Flow field simulation analysis method in starting process of water turbine

Abstract

The invention relates to the technical field of computers and simulation analysis, in particular to a flow field simulation analysis method in the starting process of a water turbine, which comprises the following steps of: performing geometric pretreatment and grid pretreatment on a movable guide vane of the water turbine, and constructing a simulation environment; constructing a basic flow simulation model of the movable guide vane of the water turbine, adding a turbulence equation to model a turbulence phenomenon in the operation process of the water turbine, and inputting the turbulence phenomenon into the simulation environment for flow field simulation; a water turbine and a steady-state solver are initialized, and transient simulation results of flow velocity and pressure in the starting process of the water turbine in the simulation environment are solved in combination with analysis of the starting transition process of the water turbine until calculation convergence is achieved; and post-processing the calculation result, and outputting a visual flow field result. The variable speed transient simulation process of the water turbine starting process can be achieved, and high-precision transient numerical simulation of flow field changes in the water turbine starting process is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of computer and simulation analysis, in particular to a flow field simulation analysis method for starting process of a hydraulic turbine. BACKGROUND

[0002] The pump-turbine is the most core part of pumped storage technology, which mainly undertakes the tasks of peak regulation and frequency regulation in the power system. The unit starts and stops frequently, and the transition process of the working condition of the hydraulic turbine has many influencing factors and is complex, which often causes strong hydraulic unit pressure pulsation, vibration and water hammer and other phenomena, seriously affecting the safe operation of the power station. Ensuring that the hydraulic turbine can start quickly, stably and reliably is one of the important indicators to measure the performance of the hydraulic turbine.

[0003] The research on the change of the internal flow state of the flow part in the starting transition process has gradually become the research frontier and hotspot at home and abroad. The current research on the flow characteristics of the Francis turbine in the transition process mainly focuses on experimental research and numerical simulation. The experimental research has high cost, limited test results, and the test cannot be carried out under extreme working conditions, and it is difficult to provide visual analysis results of the flow field.

[0004] With the rapid development of CFD technology, using numerical simulation to study the internal flow characteristics of the pump-turbine unit is becoming an important research means. Using simulation technology can analyze the internal flow field of the hydraulic turbine in detail, can predict and optimize the performance of the hydraulic turbine in the design stage, improve the efficiency of the hydraulic turbine, and reduce the cost and time of actual manufacturing and testing. Therefore, the present application provides a flow field simulation analysis method for starting process of a hydraulic turbine. SUMMARY

[0005] The purpose of the present application is to provide a flow field simulation analysis method for starting process of a hydraulic turbine, which realizes the variable speed transient simulation process of the starting process of the hydraulic turbine by combining the CFD simulation tool in a self-programming manner, and realizes high-precision transient numerical simulation of the flow field change in the starting process of the hydraulic turbine.

[0006] To achieve the above purpose, the present application provides the following scheme:

[0007] A flow field simulation analysis method for starting process of a hydraulic turbine, comprising:

[0008] Geometric pre-processing and mesh pre-processing are performed on the hydraulic turbine movable guide vane to construct a simulation environment;

[0009] A basic flow simulation model of the hydraulic turbine movable guide vane is constructed, and a turbulence equation is added to model the turbulence phenomenon in the operation process of the hydraulic turbine, and the simulation environment is input to perform flow field simulation;

[0010] initializing the hydraulic turbine and a steady-state solver, combining a hydraulic turbine start-up transient process analysis, solving a transient simulation result of a flow velocity and a pressure in a start-up process of the hydraulic turbine in the simulation environment until a calculation converges;

[0011] post-processing the calculation result and outputting a visualized flow field result.

[0012] Optionally, the hydraulic turbine blade and the guide vane are geometrically pre-processed and mesh pre-processed, and the simulation environment is constructed, including:

[0013] performing mesh division according to a three-dimensional fluid domain geometry of the hydraulic turbine movable guide vane, discretizing a fluid region containing the hydraulic turbine blade geometry and the guide vane geometry to form a mesh as the simulation environment.

[0014] Optionally, the basic flow simulation model is:

[0015] ;

[0016] wherein ρ is a density of the fluid, t is time, u is a velocity vector field of the fluid, ∇ is a gradient operator, ∇· is a divergence operator, p is a pressure field inside the fluid, τ is a viscous stress tensor, g is a gravity acceleration vector, and (u·∇)u is a convection acceleration term.

