Search Results (26)

The dam break flow problem consists of the phenomena where a fluid is suddenly released and is often used as a test case for multiphase flows numerical models or to analyze the underlying physics of complex free surface flows of both Newtonian and non-Newtonian fluids. Dam break flows of viscoplastic fluids (i.e., fluids that present a yield stress) are especially interesting for two reasons: many geological and industrial fluids can be characterized as viscoplastic fluids, and the yield stress represents a difficulty for numerical solutions. The viscoplastic fluids are simulated using the Bingham and Herschel–Bulkley models, and the results are compared with the flow development of power-law and Newtonian fluids (i.e., with no yield stress). This paper focuses on the numerical modeling of viscoplastic two-dimensional dam-break flows on an inclined bed as a means to analyze the shear stress field development over time and the formation of plug and pseudo-plug zones. It is shown that, for the very beginning of flow, the yield stress fluids were characterized by three distinctive shear stress zones, an occurrence that could not be found on the fluid with no yield stress. Full article

This study presents an innovative approach to quantifying uncertainty in Herschel–Bulkley (H-B) fluid flow through rectangular ducts, analyzing four scenarios: uncertain apparent viscosity (Case I), uncertain pressure gradient (Case II), uncertain boundary conditions (Case III) and uncertain apparent viscosity and pressure gradient (Case IV). Using the stochastic finite difference with homogeneous chaos (SFDHC) method, we produce probability density functions (PDFs) of fluid velocity with exceptional computational efficiency (243 times faster), matching the accuracy of Monte Carlo simulation (MCS). Key statistics and maximum velocity PDFs are tabulated and visualized for each case. Mean velocity shows minimal variation in Cases I, III, and IV, but maximum velocity fluctuates significantly in Case I (63.95–187.45% of mean), Case II (50.15–156.68%), and Case IV (63.70–185.53% of mean), vital for duct design and analysis. Examining the effects of different parameters, the SFDHC method’s rapid convergence reveals the fluid behavior index as the primary driver of maximum stochastic velocity, followed by aspect ratio and yield stress. These findings enhance applications in drilling fluid management, biomedical modeling (e.g., blood flow in vascular networks), and industrial processes involving non-Newtonian fluids, such as paints and slurries, providing a robust tool for advancing understanding and managing uncertainty in complex fluid dynamics. Full article

This study investigates the potential of Spirulina biomass as a lubricating additive for drilling fluid formulations. In this work, this waste protein is evaluated as a lubricant alternative that may decrease the coefficient of friction while improving the rheological profiles and/or reducing fluid loss via permeation in drilling fluids. A processed and dried Arthrospira platensis (Spirulina) biomass is incorporated into drilling fluid formulations and compared to standard lubricant additives for the drilling fluid properties of lubricity, rheology, and fluid loss. Rheological characterization includes the determination of yield stress, gel strength, and viscosity measurements. The major findings of this study include a friction value reduction of up to 30% and a fluid loss reduction of up to 51% by using 3 vol.% Spirulina. Parameters were fit to two rheological models (Bingham plastic and Herschel–Bulkley). After experimentation and analyzing the data gathered, it was determined that Spirulina and the Spirulina–Coastalube mixture in drilling fluids are good potential candidates as more environmentally benign and cost-effective alternative technologies for drilling fluids for decreasing the coefficient of friction, which results in increasing the lubrication performance of the drilling fluids. Full article

The prediction of debris flows is essential for safeguarding infrastructure and minimizing the economic losses associated with the hazards. Traditional empirical and theoretical models, while providing foundational insights, often struggle to capture the complex and nonlinear behaviors inherent in debris flows. This study aims to enhance debris flow prediction by integrating theoretical modeling with data-driven approaches. We model debris flow as a viscoplastic fluid, employing the Herschel–Bulkley rheological model to describe its behavior. By combining the kinematic wave model with lubrication theory, we develop a comprehensive theoretical framework that encapsulates the mechanical physics of debris flows and identifies key governing parameters. Numerical solutions of this theoretical model are utilized to generate an extensive training dataset, which is subsequently used to train a support vector regression (SVR) model. The SVR model targets slide depth and velocity upon impact, using explanatory variables including yield stress, material density, source area depth and length, and slope length. The model demonstrates high predictive accuracy, achieving coefficients of determination $R^2$ of 0.956 for slide depth and 0.911 for slide velocity at impact. Additionally, the relative residuals $\sigma$ are primarily distributed within the range of −0.05 to 0.05 for both slide depth and slide velocity upon impact. These results indicate that the proposed hybrid model not only incorporates the fundamental physical mechanisms governing debris flows but also significantly enhances predictive performance through data-driven optimization. This study underscores the critical advantage of merging physical models with machine learning techniques, offering a robust tool for improved debris flow prediction and risk assessment, which can inform the development of more effective early warning systems and mitigation measures. Full article

