Body Drag Research Articles

Adjoint shape optimization of Ahmed body to improve aerodynamics

Analyses are done on the bluff body of a simple ground vehicle's wake structure. A 4 million Reynolds number depending on model length. Results for various geometric configurations of the Ahmed body's flow visualization were achieved. There was a flexible geometric element called the base slant angle. Drag research found that body drag makes up about 85% of all drag. The body's rear end is where most drag is created or developed. Horseshoe vortices build a three-deck structure in wake flow. The base slant angle affects these vortices' strength, existence, and merging. Examined is the applicability of these phenomena to actual ground vehicles. To reduce drag and enhance aerodynamics, the body's shape was modified using the adjoint approach and the adjoint shape optimization tool in ANSYS Fluent. In this study, we found that by changing the tail-end vortex structure and flow separation at the rear part of the vehicle, the optimized back shape or rear slant design of the body provides better flow separation that results in better pressure recovery and reduces drag by roughly 7 to 10 percent, respectively. The comparison of experimental CD values for the Ahmed body at different rear slant angles, including 12.5o, 25o, and 30o. Since it had less variance from empirical data, the computationally computed CD for a 30° base slant angle was chosen to do adjoint shape optimization. Mesh cells of less than three lakhs were used in the CFD process, and skewness quality was checked. 60 m/s of velocity was the boundary condition for the velocity inlet.

Investigating horizontal-axis wind turbine aerodynamics using cascade flows

The simplest aerodynamic model of horizontal-axis wind turbines is the blade element momentum theory, which assumes that the blades behave as airfoils, but a correct two-dimensional representation is an infinite cascade of lifting bodies. This study analyzes the conventional and impulse forms of the forces on cascades of airfoils at spacings and pitch angles typical of wind turbine applications. OpenFOAM software was used to simulate steady, incompressible flow at a Reynolds number of 6×106 through cascades of NACA 0012 airfoils. The force equations agree well (less than 1% error) with the forces determined directly from OpenFOAM for four spacing ratios. We concentrate on the “wake vorticity” term, which is ignored in blade element momentum analysis. At a pitch angle of 90°, this term balances the viscous drag when the angle of attack is zero. At zero pitch, which models the outer region of a wind turbine blade at a high tip speed ratio, the term can account for 27% of the axial thrust when the angle of attack is about 4°. The normal force equation, like the angular momentum equation for wind turbines, has no viscous term, which forces the body drag to contribute to the circulation in the wake. It is shown that the airfoil assumption is conservative in that cascade elements have higher lift-to-drag ratios than airfoils at the same angle of attack. An associated result is that separation occurs at higher angles of attack on a cascade element compared to an airfoil.

Topological spaces of embodied becoming: queens, queerness, and (infra)structural subterfuge in Singapore

ABSTRACT This paper considers the political potential that emerges when theorizations of the body-as-infrastructure are brought into conversation with theorizations of topological space. It argues that the infrastructural body provides an interface through which structural norms can be destabilized, and the interrelationships between the state, society, and self can be reimagined. These ideas are illustrated through an empirical exploration of drag queens in Singapore. Singapore is a socially conservative Asian city-state in which heteronormative values are passed down by the state, reproduced through the family, and then used to structure societal understandings of gender and sexuality. By interpreting Singapore’s hegemonic state-society spaces in topological terms, drag queens reveal a modality of queerness that is not necessarily deviant, or apart-from, the country’s non-queer public spaces, but is mutually constitutive of them instead. Through (infra)structuralization, the drag body reveals a potentiality that transcends the strictures of everyday life. Accordingly, the paper advances the politico-theoretical promise of ‘Queer Asia’.

Physiological Demands of a Self-Paced Firefighter Air-Management Course and Determination of Work Efficiency

