Low-noise flow monitoring device and design method thereof

Abstract

The invention discloses a low-noise flow monitoring device and a design method thereof, the cross section of a detection rod at least comprises two sections of incident flow sides and two sections of back flow sides, the incident flow sides are linear, the lengths of the two incident flow sides are the same, and the back flow sides are parallel to each other; the end points of the two adjacent incident flow edges, the end points of the incident flow edges and the end points of the back flow edges and the end points of the two back flow edges are in arc smooth connection; by controlling the relative length of the incident flow edge and the back flow edge, the total change amount and the change rate of the transverse flow velocity when the detected fluid passes through the detection rod can be controlled, and the disturbance of a flow field near the pressure tapping hole is reduced. Under the conditions of the same circumcircle diameter of the detection rod, the same flow velocity and other external environments, the measurement noise can be controlled within 2% of the pressure difference, and the noise can be reduced by 4-5 times compared with the noise of a circular detection rod; meanwhile, the detection device disclosed by the invention is simple and convenient in product processing, use and mold manufacturing.

Description

Technical Field

[0001] The present invention relates to the technical field of flow monitoring, and in particular to a low-noise flow monitoring device and a design method thereof. Background Art

[0002] The insertion type average velocity tube flowmeter is a typical fluid flow and / or velocity measuring device. It mainly inserts the detection rod (also called the pressure guide tube) into the measured fluid pipeline to measure the pressure difference (abbreviated as pressure difference) between the dynamic pressure on the upstream surface (also called total pressure, positive pressure or high pressure) and the static pressure on the rear surface (also called negative pressure or low pressure). Then, the flow velocity and / or flow rate of the fluid is calculated based on the relationship between the flow velocity and the pressure difference and parameters such as the effective cross-sectional area of ​​the measured pipe.

[0003] Traditional detection rods are round, aerodynamic, and bullet-shaped, each with its own advantages and disadvantages. For details, see the Chinese invention patent with announcement number CN103364036B and the name "Pressure lead pipe for insertable average velocity tube flowmeter". However, most of the existing pressure lead pipes have problems of unstable pressure difference and high noise during actual measurement. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects in the prior art and provide a low-noise flow monitoring device and a design method thereof, which can obtain lower noise and optimize the design between noise suppression and obtaining an ideal pressure difference value.

[0005] The technical solution of the present invention includes designing a low-noise flow monitoring device (also called a flow meter), which belongs to an average-velocity tube flow meter, including a flow monitoring device body and a detection rod (also called a pressure-guiding tube) arranged on the body, wherein the detection rod is provided with a total pressure chamber and a static pressure chamber that are independent of each other, and the detection rod is provided with a plurality of total pressure holes connected to the total pressure chamber and a plurality of static pressure holes connected to the static pressure chamber on both sides (front and back of the fluid flow direction) of the detection rod, respectively, and the body is provided with a total pressure detection hole connected to the total pressure chamber and a static pressure detection hole connected to the static pressure chamber, respectively, and the fluid pressures of the total pressure chamber and the static pressure chamber are detected respectively through the detection holes, the total pressure hole is located on the flow-front surface of the measured pipeline, and the static pressure hole is located on the back-flow surface of the measured pipeline, The detection rod is an elongated body along the length direction; it is characterized in that the cross section of the detection rod includes at least 2 sections of the upstream side and the downstream side (located on the left and right sides of the fluid flow direction), the upstream side is a straight line (that is, the upstream surface is designed as a plane), the two upstream sides are the same length, and the angle is less than or equal to 90 degrees; the connection methods of the two adjacent upstream side endpoints, the upstream side and the downstream side endpoints, and the two downstream side endpoints are all arc-shaped and smooth connections, and the connection points are called endpoint connection arcs (depending on the location, they can be called upstream heads, downstream bottoms, side connection arcs, etc.), the two upstream sides are symmetrically arranged, and the two downstream sides are symmetrically arranged, and the width of the endpoint connection arc (the present invention refers to the straight length of the two end points of the arc, not the arc length) is not less than the width of the pressure taking hole and not greater than 1 / 5 of the upstream side length.