The present study investigates the flow characteristics of fly ash-based (FA) geopolymers reinforced with polypropylene (PP) fibers during the extrusion process in three-dimensional printing. By applying the Herschel–Bulkley rheological model, this research provides a sound theoretical basis to understand the flow behavior of these materials under various conditions. The Herschel–Bulkley model describes the relationship between shear stress and the shear rate in non-Newtonian fluids, capturing yield stress and flow consistency. A combination of experimental and numerical techniques based on the Finite-Element Method (FEM) in COMSOL has been used in this study. The results of both experimental and simulation approaches are compared to examine the material behavior during extrusion. The experimental results indicate that PP fiber content significantly affects the rheological properties. Mixtures with high fiber content encountered issues such as high static yield. However, mixtures with moderate fiber content showed smoother extrusion processes, suggesting an optimal fiber addition range that balances mechanical properties and extrudability. The numerical simulations generally agreed with the experimental data up to a certain fiber content level, beyond which more complex interactions necessitate further model refinements. The investigation identified a 0.25% to 0.5% fiber content range that enhances performance without complicating the extrusion process, facilitating the production of properly printed structures. Full article

In this work, the effect of sonication on the molecular characteristics of polyacrylic acid (Carbopol^® Ultrez 10), as well as on its rheological behavior in aqueous dispersions and microgels, was analyzed for the first time by rheometry, weight-average molecular weight (M_w) measurements via static light scattering (SLS), Fourier transform infrared (FTIR) spectroscopy and confocal microscopy. For this, the precursor dispersion and the microgels containing 0.25 wt.% of Ultrez 10 were sonicated in a commercial ultrasound bath at constant power and at different times. The main rheological properties of the microgel, namely, shear modulus, yield stress and viscosity, all decreased with increasing sonication time, while the microgel’s Herschel–Bulkley (H-B) behavior, without thixotropy, was preserved. Also, M_w of Ultrez 10 decreased up to almost one-third (109,212 g/mol) of its original value (300,860 g/mol) after 180 min of sonication. These results evidence a softening of the gel microstructure, which results from the reduction in the M_w of polyacrylic acid with sonication time. Separately, FTIR measurements show that sonication produces scission in the C-C links of the Carbopol^® backbone, which results in chains with the same chemistry but lower molecular weight. Finally, confocal microscopy observations revealed a diminution of the size of the microsponge domains and more free solvent with sonication time, which is reflected in a less compact and softer microstructure. The present results indicate that both the microstructure and the rheological behavior of Carbopol^® microgels, in particular, and complex fluids, in general, may be manipulated or tailored by systematic high-power ultrasonication. Full article

During shield construction in underground spaces, synchronous grouting slurry is poured between the surrounding rock and tunnel lining to ensure stability. For synchronous grouting slurries, few studies have investigated the relationship between the rheological parameters and physical properties, grout-segregation mechanism, and anti-segregation performance. Therefore, we explored the relationships between the slurry rheological parameters, segregation rate, and bleeding rate. Cement, sand, fly ash, and bentonite were used to prepare the slurry, and the effects of different polycarboxylate water-reducing agents and dispersible latex powder dosages were studied. The rheological parameters of 16 groups of uniformly designed slurries were tested, and the data were fit using the Herschel–Bulkley model. The optimal mix ratio lowered the slurry segregation rate, and its rheological behaviour was consistent with the Herschel–Bulkley fluid characteristics. High-yield-shear-stress synchronous grouting slurries with high and low viscosity coefficients were less likely to bleed and segregate, respectively. The optimised slurry fluidity, 3 h bleeding rate, 24 h bleeding rate, segregation rate, coagulation time, and 28 days compressive strength were 257.5 mm, 0.71%, 0.36%, 3.1%, 6.7 h, and 2.61 MPa, respectively, which meet the requirements of a synchronous grouting slurry of shield tunnels for sufficiently preventing soil disturbance and deformation in areas surrounding underground construction sites. Full article

