Ball valve flow characteristic determination method based on liquid hydrogen cavitation

Abstract

The invention discloses a ball valve flow characteristic measuring method based on liquid hydrogen cavitation, which comprises the following steps: selecting a cavitation model, and improving the cavitation model to obtain an improved cavitation model; the improved cavitation model is used for simulating the temperature change in the liquid hydrogen cavitation process, and the unsteady flow and cavitation characteristics of the ultralow-temperature liquid hydrogen ball valve in the dynamic opening and closing process are measured. By introducing and improving the cavitation model, accurate simulation and measurement of temperature change in the liquid hydrogen cavitation process and unsteady flow and cavitation characteristics under the dynamic working conditions of opening and closing are realized, so that a reliable basis is provided for structural optimization and safety design of the low-temperature ball valve.

Description

Technical Field

[0001] This invention relates to the field of ball valve flow analysis, and more specifically to a method for determining the flow characteristics of ball valves based on liquid hydrogen cavitation. Background Technology

[0002] Liquid hydrogen, as an important clean energy source and aerospace propellant, is widely used in aerospace engineering, cryogenic storage and transportation, and hydrogen energy systems. Liquid hydrogen delivery systems typically operate under ultra-low temperature and high safety requirements. Ball valves, as key components for pipeline opening and closing and flow regulation, directly affect the system's safety and service life. During liquid hydrogen delivery, when fluid flows through the throttling area of ​​the ball valve core, local flow channel contraction can easily cause a sharp drop in pressure, leading to liquid hydrogen vaporization and cavitation. The subsequent collapse of these cavitation bubbles generates a strong impact effect, causing cavitation, vibration, and noise. In severe cases, it can even cause material damage to the valve body and valve core surfaces, posing a potential threat to the safety of cryogenic systems.

[0003] Existing research indicates that the cavitation behavior of cryogenic working fluids differs significantly from that of room-temperature liquids. The cavitation process is not only influenced by pressure changes but also closely coupled with the temperature field. However, current research on cryogenic cavitation largely focuses on macroscopic characterization or visual observation of cavitation phenomena, lacking systematic and in-depth studies on the interaction mechanism between cavitation and the valve wall, and the impact of cavitation on the local flow and temperature fields. Particularly in the field of cryogenic ball valves, due to limitations such as complex experimental conditions and high testing costs, numerical modeling and flow characteristic analysis of liquid hydrogen cavitation processes remain scarce, making it difficult to accurately reflect the phase transition characteristics and unsteady evolution of liquid hydrogen under ultra-low temperature conditions.

[0004] Therefore, there is an urgent need for a method to determine the flow characteristics of ball valves suitable for cryogenic fluid conditions such as liquid hydrogen. By introducing and improving the cavitation model, the method can accurately simulate and determine the unsteady flow and cavitation characteristics under temperature changes and dynamic opening and closing conditions during the cavitation process of liquid hydrogen, thereby providing a reliable basis for the structural optimization and safety design of cryogenic ball valves. Summary of the Invention

[0005] In view of this, the purpose of this invention is to overcome the defects in the prior art and provide a method for measuring the flow characteristics of a ball valve based on liquid hydrogen cavitation, which can accurately simulate and measure the unsteady flow and cavitation characteristics under temperature changes and dynamic opening and closing conditions during liquid hydrogen cavitation.

[0006] The method for determining the flow characteristics of a ball valve based on liquid hydrogen cavitation of the present invention includes:

[0007] A cavitation model is selected and improved to obtain an improved cavitation model.

[0008] An improved cavitation model was used to simulate the temperature changes during the liquid hydrogen cavitation process, and the unsteady flow and cavitation characteristics of the cryogenic liquid hydrogen ball valve during the opening and closing dynamic process were determined.

[0009] Furthermore, the cavitation model adopts the Schnerr-Sauer model.

[0010] Furthermore, the improved cavitation model includes an improved saturated vapor pressure calculation model and an improved evaporation rate model.