[0006] Let the length of the two straight frontal edges be L1, the rod diameter of the frontal surface of the detection rod perpendicular to the flow direction be D1 (maximum width, generally the distance between the intersection points of the frontal edge and the back edge), and the rod diameter in the flow direction be D2. Then the diameter of the circumscribed circle of the detection rod is R=max(D1,D2); the length of the back edge is L2 (if it is an arc, the length here refers to the straight line length of the two ends of the arc, not the arc length), then D1≤D2, L1≤L2, L1≥D1 / , L2≥D2 / .

[0007] Furthermore, the shape of the back-stream edge includes a straight line type. Like the straight-line front-stream edge, this design has a small fluid velocity change rate and a small flow field disturbance, thereby reducing measurement noise.

[0008] Furthermore, the length of the upstream side is consistent with the length of the downstream side, and the angle between the two adjacent sides is 90 degrees, that is, the cross-section of the detection rod is square as a whole, with one arc-shaped end angle facing the upstream direction and the other arc-shaped end angle facing the downstream direction.

[0009] Furthermore, the shape of the back-flow edge includes a concave arc, and the back-flow side length (the present invention refers to the straight-line length of the two end points of the arc, not the arc length) is equal to the front-flow side length. Although the lateral velocity change rate of the fluid in the front section of the back-flow edge is relatively large, the lateral velocity is close to 0 in the last section, and the flow field disturbance near the static pressure tapping hole is not greatly affected, and a good noise suppression effect can still be obtained.

[0010] Furthermore, the arc radius = the length of the flow-facing side / .

[0011] Further, such as Figure 4 As shown, the shape of the back-stream edge includes a convex arc, and the back-stream edge length (the present invention refers to the straight line length of the two end points of the arc, not the arc length) is equal to the front-stream edge length. Although the lateral velocity change rate of the fluid at the back-stream edge is relatively large, especially near the static pressure taking hole, the lateral velocity of the fluid changes significantly, resulting in a weak static pressure measurement noise suppression effect, this design can obtain better differential pressure measurement results, and the noise is mainly controlled by the front-stream edge, and the total lateral velocity of the fluid is controllable.

[0012] Furthermore, the arc radius = the length of the flow-facing side / .

[0013] On the other hand, a design method for a low-noise flow monitoring device is provided, wherein the flow monitoring device (also referred to as a flow meter) includes a body and a detection rod (also referred to as a pressure-inducing tube) disposed on the body, wherein the cross-sectional shape of the detection rod is designed by comprehensively considering the magnitude of the pressure difference and the noise suppression requirements, wherein the cross-sectional shape of the detection rod includes at least two sections of the upstream edge and the downstream edge (distributed on the left and right sides of the fluid flow direction), wherein the upstream edge is a straight line, and the two upstream edges have the same length, and the included angle is less than or equal to 90 degrees; the connection modes of the two adjacent upstream edge endpoints, the upstream edge and the downstream edge endpoints, and the two downstream edge endpoints are all arc-shaped and smoothly connected, and the connection point is called an endpoint connection arc (including an arc-shaped upstream head, a downstream bottom, and a side connection arc), wherein the downstream edge includes a straight line, a concave arc, or a convex arc, and the two upstream edges are symmetrically arranged, and the two downstream edges are symmetrically arranged; other components such as a pressure instrument are conventional components of an average velocity tube flow meter, and the existing technology is adopted; The length of the two straight upstream sides is L1, the rod diameter of the upstream side of the detection rod perpendicular to the flow direction is D1 (maximum width, generally the distance between the two intersection points of the upstream side and the downstream side), and the rod diameter in the flow direction is D2, then the diameter of the circumscribed circle of the detection rod is R=max(D1,D2); the radius of the downstream side arc is R2, the length is L2, the radius of the endpoint connection arc is R3, the length is L3 (when the radius is infinite, it is expressed as a straight line, here the length refers to the straight line length of the two ends of the arc, not the arc length), the width or diameter of the pressure taking hole is D3, then D3< L3≤min(L1, L2) / 5, that is, the length of the connection arc should be greater than the width of the pressure taking hole, and less than 1 / 5 of the minimum value of the upstream side length and the downstream side length. The upper limit of L3 is min(L1, L2) / 5 mainly considering that the flow field is stabilized by the upstream side and the downstream side of sufficient length and the pressure is sampled and taken. If you need to suppress the measurement noise and obtain a higher pressure difference, then design D1=D2, L1=L2= D1 / ; This is a more commonly used design choice. Generally, the back flow edge is also straight, that is, a square detection rod, which is easy to process and use; If you want to achieve better noise suppression, design D1 <D2,L1<L2,L1> D1 / , L2>D2 / ; If you want to get better pressure difference measurement effect, design D1>D2, L1>L2, L1<D1 / , at this time, extend L2 to make L2> D2 / Still an improvement in measurement noise can be obtained.