In this study, composite particles of rGO/CoFe₂O₄ were synthesized using a solvothermal method to fabricate a low-density magnetorheological (MR) material with enhanced sedimentation stability. The morphology and crystallographic features of rGO/CoFe₂O₄ were characterized via SEM, TEM, and XRD, and its magnetic properties were tested using VSM. The MR fluid was formulated by blending rGO/CoFe₂O₄ particles into silicone oil. Under different magnet strengths (H), a rotational rheometer was used to test its MR properties. Typical MR properties were observed, including shear stress, viscosity, storage/loss modulus, and dynamic yield stress (${\tau }_{dy}$) following the Herschel–Bulkley model reaching 200 Pa when H is 342 kA/m. Furthermore, the yield stress of the MR fluid follows a power law relation as H increases and the index changes from 2.0 (in the low H region) to 1.5 (in the high H region). Finally, its MR efficiency was calculated to be about 10⁴% at H of 342 kA/m. Full article

A solvent in suspension often has non-Newtonian properties. To date, in order to determine these properties, many constitutive equations have been suggested. In particular, power-law fluid, which describes both dilatant and pseudoplastic fluids, has been used in many previous studies because of its simplicity. Then, the Herschel–Bulkley model is used, which describes fluid with yield stress. In this study, we considered how a non-Newtonian solvent affected the equilibrium position of a particle and relative viscosity using the regularized lattice Boltzmann method for fluid and a two-way coupling scheme for the particle. We focused on these methods so as to evaluate the non-Newtonian effects of a solvent. The equilibrium position in Bingham fluid was closer to the wall than that in Newtonian or power-law fluid. In contrast, the tendency of relative viscosity in Bingham fluid for each position was similar to that in power-law fluid. Full article

Many studies on magnetorheological fluid (MRF) have been carried out over the last three decades, highlighting several salient advantages, such as a fast phase change, easy control of the yield stress, and so forth. In particular, several review articles of MRF technology have been reported over the last two decades, summarizing the development of MRFs and their applications. As specific examples, review articles have been published that include the optimization of the particles and carrier liquid to achieve minimum off-state viscosity and maximum yield stress at on-state, the formulation of many constitutive models including the Casson model and the Herschel–Bulkley (H–B) model, sedimentation enhancement using additives and nanosized particles, many types of dampers for automotive suspension and civil structures, medical and rehabilitation devices, MRF polishing technology, the methods of magnetic circuit design, and the synthesis of various controllers. More recently, the effect of the temperature and thermal conductivity on the properties of MRFs and application systems are actively being investigated by several works. However, there is no review article on this issue so far, despite the fact that the thermal problem is one of the most crucial factors to be seriously considered for the development of advanced MRFs and commercial products of application systems. In this work, studies on the thermal conductivity and temperature in MRFs themselves and their temperature-dependent application systems are reviewed, respectively, and principal results are summarized, emphasizing the following: how to reduce the temperature effect on the field-dependent properties of MRFs and how to design an application system that minimizes the thermal effect. It is noted here that the review summary is organized in a chronological format using tables. Full article

The dynamics of air (gas) bubbles in a column of cement slurry is examined numerically. The air injected at the bottom of a laboratory-scale column through a porous distributor plate spatially distributes and migrates as a swarm of bubbles throughout the slurry toward the freeboard. The two-phase system of the cement slurry and the air bubbles is modeled using the conservation equations of mass and linear momentum in the framework of the volume-of-fluid (VOF) approach. The cement slurry is modeled using the Herschel–Bulkley and Bingham fluid models. Results show that the mean Sauter diameter and the mean rise velocity of the bubbles decrease with the gas flow rate. Meanwhile, it is found that the rising of the bubbles is controlled by breakup events, along with relatively weak path instabilities of the bubbles resulting in relatively straight trajectories, independent of the gas flow rate. The extent of the yielded region appears larger for the Herschel–Bulkley model compared to the Bingham fluid model (by approximately 10%). Full article

The performance of gas-liquid mixing processes in agitated vessels is commonly measured by the degree of gas dispersion, and local measurements of this parameter can provide a more accurate description of the mixing, especially for non-Newtonian fluids. For instance, the fluid flow of complex yield-pseudoplastic solutions is highly affected by the local shear stress, leading to a non-homogeneous air distribution throughout the mixing vessel. Coaxial mixers have demonstrated energy-efficient characteristics for non-Newtonian fluids that improve mixing homogeneity due to the independent rotation of a central impeller and a close-clearance impeller. Therefore, this work aims to investigate the axial profile of the local gas holdup in a PBT-anchor coaxial mixer containing xanthan gum solutions, which is a biopolymer widely utilized as an emulsion stabilizer, dispersing agent, and thickener. The rheological behavior of the solutions was described by the Herschel-Bulkley model, and the effect of the xanthan gum concentration on the gas holdup distribution was analyzed. Electrical resistance tomography (ERT) was employed to obtain the gas holdup from the conductivity measurements of the mixture in each of the four horizontal planes. Results show that the gas holdup increased downward for all solutions, and a lower xanthan gum concentration reduced the non-homogeneity in gas distribution and the overall gas volume fraction. In contrast, higher xanthan gum concentrations enhanced gas holdup in high shear stress regions while weakening air dispersion distant from those regions due to higher viscous forces. Full article

