Aerodynamic Drag Force Research Articles

Investigation of the effect of the use of top deflectors on aerodynamic performance in vehicles with CFD analysis

Carbon-containing waste gases from vehicle exhausts are one of the main causes of climatic disasters. This problem is tried to be solved by reducing the amount of energy consumed by vehicles while they are in motion. To reduce fuel consumption, it is necessary to reduce the effect of aerodynamic drag force, which is the resistance on the solid surface in motion. It is known that high aerodynamic drag force increases fuel consumption. Reducing aerodynamic drag force is important not only for fuel consumption but also for wind noise and roadholding. Heavy vehicles such as trucks have high drag forces due to the width of their surface areas. However, this situation can be minimized with changes to be made in vehicle designs. In this study, the effect of the use of top deflectors on the drag force for trucks has been investigated. In this theoretical study, separate calculations have been made for different vehicle velocities and the results have been compared among themselves. In this study, which has been carried out using the computational fluid dynamics method, k-e has been preferred as the turbulence method. As a result, it has been concluded that the use of top deflectors reduces drag force, which in turn reduces fuel consumption.

Aerodynamic multi-objective optimization on train nose shape using feedforward neural network and sample expansion strategy

Feedforward neural network (FNN) models with strong learning ability and prediction accuracy are crucial for optimization. This paper investigates the effects of the number of training samples and the hidden layers on the accuracy of the FNN model. Meanwhile, under the premise of a high space-fillingness degree, a sample expansion strategy based on the max–min distance criterion is proposed, which ensures that the expanded sample set completely contains the pre-expanded. The strategy can eliminate the interference of sample differences. Furthermore, the multi-objective optimization on the train nose shape is accomplished by minimizing the aerodynamic lift force of the tail car (LT), as well as the aerodynamic drag force of the head (DH) and tail car (DT) using the FNN model. The results indicate that the number of training samples has a greater impact on the prediction error of the FNN model than the number of hidden layers does. Prediction errors decrease as the number of training samples increases and then stabilise, the most accurate one is chosen for nose shape optimization. The DH, DT, and LT all have prediction errors of less than 2%. Compared with the original high-speed train, the DH, DT, and LT of the optimal model are reduced by 5.24%, 3.74%, and 2.61%, respectively. Meanwhile, the correlation analysis reveals that the height of the cab window and the horizontal profile have a significant impact on the aerodynamic characteristics of the high-speed train.

Study on aerodynamic characteristics and parameters of high-speed elevator car-counterweight intersection

When the high-speed elevator is running, the air in the hoistway is rapidly compressed and released to form the piston effect. Especially when the car and counterweight intersect, the piston effect makes the aerodynamic force of the car and counterweight change sharply, affecting the stability of elevator operation. In this study, a three-dimensional car counterweight intersection model is constructed, and a multi-region dynamic layered method is proposed to calculate the aerodynamic flow field in the whole moving process, the changes of aerodynamic drag force and aerodynamic lateral force of the car and the counterweight under different length ratio, blockage ratio and spacing are analyzed and simulated, and the influence of structural changes in the hoistway on the aerodynamic flow field is studied. Furthermore, the accuracy of the numerical results is verified by the real elevator test. Finally, the results show that when the car intersects the counterweight in the hoistway, the interaction between the car and the counterweight is enhanced, and the drag force coefficient and lateral force coefficient of the car suddenly change, and return to the normal state after the intersection, with the decrease of length ratio and spacing and the increase of blockage ratio, the sudden change degree of drag force also increases, and the sudden change of lateral force of the car is mainly affected by the car counterweight spacing, and increases with the decrease of spacing.

An Analytical Solution for Unsteady Aerodynamic Forces on Streamlined Box Girders with Coupled Vibration

This paper is a contribution to analyzing the aerodynamic forces on a streamlined box girder (SBG) with coupled vibration in a potential flow. The key enabling step was to assume that the normal velocity of the airflow at an arbitrary point on the surface of the SBG was equal to the normal velocity of the surface motion. The aerodynamic drag force, lift force, and pitching moment were expressed as functions of the motion state of the SBG and the SBG’s shape-related parameters. To investigate the applicability of this force model, the analytical solution at various angles of attack was compared with a numerical simulation in a viscous flow. The results imply that the amplitude of the analytical lift force and pitching moment agree well with the numerical results under the angles of attack of 0° and ±3°. Furthermore, the analytical drag force effectively predicts the second-order phenomenon resulting from the multiplication of the vertical and torsional vibration velocities. As a consequence, the present analytical solution provides an effective method for analyzing the aerodynamic forces acting on SBGs with coupled vibration.

