Lateral Aerodynamic Force Research Articles

Evaluation of active leeward side air-blowing layout on the lateral aerodynamic performance of high-speed trains in crosswinds environment: Sustainable and safe operation strategy

The lateral aerodynamic forces experienced by high-speed trains operating in crosswind environments affect trains' operating safety significantly. This paper used the Improved Detached Eddy Simulation (IDDES) method based on the Shear Stress Transport (SST) k-ω turbulence model to explore the mitigating effect of air-blowing at the leeward side of the train on the train's lateral aerodynamic forces. Different air-blowing positions and speeds were considered. The results indicate that the best mitigating effect can be achieved when simultaneously blowing air at the head, middle, and tail cars; in addition, when blowing air at the speed of 0.3 times of the resultant velocity, the rolling moment of the three cars reduced by 7.71%, 7.25%, and 25.46% respectively. Finally, the assessment of the mitigation efficiency was displayed to discuss the trade-off of rolling moment reduction and energy utilization rate for air-blowing. The research gives an insight into increasing the stability and safety of trains in crosswind based on active control, which can improve the safe operation threshold of trains.

Heavy-Vehicle Response to Crosswind: Evaluation of Driver Reactions Using a Dynamic Driving Simulator

Heavy vehicles exiting (or entering) a tunnel at high speed under a strong crosswind is a particularly critical condition since the aerodynamic load changes drastically, greatly affecting the lateral stability of the vehicle. Often, active control systems (active suspensions, active front steering, etc.) and infrastructure elements (e.g., wind fences) are proposed to reduce the induced risks. To help the design of these devices, the present paper investigates the response of the vehicle–driver system in the case of a high-sided lorry exiting a tunnel under crosswind, by using Driver-In-the-Loop simulations. The study was performed using the dynamic driving simulator of Politecnico di Milano and 28 test drivers. Vehicle and aerodynamic models have been developed to reproduce the phenomenon in a highly immersive environment. During the tests, several combinations of vehicle and wind speed were considered. The effect of vehicle loading condition (Empty and Laden) was also investigated. The performed tests allowed us to gain information about the sequence of the driver’s actions and associated delays, which may induce lane deviation or, in the worst case, rollover. It was found that lane invasion may happen for ratios of lateral aerodynamic force over vehicle weight force bigger than 0.1, while rollover could happen for ratios bigger than 0.3. Moreover, it was found that the driver’s response typically happens with a delay of ∼0.25 s with respect to the onset of the crosswind stimulus.

Research on Short-Time Wind Speed Prediction in Mountainous Areas Based on Improved ARIMA Model

In rugged mountain areas, the lateral aerodynamic force and aerodynamic lift caused by strong winds are the main reasons for the lateral overturning of trains and the destruction of buildings and structures along the railroad line. Therefore, it is important to build a strong wind alarm system along the railroad line, and a reasonable and accurate short-time forecast of a strong wind is the basis of it. In this research, two methods of constructive function and time-series decomposition are proposed to pre-process the input wind speed for periodic strong winds in mountainous areas. Then, the improved Auto-Regressive Integrated Moving Average model time-series model was established through the steps of a white noise test, data stationarity test, model recognition, and order determination. Finally, the effectiveness of the improved wind speed prediction was examined. The results of the research showed that rational choice of processing functions has a large impact on wind speed prediction results. The prediction accuracy of the improved ARIMA model proposed in this paper is better than the results of the traditional Seasonal Auto-Regressive Integrated Moving Average model, and it can quickly and accurately realize the short-time wind speed prediction along the railroad line in rugged mountains. In addition, the improved ARIMA model has verified its universality in different mountainous places.

Instability of separated shear layer around levitated freestream-aligned circular cylinder

In the present study, characteristics of a shear layer around a freestream-aligned circular cylinder and the relationship between the shear layer motion and the aerodynamic force were investigated under supportless condition. A 0.3-m magnetic suspension and balance system was employed, and experiments were conducted without a mechanical supporting device. Velocity fields were measured using particle image velocimetry with a sufficient temporal and spatial resolution, and high-frequency velocity fluctuations caused by small Kelvin–Helmholtz (KH) vortices were captured. The power spectral densities of velocity fluctuations represent phenomena such as KH vortex convection, vortex pairing, and convection of multiple vortices. Furthermore, fluctuations of the shear layer position were investigated. The results illustrate that the dominant frequency of the shear layer position is lower than the frequency of the velocity, and it shows good agreement with the characteristic frequency of lift force fluctuations. The present results together with the report in the previous study illustrate that the pressure fluctuations are considered to drive both fluctuations of the shear layer position and lateral aerodynamic force.

