Air entrainment in horizontal circular pipe flows is a critical concern in thermal and hydraulic engineering applications, such as cooling water loops in power plants and heat exchanger networks, as it can induce pipe vibrations, reduce heat transfer performance, increase energy losses, and reduce overall system efficiency. This effect becomes more pronounced when the pipe features a lateral branch exposed to the atmosphere, which facilitates the intrusion of external air into the primary flow. However, the impact of such branch structures on air entrainment dynamics remains insufficiently understood. In this study, a combined approach involving experimental testing and numerical simulation is employed to investigate the characteristics of air entrainment in horizontal pipes equipped with lateral branches. The results indicate that the presence of a branch reduces the local flow cross-sectional area, thereby accelerating the flow velocity at the branch junction. The increased velocity induces a localized pressure drop, which in turn facilitates the ingress of atmospheric air into the main water stream. The entrained air tends to accumulate near the branch region, forming a localized air-enriched zone characterized by a positive air-phase source term. Air is entrained in the form of discrete bubbles, resulting in a significant reduction in the average water volume fraction at the branch location, with gradual restoration occurring further downstream. Further analysis reveals that the degree of air entrainment is strongly influenced by the branch insertion depth, main flow velocity, and branch diameter. Specifically, a greater branch insertion depth amplifies air entrainment under increasing flow velocities; however, this trend may reverse if the branch diameter exceeds a critical threshold. Moreover, for a constant flow velocity, a larger branch diameter generally promotes higher air intake. These findings provide design guidelines for mitigating air entrainment in thermofluid systems, enabling more stable hydraulic performance and improved heat transfer efficiency.

Soils in the hydro-fluctuation belt of the Three Gorges Reservoir undergo repeated wetting-drying (W-D) cycles driven by periodic water level variation. These cycles progressively disintegrate soil aggregates, generating a multi-scale pore system consisting of intra-aggregate and inter-aggregate domains. To capture the impact of the W-D cycles on dual-porosity characteristics of such soils, this study proposes a bimodal soil-water retention curve (SWRC) model based on fractal pore size distributions (PSDs). The pore system is conceptualized as comprising macropore and micropore domains, each described by a fractal PSD, and the SWRC is explicitly derived from capillary water configuration in soil pores. The resulting formulation includes only five physically interpretable parameters and ensures natural continuity between the two pore domains without requiring additional boundary constraints. The model was validated through SWRC tests on soils from the Bazimen landslide hydro-fluctuation belt subjected to 0-7 W-D cycles using the filter paper method, complemented by SEM-based fractal analysis of pore structure evolution. The proposed model accurately reproduced the two-stage desaturation behavior across the entire suction range and achieved good agreement with experimental measurements. The fitted fractal dimensions showed consistent trends with those derived from SEM images, further supporting the model's physical interpretability. Additional validation against literature datasets, including loams, lateritic soils, and expansive clays, demonstrated the model's robustness and wide applicability for various dual-porosity soils. The proposed approach provides a reliable framework for characterizing water retention in dual-porosity soils and offers valuable support for hydromechanical modeling and slope stability assessment in reservoir fluctuation zones.

Atomized rainfall generated during flood discharge can greatly exceed extreme natural rainfall and threaten slope stability in dry-hot valleys. To clarify its hydrological effects, this study develops a coupled water-air two-phase model that links atomized rainfall, surface runoff, and unsaturated seepage in slopes with complex relief. The model treats the runoff-seepage interface as an internal boundary, thereby reducing uncertainty associated with prescribing external flow boundaries and maintaining mass balance among rainfall input, infiltration, and runoff. Simulation results show that, because of the limited permeability of slope soils, most atomized rainfall rapidly becomes surface runoff, with short generation time, large runoff volume, and fast dissipation. When runoff-seepage interaction is considered, infiltrating water penetrates deeper and the total infiltration increases. Unlike natural rainfall, atomized rainfall produces a distinct wetted boundary on the slope surface, resulting in non-airtight conditions and enhanced infiltration depth. Slope relief further controls runoff redistribution: local upward terrain forms a convergence zone, and once this zone is filled, runoff from the upper slope continues to migrate downslope. The proposed framework provides a practical tool for evaluating rainfall-induced slope hazards under flood-discharge conditions and supports risk assessment for high-altitude hydropower projects in dry-hot valley regions.

