Measuring and testing – Volume or rate of flow – By measuring transit time of tracer or tag
Reexamination Certificate
1998-08-26
2001-05-15
Noori, Max (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring transit time of tracer or tag
Reexamination Certificate
active
06230570
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention (Technical Field)
The present invention relates generally to devices for the measurement of airspeed and fluid flow rates. Specifically, the invention is of a non-intrusive velocity indicator intended for surfaces over which a boundary layer undergoes transition to turbulence, either naturally or through input disturbances.
2. Background Art
Accurate airspeed measurements are essential to safe operations of jet aircraft. Typically, airspeed is inferred from a differential pressure measurement made with a pitot-static tube. Critical to the proper usage of a pitot-static tube is an estimate of the density of air in the vicinity of the tube. As such, a pitot-static tube must be calibrated for altitude (or corrected by the pilot in the case of general aviation aircraft) as well as Mach number in high-speed flight. The present invention concerns a device for which no density corrections need be applied.
Other prior art devices have been proposed for airspeed measurements. Many rely on various embodiments of a classical thermal anemometry system. These include those described in U.S. Pat. Nos. 4,920,793, 3,995,481, 5,357,795, and 5,639,964, to Djorup, U.S. Pat. No. 4,637,253, to Sekimura et al., U.S. Pat. No. 4,070,908, to Newell, U.S. Pat. No. 5,677,484, to Stark, and U.S. Pat. No. 5,311,775, to Suski et al. Such devices rely on the physical principle that the amount of heat dissipated from a heated element exposed to a moving stream is some function of the freestream speed. U.S. Pat. No. 5,357,795, to Djorup, also employs a vortex-shedding flowmeter in addition to a thermal anemometry system. Such a flowmeter relies on another well-known physical mechanism, namely that over some range of incident flow speeds, a circular cylinder will shed vortices at a frequency which is a unique function of the incident flow speed. However, Djorup appears to use vortex shedding as a simple indicator of flow direction. That is, the sensors which detect vortex shedding frequency must be located in the actual flowstream, while those at other circumferential locations around the axis of the device may or may not be. U.S. Pat. No. 5,639,964, to Djorup, discloses a pair of sensors offset along the major axis of an aircraft and speaks of crosscorrelating the signals from the sensors in order to estimate the likelihood of the aircraft experiencing large scale (i.e. aircraft sized turbulence).
U.S. Pat. No. 5,520,047, to Takahashi, is based on the principle that the heat-flux distribution along a flat plane incident to a moving stream is an indicator of air speed.
While the prior does employ a global measurement of the heat flux distribution over a surface as an indicator of flow speed, the present invention does so by making use of a measurement of the convection speed of turbulent spots as an indicator of flow speed. The present invention is unique in that it directly measures the velocity of events occurring in the flow and uses a simple calibration to infer the true airspeed.
SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)
The present invention is of a flowmeter and flow measurement method employing the determination of convection speed of turbulent spots. In the preferred embodiment, a plurality of sensors is employed, preferably thin-film gauges operating in constant temperature, constant current, or constant voltage mode. Analog-to-digital conversion and digital signal processing is employed, particularly for crosscorrelating signals from a plurality of sensors and conditioning the signals to enhance detection of turbulent spot interfaces. Airspeed is determined from the convection speed, preferably via dividing the streamwise sensor spacing by the product of the time lag to the peak of the crosscorrelation function and a calibration constant. It is first preferred to perform a calibration between the time lag to the peak of the crosscorrelation function and the average airspeed over a plurality of sensors for a particular application. Turbulence may be artificially induced, such as by intermittent jets, electrical sparks, or protuberances.
A primary object of the present invention is to provide an airspeed indicator useful for a variety of jet aircraft, including transonic stealth aircraft and general aviation aircraft.
A primary advantage of the present invention is that it is also useful for measuring flow through any conduit through which a fluid passes, including oil pipelines, municipal water systems, and HVAC systems.
Other advantages of the present invention include that it does not intrude upon the flow that it measures and that it needs no correction for changes in fluid density.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
REFERENCES:
patent: 3995481 (1976-12-01), Djouup
patent: 4070908 (1978-01-01), Newell
patent: 4297898 (1981-11-01), Herzl
patent: 4637253 (1987-01-01), Sekimura et al.
patent: 4713970 (1987-12-01), Lambert
patent: 4770035 (1988-09-01), Kolkebeck et al.
patent: 4920793 (1990-05-01), Djorup
patent: 5022274 (1991-06-01), Klinzing et al.
patent: 5218863 (1993-06-01), Mangalam
patent: 5311775 (1994-05-01), Suski et al.
patent: 5357795 (1994-10-01), Djorup
patent: 5493906 (1996-02-01), Sen-Zhi
patent: 5520047 (1996-05-01), Tajagasgu et al.
patent: 5533412 (1996-07-01), Jerman et al.
patent: 5585557 (1996-12-01), Loschke et al.
patent: 5639964 (1997-06-01), Djorup
patent: 5677484 (1997-10-01), Stark
patent: 5719341 (1998-02-01), Reynolds et al.
patent: 5741979 (1998-04-01), Arndt et al.
Clark, J.P., T.V. Jones and J.E. LaGraff, “On the Propagation of Naturally-Occuring Turbulent Spots”,Journal of Engineering Mathematicsvol. 28, 1994, pp. 1-19.
Clark John Paul
Jones Terence V.
Myers Jeffrey D.
Noori Max
Patel Jagdish
Peacock Deborah A.
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