CN107895070A - A kind of orifice plate based on numerical simulation and hole plug division methods - Google Patents

Abstract

The invention relates to a method for dividing orifice plates and hole plugs based on numerical simulation. The length of the cavity is selected as the investigation quantity. When the cavity length is smaller than the thickness of the energy dissipation hole, it is a hole plug, and when the cavity length is greater than the thickness of the energy dissipation hole, it is a hole. plate; determine the factors that affect the length of the cavity, including the average flow velocity of the water flow in the spillway, the flow density, the viscosity of the flow, the diameter of the spillway, and the diameter of the energy dissipation hole; based on the RNG k‑ε model, the numerical simulation model of the flow through the energy dissipation hole is established ; Analyze and fit the numerical simulation results, determine the empirical expressions of the cavity length and related factors, and compare the obtained cavity length with the thickness of the energy dissipation hole to divide the orifice plate and the hole plug. The invention has the advantages of establishing the division standard of the orifice plate and the hole plug, realizing the rapid division of the orifice plate and the hole plug, improving the energy dissipation efficiency of the orifice plate or the hole plug, and popularizing the use of the orifice plate or the hole plug in the high dam flood discharge. application.

Description

A Numerical Simulation Based Orifice Plate and Hole Plug Division Method

technical field

The invention relates to the technical field of water conservancy engineering, in particular to a method for dividing orifice plates and plugs based on numerical simulation.

Background technique

With the rapid development of the hydropower industry, high dams are used more and more in hydropower engineering projects. Such a high dam has huge energy in the water flowing down. How to eliminate the huge energy released by the high dam? To protect the safety of dams and downstream rivers has always been an important issue facing the majority of hydropower workers.

Orifice plates or plugs have important applications in high dam flood discharge. With the help of their special shape, the energy dissipation of orifice plates or hole plugs will cause sudden contraction and expansion when the water flow passes through the orifice plate, thus forming strong turbulence and strong shear. , in order to achieve the purpose of energy dissipation. The orifice plate or hole plug has the characteristics of simple layout, economy, high energy dissipation efficiency, and small cavitation damage, and has an important application prospect in future hydropower energy dissipation.

Both the orifice plate and the hole plug are energy-dissipating holes. Due to the difference in thickness, when the water flows through the orifice plate, the water flow has only one sudden contraction and expansion, but when the water flow passes through the hole plug, due to the large thickness of the hole plug, the water flow has two bursts. Constriction and sudden expansion, specifically speaking, when the cavity length L is less than the thickness T of the energy dissipation hole, it is a plug, and when the cavity length L is greater than the thickness T of the energy dissipation hole, it is an orifice plate. It can be seen that the flow law of the water flow through the orifice plate or the hole plug Therefore, in the energy dissipation design of high dams, especially when using multi-level energy dissipation hole structures, it is necessary to divide the orifice plate and the hole plug to improve the energy dissipation efficiency, but no one has proposed the hole plate and the hole plug specific classification criteria.

"China Rural Water Conservancy and Hydropower" Issue 6, 2009, the article titled "Summary of Energy Dissipation Holes" introduced several implementation methods, research status and practical applications of orifice plates and hole plugs, but the orifice plates and hole plugs It is only a conceptual description of the difference, and does not involve specific standards for the division of orifice plates and hole plugs.

Contents of the invention

The purpose of the present invention is to provide a method for dividing orifice plates and hole plugs based on numerical simulation, so as to realize accurate division of orifice plates and hole plugs and improve energy dissipation efficiency.

In order to achieve the above object, the present invention adopts the following technical solutions:

A method for dividing orifice plates and hole plugs based on numerical simulation, specifically adopting the following steps:

Step 1. Select the cavity length L as the investigation quantity. When the cavity length L is less than the thickness T of the energy dissipation hole, it is a hole plug, and when the cavity length L is greater than the thickness T of the energy dissipation hole, it is an orifice plate;

Step 2. Determine the factors affecting the length L of the cavity, including the average velocity u of the water flow in the spillway, the density of the flow ρ, the viscosity of the flow μ, the diameter of the spillway D, and the diameter of the energy dissipation hole d;

Step 3. Based on the RNG k-ε model, a numerical simulation model of water flow through the energy dissipation hole is established;

Step 4: Analyze and fit the numerical simulation results, determine the empirical expressions of the cavity length L and related factors, and compare the obtained cavity length L with the energy dissipation hole thickness T to divide the orifice plate and the hole plug.

As a preference, determining the factors affecting the cavity length L in step 2 is further obtained through dimensional analysis: L/D=f(β, Re), wherein Re=uDρ/μ is the Reynolds number, and β=d/D is aperture ratio.