Development of a mathematical model of vibratory non-lift movement of light seeds taking into account the aerodynamic forces and moments

The modern practice of using vibratory machines when working with fine-size light-weight seeds is faced with such an undesirable phenomenon as the impact of aerodynamic forces and moments on the kinematics of vibrational movement of particles of the seed mixture fractions. According to the results of scientific studies devoted to the solution of this problem, only mathematical models of vibrational movement are used, where the aerodynamic factor is taken into account as taking the seeds by airflow. This is typical only for cleaning modes with the rebound of seeds from the vibrating surface. Aerodynamic forces and moments are present in them only as a force of aerodynamic resistance. The action of lateral aerodynamic forces and their moments are not taken into account. Their consideration allows to extend the range of action of the aerodynamic factor on the modes of vibration cleaning (vibroseparation) without rebound (but with sliding and rolling) which are of greater interest in terms of improving the efficiency of processing fine-size seeds. A mathematical model of seed vibration movement taking into account the action of a complete set of aerodynamic forces (dynamic resistance forces and lateral aerodynamic forces) and moments was proposed. This makes it possible to simulate non-lifting modes of vibrational movement of seeds. A system of algebraic equations that are linear with respect to the kinematic parameters of seed movement which was obtained by translating differential equations of movement into a finite-difference form was presented. The possibility of numerical solution of equations of movement by the Euler method was shown. The results of the evaluation of the model adequacy for the processes of vibration separation of tobacco seeds and false flax were presented. As shown by the results of calculations and experiments, the developed model provides an increase in the adequacy of the simulation results by 30 % in comparison with the model where the aerodynamic factor is not taken into account

Numerical Study of Bernoulli Effect on Bus Controllability and Driving Safety

A bus in motion is vulnerable to strong aerodynamic forces that may interfere with its controllability and operational safety. On mountainous highways—especially highways along deep gorges—or under extreme weather conditions, the lateral wind distribution is not always uniform and consequently produces the Bernoulli effect. The objective of this study was to investigate its specific impact on bus safety by using a hybrid method of computational fluid dynamics (CFD) and kinematics simulations. An ordinary bus was chosen as the analysis object, and its three-dimensional model was established in SolidWorks. CFD experiments were conducted in ANSYS/Fluent to estimate the lateral aerodynamic forces. The smart driving system based on the directional control model was built in MATLAB/Simulink to replicate the average driving experience. Then a cosimulation of Adams/Car with Simulink was implemented to quantify and assess the bus handling and stability performance. The CFD simulations report that the aerodynamic force induced by the Bernoulli effect is not negligible for an ordinary bus. As the gradient of wind speed variation increases to over 5 m/s per meter in the lateral direction, the ratio of the aerodynamic force to its gravity exceeds 2%. Kinematics simulations prove that the bus lateral chassis acceleration and the lateral displacement both reached alarm values under the adverse conditions. The study is expected to offer a useful tool and reference for bus accident prevention and analysis in strong wind zones with frequent asymmetric winds. It may also help improve vehicle handling and stability design, especially for oversized vehicles.

Transient aerodynamic forces of a vehicle passing through a bridge tower's wake region in crosswind environment

Super long-span bridges provide people with great convenience, but they also bring traffic safety problems caused by strong wind owing to their high decks. In this paper, the large eddy simulation together with dynamic mesh technology in computational fluid dynamics (CFD) is used to explore the mechanism of a moving vehicle`s transient aerodynamic force in crosswind, the regularity and mechanism of the vehicle`s aerodynamic forces when it passes through a bridge tower`s wake zone in crosswind. By comparing the calculated results and those from wind tunnel tests, the reliability of the methods used in the paper is verified on a moving vehicle`s aerodynamic forces in a bridge tower`s wake region. A vehicle`s aerodynamic force coefficient decreases sharply when it enters into the wake region, and reaches its minimum on the leeward of the bridge tower where exists a backflow region. When a vehicle moves on the outermost lane on the windward direction and just passes through the backflow region, it will suffer from negative lateral aerodynamic force and yaw moment in the bridge tower`s wake zone. And the vehicle`s passing ruins the original vortex structure there, resulting in that the lateral wind on the right side of the bridge tower does not change its direction but directly impact on the vehicle`s windward. So when the vehicle leaves from the backflow region, it will suffer stronger aerodynamic than that borne by the vehicle when it just enters into the region. Other cases of vehicle moving on different lane and different directions were also discussed thoroughly. The results show that the vehicle`s pneumatic safety performance is evidently better than that of a vehicle on the outermost lane on the windward.

