A new experimental and numerical simulation method for measuring ash slag fluidity using VOF based on OpenFOAM

Dynamics of cross-flow heat exchanger tubes with two loose supports has been studied. An analytical model of a cantilever beam that includes time-delayed displacement term along with two restrained spring forces has been used to model the flexible tube. The model consists of one loose support placed at the free end of the tube and the other at the midspan of the tube. The critical fluid flow velocity at which the Hopf bifurcation occurs has been obtained after solving a free vibration problem. The beam equation is discretized to five second-order delay differential equations (DDEs) using Galerkin approximation and solved numerically. It has been found that for flow velocity less than the critical flow velocity, the system shows a positive damping leading to a stable response. Beyond the critical velocity, the system becomes unstable, but a further increase in the velocity leads to the formation of a positive damping which stabilizes the system at an amplified oscillatory state. For a sufficiently high flow velocity, the tube impacts on the loose supports and generates complex and chaotic vibrations. The impact loading on the loose support is modeled either as a cubic spring or a trilinear spring. The effect of spring constants and free-gap of the loose support on the dynamics of the tube has been studied.

Nonlocal and surface effects on the flutter instability of cantilevered nanotubes conveying fluid subjected to follower forces

Sulfur particle deposition and wellbore blockage significantly hinder the productivity of high-sulfur gas wells, necessitating accurate prediction of the critical gas flow velocity to prevent deposition. This study presents a comprehensive force-based model to determine the critical gas flow velocity in vertical wells, explicitly incorporating adhesion, boundary layer effects, and particle detachment mechanisms. Through detailed analysis, the forces acting on sulfur particles of varying sizes and flow velocities, as well as the key factors influencing the critical gas flow velocity, were examined. The results demonstrated strong agreement with the experimental data, with a mean absolute percentage error of 6%, while revealing significant deviations from the conventional critical gas suspension velocity, validating the model’s enhanced accuracy and its necessity. This study identified adhesive forces as dominant for small particles (<100 µm) at low velocities (≤10 m/s), whereas gravitational and inertial forces prevailed for larger particles. Key parameters such as the particle size, sphericity, Hamaker constant, friction coefficient, and rolling arm length ratio critically influenced the deposition velocity and detachment mechanisms. These findings provide fundamental insights into sulfur deposition dynamics and establish a scientific basis for optimizing wellbore operations to mitigate sulfur accumulation and improve production efficiency in high-sulfur gas wells.

Although HFC-134a is a common refrigerant for residential and mobile refrigeration systems, investigators are dealing with replacing it with new alternatives because of its harmful environmental and global warming effects. Recently HFO-1234yf and HFO-1234ze have been introduced as suitable alternative refrigerants because they have zero ozone depletion potential (ODP) and low global warming potential (GWP) and possess thermophysical properties similar to those of HFC-134a. Because there is no experimental data on the performance of these new refrigerants in capillary tubes and short-tube orifices, a recently developed numerical model for analysis of critical two-phase flow through these tubes is used to predict the critical mass flow rate and pressure distribution of HFO-1234yf and HFO-1234ze under various operating conditions. The applied numerical model is based on a comprehensive two-fluid model including the effects of two-phase flow patterns and liquid-phase metastability. The numerical method has been validated by comparing numerical results of the critical flows of HFC-134a, R-410A, and HCFC-22 with available experimental data. The developed numerical simulation is applied in order to develop comparison and selection charts for short-tube orifices based on the common refrigerant HFC-134a and the alternative new refrigerants HFO-1234yf and HFO-1234ze.

To reduce fuel consumption of aeroengines, gearing of engines has become a trend. In geared engines, a design based on the elucidation of phenomena is necessary to achieve both high efficiency and reliability. Therefore, computational fluid dynamics (CFD) can contribute effectively to optimize its design. However, to our knowledge, examples of numerical simulation of high-speed gas-liquid two-phase flow in a planetary gear system, including multiple gear meshes and structures for oil capture, are not available in literature. Therefore, in this study, a numerical simulation method, previously developed by our research team, was used for a planetary gear system. The key feature of our numerical simulation method is that it realizes fast and numerically stable calculations by using the volume of fluid (VOF) method and surface compression scheme for the air-liquid interface, and the porosity method for the object boundary. To validate the accuracy of the numerical simulation method used, a planetary gear system with specifications equivalent to those of an aeroengine gear system was used. The numerical simulation and experimental test results obtained were then compared for fluid dynamic loss and oil capture flow rate. From this comparison, it was confirmed that the numerical simulation method used has a practically acceptable accuracy. The effects of the shape of the oil capture structure on the fluid dynamic loss and oil capture flow rate were investigated using our numerical simulation. The relationship between air flow, oil flow, and fluid dynamic loss, as well as the relationship with the oil capture flow rate were then discussed.

