Geometrical Modifications Research Articles

A Critical Review of CFD Modeling Approaches for Darrieus Turbines: Assessing Discrepancies in Power Coefficient Estimation and Wake Vortex Development

This critical review delves into the impact of Computational Fluid Dynamics (CFD) modeling techniques, specifically 2D, 2.5D, and 3D simulations, on the performance and vortex dynamics of Darrieus turbines. The central aim is to dissect the disparities apparent in numerical outcomes derived from these simulation methodologies when assessing the power coefficient (Cp) within a defined velocity ratio (λ) range. The examination delves into the prevalent turbulence models shaping Cp values, and offers insightful visual aids to expound upon their influence. Furthermore, the review underscores the predominant rationale behind the adoption of 2D CFD modeling, attributed to its computationally efficient nature vis-à-vis the more intricate 2.5D or 3D approaches, particularly when gauging the turbine’s performance within the designated λ realm. Moreover, the study meticulously curates a compendium of findings from an expansive collection of over 250 published articles. These findings encapsulate the evolution of pivotal parameters, including Cp, moment coefficient (Cm), lift coefficient (Cl), and drag coefficient (Cd), as well as the intricate portrayal of velocity contours, pressure distributions, vorticity patterns, turbulent kinetic energy dynamics, streamlines, and Q-criterion analyses of vorticity. An additional focal point of the review revolves around the discernment of executing 2D parametric investigations to optimize Darrieus turbine efficacy. This practice persists despite the emergence of turbulent flow structures induced by geometric modifications. Notably, the limitations inherent to the 2D methodology are vividly exemplified through compelling CFD contour representations interspersed throughout the review. Vitally, the review underscores that gauging the accuracy and validation of CFD models based solely on the comparison of Cp values against experimental data falls short. Instead, the validation of CFD models rests on time-averaged Cp values, thereby underscoring the need to account for the intricate vortex patterns in the turbine’s wake—a facet that diverges significantly between 2D and 3D simulations. In a bid to showcase the extant disparities in CFD modeling of Darrieus turbine behavior and facilitate the selection of the most judicious CFD modeling approach, the review diligently presents and appraises outcomes from diverse research endeavors published across esteemed scientific journals.

Thermalhydraulic assessment and design optimization of incorporating flow obstructors in a supercritical minichannel heat sink

Modulation of the thermalhydraulic characteristics of the miniaturized heat sink by geometric alteration is a less explored topic, particularly in conjunction with the supercritical fluids, which can experience both enhancement and deterioration in performance based on the conditions. The present study appraises the response of a square minichannel by incorporating rectangular obstructions, with the primary aim of identifying an optimized orientation and design. A performance evaluation criterion, defined as a combined change in both heat transfer coefficient and pressure drop because of geometric modification, is selected as the primary variable. Installation of the baffles substantially augments the turbulent mixing among the fluid layers, realizing a lower wall-to-fluid temperature differential and enhanced heat transfer coefficient. A relatively lower level of temperature is maintained within the baffled section, thereby delaying the appearance of heat transfer deterioration. Obstructions, however, considerably increases the pressure losses, necessitating careful selection of the dimensions. The use of three pairs of baffles has been identified to be the most feasible option. Desirable values of the height, thickness, and inclination angle for individual plates in this orientation have also been identified, along with a detailed thermalhydraulic assessment about the role of the operating variables with the optimum design.

Influence of cavity floor injection strategy on mixing improvement study of a splitter plate-assisted supersonic combustor

In the current research, an effort has been made to investigate the splitter plate-based scramjet combustor by inserting a cavity in the lower wall and observing how the different geometric parameters of the combustor, namely the cavity's aft wall angle, the bottom wall's divergence angle, and the splitter plate's angle of attack, affect the mixing performance of the supersonic combustor. Initially, experimental data from the published literature for a splitter plate is used to validate the implemented computational approach. Next, different aft wall angles of the cavity are compared, and the optimal value is found to be 120° The current investigation demonstrates that geometric modification significantly affects the performance of a splitter plate-assisted supersonic combustor. An increase in the cavity's aft wall angle improves the combustion efficiency. A further study is conducted on the splitter plate + cavity at various divergence angles of the bottom wall. According to our study, the separation region on the top wall increases as the divergence angle increases, resulting in a reduction in combustion performance. Finally, while simulating different angles of attack of splitter plate, it has been noticed that, for a negative angle of attack (-1°), the cavity provides a recirculation region and a sufficient shear mixing layer. This allows adequate air-fuel mixing to sustain combustion.

