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The aerodynamic performance of an aircraft can be significantly enhanced by incorporating wingtip devices, such as winglets, which primarily reduce lift-induced drag caused by wingtip vortices. This study introduces a comprehensive optimization framework for designing winglets on a Class I fixed-wing mini-UAV, aiming to maximize aerodynamic efficiency and operational performance. Using surrogate-based optimization (SBO) techniques, this research developed winglet geometries with varying geometric parameters such as length, cant angle, and sweep angle with their performance being evaluated through high-fidelity Computational Fluid Dynamics (CFD) simulations. These simulations utilized Reynolds-Averaged Navier–Stokes (RANS) equations coupled with the Spalart–Allmaras turbulence model to capture the intricate flow dynamics around the UAV in different flight phases. The integration of SBO techniques allowed for an efficient exploration of the design space while reducing computational costs associated with iterative high-fidelity simulations. In particular, the proposed SBO framework optimized the UAV's aerodynamic characteristics, including lift-to-drag ratio and drag reduction, followed by a stability and control analyses to ensure balanced performance for the optimal configurations. Dynamic stability evaluations revealed improved flight characteristics, maintaining control across operational envelopes. The results demonstrated a significant improvement in aerodynamic coefficients, range, endurance, and reduction in battery consumption throughout the entire UAV operational envelope, underscoring the potential of innovative winglet designs to enhance UAV performance across diverse mission profiles. [ABSTRACT FROM AUTHOR]

In this study, a numerical investigation into the sustained aerodynamic performance of a morphing wing equipped with a flexible leading edge, employing a 2-dimensional NACA0012 airfoil configuration, is conducted. The compressible governing equations of the flow are employed, simulating 2 distinct states: the airfoil without motion and the airfoil featuring a flexible leading edge with a chord length of 0.856 m, assessing various angles of attack utilizing the k-ω SST turbulence approach within Fluent software. Dynamic mesh, facilitated by a user-defined function, is utilized in Fluent software to simulate the movement of the airfoil wall at the leading edge. The study thoroughly analyzes the flow behavior concerning diverse angles of attack and deviations, evaluating their impact on aerodynamic coefficients, velocity, and pressure fields under steady-state settings. Validation of the chosen numerical approach demonstrates close alignment of the front and back coefficients with experimental settings. Outcomes from the steady-state flow simulation of the morphing wing reveal that positive deflection angles correspond to increased lift coefficients and decreased drag coefficients, with lift coefficient increases of up to 15% and drag coefficient reductions of up to 10% at specific angles. Meanwhile, the negative deflection angles have shown a decline in lift coefficients, with the drag coefficients increasing with the decrease in deflection angle. All these observations show that at the flexible leading edge, there is a considerable improvement in aerodynamic efficiency. Hence, it should find more applications in different regimes of flight. [ABSTRACT FROM AUTHOR]

To enhance the air–water adaptability of the aerial-aquatic vehicles (AAVs), an improved tandem twin-rotor AAV design is proposed based on the characteristics and application requirements of air–water cross-domain movement. Computational fluid dynamics (CFD) software was used to simulate the underwater cruising state and dynamic water entry process of the tandem twin-rotor AAV. Results indicate that the underwater cruise resistance of the improved tandem twin-rotor AAV is relatively small. Among them, the two sets of tandem air power systems account for a relatively large proportion of the underwater drag, about 29.8%, while the drag reduction achieved by improving the head shape is around 15.4%. The head shape, water entry angle and speed have a great influence on the water entry trajectory and attitude of the tandem twin-rotor AAV. Following improvement, the tandem twin-rotor AAV demonstrates an enhancement in reducing the deviation of the water entry trajectory, mitigating water surface ricochet and enhancement of water entry depth to a certain extent. The inclination angle should be in the range of 20–30∘ to alleviate unfavorable outcomes, including prolonged water entry time caused by water surface ricochet at lower entry angles, while concurrently mitigating the heightened impact pressure resulting from steeper entry angles. Higher entry velocities lead to greater impact pressures, necessitating careful consideration of water entry depth and impact pressure to prevent adverse effects on structural integrity. [ABSTRACT FROM AUTHOR]

The article "Tunable drag drop via flow-induced snap-through in origami" in the Journal of Fluid Mechanics explores using origami mechanisms to control drag in fluid environments. By utilizing the snap-through response of bistable origami units, the study demonstrates a sudden drop in drag with flow speed, allowing for passive drag control. Varying the geometrical and mechanical properties of the origami unit enables the tuning of drag discontinuity and critical speed, with potential applications in aerodynamics and fluidic control systems. The research showcases the potential of origami-inspired mechanisms for efficient drag control in fluid environments, offering insights into programmable drag-vs-speed behavior for various applications. [Extracted from the article]

Efficient aerodynamics significantly impact your vehicle's overall efficiency. Enhancing vehicle performance and fuel economy hinges on optimizing aerodynamics. Reduced drag equates to decreased resistance against air, requiring less energy for propulsion. This study employs numerical investigation utilizing ANSYS Fluent computational fluid dynamics (CFD) simulations to identify the aerodynamic characteristics of an SUV. The goal is to gain insights into the vehicle's aerodynamics. This study involves the creation of a 3D model of the SUV car, which is then subjected to simulated wind channel testing. ANSYS Fluent is employed to simulate the airflow around the car, enabling the estimation of drag and lift forces. The primary objective of the study is to achieve an optimal shape design for the SUV by varying the glass inclination angle within the range of 145° to 160°, and subsequently observe its effects. It has been observed that as the glass inclination angle increases, both drag and lift forces decrease gradually, with optimal results observed at a 160° inclination angle. Additionally, detailed observations of pressure and velocity fluctuations were made to further analyze flow phenomena. Adjusting the angle could potentially modify airflow around the vehicle, potentially minimizing drag by facilitating smooth airflow over the car, thus reducing resistance. [ABSTRACT FROM AUTHOR]