[0017] Optionally, the turbulent flow equation includes:

[0018] ;

[0019] ;

[0020] wherein ρ is a density of the fluid, t is time, k is turbulent kinetic energy, ∇· is a divergence operator, u is a velocity vector field of the fluid, P k is a turbulent kinetic energy generation term, D k is a turbulent kinetic energy dissipation term, D k diff is a turbulent kinetic energy diffusion term, ω is a specific dissipation rate, P ω is a specific dissipation rate generation term, D ω is a specific dissipation rate dissipation term, D ω diff is a specific dissipation rate diffusion term, and CD is a cross-diffusion term.

[0021] Optionally, the hydraulic turbine start-up transient process analysis includes:

[0022] S1, initializing a flow field simulation, and starting;

[0023] S2, performing a flow field simulation of impeller rotation, and calculating one time step;

[0024] S3, calculating a torque of the impeller by simulation integration.

[0025] S4, calculating the angular acceleration of the impeller at the current time according to Newton's second law of motion and the moment of inertia of the impeller rotating;

[0026] S5, obtaining the rotational speed of the impeller at the next time according to the angular velocity at the current time, the time step and the angular acceleration;

[0027] S6, loading the rotational speed of the impeller to the corresponding grid, and performing flow field calculation through a steady-state solver;

[0028] S7, iteratively performing S3-S6 until the complete start-up process flow field calculation result is obtained.

[0029] Optionally, the criterion for calculating convergence is:

[0030] ;

[0031] Wherein, sigma is the standard deviation of pressure fluctuation, t is time, and T is time interval.

[0032] The beneficial effects of the present application are:

[0033] The present application uses the simulation technology of combining CFD dynamic mesh and UDF self-programming technology to carry out transient numerical simulation research on the movement process of the movable vane of the water turbine under the start-up condition and dynamic process research on the rotational speed change, and can analyze the fluid pressure fluctuation and flow characteristic law in the flow passage of the water turbine, thereby providing a strong theoretical basis for the start-up safety of the water turbine. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0035] Figure 1 A flow chart of the flow field simulation analysis method of the water turbine start-up process according to an embodiment of the present application;

[0036] Figure 2 A flow chart of the water turbine start-up transition process analysis according to an embodiment of the present application. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0038] In order to make the above-mentioned purposes, features and advantages of the present application more apparent and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0039] The embodiment provides a flow field simulation analysis method for a water turbine starting process, as shown in Figure 1 , comprising:

[0040] Geometric preprocessing and mesh preprocessing are performed on the water turbine movable guide vane to construct a simulation environment;

[0041] A basic flow simulation model of the water turbine movable guide vane is constructed, and a turbulence equation is added to model the turbulence phenomenon in the water turbine operation process, and the simulation environment is input to perform flow field simulation;

[0042] The water turbine and a steady-state solver are initialized, combined with water turbine starting transition process analysis, and the transient simulation results of flow velocity and pressure of the water turbine starting process in the simulation environment are solved until the calculation converges;

[0043] The calculation results are post-processed, and the visualized flow field results are output.

[0044] Specifically, the embodiment uses the simulation technology of CFD dynamic mesh and UDF self-programming technology combination to carry out transient numerical simulation research and dynamic process research of the water turbine starting condition movable guide vane movement process, can analyze the fluid pressure pulsation and flow characteristic law in the water turbine flow passage, and provides a strong theoretical basis for the starting safety of the water turbine. Specifically, the following contents are included:

[0045] First, according to the three-dimensional fluid domain geometry of the water turbine movable guide vane, the CFD software PERASIM Fluid is used for mesh division, the fluid region containing the water turbine blade geometry and the guide vane geometry is discretized to form a calculation grid. The grid is used for inputting physical models and calculation parameters for simulation.

[0046] Second, the establishment of the water turbine movable guide vane pulsation simulation basic flow simulation model is performed, and the established model and parameters are input into the discretized grid for subsequent simulation calculation. The equation is as follows:

[0047] (1) ;

[0048] where p is the density of the fluid, t is time, u is the velocity vector field of the fluid, V is the gradient operator, V· is the divergence operator, p is the pressure field inside the fluid, T is the viscous stress tensor, g is the gravity acceleration vector, and (u·V)u is the convection acceleration term.

