CN102364476B - Method for inhibiting back cavitation of blade of mixed-flow water turbine - Google Patents

Abstract

The invention relates to a method for inhibiting back cavitation of a blade of a mixed-flow water turbine. Pressure distribution analysis is carried out for calculation results, the location of the point with the lowest pressure on the back face of the blade can be obtained, that is, the point most prone to cavitation can be obtained, a small hole with the diameter being 0.003D1 is drilled at the point with the lowest pressure on the back face of the blade, the front face and the back face of the blade are connected, and high-pressure water flow on the front face can be compensated into the low-pressure center of the back face due to pressure difference between the front face and the back face, so that the pressure on the back face cannot reach the environmental vapor pressure, and thus the cavitation can be undermined. By adopting the method, when the mixed-flow water turbine operates under all normal conditions in a power station, no cavitation can easily occur to the blades of the water turbine, and the safe and stable operation of the water turbine can be ensured.

Description

The method that suppresses back cavitation of blade of mixed-flow water turbine

Technical field:

The present invention relates to a kind of method that suppresses back cavitation of blade of mixed-flow water turbine.

Background technology:

Cavitation is a kind of liquid phenomenon, when fluid temperature one timing, while reducing pressure to a certain emergent pressure, the air that liquid can vaporize or be dissolved in liquid is grown the formation hole, this phenomenon is called cavitation, and it has comprised that nascent, the growing in hole is to the whole process crumbled and fall.Cavitation processes can occur in liquid internal, also can occur on solid boundaries.When the cavity on occurring in solid boundaries is crumbled and fall, from the center of crumbling and fall, will give off the percussive pressure Reeb, and when the percussive pressure Reeb of this high frequency acts on solid boundary, will form and destroy solid boundary, this have just formed cavitation corrosion.

The position that cavitation in the hydraulic turbine and cavitation corrosion phenomenon occur by cavitation and cavitation corrosion traditionally defines, and usually can be divided into following four kinds of fundamental types:

(1) aerofoil profile cavitation and cavitation corrosion.When liquid streams aerofoil profile, the pressure at the aerofoil profile back side is often negative pressure, when the pressure decreased of the low-pressure area at the back side is following to the environment pressure for vaporization, will cause the appearance in cavitation district.The most serious cavitation corrosion district upwards downstream expansion will appear in the end in this cavitation district.

(2) clearance cavitation and cavitation corrosion.Clearance cavitation and cavitation corrosion are to cause that when current in-situ velocity raises during by catwalk or gap, a kind of cavitation and cavitation corrosion form that pressure drop occurs to a certain extent the time.

(3) local cavitation and cavitation corrosion.Local cavitation and cavitation corrosion form the variation suddenly of the caused partial fluidizations such as surface irregularity, sand holes, pore and cause mainly due to casting and manufacturing deficiency.

(4) cavity cavitation.The cavity cavitation is the peculiar a kind of whirlpool cavitation of reaction type wheel.Because there is certain circumferential speed component in reaction type wheel outlet of rotary wheel current when off-design behaviour moves, under the effect of this circumferential speed component, after runner, produce in the band of Dai， whirlpool, whirlpool and be formed centrally very large negative pressure.

The cavitation corrosion in francis turbine runner district is mainly the aerofoil profile cavitation corrosion, for Francis turbine energy safe and stable operation under the operating mode that cavitation occurs, just must stop the generation of cavitation.Usually have three class methods to prevent cavitation:

One. change the aerofoil profile of blade, make back side low-pressure area pressure not reach the environment pressure for vaporization, thereby cavitation does not occur;

Two. by spindle hole or install the mode of making-up air device toward tonifying Qi in Francis turbine additional, by the tonifying Qi pressed gas, destroy the low-pressure area in runner, make the low-pressure area internal pressure not reach the environment pressure for vaporization, thereby cavitation does not occur;

Three. strengthen the draught-height (Francis turbine downstream tailwater level, to the height of stator center line, is generally negative value) of Francis turbine, the runner internal pressure is increased, vacuum side of blade low-pressure area pressure does not reach the environment pressure for vaporization, thereby cavitation does not occur.