To assess the physiological demands of an AMC and examine differences across BMI categories. A secondary aim was to develop an equation to assess work efficiency in firefighters. Fifty-seven firefighters (Women, n = 4; age: 37.2 ± 8.4 yr.; height: 182.0 ± 6.9 cm; body mass: 90.8 ± 13.1 kg; BMI: 27.8 ± 3.6 kg·m-2) completed an AMC per routine evaluation while wearing a department issued self-contained breathing apparatus and full protective gear. Course completion time, starting pounds per square inch (PSI) on the air cylinder, changes in PSI, and distance traveled were recorded. All firefighters were equipped with a wearable sensor integrated with a triaxial accelerometer and telemetry to assess movement kinematics, heart rate, energy expenditure, and training impulse. The AMC consisted of an initial section involving a hose line advance, rescue (body drag), stair climb, ladder raise, and forcible entry. This section was followed by a repeating loop, which consisted of a stair climb, search, hoist, and recovery walk. Firefighters repeated the course loop until the self-contained breathing apparatus air supply pressure reached 200 PSI, at which time they were instructed to lay down until the PSI reached zero. Average completion time was 22.8 ± 1.4 min, with a mean distance of 1.4 ± 0.3 km and an average velocity of 2.4 ± 1.2 m·s-1. Throughout the AMC, the mean heart rate was 158.7 ± 11.5 bpm equating to 86.8 ± 6.3% of the age-predicted max heart rate and a training impulse of 55 ± 3 AU. Mean energy expenditure was 464 ± 86 kcals and work efficiency was 49.8 ± 14.9 km·PSI-1·s. Regression analysis determined that fat-free mass index (R2 = 0.315; β = -5.069), body fat percentage (R2 = 0.139; β = -0.853), fat-free mass (R2 = 0.176; β = -0.744), weight (R2 = 0.329; β = -0.681), and age (R2 = 0.096; β = -0.571) were significant predictors of work efficiency. The AMC is a highly aerobic task with near-maximal heart rates reached throughout the course. Smaller and leaner individuals achieved a higher degree of work efficiency during the AMC.

Investigation of drag and heat flux reduction induced by a novel combinational spike-aerodisk and channel concept for hypersonic blunt body

For the drag and heat flux reduction of hypersonic blunt body, a novel combinational spike-aerodisk and channel concept has been proposed. The high pressure air behind the bow shock flows into the channel at the head of the aerodisk, and then sprays out through the lateral jet in the middle of the spike. The Reynolds-averaged Navier-Stokes (RANS) equations coupled with the shear stress transport (SST) k - ω turbulence model have been employed to simulate the flow field. The numerical results reveal that compared with the spike-aerodisk, with the application of the channel, the lateral jet pushes the separated shock wave away from the spike. The range of the recirculation zone between the shear layer and the spike is increased, and the intensity of the reattached shock wave is significantly weakened, so the drag and heat flux reduction properties of the combinational configuration are significantly improved. The influences of the channel convergent half angle and lateral jet location on the flow field, drag and heat flux reduction properties are investigated thoroughly. When the channel convergent half angle is appropriate and the location of the lateral jet is close to the middle of the spike, the drag and heat flux reduction effect becomes better. Besides, with the increase of the Mach number and the decrease of the flying height, the drag and heat flux reduction performance become more significant. In the research range, the combinational configuration in which the convergent half angle is 60° and the lateral jet is located in the middle of the spike has a better overall effect of drag and heat flux reduction, and the effect reaches the best when the Mach number is 6 and the flying height is 20 km. Compared with the spike-aerodisk, the total drag coefficient of the configuration is reduced by 12.95%, and the peak value of Stanton number along the blunt body surface is reduced by 35.19%.

Вдосконалення конструкції бітерів дозатора кормів порційної дії

Вдосконалення конструкції бітерів дозатора кормів порційної дії

Deflector effect on flow behavior and drag of an Ahmed body under crosswind conditions

This study investigates the effect of a deflector on Ahmed model drag and the flow on the slant during steady crosswind conditions by experimental methods at a based-height Reynolds number of 2.45 × 105. The length deflector is 0.09 times the length of the slant. The deflector was fixed at the leading edge of the slant with an upward angle of 5° to the horizontal axis. Force, pressure, and global skin-friction measurements were conducted to understand the relation between drag, pressure distribution, and flow fields on the slant surface. The results showed that the deflector reduces aerodynamic drag at low yaw angles. This result is due to the breakdown structure of longitudinal vortexes and the separation bubble, which leads to fully separated flow on the leading edge of the slant. However, at yaw angles above 8°, a large reversed flow region forms on the slant and the drag of the model increases. A similar flow structure on the slant is observed for yaw angles of 12° and 15°. Conversely, the model lift is reduced with the deflector at all yaw angles tested. Detailed pressure distribution and complex flow structure on the slant provide insight in this study.

Supersonic flow investigation of a drag reducing conical spike on a hemispherically blunted nose body

Experiments and computations were made at a Mach number of 2.0 on a hemispherical blunt nose body with a conical spike of L/D ratio = 1.0. Attempts were made to alter the axisymmetric cavity formation between the spike tip head and the blunt base body. Qualitative measurements and quantitative details indicate the changes which support the drag reduction beyond the conventional sharp spike. Additional drops in drag values were observed by the techniques used in the present investigation. A linear trend of drag reduction is obtained with conical spikes which lead to the drag of a pure conical body.