Computational fluid dynamics modeling of rope-guided conveyances in two typical kinds of shaft layouts.

The behavior of rope-guided conveyances is so complicated that the rope-guided hoisting system hasn’t been understood thoroughly so far. In this paper, with user-defined functions loaded, ANSYS FLUENT 14.5 was employed to simulate lateral motion of rope-guided conveyances in two typical kinds of shaft layouts. With rope-guided mine elevator and mine cages taken into account, results show that the lateral aerodynamic buffeting force is much larger than the Coriolis force, and the side aerodynamic force have the same order of magnitude as the Coriolis force. The lateral aerodynamic buffeting forces should also be considered especially when the conveyance moves along the ventilation air direction. The simulation shows that the closer size of the conveyances can weaken the transverse aerodynamic buffeting effect.

Determination of Maximum Mechanical Energy Efficiency in Energy Galloping Systems

Transverse galloping is a type of aeroelastic instability characterized by large amplitude, low frequency, normal to wind oscillations that appear in some elastic two-dimensional bluff bodies when subjected to a fluid flow, provided that the flow velocity exceeds a threshold critical value. Such an oscillatory motion is explained because of the energy transfer from the flow to the two-dimensional bluff body. The amount of energy that can be extracted depends on the cross section of the galloping prism. Assuming that the Glauert–Den Hartog quasi-static criterion for galloping instability is satisfied in a first approximation, the suitability of a given cross section for energy harvesting is evaluated by analyzing the lateral aerodynamic force coefficient, fitting a function with a power series in tan⁡α (α being the angle of attack) to available experimental data. In this paper, a fairly large number of simple prisms (triangle, ellipse, biconvex, and rhombus cross sections, as well as D-shaped bodies) is analyzed for suitability as energy harvesters. The influence of the fitting process in the energy harvesting efficiency evaluation is also demonstrated. The analysis shows that the more promising bodies are those with isosceles or approximate isosceles cross sections.

Shape optimization of a blunt body Vibro-wind galloping oscillator

The nonlinear dynamics of a transverse galloping blunt body oscillator is analyzed with respect to its geometric shape and size. The oscillator's equation of motion is studied using an approximation for the lateral aerodynamic force that is a polynomial function of the angle of attack. The harmonic balance method is used to solve the nonlinear differential equation of motion. This solution is used to determine the geometric parameters that minimize its critical wind speed for instability, increase its amplitude sensitivity to wind velocities beyond the critical speed, and minimize or eliminate amplitude hysteresis for increasing and decreasing wind speed. Optimum combinations of blunt body size and shape can be found that best satisfy these desired behaviors. These findings may be useful for creating a reliable, efficient wind energy harvesting system.

Study on the Aerodynamics Mechanism of Passenger Car under Unsteady Crosswind

Regular formulae for lateral aerodynamic force cannot give precise prediction under unsteady crosswind. By generalizing potential flow theory and taking the aerodynamic derivative into consideration, the semi-empirical expression for lateral aerodynamic force is derived. In order to determine the coefficients in the semi-empirical formula, the model of a typical double-deck coach is investigated in a sequence of numerical simulations under pure crosswind condition (i.e. linear crosswind, pseudo-step crosswind, sinusoidal crosswind). Moreover, advantages of the semi-empirical formula over the regular one are revealed. Further inspections into the flow field derived from the theory of vortex motion indicate that the deviation between the prediction given by semi-empirical formulae and that by numerical simulation is caused by the non-viscous assumption in potential flow theory. The lateral aerodynamic force depends linearly on the crosswind aerodynamic derivative. Situations in which the coach is moving in the direction perpendicular to the wind velocity are also studied to find the cause of the error in semi-empirical formula. Furthermore, the semi-empirical formula is revised by introducing the “damping model method”. A relatively complete system of prediction for lateral aerodynamic force on a coach, which is of practical engineering significance, has been constructed.