Aerodynamics is a key factor in time-trial cycling. Over the years, various aspects have been investigated, including positioning, clothing, bicycle design, and helmet shape. The present study focuses on the development of a methodology for the aerodynamic optimization of a time-trial helmet through the implementation of a reduced-order model, alongside advanced simulation techniques, such as computational fluid dynamics, radial basis functions, mesh morphing, and response surface methodology. The implementation of a reduced-order model enhances the understanding of aerodynamic interactions compared to traditional optimization workflows reported in sports-related research, facilitating the identification of an optimal helmet shape during the design phase. The study offers practical insights for refining helmet design. Starting with a baseline teardrop profile, several morphing configurations are systematically tested, resulting in a 10% reduction in the drag force acting on the helmet. The reduced-order model also facilitates the analysis of turbulent flow patterns on the cyclist's body, providing a detailed understanding of aerodynamic interactions. By leveraging reduced-order models and advanced simulation techniques, this study contributes to ongoing efforts to reduce the aerodynamic resistance of time-trial helmets, ultimately supporting the goal of improved athlete performance. [ABSTRACT FROM AUTHOR]

In aerodynamic shape optimization, geometric parameterized variables have a significant impact on the flow field, thereby influencing both the effectiveness and efficiency of the optimization process. This paper utilizes flow field data from computational fluid dynamics (CFD) to develop a data-driven approach for analyzing the influence of geometric parameterized variables on the objective function and flow field across various design spaces. A data-driven method, namely a sensitivity analysis based on the Kriging model, is proposed along with three design space variation schemes (scaling, translation, and their combination) to evaluate the influence of geometric parameters on the objective function under varying design spaces. Furthermore, the study investigates the effects of these design space variation schemes on the sensitivity results using two test functions and a wave drag reduction case. The results of the wave drag reduction case are further analyzed in relation to flow conditions, including the Mach number and shock-wave strength. The findings indicate that design space variations alter the relationship between geometric parameters and the flow field, particularly affecting the shock-wave position and strength, as reflected by the sensitivity indices of the variables. Additionally, the sensitivity results show a strong dependence on the Mach number under varying design space configurations. [ABSTRACT FROM AUTHOR]

Computational efficiency and precision pose a classic contradiction in aerodynamic shape optimization. To address this challenge, this study introduces an effective optimization framework based on multi-fidelity fully connected neural network (MFFCN). The framework utilizes transfer learning (TL) to train a multi-fidelity surrogate model that establishes direct mappings between geometric configuration parameters and aerodynamic performance by adaptively capturing linear or nonlinear relationships concealed between high-fidelity (HF) and low-fidelity (LF) information. The HF and LF data are derived from fine and coarse grids, respectively, evaluated using the same computational fluid dynamics (CFD) model. The MFFCN-TL framework is applied to optimize the National Advisory Committee for Aeronautics 0012 (NACA0012) airfoil (12 design variables) and the Office National d'Études et de Recherches Aérospatiales M6 (ONERA M6) wing (50 design variables). Simulation results demonstrate that the NACA0012 airfoil achieves a 69.47% enhancement in lift–drag ratio in 1.069 s, compared to a 12.76% gain over 24.8 h in single-fidelity CFD-based optimization. The ONERA M6 wing achieves a 24.66% reduction in drag coefficient in 694 ms compared to 18.37% over 237.3 h in the CFD model. Statistical results show that the MFFCN-TL framework can reduce optimization cost by more than 90% compared to the single-fidelity CFD-based model. These findings suggest that the MFFCN-TL framework significantly enhances optimization efficiency and provides superior feasible solutions over single-fidelity methods. [ABSTRACT FROM AUTHOR]

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On a flat road, at race speeds, aerodynamic drag is the main resistive force a cyclist must overcome. Computational fluid dynamics (CFD) can be a useful tool to predict and understand the complex flow and, therefore, drive developments to reduce drag. However, cycling aerodynamics is complex. The effects of Reynolds number, surface roughness, boundary layer transition, flow separation, and turbulent wakes are challenging to accurately predict. High fidelity time-resolved computations, such as Large eddy simulations (LES), require high-performance computing and lengthy simulation times. This paper examines whether lower fidelity CFD, such as Reynolds averaged approaches, can predict the drag of a cyclist with sufficient accuracy and within practical timescales on a desktop PC. Wind tunnel tests of a rider model (without bicycle) were conducted at Reynolds numbers equivalent to speeds of ~ 20–70 km/h. Measured drag showed a notable Reynolds number dependency with the drag coefficient reducing almost linearly by ~ 20% from 0.88 to 0.71. The computational accurately replicated this relationship but only when employing a boundary layer transition model. The steady computations underpredicted the magnitude of the measured drag coefficient by ~ 3% but the unsteady computations were within ~ 2%. Examination of the predicted flow field revealed variations in boundary layer transition, separation, and wake formation from each body part which combine in a complex wake system. Overall, the data confirm validity and suitable accuracy of the CFD, and therefore this provides a practical time and cost-effective tool for further examination of drag reduction within cycling. [ABSTRACT FROM AUTHOR]

The study examines the use of an online control strategy for flow control past a circular cylinder, utilizing synthetic jets to reduce drag force and fluctuations. Different probe arrangements and input penalty factors impact control performance, with rectangular probes showing more stable effects. The research also delves into the impact of active control on flow modes, wake characteristics, and robustness in perturbed upstream flow conditions, offering promising insights for flow control in complex environments. The document compiles research articles on various fluid mechanics and flow control topics, including deep reinforcement learning, open-source Python platforms, negative peak pressure generation, and drag reduction in wall-bounded turbulence, showcasing innovative methods for enhancing fluid dynamics in engineering applications. [Extracted from the article]

The article delves into the use of patterned heating to minimize pressure losses in sloping channels by creating separation bubbles that reduce friction and induce fluid rotation. Factors like Reynolds number, heating wavelength, and channel inclination impact the effectiveness of heating in reducing pressure losses. While judicious heating can significantly decrease pressure losses, excessive heating may lead to increased energy costs. The study suggests that heating can be a viable method for drag reduction in specific channel orientations, emphasizing the potential for energy efficiency and flow rate optimization through patterned heating. [Extracted from the article]