As a preference, in step 3, based on the RNG k-ε model, the numerical simulation model for water flow through the energy dissipation hole is specifically:

(1) The numerical simulation model of water flow through energy dissipation holes includes the following control equations:

Continuity equation:

Momentum Conservation Equation:

k-equation:

ε-equation:

Among them: x _i (=x, y) is the axial and radial coordinates, u _i (= u _x , u _y ) is the water velocity in the axial or radial direction, ρ is the density of the fluid, p is the pressure, v is the hydrodynamic viscosity, v _t is the eddy viscosity, v _t = C _μ (k ² /ε), k is the turbulent kinetic energy, ε is the dissipation rate of the turbulent kinetic energy, C _μ = 0.085, and the values of other parameters are expressed as η=Sk/ε, C ₁ =1.42, η _o = 4.377, λ = 0.012, C ₂ =1.68, α _k =α _ε =1.39;

(2) The boundary conditions of the numerical simulation model of water flow through energy dissipation holes include: inflow boundary, outflow boundary, symmetry axis boundary and wall boundary. , turbulent kinetic energy dissipation rate distribution, their mathematical expressions are u _in =u ₀ , k=0.0144u ₀ ² , ε=k ^1.5 /(0.5R), where u ₀ is the average flow velocity at the inlet, and R is the spillway Radius; the treatment method of the outflow boundary is to assume that the outflow is fully developed; the treatment method of the symmetrical axis boundary is to assume that the radial velocity is 0, and the gradient of each variable along the radial direction is also considered to be 0; the treatment method of the wall boundary is boundary The no-slip assumption is adopted in laminar flow, and the wall boundary velocity is equal to the velocity component of the boundary node.

As a preference, the empirical expression of the cavity length L and related factors in Step 4 is L/D=0.4427(d/D) ^-0.3538 , wherein d/D=0.4-0.8, Re>10 ⁵ .

Compared with the prior art, the present invention has the advantages of: based on the RNG k-ε model, the numerical simulation model of the water flow through the energy dissipation hole is established, and according to the results of the simulation model, the empirical expression of the cavity length and related factors is obtained by fitting the data According to the formula, the division standard of orifice plate and hole plug is established, and the rapid division of orifice plate and hole plug is realized.

Description of drawings

Fig. 1 is the flow state schematic diagram of water flow through orifice among the present invention;

Fig. 2 is a flow schematic diagram of water flow through a hole plug in the present invention;

Fig. 3 is a graph showing the relationship between the L/D value and the aperture ratio d/D in the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

As shown in Fig. 1 to Fig. 3, a numerical simulation-based method for dividing an orifice plate and a hole plug uses the following steps:

Step 1. Select the cavity length L as the investigation quantity. When the cavity length L is less than the thickness T of the energy dissipation hole, it is a hole plug, and when the cavity length L is greater than the thickness T of the energy dissipation hole, it is an orifice plate;

Step 2. Determine the factors affecting the length L of the cavity, including the average velocity u of the water flow in the spillway, the density of the flow ρ, the viscosity of the flow μ, the diameter of the spillway D, and the diameter of the energy dissipation hole d;

Step 3. Based on the RNG k-ε model, a numerical simulation model of water flow through the energy dissipation hole is established;

Step 4: Analyze and fit the numerical simulation results, determine the empirical expressions of the cavity length L and related factors, and compare the obtained cavity length L with the energy dissipation hole thickness T to divide the orifice plate and the hole plug.

In step 2, the factors affecting the cavity length L are determined through dimensional analysis: L/D=f(β, Re), where Re=uDρ/μ is the Reynolds number, and β=d/D is the aperture ratio.

In Step 3, based on the RNG k-ε model, the numerical simulation model of water flow through the energy dissipation hole is established as follows:

(1) The numerical simulation model of water flow through energy dissipation holes includes the following control equations:

Continuity equation:

Momentum Conservation Equation:

k-equation:

ε-equation:

Among them: x _i (=x, y) is the axial and radial coordinates, u _i (= u _x , u _y ) is the water velocity in the axial or radial direction, ρ is the density of the fluid, p is the pressure, v is the hydrodynamic viscosity, v _t is the eddy viscosity, v _t = C _μ (k ² /ε), k is the turbulent kinetic energy, ε is the dissipation rate of the turbulent kinetic energy, C _μ = 0.085, and the values of other parameters are expressed as η=Sk/ε, C ₁ =1.42, η _o = 4.377, λ = 0.012, C ₂ =1.68, α _k =αε=1.39;

(2) The boundary conditions of the numerical simulation model of water flow through energy dissipation holes include: inflow boundary, outflow boundary, symmetry axis boundary and wall boundary. , turbulent kinetic energy dissipation rate distribution, their mathematical expressions are u _in =u ₀ , k=0.0144u ₀ ² , ε=k ^1.5 /(0.5R), where u ₀ is the average flow velocity at the inlet, and R is the spillway Radius; the treatment method of the outflow boundary is to assume that the outflow is fully developed; the treatment method of the symmetrical axis boundary is to assume that the radial velocity is 0, and the gradient of each variable along the radial direction is also considered to be 0; the treatment method of the wall boundary is boundary The no-slip assumption is adopted in laminar flow, and the wall boundary velocity is equal to the velocity component of the boundary node.

The empirical expression of the cavity length L and related factors in Step 4 is specifically L/D=0.4427(d/D) ^-0.3538 , where d/D=0.4-0.8, Re>10 ⁵ .