The aim of this research is to investigate the effects of rheological models of shear-thinning fluids and their estimated parameters on the predictions of laminar, transitional, and turbulent flow. The investigation was carried out through experimental and computational fluid dynamics (CFD) studies in horizontal pipes (diameters of 19.1 mm and 76.2 mm). Six turbulent models using Reynolds averaged Navier–Stokes equations in CFD_ANSYS Fluent 19.0 were examined in a 3D simulation followed by comparison studies between numerical and experimental results. Regarding results of laminar regions in power-law rheology models, Metzner and Reed presented the best fit for the pressure loss and transitional velocity. For the turbulent region, correlations observed by Wilson and Thomas as well as Dodge and Matzner had good agreement with the experimental results. For Herschel–Bulkley fluids, pressure losses and transitional regions based on a yielded region were examined and compared to the experimental results and the modified Slatter Reynolds number, where the results provided good estimation. For both pipe diameters, the Slatter model was the best fit for pressure losses of Herschel–Bulkley fluids in the turbulent regime. Furthermore, when comparing k-omega and k-epsilon turbulence models to the power-law behaviour, numerical studies delivered the most accurate results with fluids that have a higher behaviour index. However, the error percentage significantly increased at a higher shear rate in the Herschel–Bulkley fluids with a greater yield stress effect. Moreover, the modified Herschel–Bulkley viscosity function by Papanastasiou was implemented in the current CFD study. This function was numerically stabilized, devoid of discontinuity at a low strain rate, and more effective in transitional regions. Full article

Surfactant-based viscoelastic (SBVE) fluids are innovative nonpolymeric non-newtonian fluid compositions that have recently gained much attention from the oil industry. SBVE can replace traditional polymeric fracturing fluid composition by mitigating problems arising during and after hydraulic fracturing operations are performed. In this study, SBVE fluid systems which are entangled with worm-like micellar solutions of cationic surfactant: cetrimonium bromide or CTAB and counterion inorganic sodium nitrate salt are synthesized. The salt reagent concentration is optimized by comparing the rheological characteristics of different concentration fluids at 25 °C. The study aims to mitigate the primary issue concerning these SBVE fluids: significant drop in viscosity at high temperature and high shear rate (HTHS) conditions. Hence, the authors synthesized a modified viscoelastic fluid system using ZnO nanoparticle (NPs) additives with a hypothesis of getting fluids with improved rheology. The rheology of optimum fluids of both categories: with (0.6 M NaNO₃ concentration fluid) and without (0.8 M NaNO₃ concentration fluid) ZnO NPs additives were compared for a range of shear rates from 1 to 500 Sec⁻¹ at different temperatures from 25 °C to 75 °C to visualize modifications in viscosity values after the addition of NPs additives. The rheology in terms of viscosity was higher for the fluid with 1% dispersed ZnO NPs additives at all temperatures for the entire range of shear rate values. Additionally, rheological correlation function models were derived for the synthesized fluids using statistical analysis methods. Subsequently, Herschel–Bulkley models were developed for optimum fluids depending on rheological correlation models. In the last section of the study, the pressure-drop estimation method is described using given group equations for laminar flow in a pipe depending on Herschel–Bulkley-model parameters have been identified for optimum fluids are consistency, flow index and yield stress values. Full article

In this paper, we study the boundary-layer flow of a Herschel–Bulkley fluid due to a moving plate; this problem has been experimentally investigated by others, where the fluid was assumed to be Carbopol, which has similar properties to cement. The computational fluid dynamics finite volume method from the open-source toolbox/library OpenFOAM is used on structured quad grids to solve the mass and the linear momentum conservation equations using the solver “overInterDyMFoam” customized with non-Newtonian viscosity libraries. The governing equations are solved numerically by using regularization methods in the context of the overset meshing technique. The results indicate that there is a good comparison between the experimental data and the simulations. The boundary layer thicknesses are predicted within the uncertainties of the measurements. The simulations indicate strong sensitivities to the rheological properties of the fluid. Full article