Magnitude Of Drag Research Articles

The Aerodynamic Assessment and Shot Point Position Accuracy of UAV Seismic Source

An unmanned aerial vehicle (UAV) seismic source, suitable for complex terrains due to its eco-friendly, cost-effective, and efficient nature, operates by hovering and releasing impact objects to generate seismic waves. The aerodynamic behavior of these impact objects is vital for shotpoint position accuracy and drag magnitude. Excessive drag will result in the loss of seismic source energy, whereas the deviations of the shotpoint position will disrupt the geometric structure of the observation system, significantly impacting the quality of seismic data acquisition. Through theoretical calculations, the influencing factors of air resistance and cross-wind deflection are analyzed. Air resistance increases with the increase in mass, cross-sectional area, speed, and drag coefficient. Increasing the mass and throwing height can increase the upper limit of the output, but after the air resistance and gravity are balanced, the output kinetic energy of the drone’s seismic source will no longer increase when the throwing height is increased. Using computational fluid dynamics simulations and field tests, this study examines the aerodynamics of four prevalent impact object designs. The results show that shuttle and spherical structures have the least drag during descent and are less influenced by crosswinds, thus being optimal for this application. Field measurement data are also presented for reference.

The effect of slip parameter in an axisymmetric oscillatory Stokes flow

A general solution of Stokes equations for the problem of an axisymmetric oscillatory flow of an incompressible, viscous fluid past a sphere satisfying general boundary conditions is obtained. The behavior of the magnitude of drag is observed with the variation of the slip parameter. Some more interesting behaviors are detailed, and several existing results pertaining to steady flows and flows with rigid and shear free boundary conditions are recovered as special cases. The corresponding results are discussed for four different axisymmetric oscillatory Stokes flows, namely, uniform flow, flows generated due to a dipole, a source, and a Stokeslet. A few interesting streamline patterns like formation, elongation, and disappearance of viscous eddies in the vicinity of the sphere with a periodic reversal of the flow are observed at different frequencies for different values of the slip parameter.

Dynamic Pressure Drag on Rising Buoyant Thermals in a Neutrally Stable Environment

Abstract This study examines dynamic pressure drag on rising dry buoyant thermals. A theoretical expression for drag coefficient Cd as a function of several other nondimensional parameters governing thermal dynamics is derived based on combining the thermal momentum budget with the similarity theory of Scorer. Using values for these nondimensional parameters from previous studies, the theory suggests drag on thermals is small relative to that on solid spheres in laminar or turbulent flow. Two sets of numerical simulations of thermals in an unstratified, neutrally stable environment using an LES configuration of the Cloud Model 1 (CM1) are analyzed. One set has a relatively low effective Reynolds number Re and the other has an order-of-magnitude-higher Re; these produce laminar and turbulent resolved-scale flows, respectively. Consistent with the theoretical Cd, the magnitude of drag is small in all simulations. However, whereas the laminar thermals have Cd ≈ 0.01, the turbulent thermals have weakly negative drag (Cd ≈ −0.1). This difference is explained by the laminar thermals having near vertical symmetry but the turbulent thermals exhibiting considerable vertical asymmetry of their azimuthally averaged flows. In the laminar thermals, buoyancy rapidly becomes concentrated around the main centers of rotation located along the horizontal central axis, leading to expansion of thermals via baroclinic vorticity generation but doing little to break vertical symmetry of the flow. Vertical asymmetry of the azimuthally averaged flow of turbulent thermals is attributed mainly to small-scale resolved eddies that are concentrated in the upper part of the thermals.

Study on optimization method for airfoil in supersonic case based on Particle Swarm optimization(PSO)

In order to adapt to the society demand of requiring faster aircraft, this thesis aims at combining Particle Swarm optimization (PSO) with Computational Fluid Dynamics (CFD) to get a optimized airfoil which possesses a better areodynmics performance in supersonic case. This paper adopts the method of using small disturbance equation to simulate the flow field, which is more effective and stable and easier to implement. Besides, this paper adopts traditional PSO. The results show that the magnitude of ratio of lift-drag has increased by 16.29% and the magnitude of lift has risen by 13.69%, while the magnitude of drag has decreased by 2.2% after the optimization, compared with the initial airfoil. Besides, the results also reveal that the front of the optimized airfoil is wider than that of the initial airfoil and the rear of the optimized airfoil is narrower than that of the initial airfoil, which can represent that the optimized airfoil effectively enlarge the magnitude of ratio of lift-drag and lift and suppresses the drag and influence generated by shock.

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.

