scholarly journals A New Method for Analyzing Aero-Optical Effects with Transient Simulation

Sensors ◽  
2021 ◽  
Vol 21 (6) ◽  
pp. 2199
Author(s):  
Bo Yang ◽  
Zichen Fan ◽  
He Yu ◽  
Haidong Hu ◽  
Zhaohua Yang
Keyword(s):  
Photon Energy ◽  
Optical Sensors ◽  
High Speed ◽  
Large Scale ◽  
Light Refraction ◽  
Micro Scale ◽  
Energy Scattering ◽  
Wavefront Distortion ◽  
Optical Effects ◽  
Scale Structures

Aero-optical effects reduce the accuracy of optical sensors on high-speed aircraft. Current research usually focuses on light refraction caused by large-scale density structures in turbulence. A method for analyzing photon energy scattering caused by micro-scale structures is proposed in this paper, which can explain the macro image distortion caused by moving molecules in inhomogeneous airflow. Quantitative analysis of the propagation equation indicates that micro-scale structures may contribute more to the wavefront distortion than the widely considered large-scale structures. To analyze the micro mechanism of aero-optical effects, a transient simulator is designed based on the scaling model of transient distorted wavefronts and the artificial vortex structure. The simulation results demonstrate that correct aero-optical phenomena can be obtained from the micro mechanism of photon energy scattering. Examples of using the transient simulator to optimize the parameters of the star sensor on a hypersonic vehicle are provided. The proposed analysis method for micro-scale structures provides a new idea for studying the aero-optical effects.

scholarly journals Characteristics of Large-Scale Structures in Supersonic Planar Mixing Layer with Finite Thickness

2014 ◽  
Vol 6 ◽  
pp. 878679
Author(s):  
Hailong Zhang ◽  
Jiping Wu ◽  
Jian Chen ◽  
Weidong Liu
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Finite Thickness ◽  
Mixing Layer ◽  
Mixing Enhancement ◽  
Laser Scattering ◽  
Large Scale Structures ◽  
Eddy Simulation ◽  
Planar Laser ◽  
Scale Structures

Nanoparticle-based planar laser scattering (NPLS) experiments and large eddy simulation (LES) were launched to get the fine structure of the supersonic planar mixing layer with finite thickness in the present study. Different from the turbulent development of supersonic planar mixing layer with thin thickness, the development of supersonic planar mixing layer with finite thickness is rapidly. The large-scale structures of mixing layer that possess the characters of quick movement and slow changes transmit to downriver at invariable speed. The transverse results show that the mixing layer is strip of right and dim and possess 3D characteristics. Meanwhile the vortices roll up from two sides to the center. Results indicate that the higher the pressure of the high speed side is, the thicker the mixing layer is. The development of mixing layer is restrained when the pressure of lower speed side is higher. The momentum thickness goes higher with the increase of the clapboard thickness. Through increasing the temperature to change the compression can affect the development of the vortices. The present study can make a contribution to the mixing enhancement and provide initial data for the later investigations.

Natural large-scale structures in the axisymmetric mixing layer

1984 ◽  
Vol 138 ◽  
pp. 325-351 ◽  
Author(s):  
K. B. M. Q. Zaman ◽  
A. K. M. F. Hussain
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Longitudinal Velocity ◽  
Mixing Layer ◽  
Sampling Technique ◽  
Excitation Amplitude ◽  
Initial Condition ◽  
Velocity Signal ◽  
Large Scale Structures ◽  
Scale Structures

This paper summarizes results of our investigations on: optimization of conditional sampling technique for eduction of naturally occurring large-scale structures in an axisymmetric mixing layer, comparison of the natural structure with that induced via controlled excitation, and the sensitivity of the educed structure to the excitation amplitude and of the natural coherent structure to Reynolds number and initial condition. Measurements include sectional-plane contours of various structure properties; however, coherent vorticity is the principal measure used in these considerations. All plausible alternative triggering criteria, based on reference velocity signals from fixed probes, were considered in order to arrive at the best practical eduction technique. It is shown that the simple criterion of triggering on the positive peaks of the longitudinal velocity signal derived from the high-speed edge of the mixing layer results in the optimum eduction. The characteristics of the natural structures, educed by the optimum detection criterion, are found to be independent of ReD over the measurement range 5.5 × 104−8 × 105. A mild dependence on the initial condition (viz laminar vs. turbulent) is observed, the structures being more disorganized for the initially laminar boundary-layer case. The educed natural structures agree well with those induced by controlled sinusoidal excitation at low excitation levels; higher levels, however, produce considerably stronger structures.

scholarly journals Large-scale FEM Analyses Considering the Micro-scale Structures of Filled Rubber

2014 ◽  
Vol 2014.27 (0) ◽  
pp. 449-450
Author(s):  
Hiroshi Kadowaki ◽  
Gaku Hashimoto ◽  
Hiroshi Okuda ◽  
Eisuke Seta ◽  
Hisashi Heguri
Keyword(s):  
Large Scale ◽  
Micro Scale ◽  
Filled Rubber ◽  
Scale Structures

On the coherent structure of the axisymmetric mixing layer: a flow-visualization study

1981 ◽  
Vol 104 ◽  
pp. 263-294 ◽  
Author(s):  
A. K. M. F. Hussain ◽  
A. R. Clark
Keyword(s):  
Coherent Structures ◽  
Coherent Structure ◽  
High Speed ◽  
Large Scale ◽  
Mixing Layer ◽  
Space Time ◽  
Convection Velocity ◽  
Low Speed ◽  
Large Scale Structures ◽  
Scale Structures

In an effort to resolve some controversies regarding the turbulent mixing-layer structure, the near field of a large (18 cm diameter) air jet has been investigated for the jet exit speed of 30 m s−1. The smoke-laden axisymmetric mixing layer has been illuminated by a thin sheet of laser light in an azimuthal plane passing through the jet axis. High-speed visualization films of the mixing layer in the region of its self-preservation (of which a few picture sequences depicting space-time evolutions of the structure of the layer are presented) reveal that most of the time the mixing layer is in a state of disorganization, consisting of relatively smaller scale, random and diffuse turbulent motions; only occasionally are organized distinct large-scale coherent structures formed. The survival distances of the large-scale structures are found to be comparable to their average sizes. The survival time of these structures is about one ‘turnover’ time, each being roughly about five times the local characteristic time scale of the mixing layer. It is seen that tearing is as dominant a mode of large-scale interaction as pairing is; large-scale structures are continually sheared and typically fragmented due to a segment on the high-speed side being torn and swept away from the slower-moving outer portion. Evolution of the large structures occur not primarily through complete pairing as widely believed but quite frequently through ‘fractional pairing’ between segments which have been torn from different upstream large-scale coherent structures or through ‘partial pairing’ when one structure captures only a part of another. The movies show that along with entrainment of non-vortical ambient fluid, radially outward ejection of vortical fluid into the ambient is an important aspect of jet mixing. From aligned displays of ciné film frame sequences, space-time trajectories of identifiable vortical fluid elements have been traced. The convection velocity variation across the shear layer and even the overall structure convection velocity measured from these trajectories agree with those determined from the wave-number-celerity spectra, obtained from double-Fourier transformation of longitudinal velocity space-time correlation measurements with hot-wires.The visualization films do not bear out the two-street vortex ring model recently propