Numerical simulation method of supercritical carbon dioxide jet impact process and its safety evaluation

Abstract

A numerical simulation method for supercritical carbon dioxide jet impact process and its safety assessment is proposed, comprising the following steps: 1. Designing a computational domain geometric model for the supercritical carbon dioxide jet impact process, simplifying the modeling of the high-pressure storage tank, short pipe orifice or nozzle, and downstream jet impact region; 2. Meshing the computational domain geometric model; 3. Using the Fluent platform and a pressure-based solver, selecting SST. k‑oh The method employs the following steps: 1. A turbulence model is used to dynamically invoke the actual properties of carbon dioxide through user-defined functions; 2. A homogeneous delay model is introduced to simulate rapid phase transition behavior, using user-defined memory to distinguish the phase state of carbon dioxide; 3. Boundary conditions are set, the initial field is defined, and the sub-relaxation factor and adaptive time step are adjusted; 4. Key monitoring parameters are set to complete the numerical simulation. This invention provides a reliable numerical simulation and evaluation method for the pressure relief safety analysis and engineering design of supercritical carbon dioxide systems.

Description

Technical Field

[0001] This invention relates to the fields of energy and power engineering and nuclear reactor safety analysis technology, specifically to a numerical simulation method for supercritical carbon dioxide jet impact process and its safety assessment. Background Technology

[0002] Supercritical carbon dioxide is widely used in advanced nuclear energy systems, supercritical Brayton cycles, and high-efficiency heat exchangers due to its lack of phase change, excellent thermophysical properties, stable chemical properties, and low cost. However, under long-term high-pressure operation, material corrosion, mechanical damage, structural defects, or operational errors can lead to leaks in containers, pipes, or valves, causing system depressurization accidents. When supercritical carbon dioxide leaks, it forms a high-speed jet, generating transonic flow in the near-field of the leak, accompanied by a sharp pressure drop, high-speed expansion flow, and possible non-equilibrium phase transitions. Simultaneously, the high-pressure gas jet can cause thermal shock to surrounding equipment, potentially leading to severe mechanical damage and equipment failure, posing a significant risk to equipment integrity and personnel safety. Furthermore, for supercritical carbon dioxide-cooled fast neutron reactor systems, supercritical carbon dioxide leaks can cause a significant reduction in core flow rate and an increase in overall core temperature. This imbalance between heat and flow rate can lead to excessively high fuel element temperatures or core pressure fluctuations, compromising fuel cladding integrity and thus reactor stability. Existing numerical simulation methods generally have the following shortcomings: 1. Simplification of property treatment: Using the ideal gas law or Peng-Robinson equation to calculate the thermophysical properties of supercritical carbon dioxide cannot reflect the drastic property changes of supercritical carbon dioxide near the quasi-critical region. Although this simplifies the difficulty of convergence in numerical simulation of supercritical carbon dioxide jet process to some extent, it also makes the results of numerical simulation deviate from reality. 2. The phase transition model is unreasonable: the traditional gas-liquid two-phase model is difficult to describe the transphase process from supercritical to subcritical, and the homogeneous equilibrium model (HEM) cannot take into account the differences in thermodynamics between different phases; 3. Insufficient safety assessment research: There is a lack of safety assessment methods for jet structure, impact force, temperature field and hazard zone identification. Most of the current research on carbon dioxide leakage is on pipeline leakage in the context of carbon storage and transportation, and there is no specific research on the impact of carbon dioxide jets on obstacles.

