Search Results (27)

Accurate and efficient CFD simulations are essential for a wide range of engineering and scientific applications, from resilient structural design to environmental analysis. Traditional methods such as RANS simulations often face challenges in capturing complex flow phenomena like separation, while high-fidelity approaches including Large Eddy Simulations and Direct Numerical Simulations demand significant computational resources, thereby limiting their practical applicability. This paper provides an in-depth synthesis of recent advancements in integrating artificial intelligence and machine learning techniques with CFD to enhance simulation accuracy, computational efficiency, and modeling capabilities, including data-driven surrogate models, physics-informed methods, and ML-assisted numerical solvers. This integration marks a crucial paradigm shift, transcending incremental improvements to fundamentally redefine the possibilities of fluid dynamics research and engineering design. Key themes discussed include data-driven surrogate models, physics-informed methods, ML-assisted numerical solvers, inverse design, and advanced turbulence modeling. Practical applications, such as wind load design for solar panels and deep learning approaches for eddy viscosity prediction in bluff body flows, illustrate the substantial impact of ML integration. The findings demonstrate that ML techniques can accelerate simulations by up to 10,000 times in certain cases while maintaining or improving the accuracy, particularly in challenging flow regimes. For instance, models employing learned interpolation can achieve 40- to 80-fold computational speedups while matching the accuracy of baseline solvers with a resolution 8 to 10 times finer. Other approaches, like Fourier Neural Operators, can achieve inference times three orders of magnitude faster than conventional PDE solvers for the Navier–Stokes equations. Such advancements not only accelerate critical engineering workflows but also open unprecedented avenues for scientific discovery in complex, nonlinear systems that were previously intractable with traditional computational methods. Furthermore, ML enables unprecedented advances in turbulence modeling, improving predictions within complex separated flow zones. This integration is reshaping fluid mechanics, offering pathways toward more reliable, efficient, and resilient engineering solutions necessary for addressing contemporary challenges. Full article

This paper presents an improved k-ω SST turbulence model to enhance the simulation accuracy of Bluff Body Bypassing Problems (BBBPs) within the Reynolds-Averaged Navier–Stokes (RANS) framework. Although RANS methods are computationally efficient, they are limited in resolving instantaneous turbulent fluctuations, which often results in significant errors when predicting turbulent kinetic energy variations in complex flows. To address this, a curvature correction factor (f_c) is introduced into the production term (P_k) of the turbulent kinetic energy equation. This factor is derived from the local fluid rotational rate, enabling the model to better account for streamline curvature effects and unsteady vortex dynamics. The modified model, along with the baseline k-ω SST formulation, is applied to two-dimensional (2D) square column flow cases. Numerical results show that the corrected model significantly improves predictive accuracy, reducing the error in the time-averaged drag coefficient (C_D) from 24% to 8.3%, thereby demonstrating its effectiveness in capturing key flow characteristics around bluff bodies. Full article

This study explores the potential effects of the aerodynamic parameters on the performance of the galloping piezoelectric energy harvester. By considering the geometric configurations, a bluff body cross-sectional shape evolution approach is proposed using Boolean operations on the polygons and forty-eight different cross-sectional shapes with the protruding and depressed features are considered. Computational fluid dynamics is employed to perform a time-varying simulation of the aerodynamic characteristics. The effects of the aerodynamic parameters on performance are investigated computationally using a distributed parameter electromechanical coupling model. The critical wind speed, maximum output power, and the slope of the power versus wind speed curve are introduced as the performance evaluation parameters. The results show that the rear-side protruding feature and the top-side and bottom-side depressed feature have significant potential to enhance the performance. Furthermore, a symmetrical structure of the cross-sectional shape in the downstream direction should be prioritized over asymmetric designs. Full article

This paper experimentally examines the influence of hybrid excitation on the performance of vibrational piezoelectric energy harvesting systems on a bluff body with a variable cross section along its generatrix. A combination of vibrational excitation from a shaker and airflow is considered the source from which energy is harvested. Varied excitation frequencies and airflow velocities across five different masses were considered, each defining the natural frequency of the system. The system’s performance in hybrid excitation, enhancements in energy harvesting, and challenges with these was observed, helping to determine optimal operating conditions to function effectively in ambient environments. The tests identified the conditions and ranges within which maximized harvesting responses were observed. Next, computational fluid dynamic (CFD) simulations were carried out to understand the impact of circular and square cross sections controlling the nature of the airflow and representative of the wide range of cross sections that may be utilized for such purposes. The analyses helped contextualize the opportunities and limitations of the use of such cross sections and helped in understanding if a transition from one cross section to another can lead to an assimilation of the advantages observed in using each cross section independently. Full article

