CN110132364B - Vortex street cross-correlation flowmeter based on miniature transient pressure sensor - Google Patents
Vortex street cross-correlation flowmeter based on miniature transient pressure sensor Download PDFInfo
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- CN110132364B CN110132364B CN201910356127.XA CN201910356127A CN110132364B CN 110132364 B CN110132364 B CN 110132364B CN 201910356127 A CN201910356127 A CN 201910356127A CN 110132364 B CN110132364 B CN 110132364B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/05—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects
- G01F1/20—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by detection of dynamic effects of the flow
- G01F1/32—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by detection of dynamic effects of the flow using swirl flowmeters
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/05—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects
- G01F1/20—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by detection of dynamic effects of the flow
- G01F1/32—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by detection of dynamic effects of the flow using swirl flowmeters
- G01F1/325—Means for detecting quantities used as proxy variables for swirl
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Abstract
The invention relates to a vortex street cross-correlation flowmeter based on a miniature transient pressure sensor, which takes the miniature transient pressure sensor as a measuring element, wherein the transient pressure sensor comprises a probe and a transmitting amplifier, the probe comprises a sensitive element and a pressure guiding pipe, the sensitive element is positioned at the tail end of the pressure guiding pipe, and the pressure guiding pipe is connected with a measuring pipeline; the length of the pressure guiding pipe does not exceed the thickness of the pipe wall and is as small as possible, and the diameter of the pressure guiding pipe is consistent with that of the pressure guiding hole of the probe, so that the chamber of the pressure guiding pipe is ensured to be small enough; collecting vortex-induced fluctuation pressure signals by adopting two identical transient pressure sensors, wherein the distance l between the two sensors is less than the wavelength of a vortex street signal; vortex street signals collected by the two transient pressure sensors are processed by a cross-correlation method to obtain vortex street convection velocity, the convection velocity and the incoming flow velocity are in a linear relation, and the incoming flow velocity is obtained after calibration, so that an average flow measurement value is obtained.
Description
Technical Field
The invention belongs to the field of flow measurement, and relates to a vortex street cross-correlation flowmeter.
Background
The Karman vortex street is an important phenomenon in fluid mechanics, when fluid flows through the blunt body, vortex shedding alternately occurs on two sides of the blunt body at the frequency f, a vortex street is formed in a wake flow, and flow measurement can be realized by measuring the shedding frequency of the vortex street. The vortex street is widely used in the industrial fields of chemical industry, aerospace, petroleum and the like, realizes the accurate measurement of the flow field flow of the vortex street, and has important significance for the process control and the production safety of industrial production.
The methods for measuring the fluid flow in the vortex street flow field are various, such as a conductance probe, an optical fiber probe, a piezoelectric sensor and the like. The probe type sensor has simple method and low price, but the measurement precision is greatly reduced due to the disturbance of the flow field caused by the intrusion of the probe type sensor into the flow field for measurement, and the probe type sensor has been gradually replaced in recent years. The piezoelectric sensor is also an invasive measurement, and has poor capability of resisting vibration interference signals, so that the vortex street flow measurement is distorted; in signal acquisition, only frequency information of signals is acquired, real flow field fluctuation information is hardly reflected, dynamic fluctuation of pressure in a flow field is caused by vortex shedding, dispersion, separation and other phenomena in a vortex field, and changes of internal flow conditions play an important role in improving measurement accuracy. In addition, the current measuring means often has the problem of small measuring range in the small-caliber vortex street flow field measurement, so that the measuring precision is low, the measuring range is narrow, and the practical value is reduced.
