Maximum Drag Research Articles

Optimization design of a windshield for a 12,000 TEU container ship based on a support vector regression surrogate model

This study presents the design of a windshield for a 12,000 TEU container ship using a multidisciplinary optimization system aimed at enhancing its aerodynamic performance. The framework integrates parametric modeling, design of experiment (DOE), numerical simulation, support vector regression (SVR)-based approximation, and a genetic algorithm (GA). Initially, the flow field around the ship is predicted using Reynolds-averaged Navier–Stokes (RANS) equations, with accuracy validated against computational fluid dynamics (CFD) and experimental fluid dynamics (EFD) results. The windshield’s shape is then defined by three Bezier curves, and six design variables are selected based on these curves to ensure smooth deformation. Subsequently, 120 sample points are chosen within the design space using the DOE method, and an SVR-based surrogate model is established. Optimization is performed using the multi-island genetic algorithm to determine the windshield configuration. Validation tests confirm the robustness of the optimization process. On this basis, the drag reduction mechanism of the windshield is summarized and analyzed. Results demonstrate that the optimization system effectively enhances the aerodynamic performance of the container ship, achieving a maximum drag reduction rate of 20.67% under headwind conditions and significant improvement across wind angles from 0° to 60°.

Effect of plasma excitation on aerodynamic characteristics of airfoil under Martian conditions

Due to the low density and pressure of the Martian atmosphere, the aerodynamic performance of the airfoil of the Mars UAV needs to be further improved. Plasma excitation active flow control technology is used to improve the lift of the airfoil and reduce the drag of the airfoil under Martian conditions. The effects of the action position, excitation power and incoming flow angle of attack on the lift and drag of the airfoil are studied under the low Reynolds number conditions on Mars. The results show that plasma excitation increases lift in the trailing edge area of the lower surface, with a maximum lift increase rate 37%; reduces drag in the leading edge area of the lower surface, with a maximum drag reduction rate 8%; the greater the excitation power and the smaller the incoming flow angle of attack, the more obvious the improvement of the airfoil lift-to-drag ratio. Plasma excitation induces pressure waves, forming a pressurization zone and a decompression zone upstream and downstream of the excitation, respectively, resulting in the formation of a pressurization surface and a decompression surface on the airfoil surface. When the excitation position is close to the trailing edge, the pressurization surface expands, and the pressure difference between the upper and lower surfaces of the airfoil increases, thereby achieving lift increase; when the excitation position is close to the leading edge, the decompression surface expands, and the pressure difference drag of the airfoil decreases, thereby achieving drag reduction.

Numerical investigation of unsteady aerodynamics on a grooved NACA 4415 airfoil

Surface grooves have demonstrated the capability to mitigate laminar separation bubbles and enhance airfoil aerodynamic performance. However, wind turbine operation introduces dynamic effects that significantly impact airfoil behavior, leading to substantial deviations from static conditions. Numerical simulations were carried out to discuss the effectiveness of surface groove structures in controlling separation bubbles under dynamic conditions and their potential to enhance unsteady aerodynamics. The influence of groove parameters (depth, width, position) on the NACA 4415 airfoil’s boundary layer attributes and unsteady aerodynamic properties are analyzed across various pitching amplitudes and reduced frequencies. It is found that the position of groove structures under dynamic conditions is crucial, that groove structures located ahead of separation bubbles on the airfoil surface can effectively eliminate the separation bubbles, and their control effectiveness is superior to that under static conditions. Well-designed groove structures can reduce the airfoil’s maximum lift, drag, and moment coefficients under dynamic conditions. They also reduce the aerodynamic hysteresis effect and improve the aerodynamic damping characteristics. This comprehensive analysis sheds light on the critical interplay between dynamic wind conditions, airfoil behavior, and the potential of groove structures to optimize wind turbine performance.

Design and experiment of bionic skateboard for rice direct seeding machine based on loach body surface

Aiming at the problem of heavy adhesion and large resistance of the rice direct seeding machine slide in the disturbed saturated paddy field environment, the non-smooth surface of the loach body was observed by microscopic observation; the simulation analysis was carried out using Fluent software, revealing the principle of reducing adhesion and drag of the non-smooth surface; the Box-Behnken response surface method was used to design the experiment, and the regression equation of the total resistance of the groove non-smooth surface FBand the groove width w, groove depth hand incoming flow velocity was obtained. vThe optimization analysis results show that when wis 4 mm、v1.25 m/s, 4.5 mm、hthe maximum drag reduction rate reaches 10.052%; based on the optimal parameters, the rice direct seeding machine bionic slide was trial-produced, and the indoor paddy field soil trough test was carried out, and the final drag reduction rate reached 10.23%. This study can provide new ideas for the development of adhesion and drag reduction technology for paddy field soil contact parts.

