The influences of wind angles on the behavior of a high-speed train were investigated using a scaled-down wind tunnel model (1:8 scale) at the wind angles of 0°, 5.14°, 10.2°, 15.11°, and 19.8°. ...Based on the experimental results elicited at different Reynolds numbers (9.44 × 105, 1.26 × 106, 1.57 × 106, and 1.89 × 106, corresponding to the wind speeds of 30 m/s, 40 m/s, 50 m/s, and 60 m/s, respectively), the speed of 60 m/s was determined as optimal for wind tunnel tests. The effects of the incoming flow angles on the pressure distribution of the train's streamlined zone and the aerodynamic forces of the train were analyzed. Results show that the pressure coefficients on the leeward side and the symmetrical plane profile curve of the streamlined zone decreased as the wind angle increased. However, the change in the windward side was opposite to that of the leeward side. The lateral and the absolute value of the lift forces increased rapidly as a function of the wind angle, while the drag force was maximized when the wind angle was 15.11°, followed by subsequent decreases at increasing wind angles.
•Influence of the wind angle on the aerodynamic performance of a high-speed train was investigated.•Influence of Reynolds number on the aerodynamic performance of high-speed train was investigated.•The boundary layer thickness along the train and ballast was measured and presented.•Pressure distributions along longitude direction and different cross-sections on train's streamlined zone were analyzed.
An approximation model based on convolutional neural networks (CNNs) is proposed for flow field predictions. The CNN is used to predict the velocity and pressure field in unseen flow conditions and ...geometries given the pixelated shape of the object. In particular, we consider Reynolds Averaged Navier–Stokes (RANS) flow solutions over airfoil shapes as training data. The CNN can automatically detect essential features with minimal human supervision and is shown to effectively estimate the velocity and pressure field orders of magnitude faster than the RANS solver, making it possible to study the impact of the airfoil shape and operating conditions on the aerodynamic forces and the flow field in near-real time. The use of specific convolution operations, parameter sharing, and gradient sharpening are shown to enhance the predictive capabilities of the CNN. We explore the network architecture and its effectiveness in predicting the flow field for different airfoil shapes, angles of attack, and Reynolds numbers.
This paper examines the dynamic performance of the pantograph passing through an overlap section of the catenary system, using a China's high speed railway with the 4-span overlap as an example. The ...pantograph and catenary system are simulated as a lumped mass model and finite element model, respectively. The model is verified according to EN50318:2018. The model is also assessed against an experimental study of the contact force and uplift of contact wire at 300 km/h. Then the contact force and uplift of contact wire at the speed of 150-350 km/h are calculated. The research shows that when the pantograph passes through the overlap, the maximum contact force increases beyond 14%, the standard deviation of the contact force increases by more than 26%, and the increase of the vertical displacement exceeds 38%, which becomes more apparent with the increase of speed. Under the influence of aerodynamic force, when the running speed increases from 150 to 350 km/h, the mean contact force in the knuckle-downstream and knuckle-upstream orientation increase by 59.49% and 97.85%, respectively. As a result, the contact force and vertical displacement increase greatly when passing through the overlap section, which could affect the current collection quality.
At rest, beetles fold and tuck their hindwings under the elytra. For flight, the hindwings are deployed through a series of unfolding configurations that are passively driven by flapping forces. The ...folds lock into place as the wing fully unfolds and thereafter operates as a flat membrane to generate the aerodynamic forces. We show that in the rhinoceros beetle (
), these origami-like folds serve a crucial shock-absorbing function during in-flight wing collisions. When the wing collides with an object, it collapses along the folds and springs back in place within a single stroke. Collisions are thus dampened, helping the beetle to promptly recover the flight. We implemented this mechanism on a beetle-inspired wing on a flapping-wing robot, thereby enabling it to fly safely after collisions.
Abstract
During the take-off of the seaplane on the water surface, one of the most dangerous situations is the uncontrollable porpoising of the seaplane. The coupling effect of the buoyancy, ...hydrodynamic resistance, hydrodynamic lift, and aerodynamic force of the seaplane is studied to better meet the requirements for porpoising in airworthiness clauses. In this study, we established the dynamics model of seaplane motions on the water surface and proposed a method for the simulation evaluation of seaplane porpoising. The program for simulating seaplane planning on the water surface was developed. Through simulation, we evaluated the possibility of porpoising when a seaplane plane is on the water surface and obtained the pitch attitude boundary of seaplane porpoising. The evaluation method can be adopted to develop procedures for seaplane take-off control and for risk identification and control in seaplane take-off test flights on the water surface.
To address the common issues and deficiencies associated with state-of-art static and moving train wind tunnel test, this paper devised a novel test system for the aerodynamic test of vehicles ...travelling across the bridges. A servo motor synchronous driving system was used along with a wireless module for the transducer in measuring aerodynamic forces on the high-speed train. The maximum speed of the train model can reach 15 m/s with an effective acquisition time of 0.7s. Besides, due to the independent arrangement between the bridge model and the test motion driving system, replacement of the bridge model can be achieved, enhancing the adaptability of the system. Based on the developed test system, a scaled model (including a steel-truss bridge and the CRH3 train system) was tested and aerodynamic characteristics of the moving train were measured and analyzed under various wind velocities, speeds of the train, and wind angles. It reveals that aerodynamic coefficients of the train measured with a static train model are different from those measured with the dynamic train model. The existence of truss bridge causes that the aerodynamic coefficients of model train vary significantly as the incoming wind velocity, speed of the train, and wind angle change.
•A novel wind tunnel test system for the aerodynamic test of high speed trains traveling on the bridges is presented.•Performance of the test system is evaluated.•Comparison between static model test and moving model test is conducted.•The relationship of the aerodynamic coefficient of the train and the yaw angle is changed by the truss bridge.
The flapwise free vibration characteristics of a rotating composite beam under aerodynamic force and hygrothermal environment are studied in this work. The partial differential equation governing the ...flapwise free vibration of the beam is derived based on D’Alembert’s principle. The modal problem is handled utilizing the assumed-modes method. The effects of temperature, humidity, aerodynamic force, rotational speed and ply orientation on the natural frequencies and damping ratios are investigated. Results show that the hygrothermal environment, aerodynamic force, rotational speed and ply orientation have vital influences on the flapwise free vibration characteristics of the beam. The hygrothermal environment and ply orientation have more remarkable effects on the natural frequencies and damping ratios at low rotational speed. The aerodynamic force has small influences on natural frequencies and great effects on damping ratios.
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