[0014] Furthermore, if the back flow edge is in the shape of an arc, then R3≤R2, where R2 is the arc radius of the back flow edge and R3 is the arc radius of the endpoint connection.

[0015] Furthermore, if better noise improvement is required, a concave arc back flow edge is preferred. At this time, the lateral velocity component of the fluid after passing through the back flow edge is very small, and the overall flow field is closer to the stable flow velocity and pressure when no detection rod is inserted; If a better pressure difference value is required, a convex arc backflow edge is preferred. At this time, since the detection rod has a greater overall resistance to the local flow field, the pressure difference between the front and backflow surfaces will also be greater. However, the lateral component of the fluid at the backflow edge is obvious, and the flow field disturbance is also greater, so the noise will be relatively large.

[0016] The advantages and beneficial effects of the present invention are as follows: the present invention controls the total amount and rate of change of the lateral flow velocity of the measured fluid when passing through the detection rod by designing the flow-facing edge of the detection rod as a straight line (that is, the flow-facing surface is designed as a plane), and designs the relative relationship between the lengths of the flow-facing edge and the back-flow edge, thereby reducing the flow field disturbance near the pressure-taking hole. Under the conditions of the same detection rod circumscribed circle diameter, the same flow rate and other external environments, the measurement noise of the present invention can be controlled within 2% of the pressure difference, which can be reduced by 4 to 5 times compared with the noise of a circular detection rod (experimental results for a pipeline with a diameter of 350 mm); at the same time, the detection device product processing, use and mold manufacturing of the present invention are simple and convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the structure of the flow monitoring device of the present invention; Figure 2 yes Figure 1 One of the enlarged views of the AA section; Figure 3 yes Figure 1 The second enlarged view of the AA section; Figure 4 yes Figure 1 The third enlarged view of the AA section.

[0018] Markings in the figure: 1. Detection rod; 2. Total pressure chamber; 3. Static pressure chamber; 4. Total pressure tapping hole; 5. Static pressure tapping hole; 6. Total pressure detection hole; 7. Static pressure detection hole; 11. Stream-facing edge; 12. Stream-receiving edge; 13. End point connecting arc. DETAILED DESCRIPTION

