Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Patent
1982-09-16
1984-03-20
Goldstein, Herbert
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
G01F 132
Patent
active
044373490
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
Embodiments of the invention hereinafter described pertain to devices for the generation of vortices.
BACKGROUND ART
It is known to position a generator plate in an air flow to generate Karman vortices. Detection of the frequency of these vortices can be used as an indication of the mass of air flowing by the generator plate. For example, U.S. Pat. No. 4,312,237 issued Jan. 26, 1982 discloses various embodiments of narrow, elongated generator plates used for the generation of Karman vortices in a fluid stream. In one embodiment of U.S. Pat. No. 4,312,237, a generator plate has a shedding section wherein an aperture intersects side surfaces of the generator plate to form a leading aperture edge which serves as a shedding corner for the generation of vortices.
Also, U.S. Pat. No. 4,312,236 issued Jan. 26, 1982 discloses a vortex generating device having a narrow generator plate which is immersed in a fluid flow to generate Karman vortices. The generator plate has side surfaces parallel to the direction of fluid flow. The side surfaces have a shedding region therein forming shedding corners at which vortices detach from the generator plate.
Air flow meters using such vortex generators have produced stable vortices over a wide range of fluid flow rates. Such devices have functioned particularly well and operated in accordance with the acoustical techniques disclosed in U.S. Pat. No. 3,680,375 to Joy et al.
However, there has been a problem of adjusting the vortex frequency to a precise value at a given flow for flow meters that do not have precise mechanical dimensions.
The vortex flowmeter has the characteristic of having a quasi-digital output where each output pulse represents the passage of a certain amount of fluid. This amount of fluid is determined by the flow duct area and the cross section width of the vortex generator. This relationship is defined by:
In order to produce flowmeters having an identical vortex frequency to fluid flow relation, the mechanical duct area must be held to precise tolerances.
For some applications where tight tolerances cause a cost penalty, such as in the automotive field, a means is needed to adjust some mechanical dimension to change the frequency-to-flow relation in order to offset manufacturing tolerances.
DISCLOSURE OF INVENTION
In accordance with principles of this invention, a change in the flow velocity and, hence a change in the vortex frequency, is caused by changing the flow duct area which is unobstructed by the vortex generator cross section. Such a change in the unobstructed flow duct area can be caused by either changing the width of the vortex generator or by adjusting the boundaries of the flow duct area.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top view of an air flow meter in accordance with an embodiment of this invention including provisions for varying the vortex generator width;
FIG. 2 is a top view of an air flow meter in accordance with an embodiment of this invention including means for varying the boundaries of the air flow ducts; and
FIG. 3 is an air flow meter in accordance with an embodiment of this invention wherein the vortex generator is longitudinally movable to sections of the air flow duct having different interior boundaries.
BEST MODES FOR CARRYING OUT THE INVENTION
Referring to FIG. 1, an air flow meter 10 has an air flow channel 11 with walls 12. Positioned within air flow channel 11 is an elongated plate number such as a vortex generator or strut 13 having an elliptical cross section. The vortex strut 13 dimension that governs the shed frequency is the width of the strut, measured at right angles with respect to the flow. Vortex strut 13 can be rotated about an axis 14. This will cause the cross sectional area of strut 13 exposed to the air flow to change. The change in vortex frequency correlates very closely with the expected change based upon the projected width. Therefore, an elliptical strut with a ten percent difference in its major and minor axes will cause a total frequency change of ten perc
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patent: 4062238 (1977-12-01), Herzl
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patent: 4312236 (1982-01-01), Mahany et al.
Abolins Peter
Ford Motor Company
Goldstein Herbert
Sanborn Robert D.
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