Device and method for measuring flow field around scour pile piers using stereo PIV

Abstract

The present invention discloses a device and method for measuring the flow field around scour pile piers using stereo PIV. The device of the present invention can eliminate scattering and reflection between scour pits and different media through a stereo PIV system combined with an optical refraction component, thereby ensuring the accuracy of the flow field in the scour pit to the greatest extent. Combined with PIVlab software, based on the fine resolution of the field of view, a three-dimensional joint grid is generated according to the discrete data position of the PIV particles, and the Reynolds decomposition data of the velocity vector is interpolated onto the three-dimensional joint grid to assimilate the overlapping measurement areas in the relevant field of view to the data set of the same particle displacement. The present invention quantifies the turbulent structure of the flow field around the scour pile pier; determines the vertical velocity distribution pattern of the characteristic position in the scour pit; analyzes the water flow separation process at the scour edge and its interaction with the main vortex; determines the spatiotemporal evolution of the shear stress of the water flow wall during the scour process, etc.

Description

Technical Field

[0001] The present invention relates to the field of field observation and physical model experiments related to nearshore / river water and sediment dynamics, and in particular to a device and method for measuring the flow field around a scouring pile pier using stereo PIV. Background Art

[0002] Hydraulic structures (such as bridge piers and platform supports) are the most common environmental factors in nearshore and river environments. Downwelling currents generated in the boundary layer around the pier control the overall flow field. Carrying high momentum, the downwelling currents rush toward the near-wall area, causing the water to rotate and form so-called horseshoe vortices. Localized disturbances in the surrounding water flow can increase shear stress levels near the wall, further promoting the formation of sediment scour pits around the pier. As the sediment scour pit deepens, the center of gravity shifts toward the front of the pier. The scour pit continues to evolve until equilibrium is reached, where the force exerted on the sediment particles decreases below a critical threshold. When a stable scour pit forms around a pier, a horseshoe vortex persists within its flow field. The vortex intensity is greatest within the upstream symmetric plane of the pier and weakens as it curves and extends laterally. Such scour pits can pose a serious threat to the safety of the structure. The dynamic characteristics of scour pits are essential for the design of pier foundations. Since it is difficult to accurately capture the horseshoe vortex in the scour pit through field observations, and field operations require a lot of manpower and material resources, indoor physical model experiments that take into account the scale effect are the main alternative research methods. The experimental technology for pile scour pit measurements still needs further innovation and development. At present, there is no fluid erosion model or sediment transport model that can be linked to the dynamic characteristics of the horseshoe vortex in the scour pit, which inevitably leads to the measured experimental results being far from the actual field in situ data. Specifically, a device is needed to obtain non-invasive measurement data with high spatial resolution so that the dynamics of the main vortex system can be linked to the predictive scour pit model. Summary of the Invention

[0003] Based on this, the present invention proposes a device and method for measuring the flow field around scour piers using 3D PIV (particle image velocimetry). This device and method can address the following key issues: quantifying the turbulent structure of the flow field around scour piers (including turbulent anisotropy and coherent structure); determining the vertical velocity distribution pattern at characteristic locations within the scour pit; analyzing the flow separation process at the scour edge and its interaction with the main vortex (eigenorthogonal decomposition); and determining the spatiotemporal evolution of the shear stress (including viscous shear stress, turbulent shear stress, and dispersion stress) at the water surface during the scour process.

[0004] The technical solution of the present invention is:

[0005] Construct a physical model of scour piles;

[0006] The velocity field components of the physical model are reconstructed to obtain a three-dimensional joint grid; and the Reynolds decomposition data of the velocity vector are interpolated onto the three-dimensional joint grid to assimilate the pile-pit connection field of view and the overlapping measurement areas in the pile-pit connection field of view into the same particle displacement data set.

[0007] Quantify the turbulent structure of the flow field around scour piers, including turbulent anisotropy and coherent structure.

[0008] Determine the vertical velocity distribution pattern at characteristic locations in the scour pit, and determine the self-similarity of the flow field structure with dimensionless vertical depth as the ordinate and dimensionless flow velocity as the abscissa for the velocity field of the pile-pit connection field and the area of ​​interest in the pile-pit connection field.

[0009] Using intrinsic orthogonal decomposition as an auxiliary algorithm, the water flow separation process of the scouring edge is made independent, and the shear stress of the water flow wall is decomposed into viscous shear stress, turbulent shear stress, and dispersion stress, and the contribution ratio of the three component stresses to the total water flow wall shear stress is determined.