[0003] Therefore, it is necessary to propose a numerical simulation method for supercritical carbon dioxide jets that is oriented towards real-world engineering safety analysis and can be directly embedded into commercial CFD software. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a numerical simulation method for the supercritical carbon dioxide jet impact process and its safety assessment. This method is applicable to simulating the complex flow and heat transfer behavior of supercritical carbon dioxide as it rapidly expands from a supercritical state to a subcritical state and undergoes a phase change during the process of supercritical carbon dioxide being released from a high-pressure container or pipeline through a small hole or nozzle and impacting nearby equipment. This provides a reliable numerical simulation and assessment method for the pressure relief safety analysis and engineering design of supercritical carbon dioxide systems.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A numerical simulation method for supercritical carbon dioxide jet impact process and its safety assessment includes the following steps: Step 1: Establish a computational domain geometric model to describe the supercritical carbon dioxide jet impact process. The computational domain geometric model includes a high-pressure vessel or pipe, a short pipe orifice or nozzle structure region, and a downstream jet impact region. The computational domain geometric model is then reasonably connected and simplified. Step 2: Divide the computational domain geometric model established in Step 1 into a computational grid, and refine the local grid at locations with strong pressure gradients, strong velocity gradients, and strong temperature gradients near the wall of the short pipe or nozzle, near the wall of the impact device, and in the jet outlet region and jet development region, to obtain a computational grid for numerical calculation. Step 3: Establish a transient numerical solution model for the supercritical carbon dioxide jet impact process based on FLUENT, and select SST. k-ω A turbulence model is used, and the dynamic invocation of real physical properties of the entire process from supercritical carbon dioxide to subcritical carbon dioxide is realized through user-defined functions (UDFs). Step 4: Based on Step 3, a homogeneous delayed model is introduced to describe the phase transition behavior of supercritical carbon dioxide during rapid expansion. The phase transition effect is coupled to the user-defined scalar transport equation and energy conservation equation in the form of source terms. User-defined memory (UDM) is used to resolve the phase state of carbon dioxide. Step 5: Set boundary conditions, define the initial field, set the numerical solution method, and adjust the sub-relaxation factor and adaptive time step; Step 6: Monitor the pressure, temperature, density, velocity, and phase content during the jet process, complete the numerical calculation of the supercritical carbon dioxide jet impact process, and conduct a safety assessment of the supercritical carbon dioxide jet impact process.

[0006] Preferably, in step 1, the geometrically simplified model of the high-pressure vessel is designed as a three-dimensional cylindrical or two-dimensional rectangular structure. Its advantages are: it can reduce the difficulties in mesh generation and numerical simulation caused by complex internal components while preserving key physical processes such as pressure wave propagation, fluid expansion and release, and flow characteristics near the outlet within the high-pressure vessel; it reduces computational costs and degrees of freedom, and improves modeling efficiency and computational stability. Simultaneously, this simplification method facilitates parametric studies under different volumes, aspect ratios, and opening locations, thereby improving the adaptability and engineering application value of the method for different supercritical carbon dioxide storage containers or pipeline systems.

[0007] Preferably, in step 1, the outlet geometry of the short pipe orifice or nozzle structure is simplified to a circular or rectangular narrow slit. The advantages are: a circular outlet is beneficial for characterizing the expansion, entrainment, and impact behavior of supercritical carbon dioxide jets under axisymmetric venting conditions, while a rectangular narrow slit outlet is beneficial for characterizing the non-circular jet diffusion characteristics under crack-type and crevice-type leakage conditions; by simplifying the outlet geometry model, typical orifice venting and crack venting scenarios in engineering are covered, and it helps to improve the comparability and generality of results between different rupture types.

[0008] Preferably, in step 1, the geometrically simplified model of the downstream jet impact region is designed as a three-dimensional cylindrical or two-dimensional rectangular structure, and the width of the downstream jet impact region is 200 times the equivalent break diameter. The advantage of this size setting is that it provides sufficient space for the lateral development of the jet in the downstream space, keeps the pressure outlet boundary away from the jet core and the impact zone, and improves the physical rationality of the boundary conditions and the stability of the numerical solution.

[0009] Preferably, in step 2, local mesh refinement is performed near the wall of the short pipe or nozzle, as well as near the wall of the impact device, to ensure that the y+ value is less than 1, satisfying SST. k-ω High-precision calculation of near-wall viscous heating and flow separation in turbulence models.

[0010] Preferably, in step 2, local mesh refinement is performed at locations with strong pressure gradients, strong velocity gradients, and strong temperature gradients in the jet exit region and jet development region to improve the calculation accuracy of the numerical simulation method for Mach disk morphology and shock wave structure phenomena.

[0011] Preferably, in step 3, the solver type is defined as a pressure-based solver, the time type as transient calculation, and since the jet process is very intense, the influence of gravity can be ignored, and gravity is set to 0. .