Chitosan-Silica Composites for Adsorption Application in the Treatment of Water and Wastewater from Anionic Dyes.

A series of new types of composites (biopolymer-silica materials) are proposed as selective and effective adsorbents. A new procedure for the synthesis of chitosan-nanosilica composites (ChNS) and chitosan-silica gel composites (ChSG) using geometrical modification of silica and mechanosorption of chitosan is applied. The highest adsorption efficiency was achieved at pH = 2, hence the desirability of modifications aimed at stabilizing chitosan in such conditions. The amount of chitosan in the synthesis grew to 1.8 times the adsorption capacity for the nanosilica-supported materials and 1.6 times for the silica gel-based composites. The adsorption kinetics of anionic dyes (acid red AR88) was faster for ChNS than for ChSG, which results from a silica-type effect. The various structural, textural, and physicochemical aspects of the chitosan-silica adsorbents were analyzed via small-angle X-ray scattering, scanning electron microscopy, low-temperature gas (nitrogen) adsorption, and potentiometric titration, as well as their adsorption effectiveness towards selected dyes. This indicates the synergistic effect of the presence of dye-binding groups of the chitosan component, and the developed interfacial surface of the silica component in composites.

Symmetry-protected Bose-Einstein condensation of interacting hardcore bosons

The large practical potential of exotic quantum states is often precluded by their notorious fragility against external perturbations or temperature. Here, we introduce a mechanism stabilizing a one-dimensional quantum many-body phase exploiting an emergent {{mathbb{Z}}}_{2}-symmetry based on a simple geometrical modification, i.e. a site that couples to all lattice sites. We illustrate this mechanism by constructing the solution of the full quantum many-body problem of hardcore bosons on a wheel geometry, which are known to form Bose-Einstein condensates. The robustness of the condensate against interactions is shown numerically by adding nearest-neighbor interactions, which typically destroy Bose-Einstein condensates. We discuss further applications such as geometrically inducing finite-momentum condensates. Since our solution strategy is based on a generic mapping, our findings are applicable in a broader context, in which a particular state should be protected, by introducing an additional center site.

In-Vitro Flow Validation of Third-Generation Ventricular Assist Devices: Feasibility and Challenges.

Computational fluid dynamics (CFD) is a powerful tool for the in-silico evaluation of rotodynamic blood pumps (RBPs). Corresponding validation, however, is typically restricted to easily accessible, global flow quantities. This study showcased the HeartMate 3 (HM3) to identify feasibility and challenges of enhanced in-vitro validation in third-generation RBPs. To enable high-precision acquisition of impeller torques and grant access for optical flow measurements, the HM3 testbench geometry was geometrically modified. These modifications were reproduced in silico , and global flow computations validated along 15 operating conditions. The globally validated flow in the testbench geometry was compared with CFD-simulated flows in the original geometry to assess the impact of the necessary modifications on global and local hydraulic properties. Global hydraulic properties in the testbench geometry were successfully validated (pressure head: r = 0.999, root mean square error [RMSE] = 2.92 mmHg; torque: r = 0.996, RMSE = 0.134 mNm). In-silico comparison with the original geometry demonstrated good agreement ( r > 0.999, relative errors < 11.97%) of global hydraulic properties. Local hydraulic properties (errors up to 81.78%) and hemocopatibility predictions (deviations up to 21.03%), however, were substantially affected by the geometric modifications. Transferability of local flow measures derived on advanced in-vitro testbenches toward original pump designs is challenged by significant local effects associated with the necessary geometrical modifications.