[0010] In some embodiments, the scour pit reshapes the terrain according to the measured elevation data of the pile pier scour pit, and the pile pier is placed on the scour pit reshapes the terrain and fixed, and a constant water flow condition similar to Froude is adopted; the PIV tracer particles are placed in the incoming water body to meet the uniform distribution condition.

[0011] In some embodiments, a stereo PIV component is used in the process of reconstructing the velocity field component of the physical model;

[0012] The three-dimensional PIV component includes a broadband laser, a laser steering plate, a light stabilizing plate and

[0013] Charge-coupled devices, angle adapters, optical lenses, filters and water-filled prisms are symmetrically arranged on both sides of the pier.

[0014] The broadband laser is located above the free surface of the constant water flow, and the broadband laser emission port is parallel to the free surface of the water flow; the broadband laser emits green band laser light; the laser deflection plate is at the same height as the broadband laser, and converts the horizontal laser beam into a vertical laser beam; the light stabilizing plate is located vertically directly below the laser deflection plate, and stabilizes the vertical laser beam and transitions it to the pile pier and water environment;

[0015] In some embodiments, a polymethyl methacrylate plate is further included. The polymethyl methacrylate plate is located on the free surface of the constant water flow and is connected to the pier upstream. The polymethyl methacrylate plate is used to eliminate surface waves generated by the interaction between the constant water flow and the pier.

[0016] In some embodiments, the displacement information of the same particle in the laser beam recorded from two different angles is used to reconstruct three components of the velocity field, namely the streamwise component, the vertical component, and the spanwise component.

[0017] In some embodiments, the turbulence anisotropy evaluation parameters include the Reynolds stress anisotropy tensor and the second and third turbulence anisotropy invariants.

[0018] Beneficial effects of the present invention:

[0019] 1. The device of the present invention has an ingenious structure, good integrity, high efficiency and low device cost.

[0020] 2. The device of the present invention can eliminate the scattering and reflection between the scour pit and different media by combining the stereo PIV system with the optical refraction component, thereby ensuring the accuracy of the flow field in the scour pit to the greatest extent.

[0021] 3. Combined with PIVlab software, based on the fine resolution of the field of view, a three-dimensional joint grid is generated according to the discrete data positions of the PIV particles, and the Reynolds decomposition data of the velocity vector are interpolated onto the three-dimensional joint grid to assimilate the overlapping measurement areas in the relevant field of view into the dataset of the same particle displacement.

[0022] 4. The present invention quantifies the turbulent structure of the flow field around the scour pile pier (including turbulent anisotropy and coherent structure); determines the vertical velocity distribution pattern at characteristic positions in the scour pit; analyzes the water flow separation process at the scour edge and its interaction with the main vortex (intrinsic orthogonal decomposition); and determines the spatiotemporal evolution of the water wall shear stress (including viscous shear stress, turbulent shear stress, and dispersion stress) during the scour process. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a side view of the device of the present invention.

[0024] Figure 2 yes Figure 1 Schematic front view of . DETAILED DESCRIPTION

[0025] In the description of the present invention, it should be understood that the terms "top", "vertical", "bottom", "inside", "side", "vertical", "up", "down", "upper end", "lower", "rear", "height", "front", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0026] In the present invention, unless otherwise specified or limited, the terms "disposed" and "connected" should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediate medium; internal communication between two elements, or interaction between two elements, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0027] like Figure 1 and Figure 2 As shown, the device of this embodiment is divided into a pile pier and water environment part, a flow field structure monitoring part, and a three-dimensional PIV component part.

[0028] The pile pier and water environment part includes a pile pier 5, a constant water flow 6, and a scour pit reshaping topography 10; the pile pier is located at the span center of the measurement flow field; the constant water flow flows towards the pile pier; the constant water flow provides a stable water power source; the scour pit reshaping topography is customized according to the measured field topography data; the scour pit reshaping topography is made of aluminum and undergoes an anodizing reaction; the outer layer of the scour pit reshaping topography is modified with rhodamine B to reduce surface light reflection.