Analysis about enhancement in thermal characteristics of viscous fluid flow with induction of ferrite particles by using Cattaneo Christov theory

The elevated convective heat transfer process plays vital role in performance of electronic and engineering equipment’s. Over the years various attempts have been executed in this regards, including the insertion of nano elements in poorly conducting liquids. Initially, improvement in thermophysical characteristics of ordinary fluids was observed but with advancement in nanoparticles structuring new classifications in nano elements are found. Among these discoveries experimentations have explored highly fascinating and intrinsically featured class of nanomaterials renowned as ferromagnetic nano constituents. So, the motivation regarding this investigation is execution about change in thermal features of base liquid with insertion of different ferrite particles. Here, water is considered as based liquid and Nickel Zinc Ferrite (NiZnFe2O4) and magnetite ferrite (Fe2O4) as solid particles are inserted. Impact of magnetic dipole is also envisioned to produce optimized effectiveness of ferrite particles. Energy transmission in flow domain is depicted by incorporation of Cattaneo-Christov heat flux model. Mathematical formulation containing thermo mechanical features of ferrite particles are attained in complexly structured partial differential system and afterwards similarity transformations are implemented for transmutation into ODES. Constructed problem is simulated by implementing numerical approaches. Influence of involved variables on associated distributions are displayed through graphs and tables. It is demonstrated that momentum as well as heat transfer of base fluid augments with inclusion of Nickel Zinc ferrite as compared magnetite ferrite. It is inferred that velocity shows declining behavior against Curie temperature whereas reverse behavior is seen for temperature profile. It is divulged that viscous dissipation imparts diminishing impact on momentum whereas contrary behavior is depicted in case of temperature profile. In addition, increment in wall drag magnitude and thermal flux is manipulated by incorporation of (NiZnFe2O4) rather than (Fe2O4).

Observation of Mechanical Faraday Effect in Gaseous Media.

We report the experimental observation of the rotation of the linear polarization of light propagating in a gas of fast-spinning molecules (molecular superrotors). In the observed effect, related to Fermi's prediction of "polarization drag" by a rotating medium, the vector of linear polarization tilts in the direction of molecular rotation. We use an optical centrifuge to bring the molecules in a gas sample to ultrafast unidirectional rotation and measure the polarization drag angles of the order of 10^{-4} rad (with an experimental uncertainty about 10^{-6} rad) over the propagation distance of the order of 1mm in a number of gases under ambient conditions. We demonstrate an all-optical control of the drag magnitude and direction and investigate the robustness of the mechanical Faraday effect with respect to molecular collisions.

Ionospheric drag for accelerated deorbit from upper low earth orbit

Orbit debris mitigation restrictions placed on the growing number of miniaturised spacecraft often constrain their operational altitudes to less than approximately 600km where drag accelerations are sufficient to deorbit the spacecraft within 25 year guidelines. Operation at higher, Low Earth Orbit (LEO) altitudes often necessitates active measures to deorbit miniaturised spacecraft such as propulsion systems. However, the inclusion of propulsion systems is not always desirable because of the added cost and complexity. This work investigates the feasibility of ionospheric drag, the component of drag caused by an electrically charged body’s exchange of momentum with the ionosphere, to accelerate the deorbit of miniaturised spacecraft in high LEO (600–1000 km altitude). This work studies how actively charging the surface of a miniaturised satellite in high LEO may enhance the overall magnitude of the drag acceleration, due to the ionospheric drag, acting to deorbit the spacecraft. This is achieved using surrogate models of the charged drag coefficient, as a function of plasma scaling parameters, generated by Particle-in-Cell simulations. The charged drag coefficient surrogate model is incorporated into an orbit propagator where deorbit times are predicted over various orbital and vehicular initial conditions. Results suggest that the magnitude of ionospheric drag can be an order of magnitude larger than the neutral drag at 850 km altitude compared to approximately half the magnitude of neutral drag at 500 km altitude. Therefore, ionospheric drag is relatively more efficient at deorbiting spacecraft at high LEO compared to neutral drag. Additionally, the magnitude of ionospheric drag is tailorable based on changes in the electrical surface potential of the satellite relative to a quasi-neutral free-stream plasma. The primary payload of many miniaturised spacecraft often require high-voltage electrical systems. These same electrical systems could conceivably be utilised to generate ionospheric drag via surface charging, at the end of the mission-life, at little additional cost or system complexity. Thus, the implications of this work include the possible uncovering of a simple mechanism for deorbiting miniaturised spacecraft from high LEO altitudes for compliance with orbit debris mitigation guidelines.

