Instantaneous wall shear stress calculation method considering particle influence

Abstract

The invention discloses an instantaneous wall surface shear stress calculation method considering particle influence. The instantaneous wall surface shear stress calculation method comprises the following steps: S1, calculating an average wind speed lt at a position y1 away from a wall surface position according to a large eddy simulation algorithm; u1gt; ; s2, calculating the total friction wind speed u * and the total shear stress tau * in the wind-sand flow system; s3, obtaining the average wind speed lt based on the step S1; u1gt; according to the total friction wind speed u * and the total shear stress tau * obtained in the step S2, the average surface shear stress tau w is solved through numerical algorithms such as a Newton iteration method and a Romberg method; and S4, completing instantaneous wall surface shear stress calculation based on the obtained average surface shear stress tau w. The problem that in existing sand flow coarse grid large vortex simulation prediction, due to the fact that the resolution ratio of a near wall face grid is low, and a wall model considering the particle influence is adopted, the sand transport rate is not accurately predicted is solved.

Description

Technical Field

[0001] The present application belongs to the technical field of meteorological forecasting, and in particular relates to a method for calculating instantaneous wall shear stress taking into account the influence of particles. Background Art

[0002] In recent years, due to the emphasis on environmental issues, large eddy simulation methods have gradually been applied in weather forecasting. Since the actual wind field height H is very high, the first grid spacing Δy from the ground surface is very large in actual model applications.

[0003] There are generally two methods used in existing large eddy simulation models:

[0004] Method 1: No special treatment is done on the grid closest to the surface, and the coarse grid large eddy simulation method is directly used. The instantaneous wall shear stress τ w (x,z,t) wind speed u near the wall i (i=1,3 represent flow direction and span direction respectively)

[0005] τ w,xy (x,z,t)=ρvdu1(x,y1,z,t) / dy1,

[0006] τ w,zy (x,z,t)=ρvdu3(x,y1,z,t) / dy1,

[0007] In the absence of wind and sand, this method is theoretically only applicable to the linear region where y1 is very close to the wall (y1<5v / u). τ ν is the kinematic viscosity of air, u τ is the surface friction speed of the air.

[0008] Method 2: Using the turbulent wall stress model generally used in the atmosphere without considering the influence of particles, the time-space averaged wall shear stress <τ w >By using the logarithmic law we get:

[0009]

[0010]

[0011] in,<u1(y1)> is the average wind speed of the grid points near the wall, k is the Karman constant, which is usually taken as 0.41, y0 is the surface roughness, and the instantaneous wall shear stress τ w (x,z,t) is obtained by the following formula

[0012] τ w,xy (x,z,t)=u1(x,y1,z,t) / ·<τ w <,

[0013] τ w,zy (x,z,t)=u3(x,y1,z,t) / ·<τ w ,

[0014]

[0015] In the case of no sand and wind influence, this method theoretically only applies when the input position y1 is located in the logarithmic region of the velocity profile 30v / u τ < y1 < 0.2H (y1 is not necessarily the first point of the near-wall grid).

[0016] Both of the above two methods are applicable to the case of no sand and wind influence. In the actual sand and wind flow, the particles have a great influence on the wind speed u i The influence is relatively large. Therefore, the error of the predicted wall shear stress is very large. So when applying the large eddy simulation with coarse grid to the prediction of sand and wind flow, a very large error will occur in the sand concentration. The correct prediction of sand and wind flow is beneficial for people to make scientific judgments on the sediment transport intensity, its influence range and size, and to give corresponding countermeasures. Summary of the Invention

[0017] The purpose of this application is to disclose an instantaneous wall shear stress calculation method considering the influence of particles in order to overcome the problems of the prior art, so as to solve the problem of inaccurate prediction of sediment transport rate due to low resolution of near-wall grid and the use of a wall model considering the influence of particles in the large eddy simulation prediction of existing sand and wind flow.

[0018] The purpose of this application is achieved by the following technical solutions:

[0019] An instantaneous wall shear stress calculation method considering the influence of particles, the instantaneous wall shear stress calculation method includes:

[0020] S1: Calculate the mean wind speed at the position y1 from the wall surface according to the large eddy simulation algorithm <u1>;

[0021] S2: Calculate the total friction wind speed u in the wind and sand flow system * and the total shear stress τ * ;

[0022] S3: Average wind speed obtained based on step S1 <u1>and the total friction wind speed u obtained in step S2 * and the total shear stress τ * , the average surface shear stress <τ is solved by numerical algorithms such as Newton iteration method and Romberg method w >

[0023] S4: Based on the average surface shear stress <τ w >Complete the instantaneous wall shear stress calculation.