Size-dependent Timoshenko and Euler–Bernoulli models are derived for fluid-conveying microtubes in the framework of the nonlocal strain gradient theory. The equations of motion and boundary conditions are deduced by employing the Hamilton principle. A flow-profile-modification factor, which is related to the flow velocity profile, is introduced to consider the size-dependent effects of flow. The analytical solutions of predicting the critical flow velocity of the microtubes with simply supported ends are derived. By choosing different values of the nonlocal parameter and the material length scale parameter, the critical flow velocity of the nonlocal strain gradient theory can be reduced to that of the nonlocal elasticity theory, the strain gradient theory, or the classical elasticity theory. It is shown that the critical flow velocity can be increased by increasing the flexural rigidity, decreasing the length of tube, decreasing the mass density of internal flow, or increasing the shear rigidity. The critical flow velocity can generally increase with the increasing material length scale parameter or the decreasing nonlocal parameter. The flow-profile-modification factor can decrease the critical flow velocity. The critical flow velocity predicted by classical elasticity theory is generally larger than that of nonlocal strain gradient theory when considering the size-dependent effect of flow.

Predicting critical flow velocity leading to laminate plate collapse – Cylindrical plates

This paper deals with an experimental tests campaign addressed to investigate the structural behaviour of short Glass Fibre Reinforced Polymers (GFRP) plates (PA66 GF30) under Low Velocity Impact (LVI) phenomena, characterized by different impact energy levels, according to the ASTM D7136 requirement. The scope of this research activity must be found in a wider scenario, in which the experimental characterization can be the key-step to develop an established numerical model for the simulation of the experimental tests. Under a Certification by Analysis (CbA) purpose, an established numerical model can be used, rather than to virtually characterize the behaviour of specimens (reducing the costs related to the experimental tests), to simulate LVI on large structural component difficult to test in a laboratory.

Time-dependent starting profile of velocity upon application of external electrical potential in electroosmotic driven microchannels

Experimental study on flow properties of blast furnace slag with different alumina contents based on the image measurement method

Water saturationassessment is recognized as one of the most criticalaspects of formation evaluation, reserve estimation, and predictionof the production performance of any hydrocarbon reservoir. Watersaturation measurement in a core laboratory is a time-consuming andexpensive task. Many scientists have attempted to estimate water saturationaccurately using well-logging data, which provides a continuous recordwithout information loss. As a result, numerous models have been developedto relate reservoir characteristics with water saturation. By expandingthe use and advancement of soft computing approaches in engineeringchallenges, petroleum engineers applied them to estimate the petrophysicalparameters of the reservoir. In this paper, two techniques are developedto estimate the water saturation in terms of porosity, permeability,and formation resistivity index through the use of 383 data sets obtainedfrom carbonate core samples. These techniques are the nonlinear multipleregression (NLMR) technique and the artificial neural network (ANN)technique. The proposed ANN model achieved outstanding performanceand better accuracy for calculating the water saturation than theempirical correlation using NLMR and Archie equation with a high coefficientof determination (R2) of 0.99, a low averagerelative error of 1.92, a low average absolute relative error of 13.62,and a low root mean square error of 0.066. To the best of our knowledge,the current research establishes a novel foundation using the ANNmodel in the estimation of water saturation.