Hydrodynamic comparison of different geometries of square cross-section airlift bioreactor using computational fluid dynamics

Abstract The hydrodynamics of airlift bioreactors, which offer an interesting alternative to conventional stirred-tank bioreactors, has generally been evaluated using experimental approaches, requiring time, energy, and reagents. However, computational fluid dynamics (CFD) has emerged as an important and valuable tool for the analysis and design of these devices, saving time and experimental effort, while providing a large amount of information. In this study, four geometries of a square cross-section 10-L split airlift bioreactor operating with distilled water were simulated using CFD, and the hydrodynamics variables gas hold-up and liquid velocity were evaluated. CFD satisfactorily predicted the hydrodynamic parameters, when compared to experimental data, allowing adequate prediction of the shear rate distribution in airlift bioreactors. The results indicated that different shear rate distributions were obtained by geometric modifications in the bioreactor, showing that its design should be considered to satisfy different specific bioprocess requirements.

Modeling the biomechanics of laser corneal refractive surgery

We present a finite element model of the human cornea used to simulate corneal refractive surgery according to the three most diffused laser procedures, i. e., photo-refractive keratectomy (PRK), laser in-situ keratomileusis (LASIK) and small incision lenticule extraction (SMILE). The geometry used for the model is patient-specific in terms of anterior and posterior surfaces of the cornea and intrastromal surfaces originated by the planned intervention. The customization of the solid model prior to finite element discretization avoids the struggling difficulties associated with the geometrical modification induced by cutting, incision and thinning. Important features of the model include the identification of the stress-free geometry and an adaptive compliant limbus to account for the surrounding tissues. By the way of simplification, we adopt a Hooke material model extended to the finite kinematics, and consider only the preoperative and short-term postoperative conditions, disregarding the remodeling and material evolution aspects typical of biological tissues. Albeit simple and incomplete, the approach demonstrates that the post-operative biomechanical state of the cornea, after the creation of a flap or the removal of a small lenticule, is strongly modified with respect to the preoperative state and characterized by displacement irregularities and stress localizations.

A parametric study of serration design for trailing–edge broadband noise reduction

This work discusses the physics of noise reduction achieved from serrated trailing–edges and its impact by the serration design. An experimental campaign is carried out with a benchmark 2D model based on a NACA 633–018 airfoil. Different trailing-edge serrations are tested under several flow speeds and angles of attack conditions to build a complete dataset of acoustic measurements. Systematic modifications of a reference sawtooth serration design are made to its scale and geometry. Scale modifications are based on sawtooth serrations and comprehend carefully considered variations of the serration height (2h), wavenumber (λ), and aspect ratio (2h/λ). Geometric shape modifications are represented by concave–shaped and combed–sawtooth serrations. This study represents a unique sensitivity–based parametric analysis on the scaling and geometric properties of trailing–edge serrations where the impacts of each modification are studied separately. The results obtained are used to provide guidelines for serration design choices and their impact on broadband noise reduction.

Geometric modifications to bluff body for enhanced performance in a wind-induced vibration energy harvester

Specialized sensors in wireless networks monitor the environment with minimal power, which is typically provided by batteries but it can also be powered with renewable sources using smart materials. One such solution is piezoelectric wind energy harvesting to power these sensors. However, the low output power of piezoelectric materials is still a concern. This research aims to improve piezoelectric wind energy harvesting by modifying the geometry of the bluff body. A square-shaped bluff body is used as a reference, and geometric changes are made by attaching square-shaped extensions. The study creates a mathematical model of a cantilever beam system with a piezoelectric material at fix end and a bluff body at the free end, using a multi-physics approach that combines electromechanical and aerodynamic models. The study uses MATLAB Simulink to solve the differential equations and verify the results with experiments. A parametric analysis examines the impact of external resistance, wind speed, and bluff body shape on circuit metrics. The study found that at a wind speed of 6 m/s and an optimal load resistance of 200 kΩ, the system generated 4.984 mW of power. This result demonstrates the potential of wind energy harvesting to power various distributed sensors for a wide range of applications.