[0012] Preferably, in step 3, a method for dynamically calling the physical properties of supercritical, gaseous, liquid, and solid carbon dioxide is constructed using a user-defined function (UDF). Specifically, a discretized thermal property database is pre-constructed, which includes parameters such as density, specific heat at constant pressure, dynamic viscosity, thermal conductivity, sound velocity, specific enthalpy, and specific entropy. The temperature interval of the data points in the thermal property database is 1 K, and the pressure interval is 10 kPa. The thermal property data is sourced from an authoritative thermal property database and stored as a two-dimensional or multi-dimensional array. During numerical calculation, bilinear interpolation is used to look up the property data table to obtain the thermal property parameters of carbon dioxide under different temperature and pressure conditions in real time. Finally, the gas-liquid or gas-solid mixture property parameters are calculated based on the phase change determination.

[0013] Preferably, in step 3, to accurately describe the drastically changing thermophysical properties of supercritical carbon dioxide near the quasi-critical region, the quasi-critical temperature at the current pressure is obtained by fitting a polynomial equation of quasi-critical temperature and pressure. It is assumed that when the absolute value of the slope of the isobaric specific heat change with temperature is greater than 0.05, supercritical carbon dioxide is in the quasi-critical region. The temperature interval of the data points in the thermophysical property database for supercritical carbon dioxide in the quasi-critical region is 0.01 K, and the pressure interval is 100 Pa. Its advantages are: it can more precisely capture the rapid nonlinear changes in parameters such as density, isobaric specific heat, dynamic viscosity, thermal conductivity, and sound velocity near the quasi-critical region, avoiding distortion in local flow heat transfer and phase change simulation due to excessive interpolation errors in conventional resolution property tables; simultaneously, this setting helps improve the accuracy of temperature prediction, shock wave structure calculation, and phase state determination during jet expansion, thereby enhancing the numerical model's ability to realistically describe the complex thermal flow behavior of supercritical carbon dioxide.

[0014] Preferably, in step 3, when the temperature or pressure within the local calculation unit exceeds the applicable range of the property data table, the property dynamic calling method automatically switches to the Peng-Robinson equation to ensure the continuity and stability of the numerical calculation. At the same time, after the calculation is completed, the FLUENT Console will pop up a prompt that "the temperature or pressure within the calculation unit is out of range", and the distribution of the out-of-range area can be viewed using UDM.

[0015] Preferably, in step 4, the homogeneous delayed model controls the mass transfer process during phase change through the hysteresis time parameter, while retaining the thermodynamic balance assumption. The homogeneous delayed model can describe the delayed phase change of carbon dioxide during evaporation and condensation, as well as sublimation and deposition.

[0016] Preferably, in step 4, the homogeneous delayed model is activated when the local pressure is below the critical pressure, and is used to describe the subcritical carbon dioxide gas-liquid phase change and gas-solid phase change processes.

[0017] Preferably, in step 4, the homogeneous delay model is coupled to the governing equations in the form of user-defined scalar source terms and energy source terms to describe the influence of phase change on flow and heat transfer characteristics.

[0018] Preferably, in step 4, using UDM to distinguish the phase states of carbon dioxide has the advantage of being able to directly output different regions such as supercritical state, gaseous state, liquid state, solid state, and gas-liquid two-phase or gas-solid two-phase in a visual manner, which facilitates the rapid identification of the phase change initiation position and the distribution of low-temperature dangerous areas.

[0019] Preferably, in step 5, the high-pressure carbon dioxide inlet is set as a pressure inlet, the downstream jet impact area except for the impacted wall is set as a pressure outlet, and the remaining boundaries, including the impacted wall, are set as adiabatic wall boundary conditions. The initial field is set to carbon dioxide gas at 101 kPa and 300 K within the jet impact area. Its advantages are: it can more realistically reflect the typical working condition of rapid release of high-pressure storage system to normal pressure environment, the physical meaning of the boundary conditions is clear, and it is convenient for engineering applications and test conditions to correspond.

[0020] Preferably, in step 5, the numerical solution method uses the Coupled algorithm, and the interpolation method uses the first-order upwind interpolation method to solve the convergence difficulty in the numerical simulation process. The pressure relaxation factor is 0.05, the momentum relaxation factor is 0.05, the density relaxation factor is 0.1, the volume force relaxation factor is 0.1, the turbulent kinetic energy relaxation factor is 0.075, the turbulent diffusivity relaxation factor is 0.075, the turbulent viscosity relaxation factor is 0.1, and the energy relaxation factor is 0.075. Its advantages are: the Coupled algorithm can enhance the coupling strength between the pressure field and the velocity field, and is more suitable for solving the problem of shock waves, strong expansion and violent phase transitions in supercritical high-speed compressible jets of carbon dioxide; although the first-order upwind interpolation method is relatively conservative, it has stronger numerical stability and can effectively suppress oscillations and divergences caused by drastic changes in physical properties and the introduction of phase transition source terms; with a smaller sub-relaxation factor setting, the convergence stability and robustness in the transient solution process can be significantly improved, and it is particularly suitable for the stable calculation of strongly nonlinear problems in the initial discharge stage.