[0011] Furthermore, the improved saturated vapor pressure calculation model is determined based on the following formula:

[0012] ;

[0013] in, The current temperature The saturated vapor pressure below For temperature-related correction factors, It is the saturated vapor pressure at the reference temperature. It is the latent heat of vaporization, and R is the specific gas constant. The reference temperature is the thermodynamic temperature.

[0014] Furthermore, the improved evaporation rate model is determined according to the following formula:

[0015] ;

[0016] in, The source term representing the rate of evaporation mass transfer; It is the density of the gas. It is the density of the liquid. Indicates the density of the mixture. It is the gas fraction. It is the bubble radius. It is the saturated vapor pressure of the liquid phase. It is the thermal inhibition coefficient. It is the heat capacity of the liquid. It is the latent heat of vaporization. It is the thermal diffusivity of the liquid. This indicates the time required for the bubble growth process; This represents the temperature difference between the inside and outside of the bubble.

[0017] Furthermore, the unsteady flow and cavitation characteristics of the cryogenic liquid hydrogen ball valve during the opening and closing dynamic process were measured, specifically including:

[0018] Considering the extreme low-temperature thermal effect of liquid hydrogen, the flow characteristics inside the ball valve under different opening degrees, opening and closing processes, and inlet pressures are analyzed, and the flow characteristic results are obtained.

[0019] Furthermore, the flow characteristics results include: significant asymmetry in cavitation intensity, velocity distribution, and vortex structure during valve opening and closing.

[0020] Furthermore, the flow characteristics results include: at the same opening degree, the cavitation phenomenon is more intense during the valve closing process, the valve core jet velocity is higher, and the vortex intensity is greater.

[0021] Furthermore, the flow characteristics result includes: under strong cavitation conditions, cavitation bubble groups will react on the flow field by changing the two-phase properties and energy distribution of the fluid, thus inhibiting the development of large-scale vortex structures.

[0022] Furthermore, the flow characteristics result includes: the inlet pressure and valve opening jointly determine the intensity and range of cavitation; at a smaller opening, a higher inlet pressure will significantly aggravate cavitation and prolong the downstream cavitation flow, while the valve core rotation speed will regulate the evolution rate of the downstream vortex structure.

[0023] The beneficial effects of this invention are as follows: This invention discloses a method for determining the flow characteristics of a ball valve based on liquid hydrogen cavitation. By improving the cavitation model, a low-temperature cavitation model suitable for calculating liquid hydrogen is obtained. Numerical simulations of the cavitation flow field inside the low-temperature ball valve are performed using different openings as variables. The cavitation flow field inside the low-temperature ball valve is analyzed through pressure loss, low-temperature ball valve flow performance, and cavitation isosurface contour plots, revealing the evolution law of low-temperature cavitation and its impact on the flow performance of the low-temperature ball valve. Combined with Ω-criterion eddy current analysis of the correlation between the geometry of cavitation bubbles and the vorticity distribution of the cavitation flow field, this invention not only provides a theoretical basis for optimizing valve structure design but also provides technical support for improving the overall performance of liquid hydrogen delivery systems. Attached Figure Description

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0025] Figure 1 This is a schematic diagram of the flow characteristic measurement method for ball valves according to the present invention;

[0026] Figure 2 This is a schematic diagram of cavitation phenomena at different opening degrees during the opening and closing process of the present invention;

[0027] Figure 3 This is a schematic diagram of the eddy current distribution of the cryogenic liquid hydrogen ball valve of the present invention under different opening degrees;

[0028] Figure 4 This is a schematic diagram of the loss coefficients under different opening degrees during the opening and closing process of the present invention;

[0029] Figure 5 This is a schematic diagram of the velocity distribution at different opening degrees during the opening and closing process of the liquid hydrogen ball valve of the present invention;

[0030] Figure 6 This is a schematic diagram of the pressure distribution along the centerline of the present invention;

[0031] Figure 7 This is a schematic diagram of the cavitation phenomenon under different inlet pressures according to the present invention;

[0032] Figure 8 This is a schematic diagram of the pressure distribution and gas volume fraction along the centerline of the flow channel when the valve core opening is 30° according to the present invention.

