A negative pressure balance system for water transfer tunnel

Abstract

The present invention discloses a negative pressure balance system for a water conveyance tunnel, which is arranged in the water conveyance tunnel and includes a gate shaft, a gate and a ventilation system. The ventilation system is installed in the downstream lining of the gate and is connected to the water conveyance tunnel at both ends. The ventilation system includes a ventilation steel pipe, which is a Tesla valve. The air inlet of the ventilation steel pipe is connected to a gas collection mechanism, which is an inverted funnel-shaped gas collecting pipe. After the gate is raised, the flow in the water conveyance tunnel increases, the water flow rate increases, the pressure in the tunnel decreases, and cavitation is formed. The gas released by the collapse of the cavitation enters the gas collection mechanism at the gradually expanding interface of the tunnel, passes through the ventilation system, and then enters the water conveyance tunnel, thereby reducing the cavitation erosion of the water conveyance tunnel, reducing the head loss, and increasing the water flow rate; the gas in the tunnel completes the circulation through the ventilation system, reducing the wind entering the gate shaft.

Description

Technical Field

[0001] The invention belongs to the field of water conservancy water conveyance tunnels, and particularly relates to a water conveyance tunnel negative pressure balance system. Background Art

[0002] When the gate shaft of a water conveyance tunnel in the prior art is opened, as the flow velocity in the tunnel increases, the pressure in the tunnel decreases, and external gas enters the gate shaft, impacting the gate and causing it to shake.

[0003] When the pressure inside the tunnel becomes smaller, the external atmospheric pressure becomes high pressure. The pressure difference here can suck air into the water, forming cavitations in the liquid flow. When the cavitations enter the higher pressure area with the liquid flow, they will lose the conditions for existence and suddenly collapse. The cavitations that are constantly formed and grown in the liquid flow will frequently collapse near the solid wall. The wall will suffer repeated impacts of huge pressure, causing fatigue damage to the material and even surface erosion.

[0004] Moreover, cavitation will increase head loss, reduce efficiency and flow rate. Summary of the Invention

[0005] In order to overcome the problems of gate vibration, cavitation erosion and flow reduction caused by the operation of the existing gate well, the present invention provides a water transfer tunnel negative pressure balance system.

[0006] The following technical solution is provided: a water tunnel negative pressure balancing system, installed above the water tunnel, including a gate shaft, a gate and a ventilation system, the gate is installed in the gate shaft, the ventilation system is arranged in the downstream lining of the gate and is connected to the water tunnel end to end, the ventilation system balances the air pressure in the negative pressure area formed by the flow of water in the contraction section of the tunnel, the water tunnel includes a gradually contracting section and a gradually expanding section connected to the gradually contracting section, the gate is arranged in the gradually contracting section of the water tunnel, the ventilation system includes a ventilation steel pipe, the ventilation system is arranged along the water flow direction, the downstream end and the upstream end of the ventilation steel pipe are the air inlet and the air outlet respectively, and the air inlet of the ventilation steel pipe is connected to the gas collection mechanism.

[0007] In the above scheme, the ventilation steel pipe is a Tesla valve, which is provided with a forward flow channel and a plurality of resistance flow channels arranged in sequence along the forward flow channel. The first end of the forward flow channel is connected to the air inlet, and the second end of the forward flow channel is connected to the air outlet. The flow direction of the forward flow channel in the Tesla valve is opposite to the flow direction of water.

[0008] In the above scheme, the cross-sectional area of the ventilation steel pipe is

[0009]

[0010] Where S 管——The cross-sectional area of a single ventilation system; ρ——water density; g——acceleration due to gravity; H——the height difference of the water surface before and after the tunnel; Q——water flow rate; S1——the cross-sectional area at point 1-1; S2——the cross-sectional area at point 2-2; R——the proportional constant; T——temperature; N——the number of ventilation systems; L——the length of the ventilation system; V——the volume of the residual space at the top of the tunnel.

[0011] In the above solution, the air outlet of the ventilation steel pipe is connected to the tunnel's tapered section through the longitudinal air passage between the gate and the downstream lining.

[0012] In the above solution, the gas collection mechanism is located at the junction of the gradually contracting section and the gradually expanding section of the water transfer tunnel.