Disclosure of Invention
The invention aims to provide a vortex street cross-correlation flowmeter based on a miniature transient pressure sensor, which can realize small-caliber wide-range measurement under the condition of a high-speed flow field. The technical scheme is as follows:
a vortex street cross-correlation flowmeter based on a miniature transient pressure sensor takes the miniature transient pressure sensor as a measuring element, the transient pressure sensor comprises a probe and a transmitting amplifier, wherein the probe comprises a sensitive element and a pressure-leading pipe, the sensitive element is positioned at the tail end of the pressure-leading pipe, and the pressure-leading pipe is connected with a measuring pipeline; the length of the pressure guiding pipe does not exceed the thickness of the pipe wall and is as small as possible, and the diameter of the pressure guiding pipe is consistent with that of the pressure guiding hole of the probe, so that the chamber of the pressure guiding pipe is ensured to be small enough; collecting vortex-induced fluctuation pressure signals by adopting two identical transient pressure sensors, wherein the distance l between the two sensors is less than the wavelength of a vortex street signal, and the two sensors are respectively arranged at the positions 0.2D and 1.0D away from the incident flow surface of the bluff body, wherein D is the inner diameter of the pipeline, and the radial position of the two sensors is fixed at the position which is 45 degrees above the inclined position with better signal quality; vortex street signals collected by the two transient pressure sensors are processed by a cross-correlation method to obtain vortex street convection velocity, the convection velocity and the incoming flow velocity are in a linear relation, and the incoming flow velocity is obtained after calibration, so that an average flow measurement value is obtained.
Usually, DN15 piezoelectric vortex shedding flowmeter has a measuring range of 13-25 m3The range ratio is 2: 1. The invention has the beneficial effect that through the designed transient pressure sensor with the miniature pressure guiding system,the problem of easy pressure distortion in the measurement of the small-caliber high-speed gas-phase medium is solved, and the accuracy of transient pressure measurement and the cross-correlation calculation precision are ensured. The vortex street cross-correlation flowmeter based on the miniature transient pressure sensor can expand the linear measurement range to 8-25 m3And/h, meanwhile, the uncertainty of measurement is guaranteed to be within +/-2%, the lower limit of measurement is effectively reduced, and the range ratio is improved. Meanwhile, the transient pressure sensor is small in size and embedded in the pipe wall of the experimental measurement section, disturbance influence on a flow field caused by an invasive detection device is avoided, good vibration resistance is achieved, and authenticity of a measurement result is guaranteed.
Drawings
FIG. 1 transient pressure sensor architecture
Wherein: 1-a probe, 1-a pressure leading pipe and 1-b sensitive element; 2-front end lead; 3-a transmitting amplifier; 4-back end lead
Fig. 2 is a micro pressure-guiding system of transient pressure sensor
Wherein: 5-measuring the pipeline; 6-a gasket; 7-M5 threads; 8-nut
FIG. 3 mounting location of transient pressure sensor
Wherein: 9-blunt body
FIG. 4 shows the calibration results of the vortex street convection velocity and convection coefficient in the single-phase gas medium
(experiment conditions are that the pressure in the pipeline is 300kPa, the medium is air, and the flow range is 8-25 m3/h。)
FIG. 5 shows the calibration results of vortex street convection velocity and convection coefficient under the wet gas condition
(Experimental conditions: pipe pressure 300kPa, gas phase medium is air, and flow rate is 17m3H; the liquid phase medium is water, the flow range is 1.64-5.10 mL/s, and the liquid phase loading capacity is 0-0.35)
Detailed Description
The invention provides a vortex street flow measuring device suitable for a small-diameter pipeline. The device can meet the requirement of measuring the full frequency range in a high-frequency and high-speed gas-phase vortex street flow field, and enlarges the range of a vortex street flow characteristic curve. The invention is realized by the following devices and technical methods:
a small-caliber wide-range vortex street cross-correlation flowmeter based on a miniature transient pressure sensor is suitable for measuring the flow of a small-caliber pipeline under the condition of a high-speed flow field, takes the miniature transient pressure sensor as a measuring element, and carries out speed measurement based on a cross-correlation theory. The transient pressure sensor mainly comprises a probe 1, a front end lead 2, a transmitting amplifier 3 and a rear end lead 4. The probe 1 comprises a sensitive element 1-a and a pressure guiding pipe 1-b, the sensitive element 1-a is positioned at the tail end of the pressure guiding pipe 1-b, the pressure guiding pipe 1-b is connected with a measuring pipeline 5 through a nut 8, then the pressure guiding pipe is connected into a transmitting amplifier 3 through a front end lead 2, and signals are output through a rear end lead 4.
In order to ensure the frequency response of the transient pressure sensor and improve the measurement accuracy of the transient pressure under the condition of small caliber and high air speed, it is preferable,
(1) the length L of the pressure guiding pipe 1-b does not exceed the thickness of the pipe wall and is as small as possible until close to 0, and the diameter d is consistent with the diameter of the pressure guiding hole of the probe, so that the pressure guiding pipe 1-b is ensured to be small enough and the volume thereof is negligible.