In the field of fluid dynamics, the Reynolds number is a key parameter that influences the flow characteristics around bluff bodies. While its impact on flow around stationary cylinders has been extensively studied, systematic research into flow-induced vibrations (FIVs) under these conditions remains limited. This study utilizes numerical simulations to explore the FIV characteristics of smooth cylinders and passive turbulence control (PTC) cylinders supported elastically within a Reynolds number range from 0.8 × 10⁴ to 1.1 × 10⁵. By comparing the vibration responses, lift coefficients, and wake structures of these cylinders across various Reynolds numbers, this paper aims to elucidate how Reynolds numbers affect the flow and vibration characteristics of these structures. The research employs images of instantaneous lift changes and vortex shedding across multiple sections to visually demonstrate the dynamic changes in flow states. The findings are expected to provide theoretical support for optimizing structural design and vibration control strategies in high-Reynolds-number environments, emphasizing the importance of considering Reynolds numbers in structural safety and design optimization. Full article

Vortices belong to the most important phenomena in fluid dynamics and play an essential role in many engineering applications. They can act detrimentally by harnessing the flow energy and reducing the efficiency of an aerodynamic device, whereas in other cases, their presence can be exploited to achieve targeted flow conditions. The control of the vortex parameters is desirable in both cases. In this paper, we introduce an optimization strategy for the control of vortices in the wake of a bluff body. Flow modelling is based on RANS and DES computations, validated by experimental data. The algorithm for vortex identification and characterization is based on the triple decomposition of motion. It produces a quantitative measure of vortex strength which is used to define the objective function in the optimization procedure. It is shown how the shape of an aerodynamic device can be altered to achieve the desired characteristics of vortices in its wake. The studied case is closely related to flame holders for combustion applications, but the conceptual approach has a general applicability to vortex control. Full article

A reduction in wake effects in large wind farms through wake-aware control has considerable potential to improve farm efficiency. This work examines the success of several emerging, empirically derived control methods that modify wind turbine wakes (i.e., the pulse method, helix method, and related methods) based on Strouhal numbers on the $\mathcal{O}\left(0.3\right)$. Drawing on previous work in the literature for jet and bluff-body flows, the analyses leverage the normal-mode representation of wake instabilities to characterize the large-scale wake meandering observed in actuated wakes. Idealized large-eddy simulations (LES) using an actuator-line representation of the turbine blades indicate that the $n=0$ and $\pm 1$ modes, which correspond to the pulse and helix forcing strategies, respectively, have faster initial growth rates than higher-order modes, suggesting these lower-order modes are more appropriate for wake control. Exciting these lower-order modes with periodic pitching of the blades produces increased modal growth, higher entrainment into the wake, and faster wake recovery. Modal energy gain and the entrainment rate both increase with streamwise distance from the rotor until the intermediate wake. This suggests that the wake meandering dynamics, which share close ties with the relatively well-characterized meandering dynamics in jet and bluff-body flows, are an essential component of the success of wind turbine wake control methods. A spatial linear stability analysis is also performed on the wake flows and yields insights on the modal evolution. In the context of the normal-mode representation of wake instabilities, these findings represent the first literature examining the characteristics of the wake meandering stemming from intentional Strouhal-timed wake actuation, and they help guide the ongoing work to understand the fluid-dynamic origins of the success of the pulse, helix, and related methods. Full article

Hydrogen can play a key role in the gradual transition towards a full decarbonization of the combustion sector, e.g., in power generation. Despite the advantages related to the use of this carbon-free fuel, there are still several challenging technical issues that must be addressed such as the thermoacoustic instability triggered by hydrogen. Given that burners are usually designed to work with methane or other fossil fuels, it is important to investigate their thermoacoustic behavior when fueled by hydrogen. In this framework, the present work aims to propose a methodology which combines Computational Fluid Dynamics CFD (3D Reynolds-Averaged Navier-Stokes (RANS)) and Finite Element Method (FEM) approaches in order to investigate the fluid dynamic and the thermoacoustic behavior introduced by hydrogen in a burner (a lab-scale bluff body stabilized burner) designed to work with methane. The case of CH₄-air mixture was used for the validation against experimental results and benchmark CFD data available in the literature. Numerical results obtained from CFD simulations, namely thermofluidodynamic properties and flame characteristics (i.e., time delay and heat release rate) are used to evaluate the effects of the fuel change on the Flame Response Function to the acoustic perturbation by means of a FEM approach. As results, in the H₂-air mixture case, the time delay decreases and heat release rate increases with respect to the CH₄-air mixture. A study on the Rayleigh index was carried out in order to analyze the influence of H₂-air mixture on thermoacoustic instability of the burner. Finally, an analysis of both frequency and growth rate (GR) on the first four modes was carried out by comparing the two mixtures. In the H₂-air case the modes are prone to become more unstable with respect to the same modes of the case fueled by CH₄-air, due to the change in flame topology and variation of the heat release rate and time delay fields. Full article

