CN113790322B

CN113790322B - Fluid control unit for sealing bypass pipeline

Info

Publication number: CN113790322B
Application number: CN202111019699.2A
Authority: CN
Inventors: 李玩幽; 王曦; 率志君; 殷文慧; 于涛; 曹宏博; 简洁
Original assignee: Harbin Engineering University
Current assignee: Harbin Engineering University
Priority date: 2021-09-01
Filing date: 2021-09-01
Publication date: 2024-03-15
Anticipated expiration: 2041-09-01
Also published as: CN113790322A

Abstract

The invention aims to provide a fluid control unit for sealing a bypass pipeline, which comprises a main pipeline and a bypass pipeline, wherein the two ends of the main pipeline are respectively provided with a pipeline inlet and a pipeline outlet, the bypass pipeline is directly connected with the main pipeline, the bypass pipeline is also connected with the main pipeline through a drainage tube, one end of the drainage tube is connected with an upstream area of the main pipeline, and the other end of the drainage tube is connected with the bypass pipeline. The drainage tube has the advantages of simple structure, convenient processing and strong scheme feasibility; the structure size is small, the space is not occupied too much, and the structure space in the bypass pipeline is not influenced; the decoupling of resonance frequency can be realized, vortex shedding frequency is changed, flow induced acoustic resonance is restrained from the root, and a reference is provided for treating the problem of similar closed branch pipe vibration.

Description

Fluid control unit for sealing bypass pipeline

Technical Field

The invention relates to a pipeline structure, in particular to a closed branch pipe structure.

Background

The flow medium in the primary pipeline of the primary loop of the nuclear power system is usually high-temperature and high-pressure fluid, and in order to ensure the safe operation of the nuclear power system, a pressure relief pipeline is usually arranged at a specific position of the primary pipeline, one section of the pressure relief pipeline is connected with the main pipeline, and the other end of the pressure relief pipeline is normally closed, so that the special structure of a closed bypass pipeline is formed.

The flow acoustic resonance is the result of the interaction of the acoustic field and the unstable flow field, and vortex shedding occurs when the fluid in the main pipeline flows through the T-shaped filler neck of the branch pipe, and pressure pulsation is generated; the pressure pulsation is taken as a sound source to generate pressure waves to propagate to the tail end of the branch pipe, the pressure waves are reflected by the tail end wall surface of the branch pipe section and then interact with the incident waves in the branch pipe to form standing waves, and the standing waves are coupled with vortex shedding frequencies, so that the pressure pulsation is amplified. When the natural frequency of the pipeline is close to the 2 modal frequencies, the pipeline vibration is excited, and the vibration is the external appearance of flow-induced acoustic resonance and is the result of the combined action of flow-acoustic-solid resonance.

In a nuclear power system, the safety of related parts of a nuclear reactor is critical, and the abnormal vibration of a pipeline can be caused by a flow induced acoustic resonance phenomenon, so that the parts such as a safety relief valve, the pipeline and the like on a main pipeline are damaged. Therefore, in engineering practice, the phenomenon of flow induced acoustic resonance is inhibited, and the method has important significance for prolonging the safety life and improving the economic benefit of equipment.

When fluid flows through a specific structure of the closed bypass pipeline, vortex is generated and falls off periodically, when fluid excitation generated by the vortex falling frequency is similar to the sound mode frequency, a frequency locking phenomenon is generated, pressure waves are amplified, sound resonance is formed, and when the sound resonance frequency is coincident with the pipeline structure frequency, the pipeline is excited to vibrate violently.

The methods commonly used to avoid acoustic resonances in the flow are: (1) And a section of branch pipe is introduced at one side of the branch pipe, and the acoustic sinking mode of the bypass pipeline is adjusted to avoid the frequency of the flow field. (2) And (3) performing geometric optimization (such as chamfer radius increase) on the flow field at the intersection position of the bypass pipeline and the main pipeline, and adjusting the shedding frequency of the flow field vortex so as to avoid the acoustic sinking mode. (3) An insert is designed into the branch conduit to disrupt the shear layer in the conduit, as in patent US4867190. However, the scheme is generally high in manufacturing cost, long branch pipe sections are needed to obviously change the acoustic mode, and the scheme II can reduce the amplitude of the acoustic resonance of the flow to a certain extent, but generally has limited influence on frequency. The third scheme has very obvious change of flow field frequency, but has less practical application because the side pipeline mainly has the effect of discharging the pressure in the main pipeline in emergency, thus having certain limit on the cross section area of the side pipeline.

Disclosure of Invention

The invention aims to provide a fluid control unit for sealing a bypass pipeline, which is used for inhibiting flow induced acoustic resonance from the perspective of increasing the turbulence degree of the flow field of the bypass pipeline, influencing the development progress of vortex and enabling the excitation frequency of the flow field to deviate.

The purpose of the invention is realized in the following way:

the invention relates to a fluid control unit for sealing a bypass pipeline, which is characterized in that: the device comprises a main pipeline and a bypass pipeline, wherein the two ends of the main pipeline are respectively provided with a pipeline inlet and a pipeline outlet, the bypass pipeline is directly connected with the main pipeline, the bypass pipeline is further connected with the main pipeline through a drainage tube, one end of the drainage tube is connected with an upstream area of the main pipeline, and the other end of the drainage tube is connected with the bypass pipeline.