Polymer-doped two-dimensional turbulent flow to study the transition from Newtonian turbulence to elastic instability

Detecting the flow regimes of Newtonian turbulence (NT), elasto-inertial filament (EIF), elasto-inertial turbulence (EIT), and maximum drag reduction (MDR) of polymer solution and their transition has been a hot topic in the last decade. We attempted to detect NT, EIF, EIT, and MDR by visualizing vortex shedding downstream of an array of cylinders that was inserted perpendicular to polymer-doped two-dimensional (2D) flow. Since polymers are stretched at the cylinders, the consequent vortex shedding is affected by viscoelasticity. The flow regimes are characterized based on Weissenberg (Wi) and Reynolds numbers (Re) with the relaxation time of the polymeric solution estimated from capillary-thinning experiments. The flow regimes are observed for different molecular weights of polyethylene oxide and polyacrylamide in solution and are categorized as either vortex type 1, type 2, and type 3 on a Re–Wi map based on flow visualization using particle image velocimetry. In addition, turbulent statistics of these flow regimes are calculated to more fully quantify these flow regimes. We found that vortex types from 1 to 3 have a similarity to NT, EIF, EIT, and MDR. In addition, characteristic turbulent energy transfer without an increase in turbulent energy production was found in the flow regimes of vortex types 2 and 3 of each polymer solution. Our results suggest intriguing parallels between pipe, jet, and 2D turbulent flow for drag-reducing polymeric solutions.

Numerical simulation analysis of turbulent pulsation drag reduction at different intermittent times

The shear stress generated by wall turbulence is the main cause of wall friction resistance in turbulent flow through pipes. This paper investigates the impact of inserting rest periods (regions of constant Reynolds number) within the pulsating operating cycle of velocity on the fully turbulent flow at large time-averaged Reynolds numbers, using the large eddy simulation (LES) method. The study aims to explore the effect of increasing rest periods within pulsations on drag resistance. The dimensionless shear stress and drag reduction rates during different time periods of rest were analyzed. Numerical simulation results indicate that the pulsating velocity operation mode does not necessarily lead to drag reduction; it may even result in increased resistance. Inserting rest periods within the pulsation cycle can achieve drag reduction effects, with the maximum drag reduction rate reaching 21.8%. This paper utilizes large eddy simulation (LES) to compare and validate the feasibility of LES for pipe pulsating operation modes against experimental results and direct numerical simulation (DNS) results from the literature, providing a rationale and proof of concept for further in-depth studies on other pipe pulsating flows.

Wind tunnel investigation of hemispherical forebody interaction on the drag coefficient of a D-shaped model

PurposeAn experimental investigation of hemispherical forebody interaction effects on the drag coefficient of a D-shaped model is carried out for three-dimensional flow in the subcritical range of Reynolds number 1 × 105 ≤ Re ≤ 1.8 × 105. To study the interaction effect, hemispherical shapes of various sizes are attached to the upriver of the D-shaped bluff body model. The diameter of the hemisphere (b1) varied from 0.25 to 0.75 times the diameter of the D-shaped model (b2) and its gap from the D-shaped model (g/b2) ranged from 0.25 to 1.75 b2.Design/methodology/approachThe experiments were carried out in a low-speed open-circuit closed jet wind tunnel with test section dimensions of 1.2 × 0.9 × 1.8 m (W × H × L) capable of generating maximum velocity up to 45 m/s. The wind tunnel is equipped with a driving unit which has a 175-hp motor with three propellers controlled by a 160-kW inverter drive. Drag force is measured with an internal six-component balance with the help of the Spider 3013 E-pro data acquisition system.FindingsThe wind tunnel results show that the hemispherical forebody has a diameter ratio of 0.75 with a gap ratio of 0.25, resulting in a maximum drag reduction of 67%.Research limitations/implicationsThe turbulence intensity of the wind tunnel is about 5.6% at a velocity of 18 m/s. The uncertainty in the velocity and the drag coefficient measurement are about ±1.5 and ±2.83 %, respectively. The maximum error in the geometric model is about ±1.33 %.ractical implicationsThe results from the research work are helpful in choosing the optimum spacing of road vehicles, especially truck–trailer and launch vehicle applications.Social implicationsDrag reduction of road vehicle resulting less fuel consumption as well as less pollution to the environment. For instance, tractor trailer experiencing approximately 45% of aerodynamics drag is due to front part of the vehicle. The other contributors are 30% due to trailer base and 25% is due to under body flow. Nearly 65% of energy was spent to overcome the aerodynamic drag, when the vehicle is traveling at the average of 70 kmph (Seifert 2008 and Doyle 2008).Originality/valueThe benefits of placing the forebody in front of the main body will have a strong influence on reducing fuel consumption.