Denoising diffusion algorithm for inverse design of microstructures with fine-tuned nonlinear material properties

We introduce a denoising diffusion algorithm to discover microstructures with nonlinear fine-tuned properties. Denoising diffusion probabilistic models are generative models that use diffusion-based dynamics to gradually denoise images and generate realistic synthetic samples. By learning the reverse of a Markov diffusion process, we design an artificial intelligence to efficiently manipulate the topology of microstructures to generate a massive number of prototypes that exhibit constitutive responses sufficiently close to designated nonlinear constitutive behaviors. To identify the subset of microcstructures with sufficiently precise fine-tuned properties, a convolutional neural network surrogate is trained to replace high-fidelity finite element simulations to filter out prototypes outside the admissible range. Results of this study indicate that the denoising diffusion process is capable of creating microstructures of fine-tuned nonlinear material properties within the latent space of the training data. More importantly, this denoising diffusion algorithm can be easily extended to incorporate additional topological and geometric modifications by introducing high-dimensional structures embedded in the latent space. Numerical experiments are conducted on the open-source mechanical MNIST data set (Lejeune, 2020). Consequently, this algorithm is not only capable of performing inverse design of nonlinear effective media, but also learns the nonlinear structure–property map to quantitatively understand the multiscale interplay among the geometry, topology, and their effective macroscopic properties.

Analysis of viscoelastic flow past a square cylinder in a channel with sudden contraction

The present study examines the effectiveness of the geometric modification in stabilizing the viscoelastic (VE) fluid flow through a planar channel with 5:1 sudden contraction. The geometric modification employed in this study includes a square cylinder positioned in front of the contraction plane. The square cylinder pre-deforms the fluid before entering the contraction region. The cylinder causes elongational flow in the wake region as well as shear and elongational flow between the channel and cylinder walls, significantly changing the nature of the flow. We used the open-source software OpenFoam, which is based on the finite volume method, to solve the mass, momentum, and rheological stress-constitutive equations. The Oldroyd-B model mimics the rheological characteristics of the VE fluid. Our research demonstrates that the pre-deformation of VE fluid stabilizes flow in the Wi range of 0–4. Additionally, the salient corner vortex size in the Wi range of 6–10 is effectively reduced by the square cylinder with a blockage ratio of 0.30. Furthermore, the Pakdel–Mckinley stability criterion demonstrates that an increase in Wi beyond the critical value initiates elastic turbulence in the flow.

Flow structure and performance analysis of Darrieus vertical axis turbines with swept blades: A critical case study on V-shaped blades

Blade geometric modification is one favorite way of enhancing the performance of vertical axis turbines. In this regard, V-shaped blades are a novel design featuring some leading-edge sweep angle. Currently, the relevant literature only focuses on finding the optimum parameters of the V-shaped blades and lacks a deep understanding of how they alter flow structure and whether they offer any performance improvement compared to other conventional types. To this aim, using three-dimensional numerical simulations, the flow structure and performance of two different V-shaped blade turbines, twisted and untwisted, are compared with straight and helical-blade turbines at tip speed ratios (TSRs) ranging from 0.69 to 1.5. Turbine torque average and fluctuation amplitude are chosen as the performance metrics. It is shown that the sweeping configuration of the V-shaped and helical types causes an inevitable spanwise flow, resulting in a performance loss, which makes neither type of V-shaped blade turbine advantageous at low TSRs.

Force amplification at the wheel hub due to the split in the air-cavity mode for a rolling tire

Reduction of tire/road noise has become an important issue for EV's since powertrain noise has largely been eliminated. A tire's air-cavity mode is known to be a significant contributor to increased forces at the wheel hub, which can result in significant interior noise levels near 200 Hz. Moreover, the single natural frequency of a static, undeformed tire can separate into two neighboring frequencies for a rolling, deformed tire due to the Doppler effect. In this study, the evolution of the frequency split at different speeds was observed in Tire Pavement Test Apparatus (TPTA) tests by measuring the dynamic force at the hub under rotation and load. Similar results were obtained using FE simulations to generate Campbell diagrams. Through the FE simulation, it has been shown that there can be force amplification at the hub when the split frequencies couple with adjacent treadband structural modes near 200 Hz. In addition, both material and geometrical modifications were applied to the base model to find values that would reduce force levels at the split frequencies. Finally, it is suggested that a target speed needs to be determined when evaluating a tire since the two natural frequencies are strongly influenced by rotation speed.

