CN111412956A

CN111412956A - Vortex street probe based on acceleration measurement

Info

Publication number: CN111412956A
Application number: CN202010232329.6A
Authority: CN
Inventors: 孙宏军; 杨天宇; 王伟
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2020-03-27
Filing date: 2020-03-27
Publication date: 2020-07-14

Abstract

The invention relates to a vortex street probe based on a triaxial acceleration sensor, which comprises three parts of structures, namely a top disc, a middle cylinder and a bottom cuboid, wherein probe cavities are formed in the middle cylinder and the bottom cuboid respectively, the top disc is convenient for pipeline fixation and is provided with a positioning groove for calibrating the positive direction, the triaxial acceleration sensor serving as a sensitive element is embedded into the bottom cuboid, the probe cavity of a vortex street flowmeter and a pipeline are in direct contact hard connection and are not in contact with a generator, and the sensitive element is a triaxial acceleration sensor which can sense the vibration change of the vortex street pipeline and is used for measuring the vortex street information in the pipeline.

Description

Vortex street probe based on acceleration measurement

Technical Field

The invention relates to the field of vortex street flow field measurement, in particular to a vortex street probe based on acceleration measurement.

Background

The vortex shedding flowmeter is a speed type flow meter based on the karman vortex shedding principle, and is widely applied due to the characteristics of wide measurement range, high reliability, small pressure loss, insensitivity to fluid physical property change and the like. On one hand, the karman vortex street is caused by fluid vibration and is easy to be disturbed and unstable by vibration noise, and vibration interference inevitably exists in the installation environment of the vortex street flow meter, such as natural frequency interference of a vortex street pipeline, or pressure pulsation interference caused by periodic vibration of a centrifugal pump and a compressor connected with the pipeline and valve action and the like.

On the other hand, from the perspective of spatial distribution, the conventional measurement method can only obtain a "one-dimensional" signal, which is doped with different flow field information, such as a vortex street signal, a vibration signal, and the like, and most of the signal is frequency, and the obtained information is limited, which is not beneficial to subsequent signal analysis.

At present, an acceleration sensor based on the MEMS technology tends to be miniaturized, and the possibility of realizing multidisciplinary cross measurement is brought. From newton's second law, acceleration is proportional to the resultant force experienced by the object. The acceleration is integrated to obtain velocity information, and then the velocity information is integrated to obtain displacement information. In addition, the frequency domain analysis is carried out on the acceleration time domain signal to obtain a frequency signal.

Disclosure of Invention

The invention designs a vortex street probe based on an MEMS triaxial acceleration sensor. The probe is combined with an integrated triaxial acceleration sensor and a vortex street probe, and then functions of accurate measurement of vortex street frequency and measurement of spatial three-dimensional vortex street flow field signals are realized through a reasonably designed acquisition circuit and a vortex street probe structure. The technical scheme is as follows:

the utility model provides a vortex street probe based on triaxial acceleration sensor, constitute by the triplex structure, be the top disc respectively, middle cylinder and bottom cuboid, the inside probe cavity that forms of middle cylinder and bottom cuboid, the top disc makes things convenient for the pipeline to fix and is equipped with a constant head tank and is used for demarcating the positive direction, embedding bottom cuboid in the triaxial acceleration sensor as sensing element, the connected mode between vortex street flowmeter probe cavity and the pipeline is direct contact's hard connection, and with the generator contactless, sensing element can experience the vibration change of vortex street pipeline for triaxial acceleration sensor, be used for measuring the inside vortex street flow field information of pipeline.

Drawings

FIG. 1 is a schematic view of a vortex street probe structure according to an embodiment of the present invention;

FIG. 2 is a schematic view of a probe and a pipeline connection provided in the practice of the present invention;

fig. 3 shows the gas phase flow (gas phase flow rate of 28.56m/s) of 400kPa and 19.27m3/h for P-Qg, (a) shows the measurement signal and frequency domain analysis diagram without transient excitation applied to the pipeline, and (b) shows the time and frequency signals in the Y-direction of the hammer blow of the rubber hammer;

fig. 4 is a spatial distribution diagram of forces in a two-phase flow field under the working conditions of P being 300kPa and Ql being 25m3/h according to an embodiment of the present invention;

in the drawings: the vortex shedding flowmeter comprises a probe cavity of a vortex shedding flowmeter, a 2-pipeline, a 3-generator, a 4-triaxial acceleration sensor, a 5-voltage stabilizing module and a 6-hollow structure.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

As shown in figure 1, the probe is made of magnesium aluminum alloy, and generally comprises three parts, namely a top disc, a middle cylinder and a bottom cuboid. For vortex flowmeter probe cavity 1 on the whole, mainly including hollow structure 6, the top disc makes things convenient for the pipeline fixed and is equipped with a constant head tank and is used for demarcating the positive direction, and middle cylinder structure can furthest reduce the influence of probe to the flow field, and the bottom cuboid is embedded to the sensing element, for the frictional force of increase vortex street signal and bottom cuboid contact, the bottom adopts the milling machine to process.