Aerodynamic Drag of a Tilt-Rotor UAV During Forward Flight in Rotary-Wing Mode

This paper examines the aerodynamic drag force acting on a tilt-rotor UAV that has three mini fans and a main rotor with a tilt mechanism. The mini fans are embedded in the nose and the left and right wings. The main rotor is located near the center of the vehicle, and its front half is surrounded by the trailing edge of the nose in rotary-wing mode. The downward airflow from the fans and the main rotor generates an aerodynamic drag force called momentum drag, which is linearly proportional to the airspeed of UAV. To verify the existence of momentum drag, parameter identification of drag coefficients is performed from experimental data where the UAV flies forward in rotary-wing mode. The drag force is also investigated using computational fluid dynamics simulations. These experimental and numerical results are consistent with theoretical results based on momentum theory.

Transportation and deformation of high-speed aluminum nanoparticles in inert gas with molecular dynamics study

In addition to complex deformation, high-speed nanoparticles in gas are also accompanied by significant size and interfacial effects. In this work, we simulate the transportation behavior of high-speed aluminum nanoparticles in helium gas with the classical molecular dynamics method. The evolution of aerothermodynamic quantities of solid particles and liquid particles is revealed, and different temperature rise effects are found. Furthermore, the melting of aluminum particles induced by high aerodynamic drag force is discovered, and the melting threshold conditions are proposed. In low-density (0.002 g/cm3) and high-density (0.02 g/cm3) gas, the initial velocity at which particles start to melt is 6 and 4 km/s, respectively. During the deformation of solid particles, the evolution of dislocation motion is discussed, and the evolution of the development characteristics of the molten layer is given. During the deformation of the liquid particles, vibration deformation and bag deformation modes are observed. The threshold conditions for deformation mode transitions are also given. Only in high-density gas, bag deformation occurs when the initial velocity of particles (D > 5 nm) exceeds 6 km/s. The local mechanical quantity of gas is used to explain the variation of the drag force of the particles. Moreover, the drag force model is corrected according to temperature and deformation effects. Within a certain period, the model results overestimate the drag force, and the error with the simulation results is about 25%. This provides a model reference for high-speed nanoparticle dynamics and two-phase flow problems.

Accurate and Simple Modeling of Eddy Current Braking Torque: Analysis and Experimental Validation

A compact, reliable and straightforward mathematical modeling of the eddy current braking torque is proposed in this paper. First, the braking magnetic force, which curbs the movement of a rotating disk (RD) is evaluated using the basic laws of electromagnetism. Second, the braking torque is related to the braking force through a polynomial function model. The model parameters are evaluated by plugging in measurement samples in the equation of motion taking into account the nonlinear behaviour of the aerodynamic drag forces. The proposed model neither has limitations on the braking system geometry nor the disk rotational speed as long as measurement samples cover whole speed range. Moreover, it is validated experimentally for constant and alternating magnetic flux profiles with best fit rates (BFRs) more than 85% and 93% for both rotational velocity and braking torque, respectively. Furthermore, programmable braking application is demonstrated using the proposed approach and its applicability is verified experimentally.

Effect of aerodynamic braking plates installed in Inter-car gap on aerodynamic characteristics of high-speed train

With the continuous increase of train speeds, the aerodynamic drag force provided by aerodynamic braking plates can effectively solve problems of insufficient emergency braking force. The newly proposed aerodynamic braking plates installed in the inter-car gap (ICG) avoid the destruction of the carbody’s strength. In this study, a numerical simulation model of a four-car marshalling train with a speed of 300 km/h is established to study the effect of installation position and opening height of the braking plates mounted in the ICG on the aerodynamic characteristics. The aerodynamic characteristics of the braking plate installed upstream and downstream of the ICG were investigated separately. The downstream plate, which showed better braking performance, was further studied at plate heights of 200 mm, 400 mm, 500 mm, 600 mm, and 800 mm. Results indicate that compared to upstream plates, the aerodynamic drag force coefficient generated by the downstream plates increased by 13.2%. The aerodynamic resistance of the train and the aerodynamic lift of each car increased gradually as the height of the downstream plates increased. Additionally, the braking plate in the ICG had limited anti-crosswind capabilities, with its braking effect significantly weakened in a crosswind of 10 m/s or higher. These results will serve as a guide for the design of aerodynamic braking plates for high-speed trains.

