CN110991021A

CN110991021A - Variable density three-dimensional simulation method for high dam drainage flow-picking nappe

Info

Publication number: CN110991021A
Application number: CN201911162427.0A
Authority: CN
Inventors: 吴时强; 薛万云; 张陆陈; 杨家修; 骆少泽; 卢吉; 王芳芳; 郑雪玉; 庞博慧
Original assignee: PowerChina Guiyang Engineering Corp Ltd; Nanjing Hydraulic Research Institute of National Energy Administration Ministry of Transport Ministry of Water Resources; Huaneng Group Technology Innovation Center Co Ltd; Huaneng Lancang River Hydropower Co Ltd
Current assignee: PowerChina Guiyang Engineering Corp Ltd; Nanjing Hydraulic Research Institute of National Energy Administration Ministry of Transport Ministry of Water Resources; Huaneng Group Technology Innovation Center Co Ltd; Huaneng Lancang River Hydropower Co Ltd
Priority date: 2019-11-25
Filing date: 2019-11-25
Publication date: 2020-04-10
Anticipated expiration: 2039-11-25
Also published as: CN110991021B

Abstract

The invention provides a variable density simulation calculation method capable of simulating a drainage nappe. Considering that the water body and the gas are mixed with each other and the nappe expands and diffuses towards the periphery in the nappe development process, the water body and the mixed gas in the nappe are considered as a whole, and considering that the nappe density gradually decreases in the nappe falling process. And therefore, the on-way density of the nappe is modified, and a formula of the process of changing the nappe density along with the distance is deduced.

Description

Variable density three-dimensional simulation method for high dam drainage flow-picking nappe

Technical Field

The invention belongs to the technical field of water conservancy and hydropower engineering, and relates to a flow-picking nappe simulation method, in particular to a three-dimensional simulation method of a high dam discharge flow-picking nappe.

Technical Field

At present, in the southwest area of China, part of high dam power stations are in planning and design, and how to eliminate the safety influence of high-speed water flow caused by high dam water discharge buildings on engineering is a technical problem which needs to be effectively solved in power station design. The technical problem to be effectively solved is to accurately simulate the flip flow water tongue caused by the flip bucket at the outlet of the spillway of a high dam outlet structure.

For a water release building, trajectory energy dissipation is the most common energy dissipation mode, and has the advantages of simple structure, small engineering quantity and low investment, but the trajectory of motion, the position of a water inlet point, the water inlet angle, the water inlet speed and the impact pressure on a downstream bed surface are accurately simulated and predicted, because a trajectory of a water tongue, the position of the water inlet point, the water inlet angle, the water inlet speed and the impact pressure on the downstream bed surface are accurately simulated and predicted, which is one of the most concerned problems in analysis and research of the water tongue. With the rapid development of computer performance, the research of the flow-picking nappe by using a numerical simulation method becomes a new means, but most of numerical simulation researches do not consider the mutual mixing of the nappe and the surrounding air in the movement process, and the nappe has the advantages that in order to meet a continuity equation, the section is shrunk and thinned in the falling process, and after the nappe enters a plunge pool, a local large impact pressure is formed, and the development process of the nappe calculated by the simulation method without considering the mutual mixing of the nappe and the surrounding air obviously does not conform to the change process of the prototype nappe. Therefore, a new method needs to be provided, and the aeration and expansion processes in the development process of the nappa are considered.

Disclosure of Invention

The invention aims to solve the technical problem of overcoming the defects of the existing calculation method and providing a variable density simulation calculation method capable of simulating a leakage flow nappe. The water and the gas are mixed with each other in the development process of the nappa and the nappa is expanded and diffused to the periphery. The water body and the mixed gas in the nappe are considered as a whole, and the density of the nappe is considered to be gradually reduced in the process of dropping the nappe. And therefore, the on-way density of the nappe is modified, and a formula of the process of changing the nappe density along with the distance is deduced.

The technical scheme for solving the technical problems is as follows:

based on empirical formula of the thickening of the nappy along the way:

h＝h_o+0.04s (1-1)

h is the thickness of the waterstongue along the way, h_oIs the initial nappe thickness (nappe thickness taken separately from the pick-up outlets).

And (4) deducing a formula for the variation of the density of the nappe along the way by integrating a continuity equation, a geometric relation and the like.

Deducing a formula of the variation of the density of the nappe along the way according to the following thought:

(1)：

and (4) calculating the thickness h of the waterspout along the way according to the empirical formula (1-1) of the waterspout.

(2)：

In order to facilitate numerical simulation, the relation between the on-way density rho of the nappe and the X direction is obtained, so that the relation between the on-way distance s of the nappe and the X direction only needs to be determined.

Therefore, the following calculation is also required:

water tongue angle theta, flow velocity v_oWhen the water flow leaves the flip bucket, the flow velocity can be divided into vertical motion and horizontal motion, namely, the water flow is supposed to make free-falling motion (upward deceleration motion and then downward acceleration motion) in the vertical direction H and make uniform motion (or make deceleration motion for a negative acceleration) in the horizontal direction X.

Vertical direction moving distance: h ═ v_osinθ)*t+0.5gt²(1-2)

Horizontal direction movement distance: x ═ v_ocosθ)*t (1-3)

Two positions apart the nappe spacing: ds ═ ((H)₂-H₁)²+(X₂-X₁)²)^1/2(1-4)

And (3) calculating H and X values at different moments by taking a time interval dt, considering that the water tongue along-path distance s between two moments meets a linear change relation due to small value of dt, calculating the water tongue distance ds between the two moments by using a formula 1-4, and sequentially adding ds to obtain the water tongue along-path distance s at the moment.

