阅读说明：本技术 判断表面活性剂的剪切诱导结构在流场空间上分布的方法 (Method for judging distribution of shear-induced structure of surfactant on flow field space ) 是由 付在国 梁潇天 于 2019-10-12 设计创作，主要内容包括：本发明涉及一种判断表面活性剂的剪切诱导结构在流场空间上分布的方法。本发明在表面活性剂溶液造成的减阻流动中,应用粒子成像测速(Particle Image Velocimetry,PIV)技术对槽道内瞬时速度场进行测量,根据湍流统计理论,利用计算程序对速度场进行统计计算,掌握流向速度梯度的分布,基于应力平衡方程以及流向速度梯度的分布,判断出表面活性剂的剪切诱导结构在流场空间上的分布特征。(The invention relates to a method for judging the distribution of a shear-induced structure of a surfactant on a flow field space. In the resistance-reducing flow caused by the surfactant solution, the instantaneous velocity field in the channel is measured by using a Particle Image Velocimetry (PIV) technology, the velocity field is statistically calculated by using a calculation program according to a turbulence statistical theory, the distribution of the flow direction velocity gradient is mastered, and the distribution characteristics of the shear induction structure of the surfactant in the flow field space are judged based on a stress balance equation and the distribution of the flow direction velocity gradient.)

1. A method for determining the spatial distribution of a shear-inducing structure of a surfactant in a flow field, comprising the steps of:

step 1, adding a surfactant into water to form a solution, forming drag reduction flow in a channel by taking the solution as a flowing medium, defining the flowing direction of the flowing medium as an X-axis direction, and defining the direction of a vertical wall surface of the channel as a Y-axis direction;

step 2, calibrating the measurement position and the flow size before testing, and focusing the quick-response electric coupling device camera on a plane to be tested, wherein the plane to be tested is positioned in an X-Y plane;

step 3, measuring the instantaneous velocity field in the plane to be measured by applying a Particle Imaging Velocimetry (PIV) technology;

step 4, combining with cross-correlation image analysis technology to obtain instantaneous X-Y plane velocity field of anti-drag flow of surfactant solution through statistics, and obtaining instantaneous velocity field image;

step 5, statistically analyzing the instantaneous velocity field image based on a calculation program to obtain a flow direction velocity gradient field, and judging the distribution of the shear inducing structure on the space according to the distribution of high and low velocity gradients based on a stress balance equation, wherein the stress balance equation is

based on stress balance equation

based on stress balance equationAssuming there are many SIS structures somewhere in the flow field, the elastic stress τ is here_veLarge, yet Reynolds shear stress τ_ReThe flow of the flow is negligible at higher flow rates, where internal friction is required based on stress balance

2. The method for determining the spatial distribution of a flow field in a shear-induced structure of a surfactant according to claim 1, wherein in step 1, the surfactant is water-soluble and is an ionic surfactant.

3. The method for determining the spatial distribution of a shear-inducing structure of a surfactant according to claim 1, wherein the step 5 of obtaining the flow direction velocity gradient field comprises the steps of:

and (3) taking an instantaneous velocity field image at each position with a specific distance from the wall surface by utilizing a calculation program to perform velocity statistical analysis, and obtaining the distribution of the flow direction velocity gradient in the flow field in the direction vertical to the wall surface to obtain the flow direction velocity gradient field.

Technical Field

The invention relates to a method for judging shear induced structure distribution based on statistics of velocity in drag reduction flow of a surfactant solution, belonging to the technical field of viscoelastic fluid drag reduction flow.

Background

Along with the gradual intensification of the worldwide energy crisis, energy conservation and emission reduction become great trends, and in the process of fluid transportation, frictional resistance is a main energy consumption source, so that the significance of researching turbulent drag reduction is very important.

The small amount of surfactant is added into water, so that the resistance of turbulent flow of the fluid can be effectively reduced, and the energy consumption in remote fluid delivery can be reduced.

The scientific community believes that the key to the viscoelastic drag reducing flow of a surfactant solution is the formation of an effective surfactant structure in the flow called Shear Induced Structures (SIS). It is a reticular aggregate formed by surfactant molecules after the concentration of the surfactant molecules exceeds a critical value, has viscoelasticity, and is easy to recover after being sheared. However, the microstructure of the SIS is difficult to capture, the distribution characteristics of the SIS can be mastered to be used for explaining the drag reduction mechanism of the SIS, and the SIS can also be used for establishing a constitutive model for describing the stress and deformation of the SIS in numerical simulation. The distribution characteristics of the SIS can also be used to predict flow characteristics and drag reduction characteristics of surfactant solutions in various applications, such as the application of external disturbances in turbulent flow to walls, etc.

Disclosure of Invention

The purpose of the invention is: and judging the distribution characteristics of the shear inducing structure in the flow field according to the distribution of the flow direction velocity gradient in the drag reduction flow.