[0021] Preferably, in step 5, during the numerical simulation, the time step is set to an adaptive time step, and the Courant number is set to a fixed value of 0.1. The advantages are: the time step can be automatically adjusted according to the local velocity of the flow field, the grid scale, and the intensity of phase transition, so that the numerical solution can ensure both time resolution and computational efficiency; a fixed, smaller Courant number is beneficial for accurately capturing the pressure drop, temperature change, and shock wave structure in the initial stage of the jet.

[0022] Preferably, in step 6, a comprehensive assessment is conducted on the jet impact intensity, phase change region distribution, dry ice formation risk, and safety of the release process based on numerical calculation results. The advantages are: it not only obtains the basic flow parameters during supercritical carbon dioxide release, but also allows for systematic safety analysis from multiple dimensions, including equipment load risk, low-temperature freezing risk, material embrittlement risk, dry ice sublimation risk, and surrounding facility failure risk; providing a basis for pressure relief device layout, release direction design, safety distance determination, protective structure setup, and accident consequence prediction, thereby enhancing the engineering practicality and safety assessment value of the method of this invention.

[0023] The method is applicable to the release and accident analysis of supercritical carbon dioxide energy storage systems, supercritical carbon dioxide Brayton cycle systems, and supercritical carbon dioxide high-pressure pipelines.

[0024] The beneficial effects of this invention are: 1. This invention uses a homogeneous delayed phase model (HRM) to consider the differences in thermodynamics between different phases and describes the delayed phase transition of carbon dioxide in the processes of evaporation, condensation, sublimation and deposition.

[0025] 2. This invention constructs a carbon dioxide thermophysical property database and uses real properties to calculate the supercritical carbon dioxide jet process, reflecting the drastic property changes of supercritical carbon dioxide near the quasi-critical region, making the numerical simulation results more consistent with reality.

[0026] 3. This invention can be directly deployed on the existing Fluent platform. It can evaluate the jet structure, impact force, temperature field and hazardous area through numerical simulation calculations, and proposes the impact of supercritical carbon dioxide jet impact on the thermal damage of equipment. Attached Figure Description

[0027] Figure 1 This is a flowchart of the numerical simulation method of the present invention.

[0028] Figure 2 This is a simplified model diagram of the supercritical carbon dioxide jet impact process.

[0029] Figure 3 This is a diagram showing the dense grid division of the jet outlet area.

[0030] Figure 4 This is a velocity contour map of a supercritical carbon dioxide jet under long-distance jet conditions.

[0031] Figure 5 This is a velocity contour map of a supercritical carbon dioxide jet under near-jet distance conditions. Detailed Implementation

[0032] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0033] This invention provides a numerical simulation method for supercritical carbon dioxide jet impact process and its safety assessment. Figure 1 As shown, the specific steps include: Step 1: Establish a computational domain geometric model to describe the supercritical carbon dioxide jet impact process. The computational domain geometric model includes a high-pressure vessel or pipeline, a short pipe orifice or nozzle structure region, and a downstream jet impact region. The computational domain geometric model is then reasonably connected and simplified.

[0034] The high-pressure vessel's simplified geometric model is designed as a three-dimensional cylindrical or two-dimensional rectangular structure. The outlet geometry of the short pipe orifice or nozzle is simplified to a circular or rectangular narrow slit. The downstream jet impact region's simplified geometric model is designed as a three-dimensional cylindrical or two-dimensional rectangular structure, with the width of the downstream jet impact region being 200 times the equivalent rupture diameter. The two-dimensional geometric model structure is as follows: Figure 2 As shown, Figure 2 This is a schematic diagram of a two-dimensional geometrically simplified model of the supercritical carbon dioxide jet impact process described in this invention. Figure 2 It is an axially symmetric figure. Figure 2 The left side is the boundary of the axis of symmetry; the Figure 2 The top is a simplified two-dimensional rectangular high-pressure vessel or pipe, with annotations indicating the pressure inlet boundary and the insulating wall boundary; the jet outlet is simplified to a two-dimensional rectangular narrow slit. Figure 2 The equivalent break diameter is 1 mm; Figure 2 The downstream jet impact region is simplified as a two-dimensional rectangle with a horizontal width of 200 mm. The pressure outlet boundary is annotated. The impacted wall is located 100 mm away from the jet outlet along the jet direction. The adiabatic wall boundary is annotated.

