Finite element analysis method for movable guide vanes

Abstract

This invention relates to the field of hydro-generator technology and discloses a finite element analysis method for movable guide vanes. The method includes: 1. establishing an analysis solid model containing three movable guide vanes; 2. setting nonlinear contact at the contact points of the three movable guide vanes; 3. setting an association between two separate movable guide vanes; 4. setting boundary conditions; 5. obtaining the required data after calculation. This method restores the true stress state of the guide vanes and solves the problem of large deviations in calculation results from traditional single guide vane models.

Description

Technical Field

[0001] This invention relates to the field of hydro-generator technology, and more specifically to a finite element analysis method for movable guide vanes. Background Technology

[0002] A water turbine is a device that converts water energy into mechanical energy. It uses water flow to drive an impeller to rotate, generating rotational mechanical energy. Movable guide vanes are an important component of a water turbine, evenly arranged around the impeller. By adjusting the water flow's entry angle and cross-sectional size, the guide vanes control the water flow velocity, pressure, and flow rate, ensuring the turbine operates at its optimal state under varying loads.

[0003] Chinese patent document CN103530475B discloses a novel method for optimizing the vertical clearance of movable guide vanes in a hydraulic turbine based on finite element analysis. The method includes: establishing a three-dimensional model containing two complete movable guide vanes using commercial software; meshing the model using 20-node hexahedral elements (SOLID95); defining the guide vane material's elastic modulus as 2.068e5 MPa and Poisson's ratio as 0.3; establishing contact elements at the sealing points of the guide vane's head and tail; applying degree-of-freedom coupling constraints at corresponding positions at the heads of the two guide vanes, and similarly applying degree-of-freedom coupling constraints at corresponding positions at the tails of the two guide vanes; and using a control loop... Structural parameters such as the relay, guide vane connecting rod, and guide vane arm were used to calculate the torsional moment acting on the upper end of the guide vane. This moment was then applied to the finite element model by establishing a rigid surface. Radial constraints were applied at the pivot, axial constraints were applied at the lower end of the guide vane, and water pressure loads were applied to the surface of the guide vane flap. Commercial finite element software was used for solving the problem. The gap between the head and tail sealing lines of the guide vane was derived based on the geometry and arrangement of the movable guide vane. The gap distribution curve of the guide vane facade was calculated based on the finite element results. Based on the calculated gap distribution curve, the tail sealing part of the movable guide vane was non-uniformly modified.

[0004] The existing technology has the following shortcomings: when the movable guide vane is fully closed, the pressure difference between the two sides of the guide vane is the greatest, and the rigidity problem is most likely to occur. Therefore, when reviewing the design of the movable guide vane, finite element static analysis is usually performed on the movable guide vane when it is fully closed. The existing analysis method ignores the interaction between adjacent guide vanes and cannot accurately analyze the stress state and deformation of the movable guide vane under the continuous action of the closing torque. Summary of the Invention

[0005] To address the technical problem of accurately analyzing the stress state and deformation of movable guide vanes under continuous closing torque, this invention provides a finite element analysis method for movable guide vanes. The method includes: 1. Establishing an analysis solid model containing three movable guide vanes; 2. Setting nonlinear contact at the contact points of the three movable guide vanes; 3. Setting association between two separate movable guide vanes; 4. Setting boundary conditions; 5. Obtaining the required data after calculation.

[0006] In step 1, a model of three adjacent active guide vanes is established when the active guide vanes are in the fully closed state, and the corresponding material properties are set.

[0007] In step 2, nonlinear contact is set at the points where the three movable guide vanes come into contact with each other to simulate the phenomenon of mutual compression of the guide vanes under force when they are in the fully closed state.

[0008] In step 3, the two guide vanes that are separated from each other of the three movable guide vanes are associated. Based on the characteristic that the movable guide vanes are periodically symmetrically distributed, equation constraints are set between the two separated movable guide vanes and the middle guide vane.

[0009] The present invention has the following beneficial effects: 1. Compared with existing single-blade analysis methods, this invention imposes constraints on the bearing installation positions of the three movable guide vanes and applies corresponding water pressure to the wetted surfaces of the movable guide vanes. Existing guide vane analysis methods require constraints on the guide vane shaft to prevent rotation, while the three-blade analysis method eliminates this constraint because the guide vanes do not rotate due to the squeezing effect between them. Furthermore, the three-blade analysis method can apply a closing torque to the guide vane shaft as needed to calculate the stress state and deformation of the guide vanes under the closing torque. In contrast, the single-blade analysis method constrains the rotational degree of freedom of the guide vanes, and the applied closing torque cannot be transmitted to the entire guide vane, thus making it impossible to calculate the stress state and deformation of the guide vanes under the closing torque. This invention significantly improves calculation accuracy, closely aligns with engineering practice, and fully considers the mutual squeezing and local separation interactions between adjacent guide vanes in the fully closed state through a three-blade model and nonlinear contact settings, restoring the true stress state of the guide vanes and solving the problem of large deviations in calculation results from traditional single-blade models.