[0033] Figure 9 This is a schematic diagram of the vortex position according to the present invention. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings, as shown in the figures:

[0035] This embodiment discloses a method for determining the flow characteristics of a ball valve based on liquid hydrogen cavitation, including:

[0036] A cavitation model is selected and improved to obtain an improved cavitation model.

[0037] An improved cavitation model was used to simulate the temperature changes during the liquid hydrogen cavitation process, and the unsteady flow and cavitation characteristics of the cryogenic liquid hydrogen ball valve during the opening and closing dynamic process were determined.

[0038] In this embodiment, the evolution of cryogenic cavitation is a transition process between the gas and liquid phases. In the Fluent solver, the fluid medium is typically treated as a mixture with a single density, known as a homogeneous mixture model, to ensure computational efficiency and accuracy. Predicting cryogenic turbulence requires consideration of the continuity equation, momentum equation, and energy equation, expressed as follows:

[0039] Continuity equation:

[0040] (1)

[0041] (2)

[0042] Momentum equation:

[0043] (3)

[0044] Energy equation:

[0045] (4)

[0046] (5)

[0047] (6)

[0048] (7)

[0049] Mass transfer equation:

[0050] (8)

[0051] in, Indicates the density of the mixture. It is the density of the liquid. It is the density of the gas. It is the gas fraction. It's speed. It's pressure. It is the laminar viscosity of the mixture. and These represent the dynamic viscosity of the liquid and the gas, respectively. This is turbulent viscosity. f is mass volume fraction, L is latent heat, h is enthalpy, and Pr is... T and Pr L It is the Prandtl number for turbulent and laminar flow, C p This is the specific heat under constant pressure. The subscripts (i, j, k) indicate the coordinate direction. and The source term represents the rate of mass transfer during evaporation and condensation.

[0052] Considering the complex turbulence effects induced by low-temperature cavitation, a Realizable k-ε turbulence model was selected for numerical simulation in the solver. The main improvement of this model compared to the standard k-ε model lies in the introduction of variables related to streamline curvature and rotation into its turbulent viscosity formula, thus providing better "realizability" in complex flows. Specifically:

[0053] (9)

[0054] (10)

[0055] (11)

[0056] Turbulent viscosity calculation:

[0057] (12)

[0058] (13)

[0059] in,

[0060] (14)

[0061] (15)

[0062] Where k and ε are the turbulent kinetic energy and turbulent dissipation rate, respectively, and σ k and σ ε This is the Prandtl number corresponding to the turbulent kinetic energy and dissipation rate, with values ​​of 1.0 and 1.2, respectively. G k This is the turbulent kinetic energy generation term due to the average velocity gradient. The empirical constants C1 and C2 are 1.44 and 1.9, respectively.

[0063] Furthermore, the Schnerr-Sauer model was chosen as the cavitation model. The Schnerr-Sauer model is a transport equation model based on bubble dynamics, whose core principle is to describe the evaporation and condensation processes through changes in bubble radius. Its standard form is as follows:

[0064] (16)

[0065] (17)

[0066] in, Indicates the density of the mixture. It is the density of the liquid. It is the density of the gas. It is the gas fraction. It's pressure. It is the saturated vapor pressure of the liquid phase. That is the bubble radius. and The source term represents the rate of mass transfer during evaporation and condensation.

[0067] The relationship between vapor pressure and temperature can be represented by the Clausius-Clapeyron equation, which describes the changes in vapor formation under cryogenic conditions:

[0068] Relationship between vapor pressure and temperature:

[0069] (18)

[0070] in, It is the saturated vapor pressure at the current temperature. It is temperature (in K). It is the latent heat of vaporization. It refers to the volume change during the phase transition process.