To investigate the impact of flood discharge-induced atomized rainfall on the safety and stability of accumulation slopes in dry-hot valley regions,a fully coupled model of flood discharge-induced atomization,surface runoff and seepage of complex slope was established based on the water-air two-phase flow theory.The Eulerian two-fluid model was adopted to describe the motion of water and air during flood discharge,and the coupling relationship between slope seepage and surface runoff was explicitly considered,enabling the numerical solution of the water-air flow process.The results show that the developed coupled model transforms the flux boundary between seepage and runoff into an internal boundary of the model,thereby overcoming the computational challenges caused by inaccurate boundary condition specification.For accumulation slopes,atomized rainfall primarily forms surface runoff,which is characterized by short formation time,high runoff volume,and rapid dissipation.When the influence of surface runoff on slope seepage is taken into account,the rainwater infiltration depth and volume within the slope body generally exhibit an increasing trend.

Many existing concrete thermal conductivity models are inadequate for simulating heat transfer behavior under extreme temperature conditions, as they often neglect the influence of subzero temperatures. An effective thermal conductivity model integrating the effects of phase changes in pore water has been developed on the basis of microcomposite material theory to simulate the temperature distribution of concrete dams subjected to subzero conditions. This model is a function of temperature, degree of water saturation, and porosity, incorporating pore characteristics and the thermal conductivity of each component. A concrete heat transfer test was conducted over a temperature range of-35 degrees C to 35 degrees C, employing a cylindrical concrete sample with a diameter of 1 m to maintain consistency with actual engineering materials. The experimental temperature data were used as input parameters to calculate the thermal conductivity coefficients through the least-squares finite element method, thus determining the model parameter expressions. The regularity of the change in the thermal conductivity of concrete with temperature is analyzed, and the thermal conductivity decreases with the temperature increase, with a considerable decrease observed near 0 degrees C. To validate the model's ability to simulate the temperature distribution in concrete dams under negative temperature conditions, numerical simulations were performed on a concrete arch dam. The results of these simulations demonstrated that the new model yields predictions that are more consistent with monitored values than to traditional series-parallel models are and more accurately captures the impact of pore water phase changes at low temperatures.

The effective dynamic viscosity of a soil-rock mixture (S-RM) serves as a essential parameter for simulating flow-like landslides in the context of fluid kinematics. Accurate measurement of this viscosity is significant for understanding the remote sustainability and rheological properties of landslide hazards. This study presents a method for determining dynamic viscosity, incorporating experimental measurements and numerical inversion. The experiment involves monitoring the movement of S-RMs with varying water content and rock block concentration, followed by the calculation of centroid displacements and velocities using digital image processing. The power-law model, combined with computational fluid dynamics, effectively captures the flow-like behavior of the S-RM. A grid search method is then employed to determine the optimal parameters by comparing the predicted centroid displacement with experimental results. A series of flume experiments were conducted, resulting in the observation of spatial mass distribution and centroid displacement variations over time during soil-rock movement. The dynamic viscosity model of the S-RM is derived from the experimental data. This dynamic viscosity model was then employed to simulate an additional flume experiment, with the results demonstrating excellent agreement between the simulated and experimental centroid displacements. Sensitivity analysis of the dynamic viscosity model indicates a dependence on shear rate and demonstrates a high sensitivity to water content and rock block concentration, following a parabolic trend within the measured range. This research contributes to the fields of geotechnical engineering and landslide risk assessment, offering a practical and effective method of measuring the dynamic viscosity of S-RM. Future research could explore additional factors influencing rheological behavior and extend the applicability of the proposed method to different geological environments.

The stability evolution of reservoir landslides is a dynamic process involving the interaction between water-air flow and deformation behaviour under fluctuating water levels and rainfall infiltration. Using the Shuping landslide in the Three Gorges reservoir area as a representative case, a comprehensive numerical investigation is conducted to analyse how dynamic water and air flow influences deformation and stability evolution in response to external hydrological changes. Results indicate that pore air pressure rises as a result of the formation of an almost saturated layer near the slope surface, which restricts pore air escape during rainfall infiltration. Deformation is pronounced in the central part of the landslide above the reservoir water level and exhibits a clear delay with water level changes. The stability safety factor mirrors changes in water level, decreasing during drawdown periods and increasing during water level rises, with an obvious time lag. The time delay observed in the deformation and stability changes of the Shuping landslide is linked to intricate interactions between water and air dynamics, influenced by both rainfall events and fluctuations in the reservoir's water level. The findings can provide valuable insights for landslide monitoring and mitigation strategies in reservoir regions.