[0029] The three-dimensional PIV component includes a broadband laser 1, a laser steering plate 2, a light stabilizing plate 3, a polymethyl methacrylate plate 4, a first charge-coupled device 13, a second charge-coupled device 14, a first angle adapter 15, a second angle adapter 16, a first optical lens 17, a second optical lens 18, a first filter 19, a second filter 20, a first water-filled prism 11, and a second water-filled prism 12. The broadband laser is located above the free surface of the constant water flow, and the broadband laser emission port is parallel to the free surface of the water flow; the broadband laser emits green band laser; the laser deflection plate is at the same height as the broadband laser, and converts the horizontal laser beam into a vertical laser beam; the light stabilizing plate is located directly below the laser deflection plate in the vertical direction, and stabilizes the vertical laser beam 7 and transitions it to the pier and the water environment; the polymethyl methacrylate plate is located on the free surface of the constant water flow and is connected to the pier at the upstream; the polymethyl methacrylate plate eliminates the surface waves generated by the interaction between the constant water flow and the pier; the first charge coupled device and the second charge coupled device are symmetrically arranged in the span direction of the pier. On both sides; the first and second angle adapters are connected to the first and second charge coupled devices, respectively, to facilitate the installation of the first and second optical lenses via the angle displacement method; the first and second optical lenses are connected to the first and second angle adapters, respectively; the first and second optical lenses can change their inclination angles by adjusting the first and second angle adapters, respectively; the first and second filters are connected to the first and second optical lenses, respectively; the first and second filters only allow green light within a bandwidth of 532nm±5nm to pass through, eliminating wavelength shifts to red light reflected from the scour pit surface; the first and second water-filled prisms are aligned with the central axes of the first and second optical lenses, respectively; the first and second water-filled prisms are both placed on the free surface of the constant water flow; the first and second water-filled prisms are filled with the same water as the constant water flow, eliminating optical aberrations caused by light refraction at the water-air interface.

[0030] The flow field structure monitoring portion encompasses a horseshoe vortex field of view 8 and a pile pit connection field of view 9. The horseshoe vortex field of view 8 is located upstream of the pile pier; the pile pit connection field of view 9 is located at the connection between the pile pier and the upstream scour pit.

[0031] The present invention provides a method for measuring the flow field around a scour pier using stereo PIV, specifically:

[0032] (a) Field measurement of the target area's scour pit elevation data, which can be obtained using a three-dimensional terrain scanner or high-precision side-scan sonar; customizing the scour pit reshape topography based on the acquired elevation data; placing the scour pit reshape topography on the scour pit and securing it; achieving a constant flow condition similar to that of the actual field flow field satisfying Froud's equation; and placing PIV tracer particles (which can be replaced by aluminum powder, with a diameter of 20-100 μm) in the incoming water body to ensure uniform distribution.

[0033] (b) Turn on the broadband laser, and use the green laser to illuminate the water body and the pier environment through the laser deflection plate and the light stabilization plate; place the polymethyl methacrylate plate on the surface of the constant water flow and fix it upstream of the pier; turn on the first and second charge coupled devices, adjust the first and second optical lenses using the angle displacement method, and install the first and second filters. Align the main axes of the first and second charge coupled device lenses with the first and second water-filled prisms; and adjust the focal length to achieve the target field of view.

[0034] (c) The three components of the velocity field were reconstructed using the displacement information of the same particle in a laser beam (thickness no greater than 2 mm) recorded from two different angles. Pixel calibration was performed using a 3D calibration plate, where multiple objects were required to exhibit 3D properties. A calibrated displacement mapping function was established using the commercial software PIVlab. To achieve high spatial resolution, multiple separate measurements were performed: the first focused on the horseshoe vortex field of view, and the second focused on the pile-pit junction field of view.

[0035] Based on the fine resolution of the horseshoe vortex field of view and the pile-pit junction field of view, a three-dimensional (streamwise, spanwise, and vertical) joint grid is generated based on the discrete data positions of the PIV particles. The Reynolds decomposition data of the velocity vectors are interpolated onto this three-dimensional joint grid to assimilate the overlapping measurement areas in the pile-pit junction field of view and the pile-pit junction field of view into a dataset of the same particle displacement. Due to the strong intra-field displacement, the estimated PIV particles are severely missing, and the cross-correlation algorithm ultimately cannot identify the correct field of view displacement. Valid vectors need to be treated as statistically independent samples. The number of valid samples varies between different fields of view, and emphasis should be placed on the horseshoe vortex field of view, as the efficiency of determining valid displacement vectors is lowest in this sensitive area.

[0036] (d) Quantify the turbulent structure of the flow field around the scour pier (including turbulent anisotropy and coherent structure) based on the data obtained from the physical model experiment:

[0037] The turbulence anisotropy evaluation parameters are expressed as follows:

[0038]

[0039]

[0040]

[0041] Among them, b ij is the Reynolds stress anisotropy tensor; TKE is the turbulent kinetic energy; u is the velocity vector; the right corner and the upper horizontal line represent the time fluctuation value and the average value respectively; δ ij is the Kronecker function; II and III are the second and third invariants of turbulent anisotropy, respectively; λ is the eigenvalue of the autocorrelation matrix.