About 60% of marine vessels' power is consumed to overcome friction resistance between the hull and water. Air lubrication can effectively reduce this resistance and lower fuel consumption, and consequently emissions. This study aims to analyze the use of a gas-injected liquid lubrication system (GILLS) to reduce friction resistance in a real-world scenario. A 3D computational fluid dynamics model is adopted to analyse how a full-scale ship (the Sea Transport Solutions Designed Catamaran ROPAX ferry) with a length of 44.9 m and a width of 16.5 m is affected by its speed and draught. The computational model is based on a volume of fluid model using the k-ꞷ shear stress transport turbulence model. Results show that at a 1.5 m draught and 20 knots cruising speed, injecting 0.05 kg/s of compressed air into each GILLS unit reduces friction resistance by 10.45%. A hybrid model of natural air suction and force-compressed air shows a friction resistance reduction of 10.41%, which is a promising solution with less required external power. The proposed technique offers improved fuel efficiency and can help to meet environmental regulations without engine modifications. [ABSTRACT FROM AUTHOR]

Delaying the onset of laminar-turbulent transition is an attractive method in reducing skin friction drag, especially on streamlined bodies where Tollmien–Schlichting instabilities are the dominating mechanism for transition. Miniature Vortex Generators (MVGs) offer an effective approach to attenuate these instabilities by generating counter-rotating vortex pairs. They are placed in pairs within an array and resemble small-winglet-type elements. The conventional methodology involves adjusting the MVG parameters and conducting computationally expensive DNS and/or downstream stability analyses to assess their effectiveness. However, analyzing the vortex parameters of MVG-generated vortices can potentially guide a more targeted approach to modifying the MVG parameters and identifying the critical factors for transition delay. Therefore, this study investigates the changes in three primary MVG parameters, namely inner distance, periodicity, and height, and utilizes computational fluid dynamics (CFDs) analysis to create a dataset that examines the characteristics of the generated counter-rotating vortex pairs and their potential in drag reduction. The objective is to establish correlations among these parameters and their influence on delaying transition. The results show that there is an optimal ratio between the MVG height and boundary layer thickness. Higher MVGs cause a decrease in the vortex radius and an increase in the amount of circulation, raising the likeliness of bypass transition. The derived correlations between the different MVG parameters show that the vortex radius is the most critical one and is hence an important parameter in the drag reduction potential. [ABSTRACT FROM AUTHOR]

Background: Drafting is a common technique to reduce the drag experienced by elite runners on races, leading to faster finish times. The tactic has been successfully used in previous marathon world records. In the 2023 Chicago Marathon, Kenyan runner Kelvin Kiptum broke the marathon record after a 2:00:35 finish. This feat is impressive considering the lack of use of drafting, despite the availability of two pacers for the majority of the race. Methods: In this study, the drag faced by Kiptum and his pacers during the race is calculated by means of computational fluid dynamics (CFD). The performance of each runner is evaluated from an energetic standpoint, and the analysis is extended to include more efficient drafting formations. Results: Running in proper formations results in drag reductions in excess of 70% for the main runner. Our results indicate that, by properly using the advantages of drafting, Kiptum could have finished the race at a staggering 1:57:34, a full three minutes better than his own record and 215 s better than the previous world record. Conclusion: Proper use of drafting does indeed improve the energetic performance of a runner, allowing for lower race times and potentially helping elite runners in breaking the 2-h barrier for a marathon. [ABSTRACT FROM AUTHOR]

The automotive industry continuously enhances vehicle design to meet the growing demand for more efficient vehicles. Computational design and numerical simulation are essential tools for developing concept cars with lower carbon emissions and reduced costs. Underground roads are proposed as an attractive alternative for reducing surface congestion, improving traffic flow, reducing travel times and minimizing noise pollution in urban areas, creating a quieter and more livable environment for residents. In this context, a concept car body design for underground tunnels was proposed, inspired by the mako shark shape due to its exceptional operational kinetic qualities. The proposed biomimetic-based method using computational fluid dynamics for engineering design includes an iterative process and car body optimization in terms of lift and drag performance. A mesh sensitivity and convergence analysis was performed in order to ensure the reliability of numerical results. The unique surface shape of the shark enabled remarkable aerodynamic performance for the concept car, achieving a drag coefficient value of 0.28. The addition of an aerodynamic diffuser improved downforce by reducing 58% of the lift coefficient to a final value of 0.02. Benchmark validation was carried out using reported results from sources available in the literature. The proposed biomimetic design process based on computational fluid modeling reduces the time and resources required to create new concept car models. This approach helps to achieve efficient automotive solutions with low aerodynamic drag for a low-carbon future. [ABSTRACT FROM AUTHOR]

By improving the understanding of fluid behaviour and allowing the development of cutting-edge technologies that enhance fluid-related processes in various sectors, advances in fluid dynamics serve a crucial role in both science and engineering. Sequel to the broad applicability of fluid dynamics leading to more efficient, sustainable, and innovative solutions for real-world challenges associated with the motion of liquids and gases, reviews of the recent advancements are far-fetched. The scope of the review was structured to focus on recent published facts on lift generation and drag reduction of aeroplanes, Computational Fluid Dynamics, turbulence modelling, and multiphase flow. Research synthesis which focuses on summarizing the state of the art of research facts on fluid dynamics was adopted. It is worth concluding that fluid dynamics principles stand as a cornerstone, unequivocally driving the relentless advancement of aerospace and automotive engineering, crucially contributing to the development of drag reduction techniques, precision control of lift generation, streamlined shapes for drag minimization, innovative wing profiles for enhanced lift, and effective boundary layer control for drag reduction. Recent advancements in Computational Fluid dynamics have revolutionized engineering simulations, providing unparalleled accuracy and efficiency in modelling complex fluid flow phenomena, from aerodynamics to hydrodynamics, thereby significantly accelerating the design and optimization processes across various industries. Studying of multiple fluid phases moving through a system simultaneously causes complicated interactions, phase transition events, and a variety of flow patterns, making it a complex but essential research topic. Experts face challenges validating Computational Fluid Dynamics results due to insufficient experimental data. [ABSTRACT FROM AUTHOR]