Appropriateness of three fish species (Scomber scombrus, Sarda sarda, and Thunnus thynnus) from the Scombridae family in terms of shape and hydromechanics in designing the body of a robotic fish

In this study, we first identify seven criteria for the design of biomimetic robotic fish and focus on two of these tasks: shape and hydromechanics. For this purpose, fish body part measurements were obtained using previous work and also captured and harvested fish samples to construct computer-aided design (CAD) models of three fish species: Scomber scombrus, Sarda sarda, and Thunnus thynnus. Dead body drag and caudal fin flapping were considered as two separate problems. Computational simulations were carried out to determine drag and propulsive performance. Body drag simulations showed that the Reynolds dependence of the drag coefficient of three different species can be adequately expressed by a single laminar scaling correlation. At the same length and swimming speed, the Atlantic mackerel experiences the least drag. Caudal fin deformation simulations showed that the Atlantic bluefin tuna offers the highest thrust and efficiency. Peak efficiency is in the range of 31–35 percent observed at the same optimal Strouhal number, St = 0.5, for all species. It is shown that the aspect ratio as the main length scale influences propulsion performance.

Characteristics of a small arbitrary walking and jumping composite soft actuator with origami structure

A small arbitrary walking and jumping actuator with a composited structure and size of 7 cm × 4 cm × 2.5 cm and mass of 5 g is proposed. An origami structure of polyvinyl chloride (PVC) membrane is designed for the main soft body, driven by shape memory alloy (SMA) springs and piezoelectric bimorphs. It has jumping, linear, and rotating motion modes. A simplified multi-faceted model by MATLAB software is established to perform a numerical analysis of the dynamics of jumping motion. Calculated results show that the length of the elastic belts have a directly proportional impact on the takeoff velocity, jumping legs orientation angle, shape and size of the body and air drag variably impact the jumping performance. The measured results show that the jumping height and distance are 10.3 cm and 19.8 cm, respectively, with a response time of 6.7 s at 1.4 A. The maximum rotating speed on the sandpaper and flat worktop are about 100 deg/s and 300 deg/s respectively. Its linear speed is more than 10 cm/s. • A small arbitrary walking and jumping actuator with composited structure is proposed. • A simplified multi-faceted model of jumping motion is established. • This actuator can jump and recover without motion failure.

Escaping speed of bacteria from confinement

Microswimmers such as bacteria exhibit large speed fluctuation when exploring their living environment. Here, we show that the bacterium Escherichia coli with a wide range of length speeds up beyond its free-swimming speed when passing through narrow and short confinement. The speedup is observed in two modes: for short bacteria with L <20 μm, the maximum speed occurs when the cell body leaves the confinement, but a flagellar bundle is still confined. For longer bacteria (L ≥ 20 μm), the maximum speed occurs when the middle of the cell, where the maximum number of flagellar bundles locate, is confined. The two speed-up modes are explained by a vanishing body drag and an increased flagella drag—a universal property of an “ideal swimmer.” The spatial variance of speed can be quantitatively explained by a simple model based on the resistance matrix of a partially confined bacterium. The speed change depends on the distribution of motors, and the latter is confirmed by fluorescent imaging of flagellar hooks. By measuring the duration of slowdown and speedup, we find that the effective chemotaxis is biased in filamentous bacteria, which might benefit their survival. The experimental setup can be useful to study the motion of microswimmers near surfaces with different surface chemistry.

Body Morphology and Drag in Swimming: CFD Analysis of the Effects of Differences in Male and Female Body Types

This study analyzes the effect of the morphological characteristics of swimmers on passive drag and determines whether the female or male body type is more efficient for gliding. As a result of puberty, males and females develop different body structures; this study investigates whether these changes in shape influence drag. Computational fluid dynamics (CFD) simulations carried out in Ansys Fluent software were used to calculate the drag force and coefficient from 2D models of swimmers in streamline position, generated based on common anthropometric measurements. Both the top and side view profiles of the swimmers were simulated, unique to this study. The normalized male and female body shapes were simulated at different velocities, and it was demonstrated that the male body shape has a lower drag coefficient than the female body shape by 10.1% and 2.8% for top view and side view profiles, respectively. The in-depth analysis and simulation of models with varying hip and chest dimensions found a significant and positive correlation between hip and chest size and drag, with the chest size having the largest effect of an average 12.2% increase in drag per 5% increase in chest breadth. The results from modifying anthropometric variables explain the discrepancy between the drag experienced by male and female swimmers and show that enlarged hips and chests cause an increase in resistance. The differences between drag for males and females were found to be comparable to the 6.2% and 7.7% drag differences between full-body fastskin and normal suits, indicating measurable impact on performance. These findings suggest that the morphology of swimmers does have a significant effect on drag and that the male body shape is more hydrodynamic than the female body shape.