Modeling Vehicle Flocking in Lane-Free Automated Traffic

In automated lane-free traffic, vehicles can choose any arbitrary lateral location. This enables vehicle flocking where, compared to platooning, the grouping of vehicles is possible with smaller space gaps, not only longitudinally but also laterally. Vehicle flocking can fulfill several purposes, such as increasing the road capacity, saving energy by reducing the aerodynamic drag force, and dampening shockwaves. Within this paper, we develop a control framework for modeling vehicle flocks in automated lane-free traffic. The proposed control algorithm considers two types of agents: [Formula: see text] -agents representing potential flock mates and a [Formula: see text] -agent representing the virtual leader with collective objectives (e.g., slowing down in the case of traffic congestion ahead). Our algorithm is based on energy functions for flock centering and collision avoidance, a consensus algorithm for velocity matching, and navigational feedback exerted by the virtual leader. The virtual leader’s path, which should be followed by the flock, is defined in an upper-level controller. In addition, a feedback algorithm for dynamic road boundary control is implemented. We simulate the proposed approach with very promising results. We show that vehicle flocks are efficiently formed within a few seconds, speeds are successfully aligned, and vehicle arrangements stay stable under different scenarios. In addition, the lateral and longitudinal flock extension changes with different energy functions and changing road boundaries, and vehicle flocks follow the trajectory of the virtual leader. Most importantly, vehicle flocks stay stable in the case of perturbations and the induced shock is dampened efficiently because of slight changes in the vehicles’ lateral locations.

Density estimation of an ultrahigh-speed rarefied flow field based on force analysis of a pendulum sphere

The similarity criterion for high speed or high enthalpy rarefied reaction flows is the binary scaling law, one of which is the product of the incoming flow density and the characteristic scale of the test model in a rarefied wind tunnel should be equal to that under the flight condition. This is to ensure that the ratio between the characteristic distance of the relaxation process and the characteristic length of the body is equal. However, in a rarefied wind tunnel, it is difficult to directly measure the flow density below 10−5 kg/m3 using common methods due to the relatively high rarefied degree, an indirect density estimation method based on force analysis of a pendulum sphere was proposed in this study. The oscillation trajectory of the pendulum sphere under ultrahigh-speed rarefied flow conditions was recorded and the corresponding aerodynamic drag force acted on the sphere along the trajectory was analyzed, based on which the density distribution of the flow was then estimated combined with DSMC simulations. The obtained results show that in the present study, the flow is in under-expanded condition and the measured density sharply decreased from 10−6 kg/m3 to 10−7 kg/m3 at 140–170 mm from the nozzle outlet.

A computational framework for physics-informed symbolic regression with straightforward integration of domain knowledge

Discovering a meaningful symbolic expression that explains experimental data is a fundamental challenge in many scientific fields. We present a novel, open-source computational framework called Scientist-Machine Equation Detector (SciMED), which integrates scientific discipline wisdom in a scientist-in-the-loop approach, with state-of-the-art symbolic regression (SR) methods. SciMED combines a wrapper selection method, that is based on a genetic algorithm, with automatic machine learning and two levels of SR methods. We test SciMED on five configurations of a settling sphere, with and without aerodynamic non-linear drag force, and with excessive noise in the measurements. We show that SciMED is sufficiently robust to discover the correct physically meaningful symbolic expressions from the data, and demonstrate how the integration of domain knowledge enhances its performance. Our results indicate better performance on these tasks than the state-of-the-art SR software packages , even in cases where no knowledge is integrated. Moreover, we demonstrate how SciMED can alert the user about possible missing features, unlike the majority of current SR systems.