[0013] In the above solution, the gas collection mechanism is an inverted funnel-shaped gas collecting pipe.

[0014] In the above solution, the angle between the inverted funnel-shaped gas collecting pipe wall plate and the horizontal plane is 5-30°, and the two inner angles of the inverted funnel-shaped gas collecting pipe are greater than or equal to 120°.

[0015] In the above solution, multiple ventilation systems are arranged in parallel and equidistantly perpendicular to the water flow direction.

[0016] Compared with the prior art, the present invention has the following advantages: a water tunnel negative pressure balance system of the present invention is provided with a ventilation system connected to the water tunnel at both ends, the ventilation system includes a ventilation steel pipe, the air inlet of the ventilation steel pipe is connected to a gas collection mechanism, after the gate is raised, the flow rate in the water tunnel increases, the water flow rate increases, the pressure in the tunnel decreases, and cavitation is formed. The gas released by the collapse of the cavitation enters the gas collection mechanism at the gradually expanding interface of the tunnel, reducing the pressure impact on the lining and greatly reducing the cavitation erosion of the water tunnel. The ventilation steel pipe is a Tesla valve, which is provided with a forward flow channel and a plurality of resistance flow channels arranged in sequence along the forward flow channel. The first end of the forward flow channel is connected to the air inlet, and the second end of the forward flow channel is connected to the air outlet. The flow direction in the Tesla valve is opposite to the flow direction of the water, which promotes gas to enter the ventilation steel pipe, reduces head loss, and increases flow rate. The gas outlet is a longitudinal air channel between the gate and the downstream lining, which connects to the water tunnel and relieves the negative pressure at the tapering section of the water tunnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic cross-sectional structure diagram of a water conveyance tunnel negative pressure balance system of the present invention;

[0018] Figure 2 It is a schematic diagram of the ventilation system flow;

[0019] Figure 3 1. It is a schematic diagram of the structure of the gas collection mechanism;

[0020] Figure 4This is a schematic diagram of the cross section of the water diversion tunnel.

[0021] Reference numerals: 1. Gate shaft, 2. Gate, 3. Ventilation system, 4. Gas collection device, 5. Downstream lining, 6. Gradual convergence section, 7. Gradual expansion section, 8. Air inlet, 9. Air outlet DETAILED DESCRIPTION

[0022] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0023] Example: See Figure 1 A water tunnel negative pressure balance system is installed above the water tunnel, including a gate shaft 1 and a gate 2. The gate 2 is installed in the gate shaft 1. It also includes a ventilation system 3. The ventilation system 3 is arranged in the downstream lining 5 of the gate 2 and is connected to the water tunnel. The gate 2 is arranged in the tapered section 6 of the water tunnel. The ventilation system 3 is arranged along the water flow direction. Multiple ventilation systems 3 are arranged in parallel in the downstream lining of the gate perpendicular to the water flow direction. The ventilation system 3 includes a ventilation steel pipe. The downstream end and upstream end of the ventilation steel pipe are respectively an air inlet 8 and an air outlet 9. The air inlet is connected to a gas collection mechanism 4.

[0024] See also Figure 2 The ventilation steel pipe is a Tesla valve, which is provided with a forward flow channel and several resistance flow channels arranged in sequence along the forward flow channel. The first end of the forward flow channel is connected to the air inlet, and the second end of the forward flow channel is connected to the air outlet. The flow direction of the forward flow channel in the Tesla valve is opposite to the flow direction of water. The Tesla valve is fixedly connected to the pipe mouth of the inverted funnel-shaped gas collecting pipe away from the funnel.

[0025] See also Figure 3 The angle between the inverted funnel-shaped tube wall and the horizontal plane is 5-30 degrees, the angle ∠1 between the upstream wall and the horizontal direction of the inverted funnel-shaped gas collecting pipe is greater than the angle ∠2 between the downstream wall and the horizontal direction. The inner angle ∠3 of the inverted funnel-shaped tube is greater than or equal to 120 degrees.