Large-scale control in turbulent flows over surface riblets

The drag reduction efficacy of a large-scale flow control over a rough surface is studied via direct numerical simulations of turbulent channels (at friction Reynolds numbers Reτ=180) by combining together wall riblets and streamwise counter-rotating swirls. In particular, the height of triangular riblets is h+≈10 (+indicating wall units), while the number of riblets (NRib in the range 1–56) along the periodic spanwise direction is varied to find the optimum. The swirls are generated by the spanwise opposed wall-jet forcing (SOJF) in the Navier–Stokes equation, whose controlling parameters follow the optimal ones as for the smooth wall. In total, 12 cases of combined SOJF and riblets are performed to investigate the coupling effects between the two methods. We find a range of NRib=7–14 (with the spanwise width z+≈140−280) yields the largest drag reduction (up to 20%) for Reτ=180, much higher than riblets control only (about 3%). Compared to SOJF control only, riblets suppress the secondary swirls of SOJF hence decreasing drag, while the lateral and down washing motions of SOJF impinging on riblets would increase drag—the opposite two effects thus giving rise to an optimal. Through examinations on coherent structures, we elucidate that the attenuation of both large-scale coherent motions and small-scale random fluctuations leads to the net drag reduction. We conclude that large-scale control is a robust approach in the cases of rough surfaces, and the parameters can be selected for maximum drag reduction in each particular situation.

Cenozoic India-Asia collision driven by mantle dragging the cratonic root

The driving force behind the Cenozoic India-Asia collision remains elusive. Using global-scale geodynamic modeling, we find that the continuous motion of the Indian plate is driven by a prominent upper-mantle flow pushing the thick Indian lithospheric root, originated from the northward rollover of the detached Neo-Tethyan slab and sinking slabs below East Asia. The maximum mantle drag occurs within the strong Indian lithosphere and is comparable in magnitude to that of slab pull (1013 N m−1). The thick cratonic root enhances both lithosphere-asthenosphere coupling and upper-plate compressional stress, thereby sustaining the topography of Tibetan Plateau. We show that the calculated resistant force from the India-Asia plate boundary is also close to that due to the gravitational potential energy of Tibetan Plateau. Here, we demonstrate that this mantle flow is key for the formation of the Tibetan Plateau and represents part of a hemispheric convergent flow pattern centered on central Asia.

Effect of synthetic jets actuator parameters on deep reinforcement learning-based flow control performance in a square cylinder

We conduct an active flow control study on the mass flow rate of synthetic jets on the upper and lower surfaces of a square cylinder using a deep reinforcement learning algorithm, with a focus on investigating the influence of the position and width of the synthetic jets on the flow control performance. At Reynolds numbers (Re) of 100 and 500, it is found that our proposed method significantly reduced the lift and drag coefficients of the square cylinder and completely suppressed vortex shedding in the wake. In particular, at Re = 100, placing the synthetic jets near the tail corner was beneficial for reducing drag, with a maximum drag reduction rate of 14.4%. When Re = 500, positioning the synthetic jets near the leading edge corner resulted in a maximum optimal drag reduction effect of 65.5%. This indicates that locating the synthetic jet at the main flow separation point can achieve optimal control. Furthermore, we notice that when the synthetic jets are positioned near the tail corner, vortex shedding can be completely suppressed. Additionally, a narrower width of the synthetic jets can enhance flow instability and increase the cost of flow control.

Numerical Study of Laminar Flow and Vortex-Induced Vibration on Cylinder Subjects to Free and Forced Oscillation at Low Reynolds Numbers

In this study, we aimed to numerically investigate the 2D laminar flow over a cylindrical body and performed vortex-induced vibration analyses on a circular cylinder of unit radius placed in a channel, with the cylinder assumed to be fixed. The cases of a cylinder under forced oscillation and three different scenarios of a freely oscillating cylinder were analyzed. The fluid domain dynamics were governed by the incompressible Navier–Stokes equations; however, the structural field was described using nonlinear elastodynamic equations. Fluid and solid domains were discretized with the finite volume method (FVM) in space and time. Predictions of hydrodynamic forces, namely lift and drag terms, were determined for each scenario. An increase in the Reynolds number caused an exponential increment in the lift force. In the case of a stabilized flow, the collective decrease in stiffness and damping decreased the maximal drag and lift factors. Furthermore, it was noticed that the lift factor was minimally altered by variations in damping and stiffness in comparison with the change in the drag factor. From these observations, it appears that the lift factor probably correlates with the cylinder’s structure and fluid properties.