Hardware in the loop simulation and implementation of a dragonfly-like MAV using clap and fling mechanism

The main aim of this paper is to model and simulate flight dynamics and to design a controller for a dragonfly-like micro aerial vehicle (MAV). This MAV has flapping wings using a clap and fling mechanism with a rigid abdomen. Kane’s method is applied to derive the longitudinal motion equations of the MAV as a multi-body system. Then, the aerodynamic lift and drag forces of the MAV are obtained. These equations are substituted in the derived motion equations. Furthermore, a new structure for a dragonfly-like flapping wing MAV is presented in which abdomen motion is considered in the longitudinal mode. In this work, the use of the abdomen is also formulated. A change in the motor’s speed generates differential thrust that creates a pitch moment as a control input. State space linearized equations of motion are presented by using appropriate assumptions in the aerodynamics, and dynamic nonlinear equations. To validate the linearized model, the response of the open-loop linear system is compared with the nonlinear one. In addition, the positive role of the abdomen in the open loop is discussed and analyzed. Finally, an LQR controller is designed for the pitch mode which is robust against disturbances. The validity, effectiveness, and performance of the derived equations and designed autopilot are shown by implemented hardware in the loop testbed using a fixed abdomen. Results demonstrate a good agreement between theoretical and experimental responses with accurate hovering at the desired angle.

Mathematical modeling of the rolling speed of a car on the first profile site of the slide

The article shows the consideration of the rolling friction moments (pure rolling) of the wheels on the rail threads and in the bearings of the front axlebox units. and rear bogies of the car with their subsequent replacement by conditional sliding friction. It is noted that if the active force in the form of a projection of the force of gravity and the aerodynamic drag force on the direction of rolling of the car (or release), acting on the car, is greater than the limiting friction force, then simultaneously with rolling, the wheels may also slip on the rail threads. An analytical formula was obtained for finding the difference between the driving forces and all resistance forces when rolling wheels with sliding, which, based on the theorem on the change in the momentum of a material point, made it possible to create a mathematical model for finding the speed of a single car (or cut) on the first profile section of the hump. An analysis of the results of solving the problem of determining the rolling speed of a car has been carried out. It is noted that the theorem on the change in the momentum of a material point for solving the problem of finding the time of rolling down a hill is applicable only when the final speed of the car is known, otherwise solving the problem in such a formulation will be meaningless.

ADVECTION AND DEPOSITION OF MICRODROPLETS IN STAGNATION POINT FLOW

We investigate trajectories of microscale evaporating droplets in a stagnation point flow near a wall of a respiratory airway. The configuration is motivated by the problem of advection and deposition of microscale droplets of respiratory fluids in human airways during transmission of infectious diseases, such as tuberculosis and COVID-19. Laminar boundary layer equations are solved to describe the airflow while the equations of motion of the droplet include contributions from gravity, aerodynamic drag, and Saffman force. Evaporation is accounted for at both the droplet surface and the wall of the respiratory airway and is shown to delay droplet deposition as compared to the predictions of isothermal models. Evaporation at the airway wall has a stronger effect on droplet trajectories than evaporation at the droplet surface, leading to droplets being advected away by the flow and thus avoiding deposition in the stagnation point flow region.

Kinematic modeling and analysis of transmission mechanism with joint clearance for flapping wing micro aerial vehicle

A theoretical model is built to reveal the effect of the joint clearance on the kinematic performance of the transmission mechanism of a flapping wing micro aerial vehicle (FWMAV). Massless link approach is used to model the joint clearance and the reciprocal screw is introduced to solve the kinematic model. Finite element method simulations are also performed to validate the model. The kinematic model reveals that the inertia force of the transmission mechanism contributes little to the flapping motion whereas the sign of the resultant moment of aerodynamic drag and wing inertia force plays decisive role. Besides, the joint clearance can either increase or decrease the flapping angle of the wing during a flapping period and it will significantly affect the flapping amplitude while involves little in the mean flapping angle. The effects of the positions of the joint with clearance and its magnitude on the flapping motion are also revealed.

Geometric descriptors for the prediction of snowflake drag

The dynamics of solid particles of complex shapes such as airborne snowflakes are governed by aerodynamic drag forces that are a function of the relative velocity of the particle in the flow and the particle drag coefficient, which depends on the particle geometry and its orientation. In this study, artificial snowflakes are produced by additive manufacturing and their drag coefficients are obtained by measuring the terminal velocity in a liquid container, matching the Reynolds number typically encountered in natural occurrences. The experimental results show that the convex hull of the particle is suitable to accurately predict the drag force with existing correlations. Since it is unfeasible to accurately measure the three-dimensional geometries of natural snowflakes, the approximation with the convex hull provides a useful simplification. Furthermore, the known shapes of the artificial snowflakes are used to develop correlations to estimate the most relevant three-dimensional descriptors to predict the drag of snowflakes from a two-dimensional projection onto an arbitrary plane.Graphic abstract