In order to achieve the above object, the present invention provides a method for determining the distribution of a shear-induced structure of a surfactant in a flow field space, comprising the steps of:

step 1, adding a surfactant into water to form a solution, forming drag reduction flow in a channel by taking the solution as a flowing medium, defining the flowing direction of the flowing medium as an X-axis direction, and defining the direction of a vertical wall surface of the channel as a Y-axis direction;

step 2, calibrating the measurement position and the flow size before testing, and focusing the quick-response electric coupling device camera on a plane to be tested, wherein the plane to be tested is positioned in an X-Y plane;

step 3, measuring the instantaneous velocity field in the plane to be measured by applying a Particle Imaging Velocimetry (PIV) technology;

step 4, combining with cross-correlation image analysis technology to obtain instantaneous X-Y plane velocity field of anti-drag flow of surfactant solution through statistics, and obtaining instantaneous velocity field image;

step 5, statistically analyzing the instantaneous velocity field image based on a calculation program to obtain a flow direction velocity gradient field, and judging the distribution of the shear inducing structure on the space according to the distribution of high and low velocity gradients based on a stress balance equationIn, the stress balance equation is

Wherein, tau is the total stress,

in order to be a viscous stress,

for flow direction velocity gradients, τ_ReTo Reynolds shear stress, τ_veIs a viscoelastic stress;

based on stress balance equation

Assuming there is little SIS structure somewhere in the flow field, elastic stress τ here_veSmall, yet Reynolds shear stress τ_ReThe flow of the flow is negligible at higher flow rates, where internal friction is required based on stress balance

Larger, necessarily requiring a flow-to-velocity gradient due to the small number of SIS structures and small viscosity μ there

So that it can be judged from the high flow velocity gradient that there are fewer SIS structures

Based on stress balance equation

Assuming there are many SIS structures somewhere in the flow field, the elastic stress τ is here_veLarge, yet Reynolds shear stress τ_RqThe flow of the flow is negligible at higher flow rates, where internal friction is required based on stress balance

Smaller, necessarily requiring a flow-to-velocity gradient due to the greater number of SIS structures and viscosity μ there

Small, so that it can be judged that there are more SIS structures at this point based on the low flow velocity gradient.

Preferably, in step 1, the surfactant is water-soluble and is an ionic surfactant.

Preferably, in step 5, obtaining the flow direction velocity gradient field comprises the following steps:

and (3) taking an instantaneous velocity field image at each position with a specific distance from the wall surface by utilizing a calculation program to perform velocity statistical analysis, and obtaining the distribution of the flow direction velocity gradient in the flow field in the direction vertical to the wall surface to obtain the flow direction velocity gradient field.

In the resistance-reducing flow caused by the surfactant solution, the instantaneous velocity field in the channel is measured by using a Particle Image Velocimetry (PIV) technology, the velocity field is statistically calculated by using a calculation program according to a turbulence statistical theory, the distribution of the flow direction velocity gradient is mastered, and the distribution characteristics of the shear induction structure of the surfactant in the flow field space are judged based on a stress balance equation and the distribution of the flow direction velocity gradient.

Drawings

FIG. 1 is a flow chart of an implementation of a method for determining shear-induced structural distribution based on statistics of velocity in a drag-reducing flow of a surfactant solution.

FIG. 2 is a schematic diagram of an X-Y planar velocity field test using a PIV system for channel wall turbulence.

Figure 3 is a view of the transient flow direction velocity gradient field of a drag reducing flow of a surfactant solution in a turbulent flow of a channel wall.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

As shown in FIG. 1, the present invention relates to a method for determining shear induced structural distribution based on statistics of velocity in a drag reducing flow of a surfactant solution, comprising the steps of:

step 1, taking an example that an aqueous solution of cetyltrimethylammonium chloride (CTAC) with a mass concentration of 40ppm is used as a flowing medium to form a drag reduction flow in a channel, defining the flowing direction of the flowing medium as an X-axis direction, and defining the vertical wall surface direction of the channel as a Y-axis direction.

And 2, calibrating the position of the measurement plane and the flow size before testing, and focusing a quick-response Charge Coupled Device (CCD) camera on the plane to be tested.

And step 3, measuring the instantaneous velocity field in the plane of the flow direction in the channel and the vertical wall surface direction (X-Y) by using a Particle Imaging Velocimetry (PIV) technology, wherein the PIV technology is a conventional plane laser velocimetry technology and has higher resolution. The PIV test system is shown in fig. 2.

And 4, combining a cross-correlation image analysis technology to obtain an instantaneous velocity field of the X-Y plane of the drag-reduction flow of the surfactant solution.

And 5, statistically analyzing the instantaneous velocity field image based on a calculation program to obtain each instantaneous flow direction velocity gradient field. And judging the distribution characteristics of the shear inducing structure in space according to the distribution of high and low speed gradients based on a stress balance equation.

As shown in fig. 3 for the transient streamwise velocity gradient field of the drag reducing flow of the surfactant solution, the darker striped structure sloping from bottom left to right indicates a high streamwise velocity gradient (the lighter colored areas represent low streamwise velocity gradients), with the greater the velocity gradient, the darker the color throughout the channel flow. The abscissa represents the flow direction (X direction), the ordinate represents the vertical wall direction (Y direction), and h is the half height of the channel.

The smaller the flow direction velocity gradient in region B, assuming there is less distribution of SIS structure, the corresponding elastic stress τ_veSmall, the viscosity is also small,

overall smaller, i.e. less internal friction, based on stressEquation of force balance

Taking into account the Reynolds shear stress τ everywhere_ReAll towards zero, the resultant force will not balance with adjacent layers, so the assumption about the less distributed SIS structure here does not hold. It can then be judged that more SIS structures exist in the low velocity gradient region B.

The greater the flow velocity gradient in region A, assuming more SIS structure distribution here, the corresponding elastic stress τ_veLarge, the viscosity is also large,

the whole is larger, i.e. the internal friction is larger, based on the stress balance equationTaking into account the Reynolds shear stress τ everywhere_ReAll going to zero, the resultant force will not balance with the adjacent layers, so the assumption about the greater distribution of SIS structures here does not hold. It can then be judged that there are fewer SIS structures in the high-speed gradient region a.

Based on the above analysis, it can be concluded from the change in velocity gradient that more shear-induced structures SIS appear in the low flow-direction velocity gradient region B.