[0035] Step 2: Use mesh generation software to generate a computational mesh for the computational domain geometric model established in Step 1. Local mesh refinement is performed near the walls of the short pipe or nozzle, near the walls of the impact device, and in the jet outlet and jet development regions where strong pressure, velocity, and temperature gradients exist, resulting in a computational mesh for numerical calculations. When refining the local mesh near the walls of the short pipe or nozzle and near the walls of the impact device, the y+ value must be at least less than 1 to satisfy the SST (Short-Terminal Stress Test). k-ω High-precision calculations of near-wall viscous heating and flow separation in turbulence models. For example... Figure 3 As shown, local mesh refinement is performed at locations with strong pressure gradients, strong velocity gradients, and strong temperature gradients in the jet exit region and jet development region to improve the calculation accuracy of the numerical simulation method for Mach disk morphology and shock wave structure phenomena.

[0036] Step 3: Import the generated mesh into FLUENT software. Based on FLUENT, establish a transient numerical solution model of the supercritical carbon dioxide jet impact process, define the solver type as pressure-based solver, and select SST. k-ω The turbulence model was compiled and loaded with a real carbon dioxide property UDF. The carbon dioxide property library was successfully read in the Console. A new real carbon dioxide property model was created in Materials—Fluid.

[0037] Step 4: Compile and load the homogeneous delayed carbon dioxide model UDF. In the Console, check that the homogeneous delayed carbon dioxide model UDF has been successfully read. Add two user-defined scalar transport equations. In Cell Zone Condition—Fluid—Zone Name—Source Terms, select the user-defined scalar source term UDF and energy source term UDF respectively, coupling the homogeneous delayed model to the governing equations through these user-defined scalar source terms and energy source terms. Define 10 User-Defined-Memory—Memory Locations to establish sufficient user-defined memory (UDM) to distinguish the phase state of carbon dioxide and determine whether carbon dioxide properties exceed limits.

[0038] Step 5: Set the high-pressure carbon dioxide inlet as the pressure inlet, and the downstream jet impact region (excluding the impacted wall) as the pressure outlet. All other boundaries, including the impacted wall, are set as adiabatic wall boundary conditions. The initial field is set to 101 kPa, 300 K carbon dioxide gas within the jet impact region. The Coupled algorithm is used for numerical solution, and a first-order upwind interpolation method is employed to address convergence difficulties during numerical simulation. The pressure relaxation factor is 0.05, momentum relaxation factor is 0.05, density relaxation factor is 0.1, volume force relaxation factor is 0.1, turbulent kinetic energy relaxation factor is 0.075, turbulent diffusivity relaxation factor is 0.075, turbulent viscosity relaxation factor is 0.1, and energy relaxation factor is 0.075. During the numerical simulation, the time step is set to an adaptive time step, and the Courant number is set to a fixed value of 0.1.

[0039] Step 6: Monitor the pressure, temperature, density, velocity, and phase content during the jet process, complete the numerical calculation of the supercritical carbon dioxide jet impact process, and conduct a safety assessment of the supercritical carbon dioxide jet impact process. For example... Figure 4 As shown, the Figure 4 The image shows the velocity contour plot of a supercritical carbon dioxide jet under long-distance jetting conditions with an inlet pressure of 8.0 MPa and an inlet temperature of 500 K. Due to the high inlet temperature, no gas-liquid phase change or gas-solid phase transition occurs during the jetting process. The supercritical carbon dioxide jet is a transonic flow. Figure 4 The Mach disk structure is clearly visible. The alternating velocity changes in the jet region outside the jet outlet are typical of transonic flow; after passing through the Mach disk, the gas velocity decreases and the temperature increases. For example... Figure 5 As shown, the Figure 5 The image shows the velocity contour of a supercritical carbon dioxide jet under near-jet distance conditions with an inlet pressure of 8.0 MPa and an inlet temperature of 500 K. As the distance between the impacted wall and the jet outlet decreases, the supersonic flow generates a shock wave due to the obstruction of the wall. The flow in front of the shock wave is unaffected by the obstacle, the shape of the Mach disk changes, and its structure becomes more obvious. The impact force on the wall and the wall temperature both increase significantly.

[0040] A comprehensive assessment of jet impact intensity, phase change region distribution, dry ice formation risk, and the safety of the venting process is conducted based on numerical calculation results.

Claims

1. A numerical simulation method for supercritical carbon dioxide jet impact process and its safety assessment, characterized in that, Includes the following steps: Step 1: Establish a computational domain geometric model to describe the supercritical carbon dioxide jet impact process. The computational domain geometric model includes a high-pressure vessel or pipe, a short pipe orifice or nozzle structure region, and a downstream jet impact region. The computational domain geometric model is then structurally connected and simplified. Step 2: Divide the computational domain geometric model established in Step 1 into a computational grid, and refine the local grid at locations with strong pressure gradients, strong velocity gradients, and strong temperature gradients near the wall of the short pipe or nozzle, near the wall of the impact device, and in the jet outlet region and jet development region, to obtain a computational grid for numerical calculation. Step 3: Establish a transient numerical solution model for the supercritical carbon dioxide jet impact process based on FLUENT, and select SST. k-ω A turbulence model is used, and the dynamic invocation of real physical properties of the entire process from supercritical carbon dioxide to subcritical carbon dioxide is realized through user-defined functions (UDFs). Step 4: Based on Step 3, a homogeneous delayed model is introduced to describe the phase transition behavior of supercritical carbon dioxide during rapid expansion. The phase transition effect is coupled to the user-defined scalar transport equation and energy conservation equation in the form of source terms. The user-defined memory UDM is used to distinguish the phase state of carbon dioxide. Step 5: Set boundary conditions, define the initial field, set the numerical solution method, and adjust the sub-relaxation factor and adaptive time step; Step 6: Monitor the pressure, temperature, density, velocity, and phase content during the jet process, complete the numerical calculation of the supercritical carbon dioxide jet impact process, and conduct a safety assessment of the supercritical carbon dioxide jet impact process.

2. The numerical simulation method for supercritical carbon dioxide jet impact process and its safety assessment according to claim 1, characterized in that: In step 1, the geometrically simplified model of the high-pressure vessel is designed as a three-dimensional cylindrical or two-dimensional rectangular structure; the outlet geometry of the short pipe orifice or nozzle structure is simplified as a circular or rectangular narrow slit; the geometrically simplified model of the downstream jet impact region is designed as a three-dimensional cylindrical or two-dimensional rectangular structure, and the width of the downstream jet impact region is 200 times the equivalent rupture diameter.

3. The numerical simulation method for supercritical carbon dioxide jet impact process and its safety assessment according to claim 1, characterized in that: In step 2, local mesh refinement is performed near the walls of the short pipe or nozzle, as well as near the walls of the impact equipment, ensuring that the y+ value is less than 1 and satisfying SST. k-ω High-precision calculation of near-wall viscous heating and flow separation in turbulence models; Local mesh refinement is performed at locations with strong pressure, velocity, and temperature gradients in the jet exit region and jet development region to improve the accuracy of numerical simulation methods in calculating Mach disk morphology and shock wave structure phenomena.