As shown in figure 2, the connection mode between the vortex flowmeter probe cavity 1 and the pipeline 2 is direct contact hard connection and is not in contact with the generator 3, so that the pipeline can be transmitted to the whole vortex street probe cavity when vibrating, and the sensitive element can feel the vibration change of the vortex street pipeline, thereby realizing the measurement of the pipeline resonance interference. Therefore, when the pipeline vibrates, the vibration can be transmitted to the whole vortex street probe, and the detection element can feel the vibration change of the vortex street pipeline. The sensor can be used as a sensitive detection element to measure the information of the vortex street flow field in the pipeline.

The triaxial acceleration sensor 4 has three axial, and the voltage stabilizing module 5 includes chip and voltage stabilizing circuit for ensure steady voltage power supply, prevent that the chip from being burnt.

The sensor embedded into the tail end of the probe can sensitively sense the mechanical deformation caused by the vortex street impact probe in the pipeline, so that the flow field acceleration information is obtained. On one hand, according to the uniqueness of the vortex street signals and the multi-directionality of the vibration signals, the vortex street signals are only sensitive to the x axis, the vibration is reflected in multiple axial directions, and accurate vortex street information can be effectively obtained by performing frequency domain analysis on the acquired time domain acceleration signals.

The three axes of the vortex street signal will be analyzed using the probe described above. The frequency characteristics of all axial directions can be effectively identified through the matching of the three shafts, and the vibration resistance of the acceleration type vortex street probe is reflected to a certain degree. Next, the anti-vibration characteristics of the vortex street probe will be further studied by applying transient excitation to the vortex street pipeline, and the test experiment is performed at a gas phase flow rate (gas phase flow rate of 28.56m/s) of P400 kPa and Qg 19.27m3/h, as shown in fig. 3(a), for a measurement signal and a frequency domain analysis without applying transient excitation to the pipeline, from the signal point of view, the Z axis effectively measures the vortex street lift frequency, the X axis effectively measures the vortex street resistance frequency, the Y axis reflects both the Z, X axis frequency information and the interference frequency, and similarly, the interference frequency around 5kHz and 8kHz appears due to the limitation of the structure of the sensor itself.

Fig. 3(b) is a collected signal obtained by applying excitation on the Y axis by using a rubber hammer, and a time domain signal completely reproduces the triggering and attenuation processes of a transient excitation signal, and because the excitation direction is the Y axis direction, the transient excitation signal is more sensitive to vibration, and because of the transmissibility of the vibration, the other two axes are also interfered by the vibration to different degrees. From the Y-axis frequency domain, the vibration interference is mostly concentrated in the low frequency band of 1kHz, and the excited vibration is smaller than the interference of the sensor structure.

Besides, the amplitude information of the vortex street probe is acceleration with physical significance, and there is a definite linear relationship between the acceleration and the force, so that the spatial distribution of the force in the two-phase flow field is taken as an example of the two-phase measurement, as shown in fig. 4, under the working condition that P is 300kPa and Ql is 25m 3/h. The measured acceleration time sequence signal is used for reflecting the change rule of the force in the gas-liquid two-phase flow, and the time sequence signal obviously becomes irregular due to the more complex flow environment of the mist flow, and simultaneously reflects the complexity of the force change. It can be seen that the acceleration type vortex street probe has certain superiority in signal identification.

According to the analysis, the frequency characteristics can be measured in the three axial directions of the designed acceleration type vortex street probe, the characteristics of the lift frequency, the resistance frequency and the vibration interference frequency can be effectively identified through the matching of the three axial directions, the aim of measuring the multi-dimensional frequency information of the flow field is achieved, the probe has stable vibration resistance, a solid foundation is laid for improving the measurement precision and stability of the vortex street, and a new thought is provided for the measurement and analysis of the original vortex street signal. And the spatial distribution of the resultant force of the vortex street flow field and the like can be effectively constructed through a plurality of time domain acceleration signals measured axially.

Claims

1. The utility model provides a vortex street probe based on triaxial acceleration sensor, constitute by the triplex structure, be the top disc respectively, middle cylinder and bottom cuboid, the inside probe cavity that forms of middle cylinder and bottom cuboid, the top disc makes things convenient for the pipeline to fix and is equipped with a constant head tank and is used for demarcating the positive direction, embedding bottom cuboid in the triaxial acceleration sensor as sensing element, the connected mode between vortex street flowmeter probe cavity and the pipeline is direct contact's hard connection, and with the generator contactless, sensing element can experience the vibration change of vortex street pipeline for triaxial acceleration sensor, be used for measuring the inside vortex street flow field information of pipeline.