Numerical study of hydrodynamic drag effects of streamwise riblet structures on SUBOFF bare hull model

This study performs a full-scale numerical simulation on meter-scale underwater vehicles (UWVs) with micrometer-scale V-type streamwise riblet structures, focusing on hydrodynamic drag using the SUBOFF model. The periodic simulation along the azimuthal direction enables the full-scale analysis. Two main scenarios are discussed: (1) effect of riblet structure size on drag at a constant maneuvering speed and (2) effect of maneuvering speed on drag for representative riblet cases. In scenario (1), the average wall shear stress at the central region of the body exhibited significant reduction of approximately 50%. However, owing to larger effective area at the central surface of the body fixed with riblets, the friction drag may either decrease or increase depending on the riblet size. Consequently, R100 case showed maximum total drag reduction of ∼3%, whereas R500 case showed maximum increase in drag of ∼3%, where R100 and R500 indicate riblet-applied SUBOFF models with riblet heights of 100 and 500 μm, respectively. In scenario (2), friction drag in riblet-applied region exhibited smaller variations in R100 case, showing universal drag reduction effect at all speeds. In contrast, R500 case showed significant variations, with drag increments ranging from minimum of 1% to maximum of 12% at all speeds.

Numerical comprehensive evaluation of the flow control effect on a circular cylinder with a control rod

The drag reduction of the single circular cylinder is achieved by changing the position of an additional control rod in the present work. In order to look for where to place the control rod will help the drag force exerted on the main cylinder surface as little as possible, the additional control rod is arranged at various positions in the downstream region, the upstream region, and the middle region of the single circular cylinder, respectively. The numerical results show that the maximum drag reduction rate of the single circular cylinder can be up to 21.68%. While the additional control rod is located at some specific positions in the flow field, the drag of the single circular cylinder will increase. However, if two bluff bodies (the main circular cylinder and the control rod) are considered as a whole system, due to the extra drag contribution of the control rod, the maximum drag reduction effect of the system is 8.65%. Additionally, the lift exerted on the main cylinder and the control rod has changed a lot due to the interaction between two bluff bodies. Furthermore, the Dynamic Mode Decomposition analysis method is employed to probe the mechanism of drag variation employing the dominant flow modes.

Laser Ablating Biomimetic Periodic Array Fish Scale Surface for Drag Reduction.

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.

Control effect on the divergent and convergent riblets in particle-laden turbulent boundary layer

Particle image velocimetry was employed to investigate the impact of convergent–divergent riblets on turbulent boundary layers in both clear water and liquid–solid two-phase flow fields containing 155 μm polystyrene particles. The turbulence statistics such as turbulence intensity and Reynolds stress were investigated. The spatial topology of spanwise vortex head and the development and evolution process of hairpin vortices were explored from Euler and Lagrange perspectives, respectively. Additionally, the particle distribution, concentration, and dispersion within the turbulent boundary layer were statistically analyzed. The results indicated that the boundary layer thickness, friction resistance, integrated turbulence intensity, and Reynolds stress were significantly lower on divergent riblet walls compared to convergent riblet walls. Notably, divergent riblets with a yaw angle of 30° exhibited the best drag reduction effect in both single-phase and two-phase flow fields. The addition of particles resulted in an increase in boundary layer thickness but effectively reduced turbulent fluctuations in the logarithmic region, enhancing drag reduction. This extended the drag reduction range of divergent riblets to a yaw angle of 45°, increasing the maximum drag reduction rate to 26.18%. Through spatial multi-scale local average structure function and finite-time Lyapunov exponent field analysis, it was found that the 30° divergent riblet wall significantly inhibited the development of vortex structures and reduced momentum exchange within the boundary layer. Conversely, the 30° convergent riblet wall had the opposite effect, while the particle phase inhibited the development of all wall turbulent structures. Analysis of particle concentration variations within different regions of the turbulent boundary layer revealed that as the normal height of the boundary layer increased, particle concentration gradually increased, and particle dispersion decreased accordingly. The analysis further showed that particle dispersion was mainly influenced by flow structures, whereas concentration was significantly affected by turbulence intensity. These findings elucidate the effect of the flow field on the particle phase and provide insights into the interaction mechanism between the flow field and particles.