Performance improvement of a heat sink with triangular slotted and interrupted fins: A computational study

The present study reports a three-dimensional computational analysis of free convection heat transfer from heat sinks with vertical fins mounted on a vertical base. The difference in the base and ambient temperature varies from 10 °C to 60 °C. This work proposes four novel geometrical modifications on the continuous rectangular fins intending to augment the heat transfer rate. These modifications include (a) providing triangular slots, (b) changing the value of minimum thickness at the neck of the slotted fin, (c) offsetting the position of the neck, and (d) interrupting the slotted fins. Thus, the work investigates the thermal performances of six different heat sink configurations concerning heat dissipation rate (Q), specific heat transfer rate (Q/m), average Nusselt number (Nu), the weight of the heat sink, and effectiveness. In all these cases, the heat sink volume remains the same. The current analysis shows that the heat sink with a single slot, with the neck at the base (ε=0) and having interruptions, dissipates the maximum heat (14.89% higher than the conventional continuous fin heat sink) with a weight reduction of 24.1%. The present study also proposes a correlation for the average Nusselt number in terms of relevant parameters, which has an accuracy of 6 %.

Diseño Generativo para el Centro de I+I+D de la Sede Regional de IMARPE Huanchaco

This research proposes the systematization of evolutionary design processes through a methodology applied to the design of the decentralized headquarters of the Center for Research, Innovation and Development of Aquaculture and Oceanographic Sciences of the Institute of the Sea of Peru (IMARPE), in which establishes a definition of the architectural problem, which covers requirements and restrictions, to later be translated into geometric modification instructions interpreted by an evolutionary algorithm based on machine learning, thus obtaining as a result the volumetric composition of the preliminary project, product of the evolution of 5000 different proposals. , obtained generatively, where the resulting product is the best possible based on the restrictions and requirements set forth. This work is a starting point for generative design methodologies, investigates other ways of approaching design in the teaching of local architecture, and explores the possibilities offered by the evaluation of multiple solutions to a particular problem.

AltPrint: new filling and slicing process planning based on deposited material with geometry variation

PurposeThis paper aims to address the development and implementation of “AltPrint,” a slicing algorithm based on a new filling process planning from a variation in the deposited material geometry. AltPrint enables changes in the extruded material flow toward local variations in stiffness. The technical feasibility evaluation was conducted experimentally by fused filament fabrication (FFF) process of snap-fit subjected to a mechanical cyclical test.Design/methodology/approachThe methodology is based on the estimation of the parameter E from the mathematical relationships among the variation of the material in the material flow, nozzle geometry and extrusion parameters. Calibration, validation and analysis of the printed specimens were divided into two moments, of which the first refers to the material responses (flexural and dynamic mechanical analysis) and the second involves the analysis of the printed components with localized flow properties (for estimating the response to cyclic loading). Finite element analysis assisted in the comparison of two snap-fit geometries, one traditional and one generated by AltPrint. Finally, three examples of compliant mechanisms were developed to demonstrate the potential of the algorithm in the generation of functional prototypes.FindingsThe contribution of AltPrint is the variable fill width integrated with the slicing software that varies the print parameters in different regions of the object. The alternative extrusion method based on material rate variation was conceived as an “open software” available in GitHub platform, hence, open manufacturing with initial focus on desktop 3D printer based on FFF. The slicing method provides deposited variable-width segments in an organized and replicable filling strategy, resulting in mechanical properties variations in specific regions of a part. It was implemented and evaluated experimentally and indicated potential applications in parts manufactured by the additive process based on extrusion, which requires local flexibilities.Originality/valueThis paper presents a new alternative method for application in an open additive manufacturing context, specifically for additive extrusion techniques that enable local variations in the material flow. Its potential for manufacturing functional parts, which require flexibility due to cyclic loading, was demonstrated by fabrication and experimental evaluations of parts made in acrylonitrile butadiene styrene filament. The changes proposed by AltPrint enable geometric modifications in the response of the printed parts. The proposed slicing and filling control of parameters is inserted in a context of design for additive manufacturing and shows great potential in the area of product design.