The soils in the hydro-fluctuation zone on the Three Gorges Reservoir are exposed to dynamic environments of long-term wet-dry cycles and suction variations,leading to its changes in their unsaturated shear strength and failure modes.This study investigates the effects of wet-dry cycles on the unsaturated shear strength characteristics of red soil in the hydro-fluctuation zone of a landslide area on the Three Gorges Reservoir,using nuclear magnetic resonance(NMR)and triaxial shear tests.The study also reveals the variation in the critical saturation at which the failure mode transitions from strain-softening to strain-hardening.Results indicate that matric suction significantly contributes to shear strength at low saturation levels,exhibiting obvious strain-softening and shear failure characteristics.Under high saturation conditions,the soil exhibits strain-hardening and swelling failure characteristics.Taking into account pore-size distribution and suction,we propose a critical-saturation model for the transition from strain-softening to strain-hardening.The model's applicability and reliability are verified through a comparison of predicted results and experimental data.The critical saturation degree increases with the number of wet-dry cycles,suggesting that the repeated wet and dry cycles cause particle rearrangement,destruction of the original aggregates,and the evolution of the pore structure from dense to loose.The increase in pore size requires a higher saturation state to form continuous water distribution,causing the transition from shear failure to swelling failure.

The deterioration of cement-based structures under atmospheric conditions is significantly influenced by water transport governed by capillary pressure. This study combines experimental analysis and theoretical modeling to investigate the capillary pressure-saturation relationship in hardened mortar. Capillary pressure was derived from internal relative humidity (IRH) measurements, while pore size distribution (PSD) was characterized using low-field nuclear magnetic resonance (LF NMR) with varying water-binder (W/B) ratios, sand-cement (S/C) ratios, and fly ash (FA) dosages. A novel capillary pressure model is developed based on pore geometry, incorporating maximum equivalent pore radius (R) and fractal dimension (D) to capture the influence of PSD on capillary behavior. The proposed model shows excellent agreement with experimental data across various compositions and quantitatively links mix parameters to pore structure characteristics via functional relationships between W/B, S/C, FA dosage, and model parameters R and D. Results show that capillary pressure increases as saturation decreases and is strongly affected by mix composition, with lower W/B and S/C ratio yielding higher capillary pressures. Appropriate FA dosages promote a denser microstructure and higher capillary pressures through later-stage pozzolanic reactions, whereas excessive FA dosages increase the total porosity due to reduced early-stage calcium silicate hydrate (C-S-H) formation from lower cement content. This integrated experimental-modeling approach improves understanding of the interaction between mix design, pore structure, and capillary water transport, providing a robust tool for predicting durability-related moisture behavior in Portland cement-based materials.

Understanding soil water retention behavior with both adsorption and capillarity is essential for various engineering and environmental applications. This paper presents a continuous soil water retention curve (SWRC) model that incorporates a fractal pore size distribution (PSD) and addresses both capillary and adsorptive mechanisms. The model is derived for a macroscopically homogeneous and isotropic medium, considering both capillary water and an adsorptive water film within pores. Fractal theory is employed to characterize the intricate pore structure, providing a bridge between a macroscopic SWRC and a microscopic pore structure. The final SWRC model is expressed as a simple equation with three main parameters, each with a clear physical interpretation. Validation against experimental data of 30 soil samples sourced from the UNSODA database demonstrates the effectiveness of the SWRC model across various soil types, ranging from sandy to clayey compositions. A comparison with existing models highlights the superior accuracy of the proposed model in predicting the SWRC. Furthermore, the discussion extends to the evolution of capillary and adsorptive components of suction and the advantage of using a fractal PSD. The findings indicate that the proposed model successfully captures both capillary and adsorptive water retention behaviors, using the fractal PSD to represent the complex pore structure.

A heat exchange experiment of concrete surface under different roughness conditions was conducted, and the convective heat exchange coefficient model of concrete surface influenced by many factors was deduced and developed. The model comprehensively considers the effects of concrete surface roughness, wind speed, air humidity and thermal conductivity on the surface heat exchange performance. We obtained the model parameters from experimental data, which captured the convection heat transfer process under controlled laboratory conditions. The comparison between the calculation result and the measurement data is good enough, and prove the selection value of the model parameters are very good. The new convective heat exchange model can better reflect the heat exchange of the concrete structure surface under complex boundary conditions, provide support for more accurate simulation analysis of concrete temperature field, and provide the possibility for better calculation of concrete temperature stress and control of temperature cracks.