[0019] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0020] Embodiment 1: A low noise flow monitoring device (also called a flow meter), such as Figure 1As shown, it belongs to an average velocity tube flowmeter, including a flow monitoring device body and a detection rod (also called a pressure-guiding tube) arranged on the body, the detection rod is respectively provided with a total pressure chamber and a static pressure chamber that are independent of each other, and the detection rod is respectively provided with a plurality of total pressure holes connected to the total pressure chamber and a plurality of static pressure holes connected to the static pressure chamber on both sides (front and back of the fluid flow direction) of the detection rod, the body is respectively provided with a total pressure detection hole connected to the total pressure chamber and a static pressure detection hole connected to the static pressure chamber, the fluid pressures of the total pressure chamber and the static pressure chamber are respectively detected through the detection holes, the total pressure hole is located on the flow-front surface of the measured pipeline, and the static pressure hole is located on the back flow surface of the measured pipeline. The detection rod is an elongated body along the length direction; it is characterized in that the cross section of the detection rod includes at least 2 sections of the upstream side and the downstream side (located on the left and right sides of the fluid flow direction), the upstream side is a straight line (that is, the upstream surface is designed as a plane), the two upstream sides are the same length, the angle is less than or equal to 90 degrees, and the present embodiment is designed as a 90-degree square; the connection modes of the two adjacent upstream side endpoints, the upstream side and the downstream side endpoints, and the two downstream side endpoints are all arc-shaped and smoothly connected, and the connection point is called the endpoint connection arc (depending on the position, it can be called the upstream head, the downstream bottom, the side connection arc, etc.), the two upstream sides are symmetrically arranged, and the two downstream sides are symmetrically arranged.

[0021] Let the length of the two straight frontal edges be L1, the rod diameter of the frontal surface of the detection rod perpendicular to the flow direction be D1 (maximum width, generally the distance between the intersection points of the frontal edge and the back edge), and the rod diameter in the flow direction be D2. Then the diameter of the circumscribed circle of the detection rod is R=max(D1,D2); the length of the back edge is L2 (if it is an arc, the length here refers to the straight line length of the two ends of the arc, not the arc length), then D1≤D2, L1≤L2, L1≥D1 / , L2≥D2 / .

[0022] The total pressure tapping hole and the static pressure tapping hole are symmetrically arranged at the head of the upstream flow and the tail of the downstream flow, respectively. The relative distribution of the multiple pressure tapping holes is based on the pipe size and the average pressure taking requirements, such as logarithmic interval distribution, etc., which belongs to the prior art. Other components such as pressure instruments are conventional components of the average velocity tube flowmeter and adopt the prior art.

[0023] Since the cross-sectional shape of the existing detection rod (pressure-conducting pipe) is mostly circular, when the fluid flows through the circular surface, the flow velocity direction is the tangent direction of the surface, that is, the flow velocity direction of the fluid on the circular surface is constantly changing, and the flow velocity change rate is large (that is, the acceleration is large or the force is obvious), especially the lateral velocity and its change rate are the main factors that produce pressure measurement noise; at the same time, considering the uneven surface tension and rough surface of the pressure-conducting pipe and the interference of the measured pipeline fluid environment, when the time-varying characteristics of the flow velocity direction on the surface of the pressure-conducting pipe are obvious, these interferences will also have a more obvious impact on the high and low pressure sampling of the pressure-conducting pipe, that is, it will cause the pressure value to fluctuate up and down, which is manifested as obvious pressure difference measurement noise in actual engineering applications. This is a common defect of many current pressure-conducting pipes, especially circular pipes, whose peripheral flow velocity direction has undergone a continuous change of 0 to 90 degrees (relative to the flow direction of the measured pipeline body). Although this type of pipe is easy to process, its noise is as high as more than 10% of the true value. Of course, there are also designs of pressure-guiding pipe cross-section shapes such as trapezoid, rhombus, and pentagon, but since the flow direction changes significantly at the connection between adjacent sides, the local flow field disturbance is also obvious.

[0024] The existing technology mainly focuses on the layout design of the pressure-inducing holes (also called pressure-taking holes) or the global flow field design, and rarely pays attention to the stability of the micro-motion flow field around the pressure-inducing tube, which leads to the dilemma of high noise.