Wave Impact Loads on Vertical Circular Cylinder and the effect of Hydrophobic Surface

Peculiarly cylindrical legs on offshore platforms constantly are exerted vigorously to wave stresses. For their lifetime, a test on structural deformations and pressure measurements is taken. Experimental research on the wave forces affecting cylindrical structures is presented. To determine pressure distributions and deformations in the altered cylinder's surface properties by applying a hydrophobic coating. Hence, the angle at which water drops hit the surface has increased, thus, decreasing water adhesion to the surface. The geometric modification or additional weight coated on the cylinders' surfaces is not notable. Wave loads with various amplitudes and frequencies were applied repeatedly to cylinders with hydrophobic and hydrophilic surface materials. Three pressure sensors and a strain gauge were used to measure pressure distributions and the cylinders' surface deformations respectively. Two cylinders' fluctuation in pressure is carefully examined and analyzed. Cylinder's pressure response for hydrophobic surfaces varied based on the sensor's location by lowering the maximum pressure or the impact time. The structural deformations due to changing surface properties and strain readings were contrasted. The structural deformation changed, with the impacting wave distributed throughout the surface. Image processing demonstrates the variation in the water body's volume to which the surface is exposed, reinforcing this finding.

Viscous Fluid Cosmology in Symmetric Teleparallel Gravity

AbstractIn this article, the viscous fluid cosmological model is analyzed in the framework of recently proposed gravity by assuming three different forms of bulk viscosity coefficients, specifically, , , and and a linear model, particularly, where is free model parameter. The bulk viscosity coefficients and the model parameter values using the combined H(z)+Pantheon+BAO data set are estimated. The asymptotic behavior of our cosmological bulk viscous model is studied by utilizing the phase space method. It is found that corresponding to all three cases, our model depicts the evolution of the universe from matter dominated decelerated epoch (a past attractor) to a stable de‐sitter accelerated epoch (a future attractor). Furthermore, the physical behavior of effective pressure, effective equation of state (EoS), and the statefinder parameters are studied. It is also found that the pressure component in the presence of bulk viscosity shows negative behavior and the effective EoS parameter predicts the accelerated expansion phase of the universe for all three cases. Moreover, the trajectories of the model lie in the quintessence region and it converges to the ΛCDM fixed point in the far future. It is found that the accelerated de‐Sitter like phase comes purely from the case without any geometrical modification to GR. Moreover, the late‐time behavior of all three cases of viscosity coefficients are identical. Furthermore, a non‐linear model is considered, specifically, , and then analyzed the behavior of model using dynamical approach. It is also found that the late‐time behavior of the considered non‐linear model with is similar to the linear case, whereas for the case results are quite different.

Flow dynamics in a model of a dilated thoracic aorta prior to and following prosthetic replacement

We numerically investigate the flow dynamics in a model of a dilated thoracic aorta, and compare the flow features with the case of a prosthetic replacement in its ascending part. The flow is characterized by an inlet jet which impacts the aortic walls and sweeps toward the aortic arch. Secondary flows generated by the transvalvular jet evolve downstream into a helical flow. The small curvature radius at the end of the aortic arch induces flow separation and vortex shedding in the initial part of the descending aorta, during the systole. The implantation of a prosthesis determines several modifications in the global and local flow patterns. An increase of the pulse wave velocity in the aorta leads to larger pressures inside the vessel, due to the geometrical and rigidity modifications. The sweeping jet is more aligned along the axial direction and propagates faster along the aortic arch. Consequently, a stronger separation of the flow downstream of the aortic arch is observed. By also exploiting manifold analysis, we identify regions characterized by near-wall disordered flows which may present intense accumulation and drop of concentration of biochemicals. These regions are localized downstream of the prosthetic replacement, in the aortic arch, and may be more prone to a new emergence of vessel dilation.Graphical