Influence of slip boundary on flow separation and drag of flow past bluff body at high Reynolds numbers

Influence of slip boundary on flow separation and drag of flow past bluff body at high Reynolds numbers

Experimental study on Ahmed’s body drag coefficient

The work presents an experimental designation of the aerodynamic drag coefficient for two configurations of the Ahmed body model, with slant angle of 25o and with the inactive synthetic jet generator. When analyzing the aerodynamic drag of vehicles, most authors focus on higher Reynolds numbers, describing lower values only by designated trend lines. Which is why the main contribution of this experimental work was to designate the Ahmed’s body drag coefficient for low Reynolds numbers and to verify the obtained results with other authors experiments especially with the trend lines for Reynolds number in the range 0,35x105 – 1,8x105. For data taken from the literature, it can be seen that the value of the drag coefficient for the Ahmed body model decreases when the Reynolds number increases. The results obtained during the experiment show the opposite tendency.

Principles of Magnetohydrodynamical Control of Internal and External Supersonic Flows

This paper demonstrates the possibility of active magnetohydrodynamic (MHD) control of supersonic flows containing shock waves. The shock wave configurations that occur at the inlet to a supersonic diffuser and in front of a streamlined semicylindrical model are used for the purpose of investigation. The impact is carried out by organizing local gas discharge regions when applying a magnetic field transverse to gas discharge currents. It has been shown that by changing the local region of application, the intensity and the direction of the gas discharge currents, it is possible to change the intensity and direction of the ponderomotive force acting on the gas flow during MHD interaction. The ponderomotive force control allows for acting locally on the shape and position of shock waves, the speed and direction of the flow, and the increase or reduction of pressure near the surface of the streamlined body. The experiments were carried out on a gas dynamic setup based on a shock tube in a gas dynamic path, capable of creating supersonic flows in a wide range of Mach numbers at M = 4–7. There was a possibility of organizing the electric and pulsed magnetic fields with an intensity of up to 1.5 T. The given experimental Schlieren flow patterns and the analysis of the obtained data demonstrate the MHD effect on: the change in the angle of inclination of the attached shocks, both into increase and decrease; the bow shock wave approaching the body or the removal from it; and the change in the aerodynamic drag and lift force of the streamlined bodies.

Force scaling and efficiency of elongated median fin propulsion

Several fishes swim by undulating a thin and elongated median fin while the body is mostly kept straight, allowing them to perform forward and directional maneuvers. We used a robotic vessel with similar fin propulsion to determine the thrust scaling and efficiency. Using precise force and swimming kinematics measurements with the robotic vessel, the thrust generated by the undulating fin was found to scale with the square of the relative velocity between the free streaming flow and the wave speed. A hydrodynamic efficiency is presented based on propulsive force measurements and modelling of the power required to oscillate the fin laterally. It was found that the propulsive efficiency has a broadly high performance versus swimming speed, with a maximum efficiency of 75%. An expression to calculate the swimming speed over wave speed was found to depend on two parameters: A p/A e (ratio between body frontal area to fin swept area) and C D/C x (ratio of body drag to fin thrust coefficient). The models used to calculate propulsive force and free-swimming speed were compared with experimental results. The broader impacts of these results are discussed in relation to morphology and the function of undulating fin swimmers. In particular, we suggest that the ratio of fin and body height found in natural swimmers could be due to a trade-off between swimming efficiency and swimming speed.

Active flow control using deep reinforcement learning with time delays in Markov decision process and autoregressive policy

Classical active flow control (AFC) methods based on solving the Navier–Stokes equations are laborious and computationally intensive even with the use of reduced-order models. Data-driven methods offer a promising alternative for AFC, and they have been applied successfully to reduce the drag of two-dimensional bluff bodies, such as a circular cylinder, using deep reinforcement-learning (DRL) paradigms. However, due to the onset of weak turbulence in the wake, the standard DRL method tends to result in large fluctuations in the unsteady forces acting on the cylinder as the Reynolds number increases. In this study, a Markov decision process (MDP) with time delays is introduced to model and quantify the action delays in the environment in a DRL process due to the time difference between control actuation and flow response along with the use of a first-order autoregressive policy (ARP). This hybrid DRL method is applied to control the vortex-shedding process from a two-dimensional circular cylinder using four synthetic jet actuators at a freestream Reynolds number of 400. This method has yielded a stable and coherent control, which results in a steadier and more elongated vortex formation zone behind the cylinder, hence, a much weaker vortex-shedding process and less fluctuating lift and drag forces. Compared to the standard DRL method, this method utilizes the historical samples without additional sampling in training, and it is capable of reducing the magnitude of drag and lift fluctuations by approximately 90% while achieving a similar level of drag reduction in the deterministic control at the same actuation frequency. This study demonstrates the necessity of including a physics-informed delay and regressive nature in the MDP and the benefits of introducing ARPs to achieve a robust and temporal-coherent control of unsteady forces in active flow control.