[0071] Based on this equation, the relationship between vapor pressure and temperature can be obtained by integration:

[0072] (19)

[0073] in, It is the saturated vapor pressure at the reference temperature. The thermodynamic temperature of the reference state (in K), where R is the specific gas constant.

[0074] Therefore, the improved saturated vapor pressure calculation model is as follows:

[0075] (20)

[0076] The Schnerr-Sauer cavitation model assumes a constant internal pressure within the bubble and neglects the thermodynamic effects of cavitation. In reality, the latent heat of vaporization leads to a temperature decrease in the vaporization region, further explaining the certain reduction in internal pressure. The presence of a thermodynamic boundary layer during bubble growth ensures heat transfer during phase transition.

[0077] The energy balance equation at the gas-liquid interface is:

[0078] ;(twenty one)

[0079] Where K is the thermal conductivity of the liquid. Indicates the boundary layer thickness. The temperature difference between the inside and outside of the bubble, and the temperature gradient of the boundary layer are According to Fourier's law, the heat flux to the interface is... Energy balance means that energy is provided through conduction to an area of ​​. The heat at the interface is used for vaporization and causes a decrease in the mass of the gas inside the bubble. The increase includes:

[0080] ; (twenty two)

[0081] ;(twenty three)

[0082] in, The heat capacity of a liquid, It is the bubble radius. It is the thermal diffusivity of the liquid. Temperature difference between the inside and outside of the bubble.

[0083] The improved evaporation rate model is as follows:

[0084] ;(twenty four)

[0085] in, The source term representing the rate of evaporation mass transfer; It is the density of the gas. It is the density of the liquid. Indicates the density of the mixture. It is the gas fraction. It is the bubble radius. It is the saturated vapor pressure of the liquid phase. It is the thermal inhibition coefficient. It is the heat capacity of the liquid. It is the latent heat of vaporization. It is the thermal diffusivity of the liquid. This indicates the time required for the bubble growth process; This represents the temperature difference between the inside and outside of the bubble.

[0086] In this embodiment, the traditional Schnerr-Sauer model is an isothermal cavitation model that neglects the thermodynamic effect of liquid hydrogen absorbing its latent heat of vaporization during vaporization, which lowers the temperature of the liquid surrounding the cavitation bubble and consequently reduces the saturated vapor pressure in the cavitation region, ultimately inhibiting further bubble growth. This thermodynamic effect is particularly significant in cryogenic fluids such as liquid hydrogen, and neglecting it leads to a serious overestimation of cavitation intensity.

[0087] The improved Schnerr-Sauer model, on the one hand, introduces the Clausius-Clapeyron equation to control the change of saturated vapor pressure of liquid hydrogen with temperature, and on the other hand, couples the energy balance equation to characterize the thermodynamic effects in the liquid hydrogen cavitation process. This allows for a more accurate simulation of temperature changes during liquid hydrogen cavitation, thus fundamentally correcting the physical biases of the traditional model and achieving an accurate simulation of liquid hydrogen cavitation.

[0088] The unsteady flow and cavitation characteristics of a cryogenic liquid hydrogen ball valve during the opening and closing dynamic process were determined. Specifically, considering the extreme low-temperature thermal effect of liquid hydrogen, the flow characteristics inside the ball valve under different opening degrees, opening and closing processes, and inlet pressures were analyzed, and the flow characteristic results were obtained.

[0089] To investigate the cavitation characteristics of the cryogenic liquid hydrogen ball valve during the opening and closing process, this study takes an inlet pressure of 0.2 MPa and a valve core rotation speed of 20° / s as an example to investigate the correlation between the cavitation characteristics and eddies of the liquid hydrogen ball valve at various opening degrees during the opening and closing process.