Vortex-induced vibration (VIV) of bluff bodies is one type of flow-induced vibration phenomenon, and the possibility of using it to harvest hydrokinetic energy from marine currents has recently been revealed. To develop an optimal harvester, various parameters such as mass ratio, structural stiffness, and inflow velocity need to be explored, resulting in a large number of test cases. This study primarily aims to examine the validity of a parameter optimization approach to maximize the energy capture efficiency using VIV. The Box–Behnken design response-surface method (RSM-BBD) applied in the present study, for an optimization purpose, allows for us to efficiently explore these parameters, consequently reducing the number of experiments. The proper combinations of these operating variables were then identified in this regard. Within this algorithm, the spring stiffness, the reduced velocity, and the vibrator diameter are set as level factors. Correspondingly, the energy conversion efficiency was taken as the observed value of the target. The predicted results were validated by comparing the optimized parameters to values collected from the literature, as well as to our simulations using a computational-fluid dynamics (CFD) model. Generally, the optimal operating conditions predicted using the response-surface method agreed well with those simulated using our CFD model. The number of experiments was successfully reduced somewhat, and the operating conditions that lead to the highest efficiency of energy harvesting using VIV were determined. Full article

Flow Energy Harvesters (FEHs), equipped with piezoelectric active layers, are designed to extract energy from non-pulsating flows. FEHs featuring cantilevers with tip-mounted Vibration Inducers (VIs) are designed to develop a galloping motion. In this paper, we present the modelling of a recently introduced VI shape, featuring semitubular-shaped winglets, which do not produce a wake interacting with the cantilever. Such peculiarity allows (i) to exploit the contribution of the wake to the formation of the lift, therefore opening to a more compact design; (ii) its performance to be analyzed by means of simple two-dimensional Computational Fluid Dynamics (CFD) simulations. By comparison with experimental data, we show that the minimal framework for the modelling of such new class of VIs needs to account for both the direct action of the fluid onto the cantilever and the drag on the VI, which are usually negligible for other VI shapes. Full article

Large Eddy Simulation (LES) has rapidly developed into a powerful computational methodology for fluid dynamic studies, between Reynolds-Averaged Navier–Stokes (RANS) and Direct Numerical Simulation (DNS) in both accuracy and cost. High-speed combustion applications, such as ramjets, scramjets, dual-mode ramjets, and rotating detonation engines, are promising propulsion systems, but also challenging to analyze and develop. In this paper, the building blocks needed to perform LES of high-speed combustion are reviewed. Modelling of the unresolved, subgrid terms in the filtered LES equations is highlighted. The main families of combustion models are presented, focusing on finite-rate chemistry models. The density-based finite volume method and the reaction mechanisms commonly employed in LES of high-speed H₂-air combustion are briefly reviewed. Three high-speed combustor applications are presented: an experiment of supersonic flame stabilization behind a bluff body, a direct connect facility experiment as a transition case from ramjet to scramjet operation mode, and the STRATOFLY MR3 Small-Scale Flight Experiment. Several combinations of turbulence and combustion models are compared. Comparisons with experiments are also provided when available. Overall, the results show good agreement with experimental data (e.g., shock train, mixing, wall heat flux, transition from ramjet to scramjet operation mode). Full article

One of the most common systems in engineering problems is the multi-column system in the form of an equilateral-triangular arrangement. This study used three-dimensional numerical simulations to investigate the flow around three cylinders in this arrangement at the super-critical Reynolds number $Re=3\times {10}^6$, concentrating on the influence on the spacing ratio ($L/D$) among cylinders. The instantaneous vortex structures, Strouhal numbers, fluid force coefficients, and pressure distributions are analyzed thoroughly. The present study demonstrated that fluid dynamics is sensitive to $L/D$, by which five different flow patterns are classified, namely single bluff body flow ($L/D\le 1.1$), deflected gap flow ($1.2\le L/D\le 1.4$), anti-phase flow ($1.5\le L/D\le 2.3$), in-phase flow ($2.5\le L/D<3.5$), and co-shedding flow ($L/D\ge 3.5$). Critical bounds are identified by significant transitions in the flow structure, discontinuous drop and jump of $St$, and force coefficients. Full article