(2) The sensitive element 1-a is made of polysilicon, and the volume is small and is approximately 0.
(3) Using two identical transient pressure sensors A1、B1And acquiring vortex-induced fluctuation pressure signals, wherein the distance l between the two sensors is less than the wavelength of one vortex street signal, the two sensors are respectively arranged at positions 0.2D and 1.0D away from the blunt body (wherein D is the inner diameter of the pipeline), and the radial position of the two sensors is arranged at a position which is 45 degrees above the inclined position and has better signal quality.
(4) A is to be1、B1And processing the vortex street signal with the strongest correlation by using a cross-correlation method to obtain the vortex street convection velocity, wherein the convection velocity and the incoming flow velocity are in a linear relation, and the incoming flow velocity is obtained after one-time calibration so as to obtain an average flow measurement value.
Compared with the prior art, the vortex street flow measuring device has the following characteristics:
(1) the designed transient pressure sensor with the miniature pressure guiding system improves the problem of easy pressure distortion in the measurement of small-caliber high-speed gas-phase medium, and ensures the accuracy of transient pressure measurement and the cross-correlation calculation precision.
(2) Generally, the DN15 small-caliber piezoelectric vortex shedding flowmeter has a measuring range of 13-25 m3The range ratio is 2: 1. The vortex street cross-correlation flowmeter based on the miniature transient pressure sensor can expand the linear measurement range to 8-25 m3And/h, meanwhile, the uncertainty of measurement is guaranteed to be within +/-2%, the lower limit of measurement is effectively reduced, and the range ratio is improved.
(3) The frequency response of the transient pressure sensor is ensured, the transient pressure measurement precision under the condition of small caliber and high air speed is improved, the pressure measurement error in the frequency range of 760-2230 Hz is less than 10%, and the transient pressure measurement accuracy is ensured. The pressure measuring range of the sensor is 100-400 kPa (absolute pressure), the accuracy is 0.25% FS, and the resolution is 0.02%.
(4) Meanwhile, the transient pressure sensor is small in size and embedded in the pipe wall of the experimental measurement section, disturbance influence on a flow field caused by an invasive detection device is avoided, good vibration resistance is achieved, and authenticity of a measurement result is guaranteed.
In order to further understand the features and technical means of the present invention and achieve specific objects and functions, the following detailed description of the embodiments of the present invention is provided with reference to the accompanying drawings.
The vortex street cross-correlation flowmeter is realized by the following sensor (the structure is schematically shown in figure 1) and a measuring method, a sensitive element of a transient pressure sensor selects polysilicon with very small volume, a pressure guide pipe (shown in figure 2) with the length L of 8.5mm and the diameter d of 1.5mm is designed in a DN15 test pipe section with the pipe wall thickness of 8.5mm, and the pressure guide pipe is embedded in the pipe wall of an experimental measuring section and does not invade a flow field. Transient pressure sensor A1、B1Are respectively arranged at the positions which are 45 degrees away from the inclined upper parts of the sounding bodies 0.2D and 1.0D (wherein D is the inner diameter of the pipeline), and the specific installation positions are shown in figure 3.
The measurement method is as follows, and the average flow Q of the fluid can be expressed as
Wherein the content of the first and second substances,fluid inflow velocity vlCan be obtained by vortex convection velocity. Within a certain velocity range, the convection velocity vcAnd velocity vlIs a constant k, i.e.
Where k is the convection coefficient. The average convection velocity can be estimated as follows
Where l is the spacing between the two sensors, τ0The time required for a vortex to propagate from an upstream sensor to a downstream sensor is called the transit time. Based on the cross-correlation theory, the transit time τ0Equal to the delay time corresponding to the maximum cross correlation coefficient of the upstream and downstream pressure fluctuation signals, where A1、B1Process the correlation coefficient between the signals to be
The actual system is usually a digital system, and the correlation coefficient of the actual system is expressed as discrete expression
N is the sampling point,. tau.is the delay time, fsIs the sampling frequency.