The multiple additional sampling point method has become popular for use in Efficient Global Optimization (EGO) to obtain aerodynamically shaped designs in recent years. It is a challenging task to study the influence of adding multi-sampling points, especially when multi-objective and multi-fidelity requirements are applied in the EGO process, because its factors have not been revealed yet in the research. In this study, the addition of two (multi-) sampling points (2-MAs) and four (multi-) sampling points (4-MAs) in each iteration are used to study the proposed techniques and compare them against results obtained from a single additional sampling point (1-SA); this is the approach that is conventionally used for updating the hybrid surrogate model. The multi-fidelity multi-objective method is included in EGO. The performance of the system, the computational convergence rate, and the model accuracy of the hybrid surrogate are the main elements for comparison. Each technique is verified by mathematical test functions and is applied to the airfoil design. Class Shape Function Transformation is used to create the airfoil shapes. The design objectives are to minimize drag and to maximize lift at designated conditions for a Reynolds number of one million. Computational Fluid Dynamics is used for ensuring high fidelity, whereas the panel method is employed when ensuring low fidelity. The Kriging method and the Radial Basis Function were utilized to construct high-fidelity and low-fidelity functions, respectively. The Genetic Algorithm was employed to maximize the Expected Hypervolume Improvement. Similar results were observed from the proposed techniques with a slight reduction in drag and a significant rise in lift compared to the initial design. Among the different techniques, the 4-MAs were found to converge at the greatest rate, with the best accuracy. Moreover, all multiple additional sampling point techniques are shown to improve the model accuracy of the hybrid surrogate and increase the diversity of the data compared to the single additional point technique. Hence, the addition of four sampling points can enhance the overall performance of multi-fidelity, multi-objective EGO and can be utilized in highly sophisticated aerodynamic design problems. [ABSTRACT FROM AUTHOR]

The study of aquatic organisms' ectomorphology is important to understanding the mechanisms of efficient swimming and drag reduction in fish. The drag reduction mechanism in fish remains unknown yet is needed for optimising the efficiency of bionic fish. It is thus crucial to conduct drag tests and analyses. In this paper, an optimal dolphin morphological model is constructed taking the beakless porpoise as the research object. A numerical simulation of the dolphin body model is carried out for different combinations of pitch angle and speed adopting computational fluid dynamics, and the flow field noise of the dolphin body model is solved for different speeds using the FW-H equation. When the dolphin model is oriented horizontally, the differential pressure drag accounts for approximately 20–25% of the total drag as airspeed increases. As both the pitch angle and airspeed increase, the differential pressure drag and friction drag decrease with increasing airspeed. Moreover, the acoustic energy is mainly concentrated at low frequencies for both the dolphin and Bluefin-21 models. The dolphin body model has better noise performance than the Bluefin-21 model at the same speed. The optimisation of the external morphology of the bionic underwater submarine and the analysis of the shape drag are thus important for revealing the drag reduction mechanism, reducing noise in the flow field and provide guidance for research on bionic fish. [ABSTRACT FROM AUTHOR]

Reducing resistance to surface friction is challenging in the field of engineering. Natural biological systems have evolved unique functional surfaces or special physiological functions to adapt to their complex environments over centuries. Among these biological wonders, fish, one of the oldest in the vertebrate group, have garnered attention due to their exceptional fluid dynamics capabilities. Fish skin has inspired innovation in reducing surface friction due to its unique structures and material properties. Herein, drawing inspiration from the unique properties of fish scales, a periodic array of fish scales was fabricated by laser ablation on a polished aluminum template. The morphology of the biomimetic fish scale surface was characterized using scanning electron microscopy and a white-light interfering profilometer. Drag reduction performance was measured in a closed circulating water tunnel. The maximum drag reduction was 10.26% at a Reynolds number of 39,532, and the drag reduction performance gradually decreased with an increase in the distance between fish scales. The mechanism of the biomimetic drag reduction surface was analyzed using computational fluid dynamics. Streamwise vortices were generated at the valley of the biomimetic fish scale, replacing sliding friction with rolling friction. These results are expected to provide a foundation for in-depth analysis of the hydrodynamic performance of fish and serve as new inspiration for drag reduction and antifouling. [ABSTRACT FROM AUTHOR]

This study employs computational fluid dynamics (CFD) simulations to investigate the effect of wall roughness on linear loss in circular pipelines. It specifically addresses hemispherical roughness, focusing on how changes in spacing influence linear loss, a critical determinant of fluid motion within pipelines. The simulations further assess the impact of these variables on flow characteristics, laying a theoretical groundwork for drag reduction and pipeline design improvement. Results indicate that increased spacing between roughness elements reduces the differential pressure at both pipeline ends. The dimensionless spacing value of 30 stabilizes this pressure, suggesting a limit to further changes. Additionally, a rise in roughness height at this spacing exacerbates differential pressure, highlighting a proportional relationship between roughness dimensions and linear loss—greater roughness leads to higher linear loss. Applying a nickel-plated coating on the inner wall significantly lowers roughness, thereby reducing linear loss. [ABSTRACT FROM AUTHOR]

Many species of plants and animals show an ability to resist fouling with surface topographies tailored to their environments. The mollusk species Dosinia juvenilis has demonstrated the ability to resist the accumulation of fouling on its outer surface. Understanding the functional mechanism employed by nature represents a significant opportunity for the persistent challenges of many industrial and consumer applications. Using a biomimetic approach, this study investigates the underlying hydrodynamic mechanisms of fouling resistance through Large Eddy simulations of a turbulent boundary layer above a novel ribletted surface topography bio-inspired by the Dosinia juvenilis. The results indicate a maximum drag reduction of 6.8% relative to a flat surface. The flow statistics near the surface are analogous to those observed for other ribletted surfaces in that the appropriately sized riblets effectively reduce the spanwise and wall-normal velocity fluctuations near the surface. This study supports the understanding that nature employs ribletted surfaces toward multiple functionalities including the considered drag reduction and fouling resistance. [ABSTRACT FROM AUTHOR]

