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CN-121762873-B - Method and device for measuring PIV flow field under sediment starting critical condition of stack

CN121762873BCN 121762873 BCN121762873 BCN 121762873BCN-121762873-B

Abstract

The invention discloses a method and a device for measuring PIV flow fields under a sediment starting critical condition of a pile body, wherein natural sand of the device is subjected to screening and dyeing treatment, so that specular reflection of the natural sand under laser irradiation is obviously reduced, and the identification signal-to-noise ratio of trace particles in PIV images is greatly improved. The image recognition precision is improved, and a foundation is laid for subsequent high-precision flow field measurement. Based on the two-dimensional instantaneous velocity field obtained by PIV, a distribution cloud picture of shear strain rate and vertical vorticity and an along-path change curve are further deduced. These parameters can visually reflect the shear strength and vortex structure of the water flow near the slope of the heap, revealing the inherent link between silt onset and scour pit morphology. The method is specially designed for a permeable stack model, a permeable bank slope is built by adopting dyed sand, and the permeation and bypass coupling effect of water flow in the stack is truly simulated. The key section of the slope is vertically illuminated by the laser sheet, and the precise capture of the complex flow field structure is realized by combining the synchronous acquisition of a high-speed camera.

Inventors

  • LIU XIAOMIN
  • MENG SHAOMIN
  • LIU XIAOXU
  • YANG YAOTIAN
  • LUO HONGCHUN

Assignees

  • 内蒙古农业大学

Dates

Publication Date
20260508
Application Date
20260305

Claims (8)