[0025] Starting from the local flow field disturbance factors, the present invention changes the oncoming edge into a straight line (the oncoming surface into a plane), reduces the lateral flow velocity change rate, and reduces the lateral velocity angle (generally only 0 to 45 degrees of lateral velocity direction change); small arc transitions are designed between adjacent edges, which reduces the flow velocity mutation amount overall, thereby improving the noise suppression effect.

[0026] like Figure 2 As shown, the back-flow edge of this embodiment is in a straight line shape. Like the straight front-flow edge, this design has a small fluid velocity change rate, a small flow field disturbance, and thus a small measurement noise.

[0027] Preferably, the length of the upstream side is consistent with the length of the downstream side, the width of the arc connecting the end points (the present invention refers to the straight line length, not the arc length) is not less than the width of the pressure taking hole and not greater than 1 / 5 of the length of the upstream side, and the angle between the two adjacent sides is 90 degrees, that is, the cross-section of the detection rod is square as a whole, with one arc-shaped end angle facing the upstream direction and the other arc-shaped end angle facing the downstream direction.

[0028] like Figure 1As shown, the flow monitoring device of this embodiment has a body height of 635mm, of which the detection rod height is 470±0.5mm, the upper pressure detection part is 165mm, the circumscribed circle diameter is 31±0.05mm, the total pressure cavity and the static pressure cavity apertures are both 6mm, and the total pressure taking holes and the static pressure taking holes are symmetrically arranged with 6 each. From bottom to top, the distances from each pressure taking hole to the bottom of the detection rod are 136.8±0.5mm, 158.4±0.5mm, 176.6±0.5mm, 337.5±0.5mm, 355.9±0.5mm, 377.5±0.5mm (adjacent hole distances are 21.6, 18.2, 160.9, 18.4, 21.6mm respectively), which belongs to the logarithmic linear layout scheme, the pressure taking hole aperture is 4mm, and the detection hole aperture is 6mm.

[0029] Embodiment 2: The difference from Example 1 is that the angle between the two upstream edges of this embodiment is 85 degrees, the angle between the adjacent upstream edges and the downstream edges is 95 degrees, and the detection rod is approximately square.

[0030] Embodiment 3: The difference from Example 1 is that Figure 3 As shown, the back-flow edge described in this embodiment is in the shape of a concave arc, and the back-flow edge length (the present invention refers to the straight-line length of the two end points of the arc, not the arc length) is equal to the front-flow edge length. Although the lateral velocity change rate of the fluid in the front section of the back-flow edge is relatively large, the lateral velocity is close to 0 in the final section, and the flow field disturbance near the static pressure tapping hole is not greatly affected, and a good noise suppression effect can still be obtained.

[0031] Preferably, the arc radius = the length of the flow-facing edge / The width of the arc connecting the end points shall not be less than the width of the pressure taking hole and shall not be greater than 1 / 5 of the length of the side facing the flow.

[0032] Embodiment 4: The difference from Example 1 is that Figure 4 As shown, the back-flow edge described in this embodiment is in the shape of a convex arc, and the back-flow edge length (the present invention refers to the straight line length of the two end points of the arc, not the arc length) is equal to the front-flow edge length. Although the lateral velocity change rate of the fluid at the back-flow edge is relatively large, especially near the static pressure taking hole, the lateral velocity of the fluid changes significantly, resulting in a weak static pressure measurement noise suppression effect, this design can obtain better pressure difference measurement results, and the noise is mainly controlled by the front-flow edge, and the total lateral velocity of the fluid is controllable.

[0033] Preferably, the arc radius = the length of the flow-facing edge / The width of the arc connecting the end points shall not be less than the width of the pressure taking hole and shall not be greater than 1 / 5 of the length of the side facing the flow.