The invention may further include:

1. the connection position of the drainage tube and the main pipeline is positioned above the rotation center of the vortex group in the bypass pipeline.

2. The drainage tube structure adopts the same type of pipeline model as the bypass pipeline, the pipe wall thickness is the same, the drainage tube width is consistent with the bypass pipeline width, and the section of the drainage tube structure is in a 1/4 round structure.

The invention has the advantages that:

1. the drainage tube has simple structure, convenient processing and strong scheme feasibility;

2. the structure size is small, the space is not occupied too much, and the structure space in the bypass pipeline is not influenced;

3. the decoupling of resonance frequency can be realized, vortex shedding frequency is changed, flow induced acoustic resonance is restrained from the root, and a reference is provided for treating the problem of similar closed branch pipe vibration.

Drawings

FIG. 1 is a schematic diagram of the structure of the present invention;

FIG. 2 is a schematic cross-sectional view of the present invention;

FIG. 3 is a graph showing the results of numerical simulation according to the present invention.

Detailed Description

The invention is described in more detail below, by way of example, with reference to the accompanying drawings:

with reference to fig. 1-3, the invention avoids the acoustic resonance frequency of the flow to a certain extent, reduces the excitation amplitude of the excitation source, and thereby avoids the problem of exciting abnormal vibration of the closed bypass pipeline. Therefore, the invention provides a fluid passive control unit, which is added with a drainage tube structure on the basis of a conventional closed branch tube structure, and a novel closed branch tube for communicating the front edge of the main pipeline with the side branch pipeline drainage basin. The drainage tube is through leading partial fluid into the branch pipe from the trunk line, strikes the vortex structure that itself formed in the pipeline to destroy the big vortex structure in the trunk line, reduce the vortex velocity of flow in the pipeline, thereby aggravate the shear layer instability of trunk line and branch pipe, accelerate the vortex and drop, finally make vortex drop frequency and acoustic chamber natural frequency avoid.

The closed side branch pipeline comprises a pipeline inlet and outlet, a main pipeline and a side branch pipeline structure, and the side branch pipeline is directly connected with the straight pipeline. The drainage tube is used for secondarily connecting a main pipeline and a side branch pipeline, the drainage tube is of the same type of pipeline type as the side branch pipeline, the wall thickness of the drainage tube is the same, the width of the drainage tube is identical to that of the side branch pipeline, the drainage tube is of a 1/4 round structure, one end of the drainage tube is connected with the main pipeline and passes through the upstream area of the side branch pipeline, the other end of the drainage tube is communicated with the side branch pipeline, the drainage tube has no specific requirement on the size, but the connection position of the drainage tube and the main pipeline is required to be positioned above the rotation center of a vortex group in the side branch pipeline, and the specific size is based on practical problems.

The present example provides a closed bypass pipe with a draft tube structure, which is composed of a pipe inlet 1, a pipe outlet 2, a main pipe 3, a bypass pipe 4, and a draft tube structure 5, as shown in fig. 1. The branch pipe is partially closed, no fluid flows in the branch pipe, the exhaust in the pipeline is relatively sufficient, the condition that the air cavity contracts and expands to cause vibration does not exist, and the fluid flow excitation does not exist in the branch pipe basically. The junction of the branch pipe section and the front edge of the main pipe is provided with a chamfer angle, and the specific structure is shown in the cross-section river basin diagram of the pipeline in fig. 2. Fig. 3 is an example of a numerical simulation result of adding a drainage pipeline and a normal bypass pipeline, and the result shows that the shedding frequency of the flow field vortex is obviously shifted.

In the working process of the closed branch pipe, fluid flows from an inlet to a main pipe, flows along the main pipe, flows into a bypass pipe through a drainage pipe when flowing to a drainage pipe structural area, at the moment, the fluid flow velocity in the main pipe is high, a shearing layer with high velocity gradient can be formed at the junction of the branch pipe and the main pipe, due to instability of the shearing layer, the fluid at the three-way position can form vortex at the junction, and finally falls off through a series of developments, the vortex falling frequency is similar to the acoustic modal frequency of the pipe, the acoustic resonance of the flow is induced through modulation, the abnormal vibration of the pipe is caused, the closed branch pipe of the drainage pipe structure is increased, part of fluid flows into the branch pipe through the drainage pipe structure, and the outlet of the drainage pipe collides with the large vortex in the branch pipe to change the rotating velocity of vortex in the branch pipe, so that the velocity gradient of the position is reduced, the falling velocity of the small vortex is reduced due to the instability of the junction of the flow field, the excitation frequency of the flow field is changed, the acoustic resonance is restrained, and the vibration characteristic of the pipe is optimized.

Claims

1. A fluid control unit for closing a bypass conduit, characterized by: the device comprises a main pipeline and a bypass pipeline, wherein the two ends of the main pipeline are respectively provided with a pipeline inlet and a pipeline outlet, the bypass pipeline is directly connected with the main pipeline, the bypass pipeline is also connected with the main pipeline through a drainage tube, one end of the drainage tube is connected with an upstream area of the main pipeline, and the other end of the drainage tube is connected with the bypass pipeline;

the connection position of the drainage tube and the main pipeline is positioned above the rotation center of the vortex group in the bypass pipeline;

the drainage tube structure adopts the same type of pipeline model as the bypass pipeline, the pipe wall thickness is the same, the drainage tube width is consistent with the bypass pipeline width, and the section of the drainage tube structure is in a 1/4 round structure.