In above method, a pair of existing runner of method can not change its cavitation performance, and method two need to install making-up air device additional, and method three is difficult to realize concerning Built hydropower station.Also do not have at present a kind of method to be issued in the situation that does not change runner service condition or increase tonifying Qi equipment the effect of eliminating cavitation for Built hydropower station.

Summary of the invention:

The present invention is that a kind of pressure of vacuum side of blade that makes does not reach the environment pressure for vaporization, destroy the method for the inhibition back cavitation of blade of mixed-flow water turbine of cavitation formation, technical scheme of the present invention is: a kind of method that suppresses back cavitation of blade of mixed-flow water turbine is characterized in that:

Waterpower is calculated: by using business Computational Fluid Dynamics software, the corresponding operating mode of the hydraulic turbine is carried out to analog computation, computing method are movable guide vane and runner monocycle combined calculation, and calculation process is as follows:

(1) use the business 3D sculpting software to set up full simulation mathematical model to water turbine movable guide vane and runner;

(2) use the business grid to divide software movable guide vane and the runner mathematical model set up are carried out respectively to the grid division, adopt block-structured grid when grid is divided;

(3) pre-treatment of use business Computational Fluid Dynamics software partly imports the grid of ready-portioned movable guide vane and runner, accounting equation, the boundary condition of computational fields are set, software for calculation adopts finite volume method to solve flow equation, obtain solving the flow characteristics in territory, fluid selects incompressible fluid, and its continuity equation is as follows:

$\frac{\∂{\stackrel{\‾}{U}}_j}{\∂x_j}=0$

The equation of momentum is as follows:

$\frac{\∂}{\∂t}\left({p\stackrel{\‾}{U}}_i\right)+\frac{\∂}{{\∂x}_j}\left({p\stackrel{\‾}{U}}_i{\stackrel{\‾}{U}}_j\right)=-\frac{\∂\stackrel{\‾}{P}}{\∂x_i}-\frac{\∂}{\∂x_j}({\stackrel{\‾}{\mathrm{\τ}}}_{\mathrm{ij}}+p\stackrel{\‾}{U_i^{\text{'}}{U}_j^{\text{'}}})$

In formula for average velocity

for mean pressure

ρ is density

for average shear force

T is the time

(4) calculate and solve and restrain, use the solver of computational fluid dynamics software to be solved computational fields, computing time, step-length was 0.005, and the convergence residual value is 0.00005;

(5) result of calculation analysis, use the aftertreatment of computational fluid dynamics software partly to import result of calculation, result of calculation is carried out to the pressure distribution analysis: under the command window of software, use statement min (p) can try to achieve the position, minimal pressure force of vacuum side of blade;

(6) blade boring, the aperture D1 that calculates a diameter 0.003D1 of gained pressure lowest point brill at vacuum side of blade is the nominal diameter of the hydraulic turbine, this aperture is communicated to face of blade.

The present invention makes the pressure of vacuum side of blade not reach the environment pressure for vaporization, has simple characteristics.This method is by using computational fluid dynamics software to carry out analog computation (calculation process as shown in Figure 1) to the corresponding operating mode of the hydraulic turbine, after calculating completes, use the post-processing function of this software to carry out the pressure distribution analysis to result of calculation, can draw vacuum side of blade pressure lowest point, the cavitation place namely the most easily occurs, in the aperture 12(of a diameter 0.003D1 of vacuum side of blade pressure lowest point brill is shown in Fig. 6), D1 is the nominal diameter of the hydraulic turbine, connect the positive back side of blade, utilize the pressure differential at the positive back side, positive water under high pressure fails to be convened for lack of a quorum and adds to the low-pressure centre at the back side, make the pressure at the back side not reach the environment pressure for vaporization, so just destroyed the formation of cavitation.After using the method, Francis turbine is in power station during whole nominal situations operation, and the cavitation corrosion phenomenon does not occur turbine blade, has guaranteed that the hydraulic turbine safely and steadily runs.