Dust dynamics in ramses – I. Methods and turbulent acceleration

ABSTRACT Supernova ejecta and stellar winds are believed to produce interstellar dust grains with relatively large sizes. Smaller grains can be produced via the shattering of large grains that have been stochastically accelerated. To understand this stochastic acceleration, we have implemented novel magnetohydrodynamic (MHD) particle-in-cell methods into the astrophysical fluid code ramses. We treat dust grains as a set of massive ‘superparticles’ that experience aerodynamic drag and Lorentz force. We subject our code to a range of numerical tests designed to validate our method in different physical conditions, as well as to illustrate possible mechanisms by which grains can be accelerated. As a final test as well as a foundation for future work, we present the results of decaying dusty MHD turbulence simulations with grain parameters chosen to resemble 1–2 μm grains in typical cold neutral medium conditions. We find that in these conditions, these grains can be effectively accelerated to well beyond their shattering velocities. This is true for both electrically charged and neutral grains. While the peak of the gas-grain relative drift velocity distribution is higher for neutral grains, the drift velocity distribution of charged grains exhibits an extended exponential tail out to much greater velocities. Even so, the shapes of the distributions are such that the extra gas-grain coupling provided by the Lorentz force offers grains relative protection from shattering. We also discuss the connection between our simulations and the relatively pristine ∼μm-sized pre-solar grains that do not appear to have undergone significant wear in their lifetimes.

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.

Agile Flight Control Under Multiple Disturbances for Quadrotor: Algorithms and Evaluation

In this article, a scheme of anti-disturbance agile flight control is developed for a maneuverable quadrotor unmanned aerial vehicle, subject to the aerodynamic drag, dynamic shift of center of gravity (CoG), and motor dynamics. A cascaded control framework is adopted. In the translational loop, an aerodynamic drag model that considers the drag surface change is developed, containing the deep coupling information between the aerodynamic drag and the system states. A disturbance observer based on the aerodynamic drag model is subsequently designed for suppressing the aerodynamic drag force. In the rotational loop, a full quaternion-based backstepping control is adopted and a nonlinear disturbance observer with consideration of motor dynamics is designed, which can handle the dynamic CoG shift and aerodynamic drag torque. Comparative studies on both simulations and experiments manifest that the agile ability can be ensured by the proposed control framework, especially in the presence of multiple disturbances.

The metabolic cost of emulated aerodynamic drag forces in marathon running.

The benefits of drafting for elite marathon runners are intuitive, but the quantitative energetic and time savings are still unclear due to the different methods used for converting aerodynamic drag force reductions to gross metabolic power savings. Further, we lack a mechanistic understanding of the relationship between aerodynamic drag forces and ground reaction forces (GRFs) over a range of running velocities. Here, we quantified how small horizontal impeding forces affect gross metabolic power and GRF over a range of velocities in competitive runners. In three sessions, 12 runners completed six 5-min trials with 5 min of recovery in-between. We tested one velocity per session (12, 14, and 16 km/h), at three horizontal impeding force conditions (0, 4, and 8 N) applied at the waist of the runners. On average, gross metabolic power increased by 6.13% per 1% body weight of horizontal impeding force but the increases varied considerably between individuals (4.17%-8.14%). With greater horizontal impeding force, braking GRF impulses decreased, whereas propulsive GRF impulses increased, but the impulses were not related to individual changes in gross metabolic power. Combining our findings with those of previous aerodynamics studies, we estimate that for a solo runner (52 kg) at 2-h marathon pace, overcoming aerodynamic drag force (1.39% BW) comprises 7.8% of their gross metabolic power and drafting can save between 3 min 42 s and 5 min 29 s.NEW & NOTEWORTHY We measured the metabolic and biomechanical effects of small horizontal impeding forces (representing realistic aerodynamic drag forces) on high-caliber runners across a range of velocities. Combining our metabolic results with existing aerodynamic models indicates that at 2-h marathon pace, optimal drafting likely allows a marathoner to run between 3 min 42 s and 5 min 29 s faster. Our rule-of-thumb (∼6% increase in gross metabolic power per 1% body weight of horizontal impeding force) will allow others to estimate the performance enhancement of different drafting formations.