[0090] Figure 2The volume fraction of the gas phase at different opening degrees (30°, 50°, 60°, and 70°) during the opening and closing process. During opening and closing, the cavitation evolution of the ball valve exhibits typical process dependence and asymmetry. During opening, the occurrence and development of cavitation are influenced by the flow field establishment process. In the initial stage with an opening degree of 30°, the flow field is not yet fully developed, the changes in velocity and pressure gradient are relatively gradual, and the cavitation intensity is weak. As the opening degree increases to 50° and 60°, the flow field energy strengthens, the throttling effect becomes more significant, and the cavitation area and intensity slowly increase, marking the entry of the cavitation cloud into the development stage. However, when the opening degree further increases to 70°, due to the significant increase in flow area, the downstream pressure recovery capability is enhanced, and the local pressure rises above the saturated vapor pressure, thus the cavitation phenomenon shows a weakening trend. In contrast, the cavitation characteristics during the closing process exhibit a stronger hysteresis effect. In the initial stage of closing (70°), due to the smooth and stable initial flow field and high pressure level, the cavitation phenomenon is weak, similar to the opening process. However, as the opening degree decreases further, cavitation begins to develop significantly. When the opening degree decreases to 50° and 30°, the high-speed inertia of the upstream fluid causes the downstream pressure to not recover as effectively as during the opening process due to the channel contraction. This maintains a large and more stable low-pressure zone, and the cavitation intensity is significantly enhanced, which is significantly higher than that during the opening process at the same opening degree.

[0091] To further analyze the impact of different valve core rotation speeds on flow rate, the Ω criterion was introduced to calculate the vorticity value of the cryogenic ball valve, exploring the vortex distribution during the cryogenic cavitation evolution process of the liquid hydrogen ball valve at different opening degrees. The region with Ω greater than 0.52 was defined as a vortex, and the Ω equation used for calculation is as follows:

[0092] (25)

[0093] (26)

[0094] Figure 3The diagram shows the vortex distribution at opening angles (30°, 50°, 60°, and 70°) during the opening and closing processes predicted by the Ω criterion. During the opening process, the development trends of vortices and cavitation are highly synchronized. In the initial opening stage, the flow field is not yet fully developed, and the vortex structure is initially visible and limited in range, corresponding to the initial stage of cavitation. As the opening angle increases to 50° and 60°, kinetic energy accumulates in the flow field, and the shear flow caused by the throttling effect intensifies. The vortex structure becomes more complex and its range expands, and the cavitation phenomenon also intensifies. Cavitation begins to strengthen, the vortex structure becomes more complex, and its range gradually expands. However, when the opening angle increases to 70°, the flow area increases, the flow channel becomes more unobstructed, the shear flow weakens, the vortex range shrinks significantly, and cavitation weakens accordingly. Conversely, during the closing process, as the opening angle decreases, vortices begin to generate and continuously develop. When the closing angle reaches 60°, the vortex range significantly increases. As the valve core closes further, the cavitation intensity increases significantly, while the vortex range decreases. When the valve is closed to 30°, although the cavitation intensity reaches its peak, the vortex structure in the outlet flow region decreases, distributing only near the valve core. This key phenomenon indicates that when cavitation develops to extreme intensity, its relationship with vortices changes from "co-development" to "nonlinear suppression." The mechanism may lie in the fact that the gas-liquid two-phase flow induced by intense cavitation leads to changes in the effective viscosity of the fluid. Simultaneously, the intense phase transition process consumes a large amount of flow energy, thereby inhibiting the maintenance and development of large-scale vortex structures.

[0095] In addition, to further explore the internal flow mechanism of the liquid hydrogen ball valve during the opening and closing process, a loss coefficient is introduced. The flow resistance of a cryogenic ball valve during the opening and closing process was studied. Loss coefficient. As a dimensionless parameter, it represents the energy loss of the flow in the valve. Its expression is:

[0096] (27)

[0097] in, Indicates pressure drop; Indicates the density of the fluid; This indicates the velocity of the fluid inside the pipe.