[0024] According to a preferred embodiment, in step S2, the total friction wind speed u of the wind-sand flow system is obtained by fitting the average speed distribution. * .

[0025] According to a preferred embodiment, in step S2, the total friction wind speed u of the wind-sand flow system can also be calculated by the pressure gradient driven term of the NS equation. * , And calculate the total shear stress

[0026] Among them, dp / dx represents the pressure gradient driving term of the NS equation, H represents the wind field height, and ρ represents the air density.

[0027] According to a preferred embodiment, in step S3, the average surface shear stress <τ is completed by the following formula: w > Calculate,

[0028]

[0029] Among them, y1 represents the height of the large eddy simulation input point from the surface, y0 represents the surface roughness, κ is the Karman constant, y′ represents the integration interval, and q(y) represents the distribution of particle mass flux along the vertical height y, which usually has a variety of empirical expressions, generally a negative exponential distribution.

[0030] According to a preferred embodiment, in step S4, the instantaneous wall shear stress τ w The (x,z,t) calculation process includes:

[0031] τ w,xy (x,z,t)=u1(x,y1,z,t) / ·<τ w >,

[0032] τ w,zy (x,z,t)=u3(x,y1,z,t) / ·<τ w >,

[0033] Among them, τ w,xy (x,z,t) represents the instantaneous wall shear stress in the flow direction, τ w,zy (x,z,t) represents the spanwise instantaneous wall shear stress, u1(x,y1,z,t) represents the instantaneous fluid velocity in the flow direction at the input point, and u3(x,y1,z,t) represents the instantaneous fluid velocity in the spanwise direction at the input point.

[0034] According to a preferred embodiment, step S4 further includes feeding back the instantaneous wall shear stress to the large eddy simulation solver.

[0035] The aforementioned main scheme of the present application and its further options can be freely combined to form multiple schemes, all of which are schemes that can be adopted and claimed for protection in the present application. After understanding the scheme of the present application, those skilled in the art can understand that there are multiple combinations based on the prior art and common knowledge, all of which are technical schemes to be protected by the present application, and they are not exhaustively listed here.

[0036] Beneficial effects of this application:

[0037] (1) Dynamic, multi-scale simulation forecast: This application can use existing empirical formulas or real-time wind and sand flow detection data to dynamically predict the amount of sand raised by the wind and sand flow.

[0038] (2) Improvement in accuracy: This application constructs a numerical model of wall stress that takes into account the influence of particles, better considers the physical characteristics of the particle-wind field two-phase coupling, and achieves effective improvement in the prediction of sand transport flux of wind-blown sand flows.

[0039] (3) Simple feasibility: This patent can be well implemented in the existing large eddy simulation program of wind and sand flow. It can be implemented by only replacing the calculation module of the average wall stress of the wall model without changing the overall framework of the entire program. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic diagram of the calculation flow of the instantaneous wall shear stress calculation method considering the influence of particles in this application. DETAILED DESCRIPTION

[0041] The following describes the embodiments of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. The present application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0042] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0043] In the description of this application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the product of the application is usually placed when in use. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as a limitation on this application. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0044] In addition, the terms "horizontal", "vertical", "overhanging" and the like do not mean that the components are required to be absolutely horizontal or overhanging, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0045] In the description of this application, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0046] In addition, the present application would like to point out that, in the present application, unless the specific structure, connection relationship, positional relationship, power source relationship, etc. are specifically written out, the structure, connection relationship, positional relationship, power source relationship, etc. involved in the present application are all known by those skilled in the art on the basis of the prior art without creative work.

[0047] refer to Figure 1 As shown in the figure, a method for calculating instantaneous wall shear stress considering the influence of particles is shown, and the method for calculating instantaneous wall shear stress includes the following steps.

[0048] Step S1: Calculate the average wind speed at the distance y1 from the wall using the large eddy simulation algorithm <u1>。

[0049] Step S2: Calculate the total friction velocity u * and the total shear stress τ * 。

[0050] Preferably, in step S2, the total friction velocity u * of the aeolian sand flow system is obtained by fitting according to the average velocity distribution. Or, the total friction velocity u * , of the aeolian sand flow system is calculated through the pressure gradient driving term of the NS equation,

[0051] where dp / dx represents the pressure gradient driving term of the N-S equation, H represents the wind field height, and ρ represents the air density.