[0034] Embodiment 5: A method for designing a low-noise flow monitoring device, the flow monitoring device comprising a flow monitoring device (also called a flow meter) body and a detection rod (also called a pressure-inducing tube) arranged on the body, characterized in that the cross-sectional shape design of the detection rod comprehensively considers the magnitude of the pressure difference and the noise suppression requirements, the cross-sectional shape of the detection rod comprises at least two sections of the upstream edge and the downstream edge (distributed on the left and right sides of the fluid flow direction), the upstream edge is a straight line, the two upstream edges are of the same length, and the included angle is less than or equal to 90 degrees; the connection modes of the two adjacent upstream edge endpoints, the upstream edge and the downstream edge endpoints, and the two downstream edge endpoints are all arc-shaped and smoothly connected, and the connection point is called an endpoint connection arc (including an arc-shaped upstream head, a downstream bottom, and a side connection arc), the downstream edge shape comprises a straight line, a concave arc or a convex arc, and the two upstream edges and the two downstream edges are symmetrically arranged; other components such as a pressure instrument are conventional components of an average velocity tube flow meter and adopt existing technologies; The length of the two straight upstream sides is L1, the rod diameter of the upstream side of the detection rod perpendicular to the flow direction is D1 (maximum width, generally the distance between the two intersection points of the upstream side and the downstream side), and the rod diameter in the flow direction is D2, then the diameter of the circumscribed circle of the detection rod is R=max(D1,D2); the radius of the downstream side arc is R2, the length is L2, the radius of the endpoint connection arc is R3, the length is L3 (when the radius is infinite, it is expressed as a straight line, here the length refers to the straight line length of the two ends of the arc, not the arc length), the width or diameter of the pressure taking hole is D3, then D3< L3≤min(L1, L2) / 5, that is, the length of the connection arc should be greater than the width of the pressure taking hole, and less than 1 / 5 of the minimum value of the upstream side length and the downstream side length. The upper limit of L3 is min(L1, L2) / 5 mainly considering that the flow field is stabilized by the upstream side and the downstream side of sufficient length and the pressure is sampled and taken. If you need to suppress the measurement noise and obtain a higher pressure difference, then design D1=D2, L1=L2= D1 / ; This is a more commonly used design choice. Generally, the back flow edge is also straight, that is, a square detection rod, which is easy to process and use; If you want to achieve better noise suppression, design D1 <D2,L1<L2,L1> D1 / , L2>D2 / ; If you want to get better pressure difference measurement effect, design D1>D2, L1>L2, L1<D1 / , at this time, extend L2 to make L2> D2 / Still an improvement in measurement noise can be obtained.

[0035] Preferably, if the back flow edge is in an arc shape, R3≤R2, wherein R2 is the arc radius of the back flow edge, and R3 is the arc radius of the end point connection.

[0036] like Figure 3As shown in the figure, if better noise improvement is required, a concave arc back flow edge is preferred. At this time, the lateral velocity component of the fluid after passing through the back flow edge is very small, and the overall flow field is closer to the stable flow velocity and pressure when no detection rod is inserted. like Figure 4 As shown in the figure, if a better pressure difference value is needed, the convex arc back flow edge is preferred. At this time, due to the greater overall resistance of the detection rod to the local flow field, the pressure difference between the frontal surface and the back flow surface will also be greater, but the lateral component of the fluid at the back flow edge is obvious, the flow field disturbance is also greater, and the noise will be larger.

[0037] The above are only some of the more systematic and comprehensive embodiments of the low-noise flow monitoring device and its design method of the present invention. In fact, it can also be designed into various other shapes, the end connection can be other connection methods, especially the head of the flow can be directly connected at an approximately right angle or an acute angle, etc. These combinations or preferred schemes should also be regarded as the scope of protection of the present invention, and they will not be listed here one by one.