[0098] The opening speed is 10 degrees per second, and the inlet pressure is 0.2 MPa. Figure 4 The values ​​represent the loss coefficients at different opening degrees during the opening and closing process. The loss coefficient is highest at an opening degree of 20°, regardless of whether the valve core degree is open. Then, as the valve core degree increases, the loss coefficient decreases sharply, eventually decreasing slowly. When the opening degree is greater than 30°, the pressure drop and loss coefficient during the opening process are greater than those during the closing process. However, when the valve core degree is less than 30°, the loss coefficient during the opening process is less than that during the closing process.

[0099] Figure 5This describes the velocity distribution at different opening degrees (30°, 50°, 60°, and 70°) during the opening and closing process. At all opening degrees, the maximum velocity region consistently appears in the narrow flow channel between the valve core and the outlet, and the maximum velocity increases with increasing opening degree. At the same opening degree, the maximum jet velocity during the closing process is significantly higher than that during the opening process. During the opening process, the flow channel area gradually expands from a closed state, and the establishment of the flow field is accompanied by a "mild" development process from stillness to acceleration. Conversely, in the initial stage of the closing process, the fluid inherits the high kinetic energy from the large opening. When the flow channel suddenly contracts, the upstream fluid rushes towards the narrow flow channel at a higher velocity due to inertia, leading to a rapid accumulation of kinetic energy and thus triggering a more intense and concentrated high-speed jet. Analysis shows that the closing process of the cryogenic liquid hydrogen ball valve is the critical stage for withstanding the greatest flow erosion and cavitation risks.

[0100] Furthermore, to further investigate the evolution characteristics of the internal flow field during the opening and closing dynamics of the ball valve, this invention extracts the pressure distribution along the axial position on the centerline of the flow channel, such as... Figure 6 Figure (a) shows the absolute pressure along the centerline as a function of different opening degrees during the opening and closing process. From... Figure 6 It can be seen that, regardless of whether the valve is opened or closed, the pressure inside the flow channel drops sharply and fluctuates when liquid hydrogen flows through the valve core. This is because the liquid hydrogen velocity increases significantly as the flow area decreases, leading to a corresponding pressure change. During the opening process, the pressure curve of the outlet region exhibits a characteristic of "first decreasing sharply, then gradually recovering, and finally slowly approaching the outlet pressure." Notably, the degree of pressure recovery increases significantly with increasing opening degree. However, during the closing process, the pressure recovery rate of the outlet region decreases, and the recovery process is also much slower. Especially at small opening degrees (such as 30°), the pressure recovery is very slow, indicating increased energy loss in the flow field and decreased flow stability.

[0101] To analyze the influence of different inlet pressures on the cavitation characteristics of a cryogenic liquid hydrogen ball valve, valve core angles of 60° and 30° were selected to study the changes in cavitation within the valve fluid domain. This invention selected four different valve inlet pressures (0.12 MPa, 0.15 MPa, 0.20 MPa, and 0.25 MPa). Figure 7The figure shows the gas volume fraction cloud map inside the liquid hydrogen ball valve under different valve inlet pressures. It can be seen that when the valve core opening is 60°, cavitation occurs in the outlet flow channel under four different inlet pressures, but the cavitation area is basically consistent, indicating that the inlet pressure has a weak influence on the cavitation range at this opening. However, when the valve core opening is 30°, the degree of cavitation significantly increases with increasing inlet pressure. This is because, under a constant outlet pressure, the increase in inlet pressure increases the pressure difference flowing through the valve core, leading to a significant increase in flow velocity. According to Bernoulli's principle, a higher flow velocity will cause a more severe pressure drop in the throttling region, making it easier for the local pressure to fall below the saturated vapor pressure of liquid hydrogen, thus triggering stronger cavitation. Furthermore, the high-speed flowing liquid hydrogen will transport cavitation bubbles downstream, forming a longer cavitation flow, making it difficult for the outlet flow pressure to recover, and continuously expanding the cavitation range.