[0026] The inner cross-sectional area of the ventilation steel pipe is

[0027]

[0028] Where S 管 ——the cross-sectional area of the pipe of a single ventilation system; ρ——the water density, which is 10 3 kg / m 3 ; g - acceleration due to gravity, about 9.8m / s 2H is the height difference between the water surface before and after the tunnel; Q is the flow rate; S1 is the cross-sectional area at point 1-1; S2 is the cross-sectional area at point 2-2; R is the proportionality constant. For any ideal gas, R is constant, approximately 8.31441 ± 0.00026 J / (mol·K); T is the temperature; N is the number of ventilation systems; L is the length of the ventilation system; V is the volume of the roof margin. This not only increases the aeration rate of high-speed water flow, reducing the risk of cavitation erosion in the expansion section of the water tunnel, but also reduces the wind vibration effect on the gate.

[0029] For ease of understanding, the following is the calculation process of formula (1).

[0030] At the gate, water flows to form a negative pressure area, and gas is transported from the air inlet to the negative pressure area through the Tesla valve.

[0031] 1. Calculation of water flow energy conversion at the time of gate opening, divided into sections: 1-1, 2-2 refer to Figure 4 , select reference plane 2-2, and in the process from section 1-1 to section 2-2, ignore the viscosity loss, the sum of pressure potential energy, kinetic energy and potential energy remains unchanged, and the Bernoulli equation is:

[0032]

[0033] Formula (2) can be combined and transformed to obtain formula (3):

[0034]

[0035] When the flow rate is constant, the flow area is inversely proportional to the water velocity:

[0036] Q=S1×v1=S2×v2 (4)

[0037] In the formula, P1 is the pressure potential energy at 1-1; P2 is the pressure potential energy at 2-2; h1 is the liquid level at 1-1; h2 is the liquid level at 2-2; v1 is the water flow velocity at 1-1; v2 is the water flow velocity at 2-2; H is the height difference of the water surface before and after the tunnel; ΔP is the pressure difference at the two interfaces; ρ is the water density; g is the acceleration due to gravity; Q is the water flow rate; S1 is the cross-sectional area at 1-1; S2 is the cross-sectional area at 2-2.

[0038] 2. Part of the air in the remaining space on the cave roof is mixed with the water, while the rest flows out of the cave directly due to the drag of the water flow. This part of the air that flows out directly needs to be replenished by setting up an air supply hole. It is known that the ideal gas state equation is:

[0039] PV=nRT (5)

[0040] Deformation of the ideal gas state equation:

[0041]

[0042] The changes of gas before and after entering the negative pressure area are as follows:

[0043]

[0044] In the formula, P is pressure; V is gas volume, i.e., the remaining space at the top of the cave; T is temperature; n is the amount of gas; R is the molar gas constant; ΔP is pressure change; Δn is the change in the amount of substance.

[0045] 3. The total air supply volume of the ventilation system is

[0046]

[0047] Where, N is the number of ventilation systems; S 管 ——The cross-sectional area of the pipe of a single ventilation system; L——the length of the ventilation system; 22.4——Under standard conditions, the volume occupied by 1 mole of any ideal gas is approximately 22.4 liters.

[0048] In summary,

[0049] In formula 1, H, Q, T, S1 and S2 are environmental parameters, N, L, S 管 are device parameters, while ρ, g, and R are constants. V is the clearance space at the tunnel top. my country's "Design Code for Hydraulic Tunnels" stipulates that the cross-sectional dimensions of low-velocity, pressureless tunnels should meet the following requirements: Under constant flow conditions and good ventilation conditions, the clear space above the waterline should not be less than 15% of the tunnel's cross-sectional area, and the height should not be less than 0.4 m.

[0050] During the construction process, the cross-sectional area, length and number of the ventilation system of the device can be calculated and adjusted according to the actual environmental parameters H, Q, T, S1 and S2 to adapt to the air demand under different water flow conditions.

[0051] To reduce the gas impact caused by cavitation erosion, a gas collection mechanism needs to be placed where cavitation collapse often occurs. When water flows into the diverging section, the flow rate decreases and the pressure increases, which can cause cavitation collapse. Therefore, the gas collection mechanism is placed at the junction of the diverging and converging sections of the water transfer tunnel.