In the field of biomimetics, the tiny riblet structures inspired by shark skin have been extensively studied for their drag reduction properties in turbulent flows. Here, we show that the ridged surface texture of another swimming creature in the ocean, i.e., the scallops, also has some friction drag reduction effect. In this study, we investigated the potential drag reduction effects of scallop shell textures using computational fluid dynamics simulations. Specifically, we constructed a conceptual model featuring an undulating surface pattern on a conical shell geometry that mimics scallop. Simulations modeled turbulent fluid flows over the model inserted at different orientations relative to the flow direction. The results demonstrate appreciable friction drag reduction generated by the ribbed hierarchical structures encasing the scallop, while partial pressure drag reduction exhibits dependence on alignment of scallop to the predominant flow direction. Theoretical mechanisms based on classic drag reduction theory in turbulence was established to explain the drag reduction phenomena. Given the analogous working environments of scallops and seafaring vessels, these findings may shed light on the biomimetic design of surface textures to enhance maritime engineering applications. Besides, this work elucidates an additional evolutionary example of fluid drag reduction, expanding the biological repertoire of swimming species. Lines used for shear stress data extraction of the shell model and the normalized wall shear of these lines on both models. [ABSTRACT FROM AUTHOR]

Reducing turbulence in pipe flows using polymer additives is crucial for industrial applications like crude oil, water, and sewage transportation. While previous research has accurately predicted friction factor and velocity profiles, none has fully understood turbulent kinetic energy (TKE) behavior in such fluids. Authors are now focusing on exploring turbulence models to better understand the TKE behavior. In this research, we have introduced a model to improve the behavior of TKE in a modified generalized Newtonian fluid (GNF). The developed model aims to simulate the viscoelastic effects of fluids that result in drag reduction in turbulent pipe flow. The work is noteworthy as it integrates turbulence and viscoelastic components, offering a comprehensive understanding of the phenomenon. By incorporating the rheological properties of viscoelastic fluids and replacing the damping function with a non-Newtonian alternative proposed by Cruz and Pinho, the Launder–Sharma k–ε turbulence model is now suitable for simulating dilute non-Newtonian viscoelastic fluids. The viscoelastic aspect of the model employs the modified GNF model. The developed model has been subjected to simulations using the computational fluid dynamics software. The results obtained for fluid TKE demonstrate a significant improvement in comparison to our previous research and the findings of other researchers. Furthermore, the model's prediction for the Darcy friction factor has been enhanced, resulting in an average error of only 3.71% in this section. It is noteworthy that the model consistently maintains a high level of accuracy in predicting other essential flow parameters such as mean axial velocity and Reynolds stresses. The provided model advances our understanding of viscoelastic fluid behavior in turbulent pipe flow by applying the modified GNF model. [ABSTRACT FROM AUTHOR]

Until now, various studies have been conducted on the drag coefficient of pickup trucks, but little research has been conducted on the effect of the front overhang length and roof design on the drag coefficient. In this study, the flow characteristics and drag coefficients of 54 models with different front overhang lengths, roof angles, and angular positions were compared using a computational fluid dynamics code to reduce the drag coefficient of an eco-friendly pickup truck. Reducing the aerodynamic drag of electric vehicles can improve battery utilization and improve the overall performance of the powertrain, so it is important to analyze and optimize geometric design steps to improve drag reduction strategies. The three-dimensional steady-state analysis model used in this study was verified by comparing the model results with experimental values reported in previous studies. In addition, the impacts of four factors on the drag coefficient were analyzed to develop an optimal design that takes into account smaller and better characteristics. The drag coefficient was reduced by 10.3% compared to that of the base model. Based on the numerical analysis of all models to be applied to pickup truck design, a correlation of the drag coefficient with the shape was proposed, showing a low error range of +1.9% to −1.74%. [ABSTRACT FROM AUTHOR]

This research focuses on addressing a significant concern in the aviation industry, which is drag. The primary objective of this project is to achieve drag reduction through the implementation of riblets on a wing featuring the NACA 2412 aerofoil, operating at subsonic speeds. Riblets, with the flow direction on wing surfaces, have demonstrated the potential to effectively decrease drag in diverse applications. This investigation includes computational analysis within the ANSYS Workbench framework, employing a polyhedral mesh model. The scope of this research encompasses the analysis of both a conventional wing and a modified wing with riblets. A comparative analysis is conducted to assess variations in drag values between the two configurations. Parameters, including geometry, dimensions, and riblet placement at varying angles of attack, are explored to comprehend their impact on drag reduction. Notably, 15.6% and 23% reductions in drag were identified at a 16-degree angle of attack with midspan and three-riblet models, separately. The computational mesh and method were validated using appropriate techniques.

Superhydrophobic surfaces have gained significant attention as a promising approach for drag reduction of submerged objects. Accurate evaluation and prediction of drag reduction induced by these surfaces require expensive experimental measurements, numerical simulations, or the development of reliable models and correlations. In this paper, a model is proposed for calculating the skin friction coefficient and drag reduction of superhydrophobic flat surfaces. Utilizing previous data on the skin friction coefficient of flat surfaces under noslip boundary conditions, a model is developed to estimate the skin friction reduction and skin friction coefficient of these surfaces after applying superhydrophobic coatings. The validity of the model is verified by comparing its results with those of computational fluid dynamics (CFD) simulations of flow over a flat plate at different velocities. The results of the model and simulations indicate that for inlet velocities of 1, 5, and 25 m/s and a slip length of 50 μm, drag reductions of 15%, 41%, and 77%, respectively, are expected. Additionally, the skin friction reduction increases with increasing flow Reynolds number. The developed model is validated for flat surfaces and its ability to accurately estimate the skin friction coefficient and drag force of these surfaces is thoroughly examined. However, further investigations are required to assess the model's validity for curved surfaces and variable slip lengths. [ABSTRACT FROM AUTHOR]