4. The numerical simulation method for supercritical carbon dioxide jet impact process and its safety assessment according to claim 1, characterized in that: In step 3, the solver type is defined as a pressure-based solver, the time type as transient calculation, and the gravity effect is ignored and set to 0 because the jet process is very intense. ; In step 3, the turbulence model adopts a combination of k-ω The model has high accuracy in the near-wall region and k-ε The model demonstrates robustness in free shear flow, is applicable to situations with strong adverse pressure gradients, flow separation, and complex boundary layers, and can simulate free jet SST. k-ω Turbulence model; In step 3, a dynamic method for retrieving the physical properties of supercritical, gaseous, liquid, and solid carbon dioxide is constructed using a user-defined function (UDF). Specifically, a discretized thermal property database is pre-built, which includes parameters such as density, specific heat at constant pressure, dynamic viscosity, thermal conductivity, velocity of sound, specific enthalpy, and specific entropy. The temperature interval of the data points in the thermal property database is 1 K, and the pressure interval is 10 kPa. The thermal property data is stored as a two-dimensional or multi-dimensional array. During the numerical calculation, bilinear interpolation is used to look up the property data table to obtain the thermal property parameters of carbon dioxide under different temperature and pressure conditions in real time. Finally, the gas-liquid or gas-solid mixture property parameters are calculated based on the phase change determination. In step 3, in order to accurately describe the drastic changes in the thermophysical properties of supercritical carbon dioxide near the quasi-critical region, the quasi-critical temperature at the current pressure is obtained by fitting a polynomial equation of quasi-critical temperature and pressure. It is assumed that when the absolute value of the slope of the isobaric specific heat corresponding to the temperature is greater than 0.05, supercritical carbon dioxide is in the quasi-critical region. The temperature interval of the data points in the thermophysical property database of supercritical carbon dioxide in the quasi-critical region is 0.01 K, and the pressure interval is 100 Pa.

5. The numerical simulation method for supercritical carbon dioxide jet impact process and its safety assessment according to claim 4, characterized in that: In step 3, when the temperature or pressure within the local calculation unit exceeds the applicable range of the property data table, the property dynamic calling method automatically switches to the Peng-Robinson equation to ensure the continuity and stability of the numerical calculation. At the same time, after the calculation is completed, the FLUENT Console will pop up a prompt that "the temperature or pressure within the calculation unit is out of range", and the distribution of the out-of-range area can be viewed using UDM.

6. The numerical simulation method for supercritical carbon dioxide jet impact process and its safety assessment according to claim 1, characterized in that: In step 4, the homogeneous delayed model controls the mass transfer process during phase change by using the hysteresis time parameter, while retaining the thermodynamic balance assumption. The homogeneous delayed model can describe the delayed phase change of carbon dioxide during evaporation and condensation, as well as sublimation and deposition.

7. The numerical simulation method for supercritical carbon dioxide jet impact process and its safety assessment according to claim 1, characterized in that: In step 4, the homogeneous delayed model is activated when the local pressure is below the critical pressure, and is used to describe the subcritical carbon dioxide gas-liquid phase change and gas-solid phase change processes. The homogeneous delay model is coupled to the control equations in the form of user-defined scalar source terms and energy source terms, and is used to describe the influence of phase change on flow and heat transfer characteristics. In step 4, UDM is used to distinguish the phase states of carbon dioxide.

8. The numerical simulation method for supercritical carbon dioxide jet impact process and its safety assessment according to claim 1, characterized in that: In step 5, the high-pressure carbon dioxide inlet is set as a pressure inlet, the downstream jet impact area except for the impacted wall is set as a pressure outlet, and the remaining boundaries, including the impacted wall, are set as adiabatic wall boundary conditions. The initial field is set to 101 kPa and 300 K carbon dioxide gas in the jet impact area. In step 5, the Coupled algorithm is selected as the numerical solution method, and the first-order upwind interpolation method is used to solve the convergence problem in the numerical simulation. The pressure relaxation factor is 0.05, the momentum relaxation factor is 0.05, the density relaxation factor is 0.1, the volume force relaxation factor is 0.1, the turbulent kinetic energy relaxation factor is 0.075, the turbulent diffusivity relaxation factor is 0.075, the turbulent viscosity relaxation factor is 0.1, and the energy relaxation factor is 0.

075. In step 5, during the numerical simulation, the time step is set to an adaptive time step, and the Courant number is set to a fixed value of 0.

1.

9. The numerical simulation method for supercritical carbon dioxide jet impact process and its safety assessment according to claim 1, characterized in that: In step 6, a comprehensive assessment is conducted based on the numerical calculation results to evaluate the jet impact intensity, phase change region distribution, dry ice formation risk, and the safety of the venting process.

10. The application of the numerical simulation method for supercritical carbon dioxide jet impact process and its safety assessment as described in any one of claims 1 to 9, characterized in that: The method is applicable to the release and accident analysis of supercritical carbon dioxide energy storage systems, supercritical carbon dioxide Brayton cycle systems, and supercritical carbon dioxide high-pressure pipelines.

Images