Multi-objective optimisation of drag and lift coefficients of a car integrated with canards

Canard is one of the aerodynamic add-on devices which can reduce drag coefficient of the car. In this paper, different parameters of the canard geometry are determined using a multi-objective optimisation. Design variables are entrance velocity (U), geometrical parameters of canard (L 1, L 2, r, α) and canard angle from horizontal axis (θ). The objective functions include magnitude of drag and lift coefficients that should be minimised and maximised, respectively. First, the neural network is trained by means of a series of ANSYS Fluent-based CFD calculations. A GMDH-type neural network is then applied to derive polynomials that compute the objective functions from input variables. Finally, Pareto optimal points for objective functions are obtained through using these polynomials and NSGA-II multi-objective optimisation. According to the results, the canard’s optimum state is specified as L 1 = 0.37 m, L 2 = 0.18 m, r = 0.09 m, α = 25°, θ = 20° with potential drag reduction of 4.5%.

Analysis of radiation pressure and aerodynamic forces acting on powder grains in powder-based additive manufacturing

Selection of process parameters is an important step in Powder-Based Additive Manufacturing (PBAM) of metals. In order to achieve an optimal parameter set, current literature is mainly focused on the understanding of powder dynamics by analysing the aerodynamic forces. In this letter, however, we show the importance of the laser induced force (radiation pressure) on the powder dynamics. Generalised Lorenz-Mie theory has been employed to accurately estimate the radiation pressure and it is shown that its magnitude is significant in comparison to various aerodynamic forces and the grains weight, hence, can significantly contribute to denudation and spatter observed in the manufacturing process. Furthermore, the importance of compressibility and rarefaction effects on the magnitude of drag and lift forces that a particle experiences is demonstrated by estimating the Ma and Kn numbers under process conditions, which directly impact the powder dynamics.

Numerical Simulation of a Flapping Micro Aerial Vehicle Through Wing Deformation Capture

Three-dimensional numerical simulations of a four-wing flapping micro aerial vehicle (FMAV) with actual experimentally captured wing membrane kinematics have been performed using an immersed boundary method Navier–Stokes finite volume solver. To successfully simulate the clap and fling motion involving the wing intersection, the numerical solver has been specifically modified to use a newly improved interpolation template searching algorithm to prevent divergence. Reasonable agreement was found between the numerical and experimental results, with the first and second force peaks from the experimental results well captured by the simulations, which was not possible in the past. Moreover, a “V-shaped linked” vortex was observed, which was similar to the vortical structures found in other experiments and simulations. A wing drag analysis showed that the drag magnitude of the clap and fling configuration was about 2.5 times that of the single-wing configuration. Visualizations of the flowfields through pressure contours and vortical isosurfaces led to a better understanding of the underlying flapping-wing aerodynamics. The ability to accurately simulate the FMAV with flexible wings opened up many opportunities for further FMAV design-related problems.

Drag associated with 3D trapped lee waves over an axisymmetric obstacle in two‐layer atmospheres

Mountain‐wave drag is evaluated explicitly using linear theory and verified against numerical simulations for the flow of idealized two‐layer atmospheres with piecewise‐constant stratification over an axisymmetric mountain. Static stability is either higher in the bottom layer and lower in the top layer (Scorer's atmosphere) or neutral in the bottom layer and positive in the top layer, separated by a sharp temperature inversion (Vosper's atmosphere). The drag receives contributions from long mountain waves propagating vertically in the upper layer and from short trapped lee waves propagating downstream, either in the lower layer or at the inversion. This trapped lee‐wave drag, which is typically not represented in parametrizations, acts on the atmosphere at low levels. As in flow over a 2D ridge, this drag has several maxima as a function of the height of the interface between the two layers for Scorer's atmosphere and is maximized by a marked Scorer parameter contrast between those layers. In Vosper's atmosphere, there is a single trapped lee‐wave drag maximum for Froude numbers near one, when the wind speed matches the phase speed of the dominant interfacial waves, and this drag is maximized for relatively low interface elevations, for which waves at the inversion have higher amplitude. The 3D flow geometry allows resonant wave modes to have various horizontal orientations and a continuous spectrum, forming a dispersive ‘Kelvin ship wave’ pattern, and expanding the regions in parameter space where the drag is non‐zero relative to 2D flow, but it also decreases the drag magnitude dispersively. Nevertheless, the trapped lee‐wave drag on an axisymmetric obstacle can still equal or exceed the drag associated with vertically propagating waves and the reference hydrostatic drag valid for a uniformly stratified atmosphere.