[0052] The gas collection mechanism is an inverted funnel-shaped gas collecting pipe. The angle between the inverted funnel-shaped pipe wall and the horizontal plane is 5-30 degrees. The two inner angles ∠3 of the inverted funnel-shaped pipe are greater than or equal to 120 degrees. Figure 3 As shown, the left and right panels have different inclination angles, with the left panel having a larger inclination angle than the right panel. This ensures that the inverted funnel-shaped panel has a large contact area with the water flow and has an intercepting effect, causing cavitation to collapse at the gas collection device.

[0053] After the gate is raised, the flow rate in the water transfer tunnel increases, the water flow velocity increases, and the pressure in the tunnel decreases, forming cavitation. The gas released by the cavitation collapses and enters the gas collection mechanism at the gradually expanding interface of the tunnel. The gas enters the Tesla valve along the forward flow channel and flows into the water transfer tunnel from the outlet. The air flow velocity increases and the pressure inside the Tesla valve decreases, which encourages the gas in the tunnel to enter and form an overall air flow cycle. When a water vapor mixture enters the Tesla valve from the ventilation system outlet, the gas in the resistance flow channel hinders and slows down the liquid in the forward flow channel, thereby enhancing the unidirectional flow capability.

[0054] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0055] Although the above embodiments have been shown and described, it is understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. Changes, modifications, substitutions and variations of the above embodiments by those skilled in the art are all within the scope of protection of the present invention.

Claims

1. A negative pressure balance system for a water conveyance tunnel, comprising a gate well and a gate, characterized in that: A ventilation system connected to the water transfer tunnel at both ends is set in the downstream lining of the gate, and the ventilation system balances the air pressure in the negative pressure area formed by the water flow in the contraction section of the tunnel; the ventilation system includes a ventilation steel pipe, and the ventilation system is arranged along the direction of water flow, and the downstream end and upstream end of the ventilation steel pipe are respectively an air inlet and an air outlet, and the air inlet of the ventilation steel pipe is connected to a gas collection mechanism; the ventilation steel pipe is a Tesla valve, and the Tesla valve is provided with a forward flow channel and several resistance flow channels arranged in sequence along the forward flow channel, the first end of the forward flow channel is connected to the air inlet, and the second end of the forward flow channel is communicated with the air outlet, and the flow direction of the forward flow channel in the Tesla valve is opposite to the flow direction of water.

2. A water tunnel negative pressure balance system according to claim 1, characterized in that: The water conveyance tunnel comprises a gradually contracting section and a gradually expanding section communicating with the gradually contracting section, and the gate is arranged in the gradually contracting section of the water conveyance tunnel.

3. A water tunnel negative pressure balance system according to claim 1, characterized in that: The inner cross-sectional area of the ventilation steel pipe is Where S 管 ——The cross-sectional area of a single ventilation system; ρ——water density; g——acceleration due to gravity; H——the height difference of the water surface before and after the tunnel; Q——water flow rate; S1——the cross-sectional area at point 1-1; S2——the cross-sectional area at point 2-2; R——the proportional constant; T——temperature; N——the number of ventilation systems; L——the length of the ventilation system; V——the volume of the residual space at the top of the tunnel.

4. A water tunnel negative pressure balance system according to claim 1, characterized in that: The air outlet of the ventilation steel pipe is connected to the tunnel's tapered section through a longitudinal air passage between the gate and the downstream lining.

5. The negative pressure balance system for a water transfer tunnel according to claim 1, characterized in that: The gas collection mechanism is located at the junction of the gradually contracting section and the gradually expanding section of the water conveyance tunnel.

6. A water transfer tunnel negative pressure balance system according to claim 1 or 5, characterized in that: The gas collecting mechanism is an inverted funnel-shaped gas collecting pipe.

7. A water tunnel negative pressure balance system according to claim 6, characterized in that: The angle between the inverted funnel-shaped gas collecting pipe wall plate and the horizontal plane is 5-30 degrees, and the inner angle of the inverted funnel-shaped gas collecting pipe is greater than or equal to 120 degrees.

8. The negative pressure balance system for a water transfer tunnel according to claim 1, characterized in that: There are multiple ventilation systems, and the multiple ventilation systems are arranged in parallel and equidistantly perpendicular to the water flow direction.

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