Flow structures of a Mach 6 transitional boundary layer over a 260 mm long flared cone are investigated by the particle image velocimetry (PIV). Particle images near the curved wall are initially ...transformed into surface-fitted orthogonal coordinates and spliced with their 180°-symmetric images to satisfy a no-slip condition at the wall. The results are then reversely transformed to the physical domain. Direct numerical simulation (DNS) is also performed to validate the experimental results. The experimental and numerical results are in agreement, indicating a strong dilatation process within the second-mode instability.
The prediction of the transition location (TL) in three-dimensional (3D) hypersonic boundary layers is of great importance in hypersonic engineering. In the present work, a method using machine ...learning techniques is presented for the prediction of TLs based on experiment data over a Mach 6.5 inclined cone. A mapping function is directly constructed between TLs and the circumferential angle θ by neural networks (NNs). The results show that the present NN predicts well for both interpolations of both the angle of attack (AOA) and unit Reynolds number Re0 and extrapolation of only Re0 whereas errors increase for the extrapolation of a higher AOA. This work sheds new light on the fast prediction of TLs in hypersonic complex 3D boundary layers.
The multi-degree-of-freedom spherical motion device usually requires a built-in data acquisition and processing module and a wireless charging part in its bionic design, while the traditional ...disc-shaped receiving coil increases with the deflection angle, the system coupling coefficient and mutual inductance will decrease causing the increased power transmission fluctuation and greatly decreased transmission power. In this paper, a tile-shaped receiving coil is designed to ensure the power output when the rotation offset occurs. Then, the formula of radio energy transmission characteristics is derived and verified by finite element simulation. It is proved that the coupling coefficient peak value of the new structure is increased by 12.68% and the variation fluctuation is reduced by 2.26%. The output of the new system at each deflection angle has been improved overall. Finally, an experimental platform is built to verify the accuracy of the simulation analysis and the effectiveness of power transmission.
Transition and turbulence production in a hypersonic boundary layer is investigated in a Mach 6 wind tunnel using Rayleigh-scattering visualization, fast-response pressure measurements, and particle ...image velocimetry. It is found that the second-mode instability is a key modulator of the transition process. Although the second-mode is primarily an acoustic wave, it causes the formation of high-frequency vortical waves, which triggers a fast transition to turbulence.
For the problem of fluctuation of transmission power and load voltage between magnetically coupled mechanisms in the dynamic wireless power transfer (DWPT) system of the electric vehicles (EV), a ...magnetically coupled mechanism with dual receiving coils (R-C) of electric energy on the receiving side is proposed in this paper. The transmitting coils (T-C) are connected in parallel in a multi-stage manner flat on the road, and when the EV drives above a section of T-C, this T-C is energized to charge the EV. In the paper, the theoretical model of the circuit and the theoretical model of the magnetic circuit of the dual R-C magnetic coupling mechanism are first established. The feasibility of this structure is verified through the derivation and calculation of the working principle of the system. Finally, the simulation and experimental results verify the effectiveness of the coupling mechanism. The experimental results further demonstrate that the magnetically coupled structure with dual R-C can effectively reduce the power fluctuation during the T-C switching and reduce the laying of T-C to reduce the cost.
Laser detection technology has manypromising applications in the field of motor speed and position measurement. Accurate and fast measurement of position information of spherical rotor is very ...important for motor control. In this paper, we propose a method for non-contact measurement of the angular velocity of a multi-DOF spherical motor using the Doppler effect of the laser, and further obtain the position information of the motor rotor. The horizontal laser beam from the laser generator is divided into a reference beam
and a measurement beam
through a beam splitter, and the measurement beam
reflects and undergoes Doppler effect after irradiating the rotating motor. The two beams pass through the photoelectric conversion module to obtain the corresponding frequency difference signals to derive the angular velocity and position information of the motor rotor. The correctness of the method is verified experimentally. The results show that the coordinate error of
and
axes is less than 2 mm, thatthe error of
-axes is less than 0.2 mm, and that the method can better measure the spherical rotor position information of the motor.
PDF