Drag Produced by Waves Trapped at a Density Interface in Nonhydrostatic Flow over an Axisymmetric Hill

Abstract Linear nonhydrostatic theory is used to evaluate the drag produced by 3D trapped lee waves forced by an axisymmetric hill at a density interface. These waves occur at atmospheric temperature inversions, for example, at the top of the boundary layer, and contribute to low-level drag possibly misrepresented as turbulent form drag in large-scale numerical models. Unlike in 2D waves, the drag has contributions from a continuous range of wavenumbers forced by the topography, because the waves can vary their angle of incidence to match the resonance condition. This leads to nonzero drag for Froude numbers (Fr) both <1 and >1 and a drag maximum typically for Fr slightly below 1, with lower magnitude than in hydrostatic conditions owing to wave dispersion. These features are in good agreement with laboratory experiments using two axisymmetric obstacles, particularly for the lower obstacle, if the effects of a rigid lid above the upper layer and friction are taken into account. Quantitative agreement is less satisfactory for the higher obstacle, as flow nonlinearity increases. However, even in that case the model still largely outperforms both 3D hydrostatic and 2D nonhydrostatic theories, emphasizing the importance of both 3D and nonhydrostatic effects. The associated wave signatures are dominated by transverse waves for Fr lower than at the drag maximum, a dispersive “Kelvin ship-wave” pattern near the maximum, and divergent waves for Fr beyond the maximum. The minimum elevation at the density-interface depression existing immediately downstream of the obstacle is significantly correlated with the drag magnitude.

Flow visualisation of downhill skiers using the lattice Boltzmann method

In downhill alpine skiing, skiers often exceed speeds of 120 km h−1, with air resistance substantially affecting the overall race times. To date, studies on air resistance in alpine skiing have used wind tunnels and actual skiers to examine the relationship between the gliding posture and magnitude of drag and for the design of skiing equipment. However, these studies have not revealed the flow velocity distribution and vortex structure around the skier. In the present study, computational fluid dynamics are employed with the lattice Boltzmann method to derive the relationship between total drag and the flow velocity around a downhill skier in the full-tuck position. Furthermore, the flow around the downhill skier is visualised, and its vortex structure is examined. The results show that the total drag force in the downhill skier model is 27.0 N at a flow velocity of 15 m s−1, increasing to 185.8 N at 40 m s−1. From analysis of the drag distribution and the flow profile, the head, upper arms, lower legs, and thighs (including buttocks) are identified as the major sources of drag on a downhill skier. Based on these results, the design of suits and equipment for reducing the drag from each location should be the focus of research and development in ski equipment. This paper describes a pilot study that introduces undergraduate students of physics or engineering into this research field. The results of this study are easy to understand for undergraduate students.

Flow Visualization of Downhill Ski Racers Using Computational Fluid Dynamics

In downhill alpine skiing, racers often exceed speeds of 120km/h, with air resistance substantially affecting the overall race times. To date, studies on air resistance in alpine skiing have used wind tunnels and actual skiers to examine the relationship between the gliding posture and magnitude of drag, as well as for the design of skiing equipment. However, these studies have not revealed the flow velocity distribution and vortex structure around the skier. In the present study, we used computational fluid dynamics with the lattice Boltzmann method to derive the relationship between flow velocity in the full tuck position (the downhill racer's speed) and total drag. Furthermore, we visualized the flow around the downhill racer and examined its vortex structure. The results show that the total drag force in the downhill racer model is 27.0N at a flow velocity of 15 m/s, increasing to 185.8N at 40 m/s. Moreover, the visualization of the flow field indicates that the primary drag locations at a flow velocity of 40 m/s are the head, upper arms, lower legs, and thighs (including the buttocks).

Coulomb Drag Mechanisms in Graphene

Recent measurements revealed an anomalous Coulomb drag in graphene, hinting at new physics at charge neutrality. The anomalous drag is explained by a new mechanism based on energy transport, which involves interlayer energy transfer, coupled to charge flow via lateral heat currents and thermopower. The old and new drag mechanisms are governed by distinct physical effects, resulting in starkly different behavior, in particular for drag magnitude and sign near charge neutrality. The new mechanism explains the giant enhancement of drag near charge neutrality, as well as its sign and anomalous sensitivity to the magnetic field. Under realistic conditions, energy transport dominates in a wide temperature range, giving rise to a universal value of drag which is essentially independent of the electron-electron interaction strength.