Multi-modal locomotor costs favor smaller males in a sexually dimorphic leaf-mimicking insect

BackgroundIn most arthropods, adult females are larger than males, and male competition is a race to quickly locate and mate with scattered females (scramble competition polygyny). Variation in body size among males may confer advantages that depend on context. Smaller males may be favored due to more efficient locomotion leading to higher mobility during mate searching. Alternatively, larger males may benefit from increased speed and higher survivorship. While the relationship between male body size and mobility has been investigated in several systems, how different aspects of male body morphology specifically affect their locomotor performance in different contexts is often unclear.ResultsUsing a combination of empirical measures of flight performance and modelling of body aerodynamics, we show that large body size impairs flight performance in male leaf insects (Phyllium philippinicum), a species where relatively small and skinny males fly through the canopy in search of large sedentary females. Smaller males were more agile in the air and ascended more rapidly during flight. Our models further predicted that variation in body shape would affect body lift and drag but suggested that flight costs may not explain the evolution of strong sexual dimorphism in body shape in this species. Finally, empirical measurements of substrate adhesion and subsequent modelling of landing impact forces suggested that smaller males had a lower risk of detaching from the substrates on which they walk and land.ConclusionsBy showing that male body size impairs their flight and substrate adhesion performance, we provide support to the hypothesis that smaller scrambling males benefit from an increased locomotor performance and shed light on the evolution of sexual dimorphism in scramble competition mating systems.

Spanwise-Discontinuous Grooves for Separation Delay and Drag Reduction of Bodies with Vortex Shedding

Suitably shaped grooves, placed transverse to the flow, can delay flow separation over curved surfaces. When grooves are fully extruded in the spanwise direction, they may reduce the drag of boat-tailed bodies with vortex shedding, but with the drawback of increasing the spanwise correlation of the vortex shedding. We investigate herein the effect of spanwise-discontinuous grooves through Large Eddy Simulations. A systematic analysis is carried out on the effect of the number, N, of grooves that are present for N equally long portions of the total spanwise length of the boat-tail. Discontinuous grooves further reduce the drag compared with the full-spanwise-extruded groove. Increasing N produces an improvement of the flow-control-device performance, whose maximum value is reached for N=3, corresponding to a spanwise extension of the groove roughly equal to the body crossflow dimension. Above this value, no further improvements are found. The maximum drag reduction is equal to 25.7% of the drag of the boat-tail without grooves and to 17.7% of the one of the boat-tail with the full-spanwise-extruded groove. The lowest drag value occurs for the least correlated vortex-shedding in the spanwise direction. The reduction in the correlation is mainly related to a flow separation line that is less regular in the spanwise direction.

A new species of the eurypterid Hibbertopterus from the Carboniferous of New Mexico, and a review of the Hibbertopteridae

ABSTRACT Hibbertopterus lamsdelli sp. nov., from the Late Carboniferous Kinney Quarry Lagerstätte of New Mexico (USA), is a large (ca. 1.1 m long) stylonurid eurypterid (sea-scorpion; Chelicerata), similar to H. scouleri from Scotland but with less serrate segment margins, a wider pretelson, shorter telson (tail-spine), and more parallel ventral keels. It is only the fourth, yet most reliable record of an American hibbertopterid. A taxonomic reassessment of Hibbertopterus regards Dunsopterus and Vernonopterus (but not Cyrtoctenus) as synonyms. Hibbertopterids were aquatic (benthic) scavengers and microphagous sweep-feeders, but their trackways indicate that they were capable of brief terrestrial, seasonal nuptial walks, despite their large size; Hibbertopterus had walking legs with spinose extensions at the base (Laden) to spread their load, and the ventral keels on their telson functioned like sled rails to reduce body drag. Hibbertopterids were interpreted as moving into freshwater during the Late Palaeozoic, but a trackway from the middle Permian Collingham Formation (Ecca Group) of South Africa may be from a marine setting, though further analysis is needed to fully evaluate this possibility.