The present invention carries out the model test checking: the model runner of blade having been beaten to hole carries out model test, and the operating mode that cavitation occurs at the former back side is carried out the imaging observation verification the verifying results.As shown in Figure 2, the Taper Pipe of model turbine is transparent organic glass Taper Pipe, can observe the back side of model runner blade outlet from outside, during observation, use stroboscope can see that whether the model runner vacuum side of blade outlet edge place in rotation produces cavitation bubble, can judge whether to produce cavitation thus.

The accompanying drawing explanation

Fig. 1 is calculation flow chart of the present invention

Fig. 2 is the water turbine equipment schematic diagram

Fig. 3 is the Francis turbine schematic diagram

The vertical view that Fig. 4 is turbine blade

The pressure-plotting that Fig. 5 is the vacuum side of blade that calculates by software

Fig. 6 is that cavitation zone centre drill aperture position figure occurs at the Francis Turbine Blades back side

Embodiment:

As shown in Figure 3, hydraulic turbine crown 4, turbine blade 5, encircle 6 under the hydraulic turbine, turbine blade water inlet limit 7, turbine blade outlet edge 8, Fig. 4 is the vertical view of turbine blade, turbine blade water inlet limit 7, the workplace 9 of turbine blade, the back side 10 of turbine blade, the outlet edge 8 of turbine blade.In the Francis turbine operational process, current enter the hydraulic turbine from the water inlet limit shown in Fig. 3, the turbine blade district that flows through, and, to the positive acting of turbine blade, finally from outlet edge, flow out.Because current do work to face of blade, so the water flow pressure of face of blade is higher, Fig. 5 is the pressure-plotting of the vacuum side of blade that calculates by computational fluid dynamics software, as can be seen from the figure, reason due to aerofoil profile, the pressure of vacuum side of blade is lower, and part also can the mineralization pressure lowest region, even forms cavitation.

By using software to carry out analog computation to the corresponding operating mode of the hydraulic turbine.After calculating completes, use the post-processing function of this software to carry out the pressure distribution analysis to result of calculation, can draw vacuum side of blade pressure lowest point 11, the cavitation place namely the most easily occurs.Hole on the model turbine blade, then carry out model test and verified, by the imaging observation system, vacuum side of blade is observed, the effect of checking the method.After the model test checking, the method being applied to prototype produces.

Concrete steps are as follows:

As shown in the figure 1, waterpower is calculated; By using business Computational Fluid Dynamics software to carry out analog computation to the corresponding operating mode of the hydraulic turbine, computing method are movable guide vane and runner monocycle combined calculation, and calculation process is as follows:

(1) as shown in Figure 2, use the business 3D sculpting software to set up full simulation mathematical model to water turbine movable guide vane 1 and runner 2;

(2) use the business grid to divide software movable guide vane and the runner mathematical model set up are carried out respectively to the grid division, adopt block-structured grid when grid is divided;

(3) pre-treatment of use business Computational Fluid Dynamics software partly imports the grid of ready-portioned movable guide vane and runner, accounting equation, the boundary condition of computational fields are set, software for calculation adopts finite volume method to solve flow equation, obtain solving the flow characteristics in territory, fluid selects incompressible fluid, and its continuity equation is as follows:

$\frac{\∂{\stackrel{\‾}{U}}_j}{\∂x_j}=0$

The equation of momentum is as follows:

$\frac{\∂}{\∂t}\left({p\stackrel{\‾}{U}}_i\right)+\frac{\∂}{{\∂x}_j}\left({p\stackrel{\‾}{U}}_i{\stackrel{\‾}{U}}_j\right)=-\frac{\∂\stackrel{\‾}{P}}{\∂x_i}-\frac{\∂}{\∂x_j}({\stackrel{\‾}{\mathrm{\τ}}}_{\mathrm{ij}}+p\stackrel{\‾}{U_i^{\text{'}}{U}_j^{\text{'}}})$

In formula

for average velocity

for mean pressure

ρ is density

for average shear force

T is the time

(4) calculate and solve and restrain, use the solver of computational fluid dynamics software to be solved computational fields, computing time, step-length was 0.005, and the convergence residual value is 0.00005;

(5) result of calculation analysis, use the aftertreatment of computational fluid dynamics software partly to import result of calculation, result of calculation is carried out to the pressure distribution analysis, under the command window of software, use statement min (p) can try to achieve the position, minimal pressure force of vacuum side of blade;

(6) blade boring: calculate at vacuum side of blade the aperture 12 that gained pressure lowest point bores a diameter 0.003D1, D1 is the nominal diameter of the hydraulic turbine, and this aperture is communicated to face of blade.