  1. 1. A method for measuring a pile-up sediment start critical condition PIV flow field, comprising the steps of: Step one, test sediment pretreatment, namely screening sediment for a pile body conforming to the test particle size from natural river sediment by a screening and dyeing device, dyeing and drying for later use; Paving fixed bed sand in a water tank test section, leveling, piling up a permeable stack model by adopting dyed sand according to preset geometric parameters, injecting water into a water tank until the stack is completely submerged, and soaking for a preset time; Installing and adjusting a measuring component installing unit to enable laser piece lights on the installing unit to illuminate the vertical section of the slope of the accumulation body, throwing trace particles, completing space calibration of a shooting area of the high-speed camera through a calibration plate, and establishing a mapping relation between pixel coordinates and physical coordinates; step four, simulating unsteady flow, namely simulating flood discharge unsteady flow in the flood season by adopting a stepped drop water level method, and starting from a high water level, regulating a tail gate to gradually drop the water level, and keeping the inlet flow constant; In the fourth step, the water level drop amplitude is 1cm each time, and the next drop is carried out after the water flow is stable until the start of sediment of different grades is induced; Step five, synchronously measuring and collecting data, namely observing the starting state of sediment at each level of stable water level, and synchronously carrying out PIV flow field measurement, automatic water level meter monitoring and starting position recording when the sediment reaches the standard; step six, multi-parameter flow field data analysis, namely importing the acquired image sequence into a comprehensive data processing unit to process related data; In step six, the data processing procedure of the integrated data processing unit is as follows: Processing the image by PIV analysis software to obtain an instantaneous and average two-dimensional velocity field of a flow field near the stack; The data analysis module automatically calculates and draws the following key hydrodynamic parameter distribution under different flow layers and different influence factors based on a speed field, namely a vertical average flow velocity distribution curve, a shear strain rate distribution cloud picture and an along-path distribution curve, a vertical vortex quantity distribution cloud picture and an along-path distribution curve; step seven, correlation analysis of critical conditions, namely correlating critical starting states with corresponding hydrodynamic parameters, and verifying or calibrating a starting flow speed and a shear stress formula of sediment on a bank slope of the accumulation body by using measured starting flow speed and water depth data; the specific process is that a nonlinear multiple regression method is adopted to establish a mathematical model between critical starting parameters and hydrodynamic parameters, stack geometric parameters and sediment physical parameters, and the model expression is as follows: , the critical shear stress is characterized by the dimensionless critical Shields number, The water flow Reynolds number is represented by θ, the bank slope gradient of the accumulation body, Is of non-dimensional silt particle size; At a known water depth Particle size of sediment On the premise of adopting a nonlinear least square method to fit all the effective data extracted in the step six through statistical software, and constructing a starting flow velocity empirical formula with the following formula: , wherein, In order to actually measure the start-up flow rate, Is the depth of water, the water is in the water, Is the particle size of the sediment, The acceleration of the gravity is that, As the empirical coefficient to be fitted to, Is an error term.
  2. 2. The method of claim 1, wherein the second predetermined geometric parameters include a radius and a gradient of the stack.
  3. 3. The method for measuring the PIV flow field under the critical condition for starting sediment in a pile-up body according to claim 1 is characterized in that in the fifth step, a PIV flow field measuring unit is started, a flow field image sequence is continuously collected by a high-speed camera, the along-distance water depth of a current test section is measured and recorded by using an automatic water level meter, and the current flow and the observed starting position of sediment are recorded.
  4. 4. A stack silt onset critical condition PIV flow field measurement apparatus for carrying out a stack silt onset critical condition PIV flow field measurement method according to any one of claims 1 to 3, comprising: the water tank (1) is used for simulating a water flow environment, test sand can be paved at the bottom of the water tank (1), a water pump (5) capable of adjusting flow and an adjusting tail gate (6) used for controlling the water level in the water tank (1) are respectively arranged at two ends of the water tank, and a first sliding rail (101) is fixedly arranged on the water tank (1); The screening and dyeing equipment comprises a first sliding frame (201) which is slidably arranged on a water tank (1), a screening plate (209) and a stirring rod (212) which are arranged on the first sliding frame (201) and are used for screening fixed bed sand and stack sand with target particle size from natural river sand and dyeing the stack sand; The measuring component mounting unit comprises a mounting frame (301) which is slidably mounted on the first sliding frame (201), a synchronous controller (302) which is fixedly mounted on the mounting frame (301), a high-speed camera (303) and a continuous laser (305), and the spatial position of the component relative to the water tank (1) can be adjusted through the mounting frame (301); The integrated data processing unit is connected with and controls the high-speed camera (303), built-in PIV analysis software and a data analysis module, wherein the PIV analysis software is used for calculating a two-dimensional flow velocity field from an image sequence, and the data analysis module is further used for automatically calculating and outputting a vertical average flow velocity distribution, a shear strain rate distribution and a vertical vorticity distribution cloud picture and a vertical vorticity distribution curve in a flow field section based on flow velocity field data.
  5. 5. The stack silt initiation critical condition PIV flow field measurement apparatus of claim 4 wherein: The first sliding frame (201) is slidably mounted on the first sliding rail (101) through a first sliding block (202), a second sliding block (203) is slidably connected to the first sliding frame (201), a screening bin (204) is detachably connected to the second sliding block (203) through a bolt, a feeding hole (2041) is formed in the upper surface of the screening bin (204), a driving motor (207) is arranged above the feeding hole (2041), the driving motor (207) is fixedly mounted on a motor mounting plate (206), the motor mounting plate (206) is fixedly connected with the screening bin (204) through a first connecting rod (205), a screening plate (209) is coaxially and fixedly arranged in the screening bin (204), a waste bin (210) is arranged on the side of the screening plate (209), the waste bin (210) is fixedly connected with the lower end of the screening bin (204), a waste storage area (211) is formed in a circular shape in the section, and the waste storage area (211) is communicated with the side of the screening plate (209); The output shaft of the driving motor (207) is fixedly connected with the upper end of the driving rod (208), the lower end of the driving rod (208) penetrates through the axle center of the screening plate (209), a stirring rod (212) is fixedly arranged on the surface of a part of the driving rod (208) penetrating through the screening plate (209), the stirring rod (212) is positioned in the stirring bin (213), the stirring bin (213) is fixedly connected with the lower surface of the waste bin (210), and a resistance wire (214) for heating and drying is fixedly arranged on the surface of the stirring bin (213); the lower surface axle center position of stirring storehouse (213) is fixed and is provided with discharge gate (215), and coaxial rotation is installed on discharge gate (215) and is rotated circle (216), and it is connected with oblique discharge gate (217) to dismantle on circle (216), and oblique discharge gate (217) are linked together with discharge gate (215), dismantle on circle (216) and are connected with baffle (218).
  6. 6. The stack sediment starting critical condition PIV flow field measurement device according to claim 5, wherein the second sliding block (203) is detachably provided with a mounting frame (301), a high-speed camera (303) is fixedly arranged on the mounting frame (301), the high-speed camera (303) is perpendicular to the side wall of the water tank (1), an L-shaped rod (304) is fixedly arranged on the side of the mounting frame (301) and is fixedly connected with one end of the L-shaped rod (304), the other end of the L-shaped rod (304) is fixedly connected with a continuous laser (305), a synchronous controller (302) is arranged above the high-speed camera (303), and the synchronous controller (302) is in signal connection with the high-speed camera (303) and the continuous laser (305).
  7. 7. The device for measuring the PIV flow field under the critical condition for starting sediment in a pile-up body according to claim 6, wherein the resolution of the high-speed camera (303) is not lower than 1024 x 1024 pixels, the shooting frequency is adjustable to adapt to different flow speed conditions, the power of the continuous laser (305) is not lower than 15W, the wavelength is 532nm, and the thickness of formed sheet light is smaller than 5mm.
  8. 8. The device for measuring the PIV flow field under the critical condition of starting sediment in a pile-up body according to claim 5, wherein the dye added in the stirring bin (213) adopts water-based dye, so that the color of the sediment after treatment is deepened.