[0052] Step S3: Based on the average wind speed <u1> obtained in step S1 and the total friction velocity u * and the total shear stress τ * obtained in step S2, solve the average surface shear stress <τ w > through numerical algorithms such as the Newton iteration method and the Romberg method.

[0053] Preferably, in step S3, the calculation of the average surface shear stress <τ w > is completed through the following formula,

[0054]

[0055] where y1 represents the height of the large eddy simulation input point from the ground surface, y0 represents the surface roughness, κ is the von Kármán constant, y′ represents the integration interval, and q(y) represents the distribution of the particle mass flux along the vertical height y, which usually has various empirical expressions, generally a negative exponential distribution.

[0056] Step S4: Complete the calculation of the instantaneous wall shear stress based on the obtained average surface shear stress <τ w >.

[0057] Preferably, in step S4, the calculation process of the instantaneous wall shear stress τ w (x, z, t) includes:

[0058] τ w,xy (x, z, t) = u1(x, y1, z, t) / ·<τ w >,

[0059] τ w,zy (x,z,t)=u3(x,y1,z,t) / ·<τ w >,

[0060] Among them, τ w,xy (x,z,t) represents the instantaneous wall shear stress in the flow direction, τ w,zy (x,z,t) represents the spanwise instantaneous wall shear stress, u1(x,y1,z,t) represents the instantaneous fluid velocity in the flow direction at the input point, and u3(x,y1,z,t) represents the instantaneous fluid velocity in the spanwise direction at the input point.

[0061] Furthermore, step S4 also includes feeding back the instantaneous wall shear stress to the large eddy simulation solver.

[0062] The method of the present application solves the problem of inaccurate prediction of sand transport rate in existing large eddy simulation prediction of wind and sand flow due to low resolution of near-wall grids and the use of a wall model that considers the influence of particles.

[0063] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for calculating instantaneous wall shear stress considering the influence of particles, characterized in that: The instantaneous wall shear stress calculation method comprises: S1: Calculate the average wind speed at the distance y1 from the wall using the large eddy simulation algorithm <u1> ；< / u1> S2: Calculate the total friction wind speed u in the wind and sand flow system * and the total shear stress τ * ; S3: Average wind speed obtained based on step S1 <u1>and the total friction wind speed u obtained in step S2 * and the total shear stress τ * , the average surface shear stress <τ is solved by numerical algorithms such as Newton iteration method and Romberg method w > S4: Based on the average surface shear stress <τ w >Complete the instantaneous wall shear stress calculation.

2. The method for calculating instantaneous wall shear stress according to claim 1, characterized in that: In step S2, the total friction wind speed u of the wind-sand flow system is obtained by fitting the average velocity distribution. * .

3. The method for calculating instantaneous wall shear stress according to claim 1, characterized in that: In step S2, the total friction wind speed u of the wind-sand flow system is calculated by the pressure gradient driven term of the NS equation: * , And calculate the total shear stress Among them, ρ represents the air density, dp / dx represents the pressure gradient driving term of the NS equation, and H represents the wind field height.

4. The method for calculating instantaneous wall shear stress according to claim 1, characterized in that: In step S3, the average surface shear stress < τ is completed by the following formula w > Calculate, Among them, y1 represents the height of the LES input point from the surface, y0 represents the surface roughness, κ is the Karman constant, y′ represents the integration interval, and q(y) represents the distribution of particle mass flux along the vertical height y.

5. The method for calculating instantaneous wall shear stress according to claim 1, characterized in that: In step S4, the instantaneous wall shear stress τ w The (x, z, t) calculation process includes: τ w，xy (x, z, t) = u1(x, y1, z, t) / ·<τ w >, τ w,zy (x,z,t)=u3(x,y1,z,t) / ·<τ w >, Among them, τ w,xy (x, z, t) represents the instantaneous wall shear stress in the flow direction, τ w,zy (x, z, t) represents the spanwise instantaneous wall shear stress, u1(x, y1, z, t) represents the spanwise instantaneous fluid velocity at the input point, and u3(x, y1, z, t) represents the spanwise instantaneous fluid velocity at the input point.

6. The method for calculating instantaneous wall shear stress according to claim 1, characterized in that: Step S4 also includes feeding back the instantaneous wall shear stress to the large eddy simulation solver.

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