To ensure the convection velocity vcEstimation accuracy, requiring accurate acquisition of the transit time τ0The sensor system should have a sufficiently high sampling frequency f and integration timesNeed to satisfy
vcmaxMaximum convection velocity, maximum relative error.
Integration time T needs to be satisfied
T≥10τ0max\*MERGEFORMAT (7)
For further explanation, experimental verification was performed. The pressure of the pipeline in the experiment is 300kPa, the experiment medium is air, and the flow range is 8-25 m3/h。
According to the above, to obtain the vortex street convection speed in the related speed measurement, the sampling frequency f needs to be determined firstsAnd an integration time T. When the maximum vortex street convection velocity is according to vcmax37.7m/s (flow rate 20 m)3H converted), when the maximum relative error of time measurement is +/-5% and the sensor distance l is 0.8D 0.012m, f is obtained from formula 6s30.7kHz, and finally determining the sampling frequency to be 60 kHz; minimum vortex street convection velocity according to vcmin14.1m/s (flow rate according to 10 m)3H converted) from equation 7 to a maximum transit time of 7.07 x 10-4s, so the integration time should be 7.07X 10 or more-3s, i.e. the number of integration points is at least 700, and finally the number of experimental integration points is determined to be 800. In order to ensure the accuracy of the result, the average value of 500 calculation results is finally used as a correlation coefficient.
Experimental results show that the vortex street cross-correlation flowmeter has gas phase flow of 8-25 m3In the/h range, k in the gas-phase vortex street field is 0.866 with uncertainty of +/-2%, and the result is shown in fig. 4.
In addition, experiments prove that the invention is also applicable to vertically downward gas-liquid mist flow. The experimental pipeline pressure is 300kPa, the gas-phase medium is air, and the flow rate is 17m3The liquid phase medium is water, the flow range is 1.64-5.10 mL/s, and the liquid phase loading capacity is 0-0.35. The experimental results show that k is 0.6, the uncertainty is ± 5%, and the results are shown in fig. 5.
The invention improves the problem of volatile real time in the pressure measurement of the small-caliber high-speed gas-phase medium by designing the miniature pressure sensor, and ensures the accuracy of transient pressure measurement and the cross-correlation calculation precision. Effectively reduces the lower limit of measurement, improves the range ratio to 3:1 and is 8-25 m3Implementation in the/h rangeThe gas phase flow measurement precision is +/-2%, and k is 0.866, so that the application range of flow measurement is widened.
Claims (1)
1. A vortex street cross-correlation flowmeter based on a miniature transient pressure sensor takes the miniature transient pressure sensor as a measuring element, the miniature transient pressure sensor comprises a probe and a transmitting amplifier, wherein the probe comprises a sensitive element and a pressure guiding pipe, the sensitive element is positioned at the tail end of the pressure guiding pipe, and the pressure guiding pipe is connected with a measuring pipeline; the length of the pressure guiding pipe does not exceed the thickness of the pipe wall, and the diameter of the pressure guiding pipe is consistent with that of the pressure guiding hole of the probe; two same micro transient pressure sensors are adopted to collect vortex-induced fluctuation pressure signals, and the distance between the two micro transient pressure sensorslLess than one vortex street signal wavelength, respectively arranged at a distance of 0.2 to the upstream side of the bluff bodyDAnd 1.0DTo，WhereinDThe radial position of the inner diameter of the pipeline is fixed at the position of 45 degrees above the inclined position; processing vortex street signals collected by two miniature transient pressure sensors by using a cross-correlation method to obtain vortex street convection velocity, wherein the convection velocity and the incoming flow velocity are in a linear relation, and obtaining the incoming flow velocity after calibration to further obtain an average flow measurement value; the measurement method is as follows:
mean flow of fluidQIs shown as
Wherein the incoming flow velocity of the fluidV l Obtained by the convection velocity of the vortex street, the convection velocity in a certain velocity rangeV c And speedV l Is a constantkI.e. by
Wherein the content of the first and second substances,kas convection coefficient, convection velocity
Where two miniature transient pressure sensors, one upstream, called upstream sensor, and the other downstream, called downstream sensor, τ0The time required for propagation from an upstream sensor to a downstream sensor, called the transit time, the transit time τ0Equal to the delay time corresponding to the maximum cross correlation coefficient of the upstream and downstream pressure fluctuation signals.
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