Similarly, the gradual spreading of the nappe is also considered in the spanwise direction, in which the nappe is considered to spread slower due to the absence of gravity, and its width widens as follows, where B_oOutlet width:

B＝B_o+0.005s (1-5)

(3)：

then according to flux conservation formula rho_oh_oB₀Each along the way is obtainedThe density of each position, thereby obtaining the relation between the on-way distance s of the nappe and the density rho of the nappe,

where ρ ═ f(s) (s ═ 0, h ═ h_o，ρ＝ρ_o) (1-6)

And (3) obtaining the relation between the water tongue along-way distance s and X by combining the formulas (1-2), (1-3) and (1-4). Then according to equations (1-1), (1-5), and the flux equation ρ_oh_oB₀And (6) solving the change relation between the water tongue distance s and the water tongue density rho.

The invention has the beneficial effects that:

the invention can better simulate the development process of the nappe and accurately calculate index parameters such as nappe flow velocity, nappe shape, impact pressure caused by the nappe in a downstream river channel and the like. And the reasonable design of the hydraulic structure by designers according to the calculation structure is facilitated.

Drawings

FIG. 1 is a schematic view of a nappe

FIG. 2 is a shape diagram of a nappe

FIG. 3 curve of density of flood spillway nappy varying with height

Detailed Description

The embodiment provides a method for simulating the on-way of a discharge flow tongue of a high dam spillway.

Empirical formula h ═ h based on nappe thickening along the way_o+0.04s, h is the in-path nappy thickness, h_oIs the initial nappe thickness, and s is the nappe curve length.

Moving distance from vertical direction: h ═ v_osinθ)*t+0.5gt²And horizontal direction movement distance: x ═ v_ocos θ × t, and ds ((H) is calculated for different dt times (dt is 0.01s)₂-H₁)²+(X₂-X₁)²)^1/2The ds at different dt times are added up, i.e. the entire along-the-way distance s. Empirical formula h ═ h for thickening water tongue along course_o+0.04s, calculating the thickness h along the way; then according to the wingspan width formula B ═ B_o+0.005s, along the span width B. Finally, the flux formula rho_oB_oh_oρ available as ρ Bh_oB_oh_o＝ρ(B_o+0.005s)(h_o+0.04s) to obtain a formula of density change along the way.

Respectively calculating the parameter v of the current working condition_o＝42.346m/s，θ＝15°，h_oCarry over into flux formula p 4.87m_oB_oh_o＝ρ(B_o+0.005s)(h_o+0.04 s). Obtaining a spillway path change formula:

ρ＝-0.0000000101x⁴+0.0000168x³-0.00675x²-0.62x+590.87

wherein x is a distance which is the distance of the self-picking outflow port along the x direction (the picking outflow port is 0, the length of the plunge pool is about 305m), the formula is a fitting empirical formula, and the application range is 0< x <350m

Add computer statements to the N-S equation solver (unknowns include flow rate, pressure, etc.) by ansys (fluent) commercial software computer program second development function (UDF). See FIG. 3

And carrying out numerical simulation calculation on the change process of the flood spillway water tongue and the change process of the water flow pressure in the plunge pool.

As can be seen from fig. 1 and 2, the nappe also widens horizontally, consistent with the trend of the prototype nappe to change in form.

In addition to the above embodiments, other embodiments of the present invention are also possible. All technical solutions formed by adopting equivalent substitutions or equivalent transformations fall within the protection scope of the claims of the present invention.

Claims

1. A variable density three-dimensional simulation method for a high dam drainage trajectory nappe comprises the following steps:

(1) calculating the thickness h of the on-way nappe according to a nappe empirical formula:

h＝h_o+0.04s (1-1)

in the formula h_oIs the initial nappe thickness, s is the nappe on-way distance;

(2) calculating the on-way distance s of the nappe at different moments;

H＝(v_osinθ)*t+0.5gt²(1-2)

X＝(v_ocosθ)*t (1-3)

ds＝((H₂-H₁)²+(X₂-X₁)²)^1/2(1-4)

in which theta is the water tongue angle v_oThe flow velocity of the nappe leaving the flip bucket, t is the movement time of the nappe, H is the moving distance in the vertical direction, and X is the moving distance in the horizontal direction; ds is the distance between two positions separated by the nappe;

calculating H and X values at different moments, obtaining the space ds of the nappe between two moments by using a formula 1-4, and then adding the sequential ds before each moment to obtain the nappe along-path distance s at the moment;

(3) the spanwise width formula of the nappe is as follows:

B＝B₀+0.005s (1-5)

in the formula B₀The width of the outlet, s is the distance of the nappe along the way;

(4) according to the flux conservation formula rho_oh_oB₀Rho hB, i.e. the flux of each section along the length of the nappe is equal. And (3) solving the density of the nappe at each position along the way:

where ρ ═ f(s) (s ═ 0, h ═ h_o，ρ＝ρ_o) (1-6)

The relation between the on-way distance s of the nappe and H, X is obtained by combining the formulas (1-2), (1-3) and (1-4), and then the formula rho is obtained according to the formulas (1-1), (1-5) and the flux formula_oh_oB₀And (6) solving the change relation between the water tongue distance s and the water tongue density rho.