FIG. 14 there is illustrated a cross section of yet another embodiment 
of the vortex generator-detector of the present invention, which is 
designed and operating on the same principles as those combinations 
respectively shown in FIGS. 9 and 13. The U-shaped pressure detector 
assembly 100 including a pair of pressure detector panels 101 and 102 is 
completely confined within a cavity 103 of U-shaped cross section included 
in the bluff body 104 having a rectangular cross section. The first sides 
of the pressure detector panels facing the first lateral side 105 of the 
bluff body 104 are exposed to the pressure of the fluid adjacent to the 
first lateral side 105 by first sets of pluralities of pressure 
transmitting holes, while the second sides of the pressure detector panels 
facing the second lateral side 106 of the bluff body 104 are exposed to 
the pressure of the fluid adjacent to the second lateral side 106 by the 
second sets of pluralities of pressure transmitting holes, which holes are 
disposed in an arrangement similar to these shown in FIGS. 9 and 10. The 
vent holes such as the holes 107, 108, 109, etc. may be included in order 
to provide means for ventilating the cavity 103. The oscillatory motions 
of the pressure detector assembly 100 are detected by the transducer 
arranged in the same manner as those illustrated in FIG. 11 or 12. The 
particular embodiment shown in FIG. 14 has a cross section symmetric in 
the up and downstream directions and, consequently, measures fluid flows 
in both directions. It should be mentioned that those embodiments shown in 
FIG. 9 or 13 may include a bluff body with a rectangular cross section 
instead of one with a taperzoidal cross section. The specific cross 
sectional geometry of the bluff body is a matter of design, which should 
be determined on the basis of vortex shedding characteristics as well as 
the design requirement dictated by the combination of the bluff body and 
the pressure detector assembly. 
While the principles of the present invention have now been made clear by 
the illustrative embodiments, there will be obvious to those skilled in 
the art many modifications of the structures, arrangements, proportions, 
elements and materials which are particularly adapted to the specific 
working environments and operating conditions in the practice of the 
invention without departing from those principles.