[0049] Third, the above basic flow simulation model is added with a turbulence equation to model the turbulence phenomenon in the operation process of the hydraulic turbine, which is used for accurate turbulence phenomenon calculation in the simulation. The turbulence equation is as follows:

[0050] Turbulence energy (k) equation:

[0051] (2);

[0052] Specific dissipation rate (ω) equation:

[0053] (3);

[0054] where p is the density of the fluid, t is time, k is the turbulence energy, V· is the divergence operator, u is the velocity vector field of the fluid, P k is the turbulence energy generation term, D k is the turbulence energy dissipation term, D k diff is the turbulence energy diffusion term, ω is the specific dissipation rate, P ω is the specific dissipation rate generation term, D ω is the specific dissipation rate dissipation term, D ω diff is the specific dissipation rate diffusion term, CD is the cross-diffusion term. ∂(p) / ∂t is the non-steady term, and V·(pu) is the convection term.

[0055] Fourth, the definition method of the starting transition process of the hydraulic turbine.

[0056] The initial field of the starting process of the hydraulic turbine is defined according to the amount of water received by the hydraulic turbine. The rotational speed of the formal starting process of the hydraulic turbine is related to the torque of the actual simulation calculation, and a rotational speed judgment method is constructed by using self-programming in the simulation process for the calculation of the whole starting variable speed process.

[0057] Combined with the sliding mesh in the simulation software, the impeller motion law of the runner rotational speed starting change process is given by user-defined code. As Figure 2 shown, including:

[0058] S1, initialize the simulation flow field and start;

[0059] S2, perform flow field simulation of impeller rotation and calculate one time step;

[0060] S3, calculate the torque of the impeller by simulation integration;

[0061] S4, calculating the angular acceleration of the impeller at the current time according to Newton's second law of motion and the moment of inertia of the impeller rotating;

[0062] S5, obtaining the impeller speed at the next time according to the angular velocity at the current time, the time step and the angular acceleration;

[0063] S6, loading the impeller speed onto the corresponding grid, and performing flow field calculation through a steady-state solver;

[0064] S7, iteratively performing S3-S6 until the flow field calculation results of the complete starting process are obtained.

[0065] The specific process is as follows:

[0066] ① initialization of simulation flow field data;

[0067] ② fluid simulation calculation of impeller rotation for a time step Δt1;

[0068] ③ calculating the torque M of the impeller (the torque includes M1 generated by water power and M2 applied on the shaft) through simulation integration;

[0069] ④ calculating the angular acceleration of the impeller at the current time according to Newton's second law of motion and the moment of inertia of the impeller rotating : wherein J represents the moment of inertia of the impeller;

[0070] ⑤ obtaining the impeller speed at the next time Δt+1 according to the angular velocity at the current time, the time step and the angular acceleration ; ω represents the angular velocity of the impeller at the current time, ω+1 represents the speed of the impeller at the next time;

[0071] ⑥ the above process is written in C language, and then compiled to form a dll library file, which is loaded into the solver;

[0072] ⑦ loading the impeller speed onto the grid of the corresponding calculation region, which is used for subsequent solver flow field calculation.

[0073] By dynamically loading this code into the impeller area, the full closed-loop coupling transient simulation of "flow field calculation → torque integration → speed update → grid motion" is realized. This method first realizes the simulation of the real physical starting process of the hydraulic turbine from static (ω=0) to rated speed in CFD simulation, breaking through the limitations of traditional fixed speed simulation.

[0074] Fifth, solving iterative calculation.

[0075] In the PERASIM Fluid software solver, the three-dimensional simulation transient solution of the grid is obtained by using the coupling mode of COUPLE according to the above simulation settings, and the transient simulation results of the flow velocity and pressure of the hydraulic turbine are obtained. During the calculation process, the residual monitoring and the numerical value of the custom monitoring point are checked to determine the convergence condition. Then the time step is adjusted until the calculation converges. The pressure monitoring points are set at the tail edge of the guide vane and the inlet of the runner, and the iterative calculation is performed until the pressure fluctuation reaches the statistical steady state.

[0076] Statistical convergence criterion:

[0077] (4) ;

[0078] Wherein, σ is the standard deviation of pressure fluctuation, and ΔT is the time interval, ΔT = 0.1s.

[0079] Sixth, the calculation result post-processing, obtains the simulation result.