Simulation Analysis of Vehicle Crosswind Stability in ADAMS/CAR

The vehicle simulation model of 78-DOF is built based on ADAMS/CAR. Both rationality and accuracy of simulation model are verified by comparison analysis methods between real vehicle test and virtual simulation test. The mathematical model of wind pressure center and lateral aerodynamic force are formulated by using the STEP function. The simulation results indicate that the vehicle has the excellent crosswind stability and congruent dynamic response, which agrees with United States (ESV) standard.

The aerodynamic performance of a range of FIFA-approved footballs

Much discussion surrounds the flight of a football, especially that which is perceived as irregular, and is typically done so with little understanding of the aerodynamic effects or substantive evidence of the path taken. This work establishes that for a range of FIFA-approved balls there is a significant variation in aerodynamic performance. This paper describes the methods used for mounting stationary and spinning footballs in a wind tunnel enabling accurate force data to be obtained, and the analysis techniques used. The approach has been to investigate a number of scenarios: the non-spinning Reynolds sweep, unsteady loads, orientation sensitivity (yaw sweep), and the spinning Reynolds sweep. The techniques are applied to a number of footballs with differing constructions and the results reported. To put the aerodynamic data into context, the results are applied in a flight model to predict the potential differences in the behaviour of each ball in the air. This paper concludes that, although the drag characteristics are different for each different ball tested, the simulation suggests that this has only a limited effect on the flight of the ball. It is also shown that the unsteadiness of the aerodynamic loads is unlikely to be responsible for unpredictable behaviour. However, it is also shown that there are significant differences in the lateral aerodynamic forces for a range of FIFA-approved match balls, and that these aerodynamic differences have a significant effect on the flight path for both spinning and slowly rotating balls.

The effect of atmospheric rotation on a satellite orbit, when scale height varies with height

The upper atmosphere at heights of 200–300 km rotates at least as fast as the Earth, and a satellite in this region therefore suffers a lateral aerodynamic force, which slightly reduces the inclination of the orbit to the equator. The theoretical expressions previously obtained for the changes in inclination and in longitude of the node apply to an exponential atmosphere, in which the density scale height H is constant. The present paper develops the theory for orbits of eccentricity less than 0.2 with a more realistic atmospheric model in which H varies linearly with height y: it is assumed that μ = dH/ dy is less than 0.2. The results show that the values given by the constant- H theory can be altered by up to 9 per cent when μ is included, if perigee is near the equator. But the effect of μ can be nearly eliminated if H is evaluated at a height 0.75 H above perigee. Graphs are given to show the effective average height at which the inclination-changing forces act, i.e. the effective height at which the atmospheric rotational speed is being sampled. This height depends on the eccentricity e and the argument of perigee: for e > 0.01 the height is between 0.5 H and 1.2 H above perigee.

The rotational speed of the upper atmosphere determined from changes in satellite orbits

Abstract Because the atmosphere rotates, a satellite is subjected to a small lateral aerodynamic force which has the effect of slightly changing the inclination of the orbit to the equator. For an eastbound satellite the inclination decreases, sometimes by as much as 0.1°, and the amount of the change is a measure of the angular velocity of the atmosphere at heights near that of the satellite's perigee. In this paper the angular velocity of the upper atmosphere is determined by examining the changes in orbital inclination of all suitable satellites. Although the orbital information is imperfect, useful values were obtained from 9 satellites, covering the years 1958–63, heights of 200–300 km and latitudes from 0–60°. If the angular velocity of the atmosphere is expressed as Λ times the angular velocity of the Earth, the values of Λ obtained all exceed 1, ranging between 1.1 and 1.9, with a mean of 1.46 and rms scatter of 0.28. This corresponds to a mean west-to-east wind speed in mid latitudes of over 100 m/sec. The results thus indicate that the upper atmosphere at 200–300 km height rotates faster than the Earth. A possible explanation is suggested.

Rotational Speed of the Upper Atmosphere, at Heights of 200–300 km

BECAUSE the atmosphere rotates, a close Earth satellite is subjected to small lateral aerodynamic forces which have the effect of slightly changing the inclination of the orbit to the equator1,2. For an eastbound satellite the inclination decreases, sometimes by as much as 0.1°, and the amount of the decrease is a measure of the angular velocity of the atmosphere at heights near that of the satellite's perigee. Such a decrease was first noted3 in 1958 with Sputnik 2, and it was pointed out4,5 that the decrease was rather greater than would be caused by an atmosphere rotating at the same rate as the Earth.