A comprehensive review of modelling techniques for the flow-induced vibration (FIV) of bluff bodies is presented. This phenomenology involves bidirectional fluid–structure interaction (FSI) coupled with non-linear dynamics. In addition to experimental investigations of this phenomenon in wind tunnels and water channels, a number of modelling methodologies have become important in the study of various aspects of the FIV response of bluff bodies. This paper reviews three different approaches for the modelling of FIV phenomenology. Firstly, we consider the mathematical (semi-analytical) modelling of various types of FIV responses: namely, vortex-induced vibration (VIV), galloping, and combined VIV-galloping. Secondly, the conventional numerical modelling of FIV phenomenology involving various computational fluid dynamics (CFD) methodologies is described, namely: direct numerical simulation (DNS), large-eddy simulation (LES), detached-eddy simulation (DES), and Reynolds-averaged Navier–Stokes (RANS) modelling. Emergent machine learning (ML) approaches based on the data-driven methods to model FIV phenomenology are also reviewed (e.g., reduced-order modelling and application of deep neural networks). Following on from this survey of different modelling approaches to address the FIV problem, the application of these approaches to a fluid energy harvesting problem is described in order to highlight these various modelling techniques for the prediction of FIV phenomenon for this problem. Finally, the critical challenges and future directions for conventional and data-driven approaches are discussed. So, in summary, we review the key prevailing trends in the modelling and prediction of the full spectrum of FIV phenomena (e.g., VIV, galloping, VIV-galloping), provide a discussion of the current state of the field, present the current capabilities and limitations and recommend future work to address these limitations (knowledge gaps). Full article

This study investigates the gas dynamic effects and atomization behavior of a novel sonic bluff body-assisted two-fluid atomizer with three different geometric configurations based on airflow orifice diameters (d) of 2.0 mm, 3.0 mm, and 4.0 mm. Along with a 280 µm annular liquid sheet, atomizers that employed a central bluff body (cone) with 6.0 mm cone distance (L_c) are compared based on the range of different air and liquid (water) flow rates. The spray-bluff body-impacted secondary atomization was characterized through volume-normalized droplet size distribution (DSD) and cumulative droplet distribution, excentricity plots, Sauter mean diameter (SMD), and relative span factor (Δ). Droplet number density decreases with the increase in radial location, with lesser droplet density for the 3.0 mm atomizer. DSD and cumulative droplet distribution become less uniform with the increase in the radial locations with wider distribution for larger diameter atomizers (4.0 mm). Droplet excentricity follows an inverse relationship with the droplet diameter such that high diameter droplets have low excentricity (%) and vice versa. SMD and relative span factor (RSF) showed opposite trends when plotted (line plots) against the air-to-liquid ratio (ALR) with larger fluctuation in the SMD than the RSF (Δ) value. The spray pattern spread increases gradually with increasing liquid loading and with decreases in the ALR value for all atomizers. Full article

The impacts of conflicting aerodynamic forces and side drifting forces are the primary unstable elements in automobiles. The action of an unstable environment in automobile vehicles increases the chance of an accident occurring. As a result, much study is required to determine how opposing aerodynamic forces and side drifting force affects function, as well as how to deal with them for safe and smooth navigation. In this work, an intercity bus is chosen as a main object, and computational fluid dynamics (CFD) analysis is used to estimate aerodynamic forces on the bus in all major directions. Experimentation is also carried out for validation reasons. CFD findings for a scaled base model and a dimple-loaded model based on experimental results from a subsonic wind tunnel are demonstrated to be correct. The drag forces generated by CFD simulations on test models are carefully compared to the experimental drag findings of same-dimensioned models. The error percentages between the results of these two methods are acquired and the percentages are determined to be within an acceptable range of significant limitations. Following these validations, CATIA is used to create a total of nine distinct models, the first of which is a standard intercity bus, whereas the other eight models are fitted with drag reduction techniques such as dimples, riblets, and fins on the surface of their upper cumulus side. A sophisticated computational tool, ANSYS Fluent 17.2, is used to estimate the comparative assessments of the predictions of aerodynamic force fluctuations on bus models. Finally, dimples on the top and side surfaces of the bus model (DESIGN–I) are proposed as a more efficient model than other models because dimples are a vital component that may lower pressure drag on the bus by 18% in the main flow direction and up to 43% in the sideslip direction. Furthermore, by minimizing the different aerodynamic force sources without impacting the preparatory needs, the proposed model may provide comfortable travel. The real-time bus is created, and the finalized drag reduction is applied to the optimized places over the whole bus model. In addition, five distinct size-based bus models are developed and studied in terms of aerodynamic forces, necessary energy to resist aerodynamic drag, required forward force for successful movement, instantaneous demand for particular power, and fuel consumption rate. Finally, the formation of aeroacoustic noise owing to turbulence is estimated using sophisticated computer simulation. Last, for real-time applications, multi-parametric studies based on appropriate intercity buses are established. Full article