Reducing the aerodynamic drag and noise levels of high-speed pantographs is important for promoting environmentally friendly, energy efficient and rapid advances in train technology. Using computational fluid dynamics theory and the K-FWH acoustic equation, a numerical simulation is conducted to investigate the aerodynamic characteristics of high-speed pantographs. A component optimization method is proposed as a possible solution to the problem of aerodynamic drag and noise in high-speed pantographs. The results of the study indicate that the panhead, base and insulator are the main contributors to aerodynamic drag and noise in high-speed pantographs. Therefore, a gradual optimization process is implemented to improve the most significant components that cause aerodynamic drag and noise. By optimizing the cross-sectional shape of the strips and insulators, the drag and noise caused by airflow separation and vortex shedding can be reduced. The aerodynamic drag of insulator with circular cross section and strips with rectangular cross section is the largest. Ellipsifying insulators and optimizing the chamfer angle and height of the windward surface of the strips can improve the aerodynamic performance of the pantograph. In addition, the streamlined fairing attached to the base can eliminate the complex flow and shield the radiated noise. In contrast to the original pantograph design, the improved pantograph shows a 21.1% reduction in aerodynamic drag and a 1.65 dBA reduction in aerodynamic noise. [ABSTRACT FROM AUTHOR]

In the present study, the effect of taper on the lateral sides on fluid flow and heat transfer characteristics on a square cylinder has been analyzed numerically. Two-dimensional simulations have been carried out in the laminar flow regime (Re 100–800) for divergent blockage ratios (ϵ = H/D) and taper angles on the forward and backward sides of the lateral cylinder. Compared to the square cylinder, the forward tapered modification cylinders led to significant total drag reductions, pressure drop, and higher heat dissipation for low Re. The backward taper cylinder illustrates a minor increase in heat dissipation; however, the high drag coefficient and pressure drop penalty cannot be neglected. Moreover, an optimized geometry has been identified as a function of all the parameters. The reduction in blockage ratio has been determined to suppress the vortex shedding for higher Re completely. Results also indicate that the decrease in blockage ratio reduces the critical Re of the domain. The slightly tapered surfaces on either side of the square geometry significantly influence heat transfer and apply to modern industrial electronics and their cooling. [ABSTRACT FROM AUTHOR]

(1) Background: Previous studies have compared research into ski jumping in different motor processes, but there is a lack of comparative analysis of the biomechanical research methods used to investigate different ski jumping sports. (2) Content: Our study compared the advantages and disadvantages of six research methods and proposes future research directions. Motion video collection and analysis show that controlling angular momentum and achieving stable flight attitude in the take-off process are the most critical factors in ski jumping performance. Most research on force platforms focuses on dynamic performance at the time of take-off, but there are few training sites with an embedded force platform, and so, more empirical research is required. Wearable inertial measurement units, including gyroscopes and accelerometers, can be used to determine a series of forces, calculate the joint angle, and speculate the position of the centroid during motion. Surface EMG studies are primarily used to compare the activity characteristics of the lower limb muscles in the actual field of the jump, the exercise simulation, and the lack of complete training process data. Wind tunnel measurement can satisfy fluid mechanics simulation experiments and provide theoretical support for optimizing special ski jumping technology. Based on the theory of computational fluid dynamics, the optimal drag reduction posture data of ski jumpers can be derived using computer simulations. (3) Conclusions: Due to the wide range of ski jumping sports, the present research focused on the kinematics and dynamics of different movement stages, lacking the study of the complete exercise training process. The range of wearable inertial measurement and sensor equipment can cover the whole process of ski jumping, including kinematics and dynamics data, and is a feasible and reliable test method for monitoring ski jump training in natural environments. The simultaneous testing of surface electromyography, kinematics, and dynamics requires further exploration. (4) Future direction of development: Under computational fluid dynamics, wearable inertial measurement units and global navigation satellite systems (GNSSs), intelligent wind tunnel experimental training areas will become essential tools for ski jumping research. [ABSTRACT FROM AUTHOR]

For high‐speed moving objects, drag reduction has been a prolonged major challenge. To address this problem, passive and negative strategies have been proposed in the preceding decades. The integration of creatures and nature has been continuously perfected during biological evolution. Unique structure characteristics, material properties, and special functions of marine organisms can provide inexhaustible inspirations to solve this intractable problem of drag reduction. Therefore, a simple and low‐cost laser ablation method was proposed. A multi‐scale and multi‐level riblet (MSLR) surface inspired by the denticles of the sharkskin was fabricated by controlling the density of the laser path and ablation times. The morphology and topographic features were characterised using an electron microscope and a scanning white‐light interfering profilometer. Then, the drag reduction capacity of the bionic riblet surface was measured in a circulating water tunnel. Finally, the mechanism of drag reduction was analysed by the computational fluid dynamics (CFD) method. The results show that the MSLR surface has a stable drag reduction capacity with an increase in Reynold (Re) number which was contributed by high‐low velocity stripes formed on the MSLR surface. This study can provide a reference for fabricating spatial riblets with efficient drag reduction at different values of Re and improving marine antifouling. [ABSTRACT FROM AUTHOR]

Biomimetics, which draws inspiration from nature, has emerged as a key approach in the development of underwater vehicles. The integration of this approach with computational fluid dynamics (CFD) has further propelled research in this field. CFD, as an effective tool for dynamic analysis, contributes significantly to understanding and resolving complex fluid dynamic problems in underwater vehicles. Biomimetics seeks to harness innovative inspiration from the biological world. Through the imitation of the structure, behavior, and functions of organisms, biomimetics enables the creation of efficient and unique designs. These designs are aimed at enhancing the speed, reliability, and maneuverability of underwater vehicles, as well as reducing drag and noise. CFD technology, which is capable of precisely predicting and simulating fluid flow behaviors, plays a crucial role in optimizing the structural design of underwater vehicles, thereby significantly enhancing their hydrodynamic and kinematic performances. Combining biomimetics and CFD technology introduces a novel approach to underwater vehicle design and unveils broad prospects for research in natural science and engineering applications. Consequently, this paper aims to review the application of CFD technology in the biomimicry of underwater vehicles, with a primary focus on biomimetic propulsion, biomimetic drag reduction, and biomimetic noise reduction. Additionally, it explores the challenges faced in this field and anticipates future advancements. [ABSTRACT FROM AUTHOR]