[0102] To further analyze the internal pressure of liquid hydrogen flowing through the valve under different inlet pressures, a valve core opening of 30° was used as the research object, and the pressure distribution along the centerline of the flow channel was monitored. Figure 8 As shown in (a), the analysis reveals that under four different valve inlet pressures, the pressure fluctuates when liquid hydrogen flows through the valve core, drops sharply after exiting the valve core, and gradually recovers to the outlet pressure in the outlet region. With increasing inlet pressure, the pressure drop at the valve core is significantly greater, and the low-pressure zone in the outlet region also extends accordingly. Figure 8 (b) shows the gas volume fraction along the flow path. The results indicate that the maximum gas volume fraction remains consistent across different inlet pressures, consistently occurring near the valve core outlet. With increasing inlet pressure, both the scale and duration of cavitation flow increase. These results demonstrate that rising inlet pressure not only exacerbates the pressure drop near the valve core but also extends the flow region affected by cavitation, providing crucial insights for cavitation control and valve optimization.

[0103] To analyze the effect of valve core rotation speed on the flow characteristics of a cryogenic liquid hydrogen ball valve, this invention selects four rotation speeds (5, 10, 20, 40 deg / s) for numerical research at an inlet pressure of 0.2 MPa. Given... Figure 2 The vortex structure is most complex and has the largest range when the valve opening is 60° during the closing process, so this opening was selected as the research object. To observe the evolution of the vortex in the outlet flow area, four vertical sections (0.2 m, 0.4 m, 0.6 m, and 0.8 m from the valve core) were selected sequentially along the flow channel for analysis. Figure 9The generation, development, and dissipation processes of vortices at different rotational speeds are illustrated. The results show that the downstream flow field is dominated by large-scale vortex structures, whose intensity, morphology, and evolution are significantly influenced by the valve core rotational speed and downstream location. Significant large-scale vortices appear under all operating conditions, indicating strong flow separation and shear layer instability after liquid hydrogen flows through the throttling region. Although the overall evolution process of the vortices is similar at all rotational speeds, their evolution rate increases significantly with increasing rotational speed. Taking 20 deg / s as an example, two main vortices form and continue to develop in the central region at the 0.2 m to 0.4 m section; by 0.8 m, they have essentially occupied the entire flow channel, while the two secondary vortices above have been largely dissipated at 0.6 m. As the valve core rotational speed increases, the vortex generation location moves upstream, development becomes more rapid, and the dissipation process is correspondingly accelerated, indicating that the flow field under high rotational speed conditions has higher instability and energy dissipation rate.

[0104] This invention considers the thermal effect of cryogenic liquid hydrogen and modifies the traditional cavitation model. Through numerical simulation, it explores the unsteady flow and cavitation characteristics of a cryogenic liquid hydrogen ball valve during the opening and closing dynamic process. Specifically, it analyzes the influence of opening degree, operation process, inlet pressure and valve core rotation speed on the internal flow field structure, cavitation evolution and eddy current dynamics.

[0105] Among them, the dynamic characteristics of ball valves exhibit strong path dependence and nonlinear effects. The valve opening and closing process shows significant asymmetry in cavitation intensity, velocity distribution, and vortex structure. At the same opening degree, cavitation is more severe during the closing process, with higher valve core jet velocity and greater vortex intensity. This is mainly due to the more severe pressure drop and flow separation caused by fluid inertia during the closing process, indicating that the valve closing process is the critical stage for bearing the maximum risk of flow erosion and cavitation erosion.