[0042] The coherent structure parameter Q is expressed as follows:

[0043]

[0044] Among them, x, y, z represent the stream direction, span direction and vertical direction respectively; u, v, w represent the velocity components in the stream direction, span direction and vertical direction respectively.

[0045] The vertical velocity distribution pattern at characteristic locations within the scour pit was determined. The velocity field within the aforementioned pile-pit connection field and the region of interest within the pile-pit connection field was analyzed using dimensionless vertical depth as the ordinate and dimensionless streamwise velocity as the abscissa to determine the self-similarity of the flow field structure. Using proper orthogonal decomposition as an auxiliary algorithm, the flow separation process at the scour edge was isolated, with the independent parameters based on the length scales of the outflow zone and the boundary layer. The wall shear stress was decomposed into viscous shear stress (caused by bed viscosity), turbulent shear stress (caused by temporal pulsation), and dispersion stress (caused by spatial pulsation), and the contribution of these three stress components to the total wall shear stress was determined.

[0046] The above description of the present invention is only a preferred embodiment of the invention, and does not limit the patent scope of the present invention. Any equivalent structural transformation made by using the contents of the present invention specification, or directly or indirectly applied to the technical field of other related products, is included in the patent protection scope of the present invention.

Claims

1. A method for measuring the flow field around scour piles using stereo PIV, characterized by: Construct a physical model of scour piles; Reconstructing the velocity field components of the physical model to obtain a three-dimensional joint grid; interpolating the Reynolds decomposition data of the velocity vector onto the three-dimensional joint grid to assimilate the pile-pit connection field of view and the overlapping measurement areas in the pile-pit connection field of view into a data set of the same particle displacement; the three-dimensional joint grid is a streamwise, spanwise, and vertical joint grid generated based on the discrete data positions of the PIV particles; Quantify the turbulent structure of the flow field around scour piers, including turbulent anisotropy and coherent structure: Determine the vertical velocity distribution pattern at characteristic locations in the scour pit, and determine the self-similarity of the flow field structure with dimensionless vertical depth as the ordinate and dimensionless streamwise velocity as the abscissa for the velocity field in the pile-pit connection field and the area of ​​interest within the pile-pit connection field; Using intrinsic orthogonal decomposition as an auxiliary algorithm, the water flow separation process of the scouring edge is made independent, and the shear stress of the water flow wall is decomposed into viscous shear stress, turbulent shear stress, and dispersion stress, and the contribution ratio of the three component stresses to the total water flow wall shear stress is determined.

2. The method for measuring the flow field around a scour pier using stereo PIV according to claim 1, characterized in that: The scour pit reshapes the terrain according to the measured elevation data of the pile pier scour pit. The pile pier is placed on the reshape terrain and fixed, and a constant water flow condition that satisfies Froude similarity is adopted. The PIV tracer particles are placed in the incoming water body to meet the uniform distribution condition.

3. The method for measuring the flow field around a scour pier using stereo PIV according to claim 2, characterized in that: Stereo PIV components are used in the process of reconstructing the velocity field components of the physical model; The three-dimensional PIV component includes a broadband laser, a laser steering plate, a light stabilizing plate and Charge-coupled devices, angle adapters, optical lenses, filters, and water-filled prisms are symmetrically arranged on both sides of the pier; The broadband laser is located above the free surface of the constant water flow, and the emission port of the broadband laser is parallel to the free surface of the water flow; the broadband laser emits green band laser; the laser deflection plate is at the same height as the broadband laser, and converts the horizontal laser beam into a vertical laser beam; the light stabilizing plate is located directly below the laser deflection plate in the vertical direction, and stabilizes the vertical laser beam and transitions it to the pile pier and water environment.

4. The method for measuring the flow field around a scour pier using stereo PIV according to claim 3, characterized in that: It also includes a polymethyl methacrylate plate, which is located on the free surface of the constant water flow and connected to the pier at the upstream; the polymethyl methacrylate plate is used to eliminate surface waves generated by the interaction between the constant water flow and the pier.

5. The method for measuring the flow field around a scour pier using stereo PIV according to claim 3 or 4, characterized in that: The three components of the velocity field, namely the streamwise component, the vertical component and the spanwise component, are reconstructed using the information of the displacement of the same particle in the laser beam recorded from two different angles.

6. The method for measuring the flow field around a scour pier using stereo PIV according to claim 1, characterized in that: The turbulence anisotropy evaluation parameters include the Reynolds stress anisotropy tensor and the second and third turbulence anisotropy invariants.

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