Claims

1. A low-noise flow monitoring device, comprising a body and a detection rod (1) arranged on the body, wherein the detection rod is provided with a total pressure chamber (2) and a static pressure chamber (3) which are independent of each other, and the detection rod is provided with a plurality of total pressure holes (4) connected to the total pressure chamber and a plurality of static pressure holes (5) connected to the static pressure chamber on both sides, and the body is provided with a total pressure detection hole (6) connected to the total pressure chamber and a static pressure detection hole (7) connected to the static pressure chamber; the device is characterized in that: The cross section of the detection rod comprises at least two sections, namely, a flow-up side (11) and a back-flow side (12); the flow-up side is a straight line, the two flow-up sides are of the same length, and the included angle is less than or equal to 90 degrees; the connection modes of the two adjacent flow-up side endpoints, the flow-up side and the back-flow side endpoints, and the two back-flow side endpoints are all circular arc-shaped and smoothly connected, and the connection point is called an endpoint connection arc (13); the two flow-up sides are symmetrically arranged, and the two back-flow sides are symmetrically arranged, and the width of the endpoint connection arc is not less than the width of the pressure-taking hole and not greater than 1 / 5 of the flow-up side length; Let the length of the straight-line frontal side be L1, the rod diameter of the frontal surface of the detection rod perpendicular to the flow direction be D1, the rod diameter in the flow direction be D2, and the length of the back side be L2, then D1≤D2, L1≤L2, L1≥D1 / , L2≥D2 / .

2. A low-noise flow monitoring device according to claim 1, characterized in that: The back flow edge shape includes a straight line shape.

3. A low noise flow monitoring device according to claim 2, characterized in that: The length of the upstream side is consistent with the length of the downstream side, and the angle between the two adjacent sides is 90 degrees.

4. A low noise flow monitoring device according to claim 1, characterized in that: The shape of the back-stream side includes a concave arc shape, and the length of the back-stream side is equal to the length of the front-stream side.

5. A low noise flow monitoring device according to claim 4, characterized in that: The arc radius = the length of the upstream side / .

6. A low-noise flow monitoring device according to claim 1, characterized in that: The shape of the back-stream side includes a convex arc shape, and the length of the back-stream side is equal to the length of the front-stream side.

7. A low noise flow monitoring device according to claim 6, characterized in that: The arc radius = the length of the upstream side / .

8. A method for designing a low-noise flow monitoring device, the flow monitoring device comprising a body and a detection rod arranged on the body, characterized in that: The cross-sectional shape design of the detection rod comprehensively considers the magnitude of the pressure difference and the requirements for noise suppression. The cross-sectional shape of the detection rod includes at least two sections of the upstream side and the downstream side. The upstream side is a straight line, and the lengths of the two upstream sides are the same. The connection modes of the two adjacent upstream side endpoints, the upstream side and the downstream side endpoints, and the two downstream side endpoints are all arc-shaped and smoothly connected. The connection point is called the endpoint connection arc. The downstream side includes a straight line, a concave arc or a convex arc. The two upstream sides are symmetrically arranged, and the two downstream sides are symmetrically arranged. The length of the straight-line frontal side is L1, the rod diameter of the frontal side of the detection rod perpendicular to the flow direction is D1, and the rod diameter in the flow direction is D2; the arc radius of the back side is R2, the length is L2, the end point connection arc radius is R3, the length is L3, and the width or diameter of the pressure hole is D3, then D3 <L3≤min(L1, L2) / 5; If you need to suppress the measurement noise and obtain a higher pressure difference, then design D1=D2, L1=L2= D1 / ; If you want to achieve better noise suppression, design D1 <D2,L1<L2,L1> D1 / , L2> D2 / ; If you want to get better pressure difference measurement effect, design D1>D2, L1>L2, L1<D1 / , at this time, extend L2 to make L2> D2 / Still an improvement in measurement noise can be obtained.

9. A method for designing a low-noise flow monitoring device according to claim 8, characterized in that: If the back flow edge is in the shape of an arc, then R3≤R2, where R2 is the arc radius of the back flow edge and R3 is the arc radius of the endpoint connection.

10. A method for designing a low-noise flow monitoring device according to claim 9, characterized in that: If better noise improvement is required, a concave arc back flow edge is preferred; If a better pressure difference value is required, a convex arc back flow edge is preferred.

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