[0080] The post-processing can realize the extraction and display of point, line and surface data, has multiple flow field result visualization functions such as streamline diagram, vector diagram and curve diagram, and provides user-defined field variable calculation, result dynamic preview, animation production and other functions. In the Perasim Fluid software, the flow field change and pressure field data in the motion process of the hydraulic turbine working condition are extracted, the cross section and surface cloud diagram are used for visualizing the flow velocity and pressure data.

[0081] This embodiment dynamically loads the code to the impeller area, realizes the full closed loop coupling transient simulation of “flow field calculation → torque integration → speed update → grid motion”, realizes the real physical starting process simulation of the hydraulic turbine from static (ω = 0) to rated speed for the first time in the CFD simulation, and breaks through the limitation of the traditional fixed speed simulation. The change of the runner speed under the action of the hydraulic torque in the starting process of the hydraulic turbine is accurately simulated, and the dynamic characteristics of the starting process of the hydraulic turbine are reasonably predicted. Based on the dynamic grid technology and UDF, the movement of the movable guide vane and the real-time passive update of the speed are realized.

[0082] The above-described embodiments are only descriptions of the preferred modes of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements of the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A method for flow field simulation analysis of a hydraulic turbine starting process, characterized in that, The method comprises the following steps: carrying out geometric preprocessing and mesh preprocessing on the guide vane of the water turbine, and constructing a simulation environment; constructing a basic flow simulation model of the guide vane of the water turbine, adding a turbulence equation to model turbulence phenomena in the operation process of the water turbine, and inputting the simulation environment to perform flow field simulation; initializing the water turbine and a steady-state solver, combining a water turbine start-up transition process analysis, solving the transient simulation results of flow velocity and pressure of the water turbine start-up process in the simulation environment until the calculation converges; and post-processing the calculation results and outputting visualized flow field results.

2. The method of flow field simulation analysis of a hydraulic turbine starting process according to claim 1, characterized in that, The method comprises the following steps: carrying out geometric preprocessing and mesh preprocessing on the guide vane of the water turbine, and constructing a simulation environment; 3. The method of flow field simulation analysis of hydraulic turbine starting process according to claim 1, characterized in that, carrying out mesh division according to the three-dimensional fluid domain geometry of the guide vane of the water turbine, discretizing the fluid region containing the blade geometry and the guide vane geometry of the water turbine to form a mesh, and taking the mesh as the simulation environment. ； The basic flow simulation model comprises:

4. The method of flow field simulation analysis of hydraulic turbine starting process according to claim 1, characterized in that, wherein, ρ is the density of the fluid, t is time, u is the velocity vector field of the fluid, ∇ is the gradient operator, ∇· is the divergence operator, p is the pressure field inside the fluid, τ is the viscous stress tensor, g is the gravity acceleration vector, and (u·∇)u is the convection acceleration term. ； ； where p is the density of the fluid, t is time, k is the turbulent kinetic energy, V. is the divergence operator, u is the velocity vector field of the fluid, P k is the turbulent kinetic energy production term, D k is the turbulent kinetic energy dissipation term, D k diff is the turbulent kinetic energy diffusion term, w is the specific dissipation rate, P ω is the specific dissipation rate production term, D ω is the specific dissipation rate dissipation term, D ω diff is the specific dissipation rate diffusion term, CD is the cross-diffusion term.

5. The method for flow field simulation analysis of water turbine starting process according to claim 1, characterized in that, The turbulence equation comprises: The water turbine start-up transition process analysis comprises: S1, initializing the simulation flow field and starting; S2, performing flow field simulation of impeller rotation and calculating one time step; S3, calculating the torque of the impeller through simulation integration; S4, calculating the angular acceleration of the impeller at the current time according to Newton's second law of motion and the moment of inertia of the impeller; S5, obtaining the impeller speed at the next time according to the angular velocity at the current time, the time step and the angular acceleration; S6, loading the impeller speed onto the corresponding mesh and performing flow field calculation through the steady-state solver; 6. The method for flow field simulation analysis of water turbine starting process according to claim 1, characterized in that, S7, iteratively performing S3-S6 until the flow field calculation results of the complete start-up process are obtained. ； The criterion for calculation convergence comprises: wherein, σ is the standard deviation of pressure fluctuation, t is time, and T is the time interval.

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