汉江雅口航运枢纽工程二期围堰是以粉细砂为主要填筑材料,并辅以土工复合材料和素混凝土板抵抗水流冲刷的过水围堰.围堰经 2021 年洪水过流后,过流面混凝土板出现了局部脱空、板间连接钢筋断裂等局部破坏现象,采用非线性有限元方法对过水围堰的应力-变形情况进行数值模拟,进而分析围堰局部破坏原因,提出预防措施.结果表明,在重力及水荷载共同作用下,围堰过流坝坡面不均匀沉降变形过大,致使抗冲刷混凝土板与堰体填筑料间存在不同程度的脱空,板间连接钢筋受力状态由受拉转变为受剪,局部因强度不足发生剪断破坏,最终导致混凝土板的整体性降低,抗水流冲刷能力不足.减小不均匀沉降是预防此类破坏的关键所在,为此可加强填筑碾压,提高材料的密实度,进而增强坝体的抗沉降变形能力;在混凝土板下方设置土工膜反滤,提高材料的抗渗透变形和抗水力冲刷的能力.

The flood discharge atomization of high dams involves a complex coupled flow of water and air. Small-scale model tests are typically used to predict the atomization of flood discharge. However, the accuracy of the prediction results often suffers because of the scale effect between the model and the prototype. Considering that the numerical simulation method has the advantage of not being restricted by similarity scales, this paper studies the influence of the scale effect on the atomization of flood discharge based on the principle of water-air two-phase flow. Taking the Shuibuya Hydropower Station as the research object, the distribution of the flood discharge atomized rainfall and the atomized wind speed are studied when the boundary conditions, ambient atmospheric pressure, and geometric dimensions meet similar requirements. The research results show that under the same boundary conditions, the geometric scale is the most important factor affecting flood discharge atomization. The smaller the geometric scale, the smaller the atomization wind speed and rainfall intensity obtained by the model, which means that smaller monitoring errors lead to larger prediction deviations. When the calculation model satisfies similar atmospheric pressure conditions, the atomization wind speed and rainfall obtained by the models with different geometric scales satisfy the standard exponential function relationship. By comparing with the atomized rainfall and wind speed data observed by the Shuibuya prototype, it is found that the prediction accuracy of the prototype can be greatly improved when the model satisfies a similar atmospheric pressure.

雅口航运枢纽二期围堰是采用河砂填筑、管袋砂护坡、复合土工膜防渗、土工布反滤、丙纶布防冲的新型复合结构,过水条件下易诱发围堰失稳问题.以试验数据为支撑,从渗流、应力变形、稳定性角度分析复杂工况下围堰稳定安全性,对比土工布、丙纶布与管袋砂层间稳定性.结果表明:围堰过水对坡脚处渗透梯度影响明显,加固后可增强局部抗渗透破坏的能力;过水条件对围堰基坑侧边坡稳定最不利,加固后应力变形、整体稳定性满足规范要求;丙纶布与管袋界面摩擦作用小,存在层间滑动的可能,在丙纶布与管袋砂间布置土工布可有效提高层间稳定性.经 2021 秋季汉江特大洪水考验,围堰在挡、过水工况下均能稳定安全运行.

汉江雅口航运水利枢纽工程二期围堰是以粉细砂为堰体填筑料,土工膜为主要防渗体的新型围堰.粉细砂透水性强且抗渗透破坏能力差,其渗透稳定性依赖于土工膜的防渗性.通过试验研究土工膜损伤后的渗透特性,并结合渗流数值模拟评价围堰渗透稳定.试验发现土工膜渗透系数随着压力水头的增大呈逐渐减小趋势.有限元模拟表明,当渗透系数取值最大时,土工膜仍能有效控制渗透梯度,防止粉细砂堰体发生渗透破坏.该围堰经受2021年秋汉江特大洪水且未发现明显渗透破坏,证明该新型围堰结构的可靠性.

The water and air flow in soil pores in response to rainfall infiltration is an important factor affecting the stability of rainfall-induced landslides. The objective of this paper is to investigate the effect of water-air flow on the deformation and stability of rainfall-induced landslides based on a coupled infiltration and hydromechanical model. The model is formulated by the water and air flow equation, the mechanical equilibrium, and porosity equations. The rainfall infiltration is introduced as a flux boundary, which is determined according to the comparison of the infiltration capacity and rainfall intensity. The numerical model and solution approach are validated by simulating the Liakopoulos drainage test and a rainfall infiltration experiment with satisfactory results. Taking the Tanjiawan landslide as a case study, the water and air flow in response to rainfall infiltration and its effect on deformation and stability are examined. The results show that the pore air is gradually trapped and compressed due to rainwater infiltration. The entrapped air has a slowing effect on the rainfall infiltration and a pushing-out effect on the front sliding body, which is an important driving force for the evolution of the slope deformation and stability due to rainfall infiltration.