Model test checking of the present invention: the model runner of blade having been beaten to hole carries out model test, and the operating mode that cavitation occurs at the former back side is carried out the imaging observation verification the verifying results.The Taper Pipe of model turbine (in Fig. 2,3 show) is transparent organic glass Taper Pipe, can observe the back side of model runner blade outlet from outside, during observation, use stroboscope can see that whether the model runner vacuum side of blade outlet edge place in rotation produces cavitation bubble, can judge whether to produce cavitation thus.

Four, apply to prototype.After the model test checking, in the boring of prototype blade same position place, and drop into the prototype operation.

When using above-mentioned two equation solution VISCOUS FLOW, due to the existence of eddy stress item, need to supplement suitable Turbulent Model and could form the Closure equation group, the Turbulent Model of employing is standard k-ε model.When carrying out the Computational Fluid Dynamic Analysis of runner, for the condition for import that guarantees runner is more realistic, flow, adopt the method for the combined calculation of runner and stator to carry out.During calculating, to flow be permanent in supposition, and wherein rotary part steady relative, fixed part are definitely permanent, homogenizing processing while will the face of being association of activity and inertia when sound connects carrying out.Condition for import is given as mass rate, and exit condition is static pressure.

Claims (1)

1. a method that suppresses back cavitation of blade of mixed-flow water turbine is characterized in that:

Waterpower is calculated: by using business Computational Fluid Dynamics software, the corresponding operating mode of the hydraulic turbine is carried out to analog computation, computing method are movable guide vane and runner monocycle combined calculation, and calculation process is as follows:

(1) use the business 3D sculpting software to set up full simulation mathematical model to water turbine movable guide vane and runner;

(2) use the business grid to divide software movable guide vane and the runner mathematical model set up are carried out respectively to the grid division, adopt block-structured grid when grid is divided;

(3) pre-treatment of use business Computational Fluid Dynamics software partly imports the grid of ready-portioned movable guide vane and runner, accounting equation, the boundary condition of computational fields are set, described business Computational Fluid Dynamics software adopts finite volume method to solve flow equation, obtain solving the flow characteristics in territory, fluid selects incompressible fluid, and its continuity equation is as follows:

$\frac{\∂{\stackrel{\‾}{U}}_j}{\∂x_j}=0$

The equation of momentum is as follows:

$\frac{\∂}{\∂t}\left({p\stackrel{\‾}{U}}_i\right)+\frac{\∂}{{\∂x}_j}\left({p\stackrel{\‾}{U}}_i{\stackrel{\‾}{U}}_j\right)=-\frac{\∂\stackrel{\‾}{P}}{\∂x_i}-\frac{\∂}{\∂x_j}({\stackrel{\‾}{\mathrm{\τ}}}_{\mathrm{ij}}+p\stackrel{\‾}{U_i^{\text{'}}{U}_j^{\text{'}}})$

In formula,

for average velocity,

for mean pressure,

ρ is density,

for average shear force,

T is the time;

(4) calculate and solve and restrain, use the solver of computational fluid dynamics software to be solved computational fields, computing time, step-length was 0.005, and the convergence residual value is 0.00005;

(5) result of calculation analysis, use the aftertreatment of computational fluid dynamics software partly to import result of calculation, result of calculation is carried out to the pressure distribution analysis: under the command window of software, use statement min (p) can try to achieve the position, minimal pressure force of vacuum side of blade;

(6) blade boring, calculate at vacuum side of blade the aperture that gained pressure lowest point bores a diameter 0.003D1, and D1 is the nominal diameter of the hydraulic turbine, and this aperture is communicated to face of blade.

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