Description

Method and device for measuring PIV flow field under sediment starting critical condition of stack Technical Field The invention relates to the technical field of sediment detection tests, in particular to a method and a device for measuring a PIV flow field under a sediment starting critical condition of a pile. Background The braided river often forms a large amount of bank piles due to landslide, collapse and the like, and the silt starting conditions are directly related to stable river potential, safe flood discharge and running of a downstream hydropower station. The key point of researching the sediment starting rule on the slope of the stack is to accurately acquire hydrodynamic parameters such as flow velocity, shear strain rate, vorticity and the like of a complex three-dimensional flow field near the stack at the moment of starting. Traditional researches are mostly based on a fixed bed model or by adopting a contact type single-point flow rate meter (such as an electromagnetic flow rate meter and an ADV). The fixed bed model cannot simulate the water flow permeation and bypass coupling effect of the real permeable stack, so that the flow field is distorted. The contact type velocimeter probe can generate disturbance to a flow field, particularly in a strong shearing and vortex area formed by the flowing around of a stacking body, the disturbance can obviously influence the observation of stress balance of sediment particles, and a starting critical state can not be accurately captured. In addition, single point measurements cannot synchronously acquire velocity gradients, shear strain rates, and vorticity distributions in the flow field plane, which are key to reveal the mechanism of silt initiation dynamics (e.g., bypass flow flushing). Taking 'an indoor water tank sediment starting speed measuring system and method' with a Chinese patent publication number of CN121008059B as an example, the scheme provides a non-contact measuring system based on PIV technology, a flow field image is obtained through an imaging unit and a laser lighting unit, and image calibration, particle displacement calculation and flow field generation are carried out by a data processing unit. The method can effectively obtain the section average flow velocity in the straight water tank, and is suitable for preliminary silt starting flow velocity measurement. However, this solution has the following technical limitations: The interference of the reflection of the sediment is not effectively solved, and although the patent mentions 'optimization treatment of the sediment characteristics', a specific solution is not provided for the problem of strong specular reflection generated by mineral components such as quartz in natural sand and the like under the irradiation of laser. The reflected light can seriously interfere with the identification of trace particles in the PIV image, reduce the signal-to-noise ratio of the image and influence the accuracy of flow velocity measurement. The data processing mode is single, and is difficult to adapt to complex flow fields, the data processing of the scheme is mainly concentrated on statistics of average flow velocity of the section, and a cross-correlation algorithm of 32 multiplied by 32 pixel windows is adopted, so that the method is suitable for a relatively uniform flow field structure. However, for areas near the bank slope of the stack with complex three-dimensional flow characteristics such as strong shear, orbiting vortex, etc., single average flow velocity analysis cannot reveal the intrinsic mechanical mechanisms of silt initiation, such as key parameters of shear strain rate, vortex flow distribution, etc. The system can not adapt to the flow field characteristics of the permeable structure of the accumulation body, wherein the test object of the system is smooth bed surface sediment, the coupling effect of the permeability of the accumulation body on water flow permeation and detouring is not considered, and the starting process of the bank slope accumulation body under the condition of unsteady flow is difficult to simulate truly. Therefore, the prior art lacks a targeted pretreatment means, a refined flow field analysis capability and a measurement strategy matched with an unsteady flow process when dealing with the study of critical conditions of the sediment start of the permeable stack. Disclosure of Invention The invention aims to provide a method and a device for measuring a PIV flow field under a sediment starting critical condition of a pile body, so as to solve the problems in the background art. In order to achieve the purpose, the invention provides the following technical scheme that the method for measuring the PIV flow field under the critical condition of starting sediment in a pile comprises the following steps: Step one, test sediment pretreatment, namely screening sediment for a pile body conforming to the test particle size from natural river sediment