In this study, experimental work in the literature about friction on bird-feather like structures has been reviewed and one of these was modeled by using CFD (Computational Fluid Dynamics) to obtain minimum grid parameters. Coupled with obtained optimal grid parameters, the shear stresses of the two-dimensional models were investigated at the values of Reynolds number 110,000-470,000. Based on the concluded previous study, three-dimensional geometries were modeled with reference to two-dimensional models and analyzed with the determined grid structure. The results of the analysis are compared with those of the previous experimental study in the literature. In the final phase of the study, a drag reduction was found to be approximately 30% on the surfaces inspired by bird feathers. [ABSTRACT FROM AUTHOR]

To reduce the drag of underwater vehicles during navigation, this paper proposes a skin imbricated with bionic placoid scale based on micro-Stewart mechanism. The skin is composed of bionic shark placoid scales and Stewart structure with multi-dimensional motion characteristics, which can well simulate the multi-dimensional oscillation motion of shark scales during swimming. A co-simulation platform of computational fluid dynamics and multi-body dynamics is established to investigate the impact of oscillating parameters (heave and pitch) on the drag reduction performance of the skin. The novel skin shows a remarkable drag reduction performance, with a relative drag reduction rate over 20% (up to 33%) in the range of Re = 105 ∼ 106. It is found that the oscillation motion generated by the placoid scales can cause the fluid inside the skin to spray upward, which can increase the thickness of the fluid boundary layer, revealing the drag reduction mechanism of the skin to some extent. Moreover, the pitching motion of the placoid scale is more effective in drag reduction than the heaving motion in the condition of Re = 105. It is expected that applying this skin to underwater vehicles can achieve satisfactory drag reduction effects. [ABSTRACT FROM AUTHOR]

Aerodynamic shape optimization involving a complex geometric model or problem may have tens or hundreds of design variables, necessitating multiple accurate but time-consuming computational fluid dynamics simulations to produce optimal designs, which greatly affects the efficiency of optimization and. To address this challenge, this article proposes an efficient optimization method based on design-variables-screening. Within the framework of the method, a complicated input–output relationship is broken down into quantitative effects. The influence of design variables on the objective function is calculated by the Kriging regression model and functional analysis of variance. In the meantime, a screening strategy is proposed to facilitate the selection of design variables for optimization. The less important design variables in the problems of interest are fixed so that the dimensionality of the problems is reduced to save computational cost. Experimental results on the National Advisory Committee for Aeronautics airfoil (NACA0012) demonstrate that the simplified model with the screening strategy achieves nearly the same reduction in drag coefficient as the conventional method that optimizes all design variables. Moreover, it significantly enhances the efficiency of optimization and contributes to the enhancement of flow stability. [ABSTRACT FROM AUTHOR]

This study focused on the effects of longitudinal and lateral spacing on the aerodynamic drag characteristics of the whole team and each member in speed skating team pursuit competition (SSTPC). To further understand the effect of formation spacing on the aerodynamic drag distribution on the skater body surface, a combination of experiments and numerical simulations was performed. Three identical mannequins were used to conduct wind tunnel tests and the results were compared with computational fluid dynamics (CFD) simulation results obtained using a 3D digital model of the mannequin. The results showed that, as the longitudinal spacing decreased, greater drag reduction was gained by the whole team and three members (leading, middle, and last). When the longitudinal spacing was 1.05 L (L refers to body length), the whole team and the three members had drag reduction of 31.5%, 10.1%, 42.1%, and 42.3%, respectively. After each 0.1 L increase in longitudinal spacing, the whole team and the leading, middle, and last skaters lost 2.0%, 1.8%, 2.3%, and 1.8% of their drag reduction, respectively. When the leading skater moved laterally to 0.2 W (W refers to body width), the whole team and the last skater achieved an additional drag reduction of 0.7% and 4.2%, respectively. The CFD simulation results further revealed that the body surface drag distribution trend of the leading skater was similar to that of the isolated skater, with the largest proportion of drag being located on the calves. The drag on the torsos, thighs and calves of the middle and last skaters was significantly smaller than that on the corresponding parts of the isolated skater, and its proportion was comparable. [ABSTRACT FROM AUTHOR]

The integration of chemical looping combustion with fluid catalytic cracking (CLC-FCC) is an innovative concept that serves as a cost-effective method for CO2 capture in refineries. This approach has the potential to reduce refinery CO2 emissions by 25–35%, offering a promising solution. As in the conventional FCC unit, it is common for CLC-FCC regenerators to be exposed to an on-off process while they are being maintained and cleaned. The novelty of this research lies in its specific focus on a less-explored phase (start-up) of CLC-FCC regenerators, the application of advanced CFD modeling, and the comprehensive analysis of operational parameters that influence the system’s performance. To validate the CFD simulations of the different drag models for solid-gas granular, bed density profiles under steady-state conditions, collected from industrial processes, were used. For the flow period based on the start-up process of the drag models, the fluidization gas inlet geometry of the regenerator, flow regime (laminar and turbulent), and superficial gas velocity were comprehensively investigated to reveal their effects on hydrodynamic characteristics. The results show that Gidaspow and Syamlal-O’Brien drag models of the solid-gas multiphase granular flow exhibited a better fit with industrial data. The SyamlalO’Brien and Gidaspow models closely align with industrial data under steadystate conditions, displaying similar bed densities in the dense phase region (230– 310 kg/m³ for Syamlal-O’Brien and 235–300 kg/m³ for Gidaspow). During the initial stage (less than 0.2 seconds), both laminar and turbulent models yield comparable bed density profiles, approximately 510 kg/m³ in the dense phase. However, as the process progresses, the dense phase density decreases to about 250–350 kg/m³ at around 0.5 seconds, with laminar flow models showing a slightly better fit with industrial data. Notably, at 0.5 seconds of fluidization time, inlet geometries having better gas distribution achieve a highly diluted phase with bed densities of 10–20 kg/m³. Reaching a steady state, the bed density decreases from around 400 kg/m³ to 260–300 kg/m³, expanding into a higher section of the regenerator where it aligns well with industrial data. The increase in superficial gas velocity would result in the clarification of the difference and well mixing of the solid-gas multiphase flow. [ABSTRACT FROM AUTHOR]