Critical flows are widely used in power engineering. Such flows are characterized by non-stationary processes, active vaporization due to a sharp drop in pressure when the mixture flows from a high-pressure medium to an atmospheric pressure medium, which especially necessitates the study of the parameters of such flows in emergency situations, such as an emergency depressurization of a pipeline or cooling system. Due to the presence of two phases and the transiency of the processes, it is necessary to develop methods for numerical simulation of this process. The energy apparatus with a granular layer adds an additional level of complexity to the study of critical flows, namely, the effect of granular backfill on the characteristics of a two-phase flow. A new model for numerical simulation of the critical outflow of a vapor-liquid flow from a channel with a granular backfill has been created. The values of the mass flow rate of the mixture, the effect of vapor content on the critical flow rate, and the effect of geometric parameters of the granular backfill on the critical mass flow rate are obtained. The calculated data were compared with the experiment, and new data were obtained in a wider range of mass vapor content compared to experimental study.

Products bear a lot of risks of getting damaged because of falling, getting compressed, etc. during transportation of logistics. In order to preserve products shape and quality, we can reduce the impact force during the logistics using packaging system. In general, we consider that packaging materials would not exhibit the strain rate effect while we predict free drop test results. In other words, the quasi-static compression stress-strain curve is used to simulate the results. But some packaging materials probably have the strain rate effect. Therefore, the foam packaging system of free drop test in this research considers the strain rate effect, that is the packaging materials are strain rate dependent. The energy loss is also considered into account when using numerical simulation methods to predict the maximum acceleration. The aim of this research is to understand the behavior of foam packaging materials during free drop by numerical simulation methods. Most of the literature on relevant research of foam packaging system neglects the strain rate effect to simplify the numerical simulation. But in this research it is shown that the strain rate effect would influence the maximum strain captured by high speed camera, even if there is no difference between free drop test and numerical simulation on maximum acceleration if the strain rate effect is not considered. So this research generalizes some experimental results to coordinate the relationship between the strain rate effect and the energy loss. Later, both energy method and single degree-of-freedom of nonlinear spring system are used to predict the results from free drop test. The constitutive law of foam packaging materials used in this research, for example expanded polypropylene (EPP), is constructed by series of quasi-static compression test and high-rate dynamic impact test. A numerical material constitutive law model considering the strain rate effect is also published to simulate the strain rate dependent property about EPP. We can accomplish the aim, considering the strain rate effect is used in this model when we are simulating the results, and to develop the numerical simulation which can predict maximum strain more accurately. In addition, for verifying that EPP has the strain rate effect, the high speed camera cooperated with the accelerometer through free drop test is used to derive the actual stress-strain curve of EPP packaging system. Finally, the fact that EPP is strain rate depenedent material has been proved. The microstructure photos of EPP by both optical electron microscope (OEM) and scanning electron microscope (SEM) were captured. This research also attempts to understand the relationship between strain rate effect and the microstructure of EPP. Furthermore, for designing EPP packaging system of real products, the appropriate range of strain energy density of EPP was chosen. The maximum acceleration, maximum strain and actual stress-strain curve of free drop test are predicted by numerical simulation methods considering the strain rate effect or not. To conclude, the results by several numerical simulation methods and free drop test are compared to explain that these methods which considers strain rate effect are feasible and accurate.

In plasma arc cutting (PAC), the characteristics of the gas flow exiting the nozzle significantly influence the cut quality. The high-pressure jet in PAC forms complex shockwave structures when it is incident on the metal to be cut. In this study, the flow behavior inside the kerfs of various geometries derived from an actual PAC workpiece is assessed. The shape of the cutting front in the kerf varies with the changing cutting speed. A high cutting speed yields a curved cutting front, resulting in unwanted gas flow behavior and adversely influencing the cutting performance. In this study, a computational fluid dynamics simulation model was used to analyze the effects of a curved cutting front on the gas flow behavior during the PAC process. The gas flow patterns obtained from the numerical simulations were qualitatively compared with the Schlieren experiment results. The analysis results indicated that the curvature of the cutting fronts generated oblique shockwave structures that significantly reduced the flow velocity. In particular, the weak shock structures throughout the curved cutting front gradually decreased the flow velocity. The critical flow velocity was realized in the kerf with a highly curved cutting front, beyond which the vertical penetration of the material was not possible. The shear stress lines concurred with the striation patterns on the kerf walls, thereby validating the numerical analysis results.

Numerical simulation of interactions between water waves and inclined-moored submerged floating breakwaters