[0010] 2. High functional integration and strong engineering applicability: It can simultaneously complete the verification of guide vane rigidity and the accurate assessment of leakage area in the fully closed state, and directly extract contact gap data to guide the modification of guide vane sealing line without additional modeling and calculation, which greatly improves the efficiency of design optimization. Attached Figure Description

[0011] Figure 1 This is a flowchart of the finite element analysis method for the movable guide vane of the present invention; Figure 2This is a schematic diagram of the guide vane for the finite element analysis method of the movable guide vane of the present invention; Figure 3 This is a schematic diagram of the calculation results. Detailed Implementation

[0012] The following detailed description illustrates the specific implementation method: The reference numerals in the accompanying drawings include: guide vane 1, guide vane 2, guide vane 3, nonlinear contact area, and setting equation constraints.

[0013] Example 1 like Figure 1-3 As shown, this invention provides a finite element static analysis method for a movable guide vane when it is fully closed, based on the general-purpose ANSYS finite element analysis software. The method includes: Step 1, establishing a model of three adjacent movable guide vanes when the movable guide vane is fully closed, namely guide vane 1, guide vane 2, and guide vane 3. Step 2: Set nonlinear contact 4 at the points where the three movable guide vanes contact each other to simulate the phenomenon of mutual squeezing of the guide vanes under force when they are fully closed. Step 3: Assign relationships between the two separated guide vanes of the three movable guide vanes. Based on the periodic symmetrical distribution of the movable guide vanes, set equation constraints 5 between the two separated movable guide vanes and the middle guide vane. Set equation constraints for the head sealing lines of guide vane 1 and guide vane 2, forcing them to always be on the same distribution circle. Design equation constraints for the tail sealing lines of guide vane 3 and guide vane 2, forcing them to always be on the same distribution circle. Step 4: Set boundary conditions: Apply corresponding water pressure to the wetted surfaces of the three movable guide vanes; apply compression-only support constraints to the bearing mounting positions of the three movable guide vanes; apply a closing torque to the upper ends of the guide vane shafts of the three movable guide vanes; and apply axial constraints to the upper end faces of the guide vane shafts of the three movable guide vanes. Unlike the traditional single-guide vane analysis method, the three-guide vane analysis method, due to the equation constraints between the guide vanes and the interlocking effect of mutual compression, does not require applying axial rotational constraints to the guide vane shafts and can apply a closing torque to the guide vane shafts.

[0014] Similar to the traditional single-blade analysis method, constraints are applied to the bearing mounting positions of the three movable guide vanes; corresponding water pressure is applied to the wetted surfaces of the movable guide vanes. The traditional single-blade analysis method requires constraint on the axial rotation of the guide vanes to prevent rotation, while the three-blade analysis method, due to the squeezing effect between the guide vanes, prevents rotation and therefore eliminates the need for this constraint. Furthermore, the three-blade analysis method can apply a closing torque to the guide vane shaft and calculate the stress state and deformation of the guide vanes under this closing torque. In contrast, the single-blade analysis method, because it constrains the rotational freedom of the guide vanes, cannot transmit the applied closing torque to the entire guide vane, thus making it impossible to calculate the stress state and deformation of the guide vanes under the closing torque. Step 5: After the calculation is completed, obtain the required data and extract the stress and deformation results of guide vane 2 as the calculation results of all guide vanes. Since the head of guide vane 1 and the tail of guide vane 3 lack the squeezing effect of nonlinear contact simulation, at least 3 guide vanes are used for calculation. Extract the contact gap distribution of nonlinear contact between guide vane 1 and guide vane 2 to evaluate the leakage area of ​​the guide vane and the modification of the guide vane sealing line.

[0015] Combined with appendix Figure 3 As can be seen, the left side is the stress cloud diagram, the middle side is the deformation cloud diagram, and the right side is the gap cloud diagram. From the stress and deformation diagrams of the guide vane, it can be seen that due to the mutual compression and support effect, the guide vane blades exhibit an overall state of bending under load, without the large torsional deformation phenomenon observed in the single guide vane analysis. The gap cloud diagram shows that after the guide vane deforms under load, the closure of the sealing line exhibits a state where the gap is larger in the middle and smaller at both ends.

[0016] By adopting the above technical solution and using the analysis method described in this invention, the mutual squeezing effect between the guide vanes in the closed state is considered, and a corresponding closing torque is applied. The calculation results obtained are more consistent with engineering practice than those of traditional analysis methods. At the same time, the contact gap between the guide vanes can be directly extracted to evaluate the leakage area when the active guide vane is closed, and to guide the modification process of the guide vane sealing line.

[0017] The above descriptions are merely embodiments of the present invention. Commonly known structures and characteristics of the solutions are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, under the guidance of this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A finite element analysis method for movable guide vanes, characterized in that: The method includes:

1. Establishing an analytical solid model containing three movable guide vanes; 2. Setting nonlinear contact at the contact points of the three movable guide vanes; 3. Setting an association between two separate movable guide vanes; 4. Setting boundary conditions; 5. Obtaining the required data after calculation.

2. The finite element analysis method for the movable guide vane according to claim 1, characterized in that: In step 1, a model of three adjacent active guide vanes is established when the active guide vanes are in the fully closed state.

3. The finite element analysis method for the movable guide vane according to claim 2, characterized in that: In step 2, nonlinear contact is set at the points where the three movable guide vanes contact each other to simulate the phenomenon of mutual compression of the guide vanes under force when they are in the fully closed state.

4. The finite element analysis method for the movable guide vane according to claim 3, characterized in that: In step 3, the two guide vanes that are separated from each other of the three movable guide vanes are associated. Based on the characteristic that the movable guide vanes are periodically symmetrically distributed, equation constraints are set between the two separated movable guide vanes and the middle guide vane.

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