Over the years, air lubrication technology has been widely applied to maritime vessels, demonstrating its significant energy-saving and emission-reducing effects. However, the application of this technology in inland waterway transportation faces unique challenges due to the shallower water depths, particularly during low water periods. Under such conditions, the formation of the air layer and its associated drag-reduction effects may undergo alterations. Conducting research on air lubrication technology in shallow water conditions holds great practical significance for promoting its application in inland waterway vessels. Therefore, a numerical study is undertaken to examine the impact of water depth on Air layer Drag Reduction (ALDR) to promote the use of ALDR technology on inland canal boats with shallow water depths. The object was a specific river-sea direct ship model, and a groove was created at the bottom of the model with air injection. At two distinct speeds, numerical simulations were run for four different depths: deep water, moderate water, shallow water, and ultra-shallow water. A comparative examination of the air layer morphology on the ship bottom and drag reduction was conducted to investigate the impact of water depth on ALDR and confirm the viability of using ALDR technology on shallow-water navigation boats. The results indicate that due to the change in the velocity and pressure fields at the bottom of the ship, the efficiency of drag reduction and the form of the air layer on the ship's bottom are significantly impacted by variations in water depth in restricted waters. However, the total resistance can still be significantly reduced by setting grooves on the hull with air injected in shallow waterways. Reduced frictional resistance no longer predominates the overall resistance reduction in shallow water; the proportion of the decrease in viscous pressure resistance rises and can reach up to 4.8 times the decrease in frictional resistance. The research confirms the application prospects of this technology on inland waterway transport ships. [ABSTRACT FROM AUTHOR]

Supercavitation has been recently presented as an effective method for the drag reduction of underwater vehicles. However, maintaining the supercavitating state requires a lot of energy, making vehicles difficult to control. Therefore, it is necessary to design an underwater vehicle with low drag in the fully wetted state while being able to move at ultra-high speed in the supercavitating state. In this study, a detachable fairing design for underwater vehicles is proposed, which has the advantage of increasing the total voyage and avoiding the problem of difficult steering in the supercavitating state. On the other hand, the study of non-body-of-revolution (non-BOR) has become a prevalent area of interest in the shape design of underwater vehicles. The cavity generated by an elliptical disk-shaped cavitator is studied numerically. It is found that the cavity profile on the cross-section near the cavitator is approximately elliptical. The cavity length of an elliptical disk-shaped cavitator is almost the same as that of a disk-shaped cavitator when they have the same inflow area. Based on these two characteristics, the parameters of the internal elliptical disk-shaped cavitator are optimized, which provides a promising strategy for the issue of cavitators increasing drag in a fully wetted state. [ABSTRACT FROM AUTHOR]

To effectively evaluate the structural responses, it is crucial to possess relevant knowledge regarding the blast load on the structure. The loading characteristics of two columns differ from those of a single column due to complex flow-field interference. The spacing effect on blast loading characteristics of two tandem rigid square columns is examined numerically and experimentally for different center spacing between the columns (L = 1.2B–12B, where B represents the side length of a column). This includes studying drag characteristics, distribution patterns of reflection overpressure and impulse, and understanding the physical mechanism under blast load. The experimental tests use a shock tube device powered by high-pressure gas, while numerical simulations solve Euler equations using computational fluid dynamics techniques. Our findings reveal that spacing cases can be categorized into four situations: small and medium spacings (L/B = 1.2–2 and 2.5–4), where the upstream column exhibits a significant shielding effect on the downstream column, resulting in the reduced drag coefficient for the downstream column; large spacings (L/B = 5–7), where drag coefficient improves but remains lower than that of a single column; superlarge spacings with negligible shielding effect (L/B = 8–12), leading to similar blast loading for the downstream column compared to a single column. [ABSTRACT FROM AUTHOR]

The developments and involved factors of mature passive drag reduction technologies, i.e., compliant coating, superhydrophobic surfaces, and epoxy coating, are reviewed. Alterations in critical Reynolds number are observed in the presence of passive drag reduction technologies. With the advancement in technology, numerical approaches are introduced to lower the cost and achieve better understanding of physical phenomena such as lowering energy, flow control, designing the surfaces of materials, and so on. Experimental results as well as numerical results are stated. The effects of factors like wetting, contact angle, contact angle hysteresis, roughness, pot life, and coating aging responsible for drag reduction are also briefly presented with numerical and experimental perspective analyses. [ABSTRACT FROM AUTHOR]

Bayesian optimization based on Gaussian process regression has recently spread into a range of computational fluid dynamics problems. It still remains to be explored and developed for the complex flow problems with high dimensions and large computational cost. In this work, we present the application of multi-fidelity Bayesian optimization (MFBO) to drag reduction control of flow over a two-dimensional circular cylinder. The flow is modified by the spatially distributed tangential velocity on the cylinder surface, which is optimized by utilization of MFBO. It is shown that 50% reduction of the computational cost is obtained by using MFBO, as compared with that of single-fidelity Bayesian optimization, by involving low-fidelity simulations. The optimal tangential velocity distribution designed by MFBO is successfully applied to modify the wake of cylinder. As a result, an average drag coefficient reduction rate of 36.2% and decrease in the fluctuation amplitude of lift coefficient by 85.7% at Re = 200 are obtained. Effects of the hyper-parameters of the proposed MFBO control architecture are also examined. [ABSTRACT FROM AUTHOR]

This study investigates the drag reduction effect and mechanism of modified transverse grooves by employing "Constant Width" and "Constant Height" filleting methods on the top and valley of two-dimensional transverse V -shaped grooves. Results revealed a significant increase in the total drag reduction rate, from 13.29% to 23.24%, when a constant width fillet was applied to the grooves top at r³ = 0.3/v²mm. However, minimal or negative effects were observed in other cases. These findings establish a preliminary theoretical basis for future transverse groove design and processing. [ABSTRACT FROM AUTHOR]