Pregnancy is a drag: hydrodynamics, kinematics and performance in pre- and post-parturition bottlenose dolphins (Tursiops truncatus)

Constraints on locomotion could be an important component of the cost of reproduction as carrying an increased load associated with eggs or developing fetuses may contribute to decreased locomotor performance for females across taxa and environments. Diminished performance could increase susceptibility to predation, yet the mechanism(s) by which gravidity and pregnancy affect locomotion remains largely unexplored. Here we demonstrate that morphology, hydrodynamics and kinematics were altered during pregnancy, providing a mechanism for diminished locomotor performance in two near-term pregnant (10 days pre-parturition) bottlenose dolphins (Tursiops truncatus). Near-term pregnancy resulted in a 56 ± 13% [corrected] increase in frontal surface area, coinciding with dramatic increases in drag forces while gliding. For example, pregnant females encountered 80 N of drag at 1.7 m s(-1) whereas that magnitude of drag was not encountered until speed doubled for females 18 months post-parturition. Indeed, drag coefficients based on frontal surface area were significantly greater during pregnancy (C(d,F)=0.22 ± 0.04) than at 18 months post-parturition (C(d,F)=0.09 ± 0.01). Pregnancy also induced a gait change as stroke amplitude and distance per stroke were reduced by 13 and 14%, respectively, compared with non-pregnant periods (1-24 months post-parturition). This was concomitant with a 62 and 44% reduction in mean and maximum swim speeds, respectively, during the pregnancy period. Interestingly, attack speeds of known predators of dolphins surpass maximum speeds for the pregnant dolphins in this study. Thus, pregnant dolphins may be more susceptible to predation. This study demonstrates unequivocally that changes in morphology, hydrodynamics and kinematics are associated with diminished performance during pregnancy in dolphins.

Estimation of orographically induced wave drag in the stable boundary layer during the CASES-99 experimental campaign

This paper addresses the quantification of gravity wave drag due to small hills in the stable boundary layer. A single column atmospheric model is used to forecast wind and temperature profiles in the boundary layer. Next, these profiles are used to calculate vertical profiles of gravity wave drag. Climatology of wave drag magnitude and “wave drag events” is presented for the CASES-99 experimental campaign. It is found that gravity wave drag events occur for several relatively calm nights, and that the wave drag is then of equivalent magnitude as the turbulent drag. We also illustrate that wave drag events modify the wind speed sufficiently to substantially change the surface sensible heat flux.

Stroking Characteristics during Time to Exhaustion Tests

Race analyses during swimming reveal how exercise duration affects both clean swimming speed (v), stroke rate (SR), and stroke length (SL). The aim of this study is to provide an explanation for the change of SL and SR during paced exercise swimming the front crawl through an analysis of intracycle changes in motor organization. Trained swimmers (N = 10) swam three times to exhaustion (TTE in seconds) at predetermined velocities corresponding to 95%, 100%, and 110% of the mean speed attained in a 400-m race (V 400). During TTE tests, SR, SL, durations of the glide + catch, pull, push, and recovery phases (s) were measured. Assessment of arm coordination was made through the calculation of the index of coordination (IdC). The time allotted to propulsion per distance unit was estimated (T prop). For all tested speeds, fatigue development induced a gradual increase of SR with concomitant decrease of SL. The duration of the nonpropulsive phases decreased, whereas the duration of the propulsive phases per stroke remained constant. The IdC increased reflecting a reduction of the lag time between two consecutive propulsive actions. Consequently, T prop increased. Fatigue development induced an increase of the SR to compensate for the reduced capacity to generate a propulsive impulse per stroke. The change in arm coordination allows a better chain of the propulsive actions and leads to a greater time allotted to propulsion per distance unit. Such motor adaptation ensures that the overall propulsive impulse remained constant whereas average propulsive force per arm stroke is reduced.

Coulomb drag at the onset of Anderson insulators

I study the Coulomb drag between two identical layers in the Anderson insulating state. The dependence of the transresistance ${\ensuremath{\rho}}_{t}$ on the localization length \ensuremath{\xi} is considered, for both a Mott insulator and an Efros-Shklovskii (ES) insulator. In the former, ${\ensuremath{\rho}}_{t}$ is monotonically increasing with \ensuremath{\xi}; in the latter, the presence of a Coulomb gap leads to an opposite result: ${\ensuremath{\rho}}_{t}$ is enhanced with a decreasing \ensuremath{\xi}, with the same exponential factor as the single layer resistivity. This distinction reflects the relatively pronounced role of excited density fluctuations in the ES state, implied by the enhancement in the rate of hopping processes at low frequencies. The magnitude of drag is estimated for typical experimental parameters in the different cases. It is concluded that a measurement of drag can be used to distinguish between the interacting and noninteracting insulating state.