[0106] Cavitation and vortex structures exhibit a close spatiotemporal coupling. The low-pressure region of the vortex core is the dominant area for the initial formation of cavitation; however, under strong cavitation conditions, cavitation bubble swarms can alter the two-phase properties and energy distribution of the fluid, thus influencing the flow field and inhibiting the development of large-scale vortex structures, revealing a complex two-way interaction mechanism between the two. Furthermore, the inlet pressure and valve opening jointly determine the intensity and extent of cavitation. In particular, at smaller openings, higher inlet pressures significantly exacerbate cavitation and prolong downstream cavitation flow, while the valve core rotation speed regulates the evolution rate of downstream vortex structures.

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for determining the flow characteristics of a ball valve based on liquid hydrogen cavitation, characterized in that: include: A cavitation model is selected and improved to obtain an improved cavitation model. An improved cavitation model was used to simulate the temperature changes during the liquid hydrogen cavitation process, and the unsteady flow and cavitation characteristics of the cryogenic liquid hydrogen ball valve during the opening and closing dynamic process were determined.

2. The method for determining the flow characteristics of a ball valve based on liquid hydrogen cavitation according to claim 1, characterized in that: The cavitation model adopted is the Schnerr-Sauer model.

3. The method for determining the flow characteristics of a ball valve based on liquid hydrogen cavitation according to claim 2, characterized in that: The improved cavitation model includes an improved saturated vapor pressure calculation model and an improved evaporation rate model.

4. The method for determining the flow characteristics of a ball valve based on liquid hydrogen cavitation according to claim 3, characterized in that: The improved saturated vapor pressure calculation model is determined based on the following formula: ； in, The current temperature The saturated vapor pressure below For temperature-related correction factors, It is the saturated vapor pressure at the reference temperature. It is the latent heat of vaporization, and R is the specific gas constant. The reference temperature is the thermodynamic temperature.

5. The method for determining the flow characteristics of a ball valve based on liquid hydrogen cavitation according to claim 3, characterized in that: The improved evaporation rate model is determined based on the following formula: ； in, The source term representing the rate of evaporation mass transfer; It is the density of the gas. It is the density of the liquid. Indicates the density of the mixture. It is the gas fraction. It is the bubble radius. It is the saturated vapor pressure of the liquid phase. It is the thermal inhibition coefficient. It is the heat capacity of the liquid. It is the latent heat of vaporization. It is the thermal diffusivity of the liquid. This indicates the time required for the bubble growth process; This represents the temperature difference between the inside and outside of the bubble.

6. The method for determining the flow characteristics of a ball valve based on liquid hydrogen cavitation according to claim 1, characterized in that: The unsteady flow and cavitation characteristics of a cryogenic liquid hydrogen ball valve during the opening and closing dynamic process were determined, specifically including: Considering the extreme low-temperature thermal effect of liquid hydrogen, the flow characteristics inside the ball valve under different opening degrees, opening and closing processes, and inlet pressures are analyzed, and the flow characteristic results are obtained.

7. The method for determining the flow characteristics of a ball valve based on liquid hydrogen cavitation according to claim 6, characterized in that: The flow characteristics results include: significant asymmetry in cavitation intensity, velocity distribution, and vortex structure during valve opening and closing.

8. The method for determining the flow characteristics of a ball valve based on liquid hydrogen cavitation according to claim 6, characterized in that: The flow characteristics results include: at the same opening degree, cavitation is more severe during valve closing, valve core jet velocity is higher, and vortex intensity is greater.

9. The method for determining the flow characteristics of a ball valve based on liquid hydrogen cavitation according to claim 6, characterized in that: The flow characteristics results include: under strong cavitation conditions, cavitation bubble groups will react on the flow field by changing the two-phase properties and energy distribution of the fluid, thus inhibiting the development of large-scale vortex structures.

10. The method for determining the flow characteristics of a ball valve based on liquid hydrogen cavitation according to claim 6, characterized in that: The flow characteristics results include: the inlet pressure and valve opening jointly determine the intensity and range of cavitation; at a smaller opening, a higher inlet pressure will significantly aggravate cavitation and prolong the downstream cavitation flow, while the valve core rotation speed will regulate the evolution rate of the downstream vortex structure.

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