The factors that affect the cavity length L include the average velocity u of the water in the flood tunnel, the current density ρ, the viscosity of the water μ, the diameter of the flood tunnel D, and the diameter of the energy dissipation hole d. The factors are the Reynolds number Re and the aperture ratio d/D. When the aperture ratio is fixed at 0.5 and the Reynolds number is changed, the calculation is based on the RNG k-ε model, and a set of data of L/D value changing with the Reynolds number is obtained. , the results are shown in Table 1. The results show that when the Reynolds number is greater than 0.9×10 ⁵ , the Reynolds number has little effect on the cavity length, almost negligible.

Table 1 When the aperture ratio d/D=0.5 is fixed, the value of L/D changes with the Reynolds number Re

When the Reynolds number is greater than 10 ⁵ , the influence of the Reynolds number on the cavity length can be ignored at this time, and the value of the aperture ratio can be changed to obtain a set of data on the change of the L/D value with the aperture ratio. The obtained data is plotted as shown in Figure 3 The relationship between the L/D value and the aperture ratio d/D is shown in Fig. 3, and the empirical expression of the cavity length and the aperture ratio is obtained as L/D=0.4427(d/D) ^-0.3538 , where the aperture ratio The applicable range is d/D=0.4-0.8, and the applicable range of Reynolds number is Re>10 ⁵ .

According to the known aperture ratio and the diameter of the spillway tunnel, the empirical expression of the cavity length and aperture ratio can be used to calculate the cavity length, and then the cavity length is compared with the energy dissipation hole thickness, and the cavity length is less than the energy dissipation hole When the thickness is thicker, it is a hole plug, and when the cavity length is greater than the thickness of the energy dissipation hole, it is an orifice plate, which realizes the rapid division of the orifice plate or hole plug, improves the energy dissipation efficiency of the orifice plate or hole plug, and further promotes the orifice plate or hole plug at high Application in dam flood discharge.

Claims (4)

1. a kind of orifice plate based on numerical simulation and hole plug division methods, it is characterized in that, a kind of orifice plate based on numerical simulation with Hole plug division methods specifically use following steps：

Step 1: selected cavity length L is investigation amount, cavity length L fills in when being less than energy dissipating hole thickness T for hole, and cavity length L is big It is orifice plate when the thickness T of energy dissipating hole；

Step 2: determine to influence cavity length L factor, including in flood discharging tunnel current mean flow rate u, jet density ρ, current Viscosity, mu, flood discharge hole dia D, energy dissipating bore dia d；

Step 3: numerical simulator of the current by energy dissipating hole is established based on RNG k- ε models；

Step 4: logarithm value analog result carries out analysis fitting, cavity length L and the empirical representation of correlative factor, root are determined According to the cavity length L of acquisition compared with the thickness T of energy dissipating hole, orifice plate and hole plug are divided.

2. a kind of orifice plate based on numerical simulation according to claim 1 and hole plug division methods, it is characterized in that, step 2 It is middle to determine that the factor for influenceing cavity length L further obtains specifically by dimensional analysis：L/D=f (β, Re), wherein Re=uD ρ/ μ is Reynolds number, and β=d/D is aperture ratio.

3. a kind of orifice plate based on numerical simulation according to claim 1 and hole plug division methods, it is characterized in that, step 3 In current established based on RNG k- ε models be specially by the numerical simulator in energy dissipating hole：

(1) current include following governing equation by the numerical simulator in energy dissipating hole：

Continuity equation：

Momentum conservation equation：

K- equations：

ε-equation：

Wherein：x_i(=x, y) for axially and radially direction coordinate, u_i(=u_x, u_y) for the water velocity in axially or radially direction, ρ It is the density of fluid, p is pressure, and v is flow dynamic viscosity, v_tIt is vortex viscosity, v_t=C_μ(k²/ ε), k represents Turbulent Kinetic, and ε is Dissipation turbulent kinetic energy, C_μ=0.085, other specification value is expressed asη=Sk/ ε, C₁= 1.42η_o=4.377, λ=0.012,C₂=1.68, α_k=α_ε= 1.39；

(2) current are included by the boundary condition of the numerical simulator in energy dissipating hole：Become a mandarin border, Outlet boundary, symmetry axis side Boundary and wall border, the processing method of each boundary condition are：The boundary condition that becomes a mandarin becomes a mandarin mean flow rate, Turbulent Kinetic point Cloth, dissipation turbulent kinetic energy distribution, their mathematic(al) representation is respectively u_in=u₀, k=0.0144u₀ ², ε=k^1.5/ (0.5R), Wherein u₀For entrance mean flow rate, R is flood discharging tunnel radius；Outlet boundary processing method is to assume that stream attains full development；It is right The processing method on axle border assumes that radial velocity is referred to as 0, and the gradient of each variable radially is also considered as 0；Wall side The processing method on boundary is to be employed in boundary layer flow without sliding it is assumed that the velocity component phase of wall boundary speed and boundary node Deng.

4. a kind of orifice plate based on numerical simulation according to claim 2 and hole plug division methods, it is characterized in that, step 4 Middle cavity length L and the empirical representation of correlative factor are specially L/D=0.4427 (d/D)^-0.3538, wherein d/D=0.4- 0.8, Re ＞ 10⁵。