毛细吸力为非饱和混凝土中驱动孔隙水—气流动、控制材料收缩开裂的重要作用力,其大小取决于混凝土细观孔隙结构,与混凝土的主要指标—水灰比密切相关.因此,基于相对湿度法,研发了一套非饱和混凝土毛细吸力的间接测试装置及方法,分析不同水灰比条件下毛细吸力的演化特征,并从孔隙尺度探析了毛细吸力演变的内在机制.结果表明,毛细吸力随水饱和度的减小呈非线性增长趋势,饱和度越低增长速率越大;水灰比减小会导致混凝土孔隙更加细密,从而使毛细吸力增大.

Thermal conductivity of concrete greatly influences the heat transfer of buildings and affected by many factors. This paper presents a prediction model for thermal conductivity of concrete by adopting the theory of Wiener bounds and considering concrete to have four components (water, air, aggregate, and cement mortar). The proposed model considers the combined effects of porosity, water saturation, and the volume fraction of aggregate on the thermal conductivity of concrete by weighting parameters of $${\eta }_{1}$$ , $${\eta }_{2}$$ , $${\eta }_{3}$$ , respectively. By adjusting the weighting parameters of each component, the model can consider the influence of various factors on the thermal conductivity of concrete more comprehensively. Thermal conductivity of each component and expression of weighting parameters are determined by literature and experiments. The proposed model has been verified by the measured thermal conductivity of concrete under different porosities, water content, and volume fractions of aggregate with the prediction accuracy of $$\pm 12\mathrm{\%}$$ . Finally, the regularity of the change in the thermal conductivity of concrete with porosity, water saturation, the volume fraction of aggregate, and temperature is analyzed.

为了定性、定量研究钢筋对混凝土结构整体导热性的影响,采用复合形法并结合有限元数值模拟分析了配筋率及钢筋布设方式对混凝土导热性的影响规律,进而基于Weiner-bound模型,引入参数μ1、μ2作为表征上下限数值对钢筋混凝土有效导热系数的权重,发展了一种考虑不同方向配筋率影响的混凝土导热系数模型.研究表明:钢筋混凝土的导热性随着配筋率的增大而增大,钢筋的布设方式对混凝土导热性的影响同样明显.当竖向钢筋的配筋率从0％增长到8.0384％时,竖向导热系数λz最大增幅为64.52％,而平面正交方向的导热系数增幅仅为15.34％,这说明在相同配筋率的条件下,平行于热流传导主向布置的钢筋对于结构整体的导热性提升较大,而垂直于热流传导主向布置的钢筋对于结构导热性提升相对较小.不同方向布置的钢筋对于导热张量主元的影响程度不一,使得钢筋混凝土的导热性呈现出各向异性.将钢筋混凝土模型实测数据与模型预测值相对比,两者数据偏差基本在±10％以内,模型适应性强,可用于考虑不同方向配筋率的钢筋混凝土导热系数预测.

Rainfall infiltration on a soil slope is usually an unsaturated seepage process that can be described by a water-air two-phase flow model. The effect of pore air pressure on rainfall infiltration has been widely recognized and validated by means of numerical simulations and laboratory experiments. However, whether a slope can actually seal pore air continues to be debated by researchers. In this study, a water-air two-phase flow model is used to simulate the rainfall infiltration process on a soil slope, and a field experiment is conducted to realistically test the sealing conditions of a slope. According to the numerical simulation, the areas of water and air flow in and out on the slope surface are relatively stable and can be classified as the “inhalation zone” and “overflow zone”, respectively. Intermittent rainfall on the soil slope has an amplifying effect on pore air pressure because rainfall intensity is usually at the millimeter level, and it causes pore air pressure to reach the cm level. A field experiment was performed to determine whether a slope can realistically seal pore air and subsequently verify the regularity of rainfall infiltration. Air pressure sensors were buried in the slope to monitor the pore air pressures during the rainfall process. The monitoring results show that the pore air pressure in the slope changed, which indicates that the slope can seal air. Moreover, the amplification effects of intermittent rainfall on pore air pressure were observed for natural rainfall, which agrees well with the numerical simulation results.