The Impact of Using Dimpled Surfaces on Ahmed Body on The Flow Characteristics

Vehicle aerodynamics which directly affects fuel consumption values in vehicles has great importance in terms of vehicle stability, acceleration ability, vehicle noise, and environmental pollution. Ahmed car model is one of the most important generic models, so this popular car model is widely used in the literature on fluid mechanics and vehicle aerodynamics studies. This study investigates the effect of a passive drag reduction technique which is known as dimple surface, on Ahmed car model with a 35° slant angle. The flow control methods were applied numerically also these methods were compared with similar works. Analysis made in this study were conducted with 2.4 million cell numbers and the maximum drag reduction is 3.5 % with optimum dimple surfaces. Moreover, the applicability and manufacturability factors were also evaluated in terms of implementing the dimpling modification to today’s current road vehicles.

Leidenfrost spheres, projectiles, and model boats: Assessing the drag reduction by superhydrophobic surfaces

Superhydrophobic surfaces are expected to reduce drag on bluff bodies moving in water due to the introduction of a thin air layer around the solid and the resulting partial slip boundary condition. The use of Leidenfrost vapor layers, sustained on the surface of a heated metal body is a reliable method to estimate the maximum drag reduction possible due to such air layers. In the past such an approach was used to estimate the drag reduction on a free-falling heated sphere, in which case the form drag is the lead component of the drag force. Here, we extend this approach to evaluate the effect of the thin gas layers on the hydrodynamic drag of free-falling streamlined projectiles and towed model boats, where the form drag is minimal, and the skin friction drag is the lead component of the drag force. By comparing the drag for streamlined bodies with and without sustained air-layers, we see only incremental drag reductions, for the sub-critical Reynolds number tested herein. The same is true for towed model boats. These results hold both for superhydrophobic surface treatments and Leidenfrost vapor layers. Thus, we concluded that for the investigated range of sub-critical Reynolds numbers, the skin friction drag is less sensitive to the effect of the thin gas layers compared to the form drag. These novel findings have important implications for the practical potential of energy savings using gas layers sustained on superhydrophobic surfaces.

Preliminary Analysis of Hydrodynamic Drag Reduction and Fouling Resistance of Surfaces Inspired by the Mollusk Shell, Dosinia juvenilis.

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.

Drag Reduction by Dried Malted Rice Solutions in Pipe Flow

In this study, the friction factor of a turbulent pipe flow for dried rice malt extract solutions was experimentally reduced to that of a Newtonian fluid. The friction factor was measured for four types of solutions at different culture times and concentrations. The results indicate that the experimental data points of the test solutions diverged from the maximum drag reduction asymptote at and above Re√f ≅ 200~250 and aligned parallel to those of Newtonian fluids. This drag reduction phenomenon differed from that observed in artificial high-molecular-weight polymer solutions, called Type A drag reduction, in which the drag reduction level is dependent on the Reynolds number in the intermediate region. This is classified as a Type B drag reduction phenomenon in biopolymer solutions and fine solid particle suspensions. The order of drag reduction corresponded to approximately 5–50 ppm xanthan gum solutions, as reported previously. Furthermore, the velocity profile in a turbulent pipe flow was predicted using a semi-theoretical equation in which the friction factors were determined using the difference between the experimental results of the tested solutions and Newtonian fluids. The results indicate considerable thickening of the viscous sublayer in the turbulent pipe flow of the test solutions compared with that of Newtonian fluids.

Numerical investigation of the influence of different barrel lengths on the interior ballistic process within an underwater submerged launch

Although underwater submerged launching has been rigorously investigated for decades, there remains a dearth of comprehensive understanding regarding the underwater interior ballistic characteristics for varying barrel lengths. To address this knowledge gap, the present study aims to explore, via numerical simulations, the initial velocity of interior ballistics, projectile drag, and the mechanism of initial flow field formation at the muzzle under various barrel lengths, thereby considering the influence of differing barrel lengths. The five distinct lengths of barrels are expressed as dimensionless ratios of the weight of water column in front of the projectile to the weight of the projectile in order to be more general. Five different ratios of water-to-projectile weight are investigated: 1.0, 1.2, 1.5, 1.8, and 2.0, all possessing identical diameters and evaluated under equivalent launch conditions. Different ratios significantly impact muzzle velocity, with shorter barrels yielding higher muzzle velocities, while ensuring complete propellant combustion. Further investigations indicate that variations in drag constitute the fundamental cause of initial velocity changes. Furthermore, it is observed that barrels of different lengths exhibit identical characteristics at the point of maximum drag. The initial flow field at the muzzle exhibits considerable variations in terms of length, profile dimensions, and intensity. The findings of this study offer valuable insights into exploring the mechanism of submerged launching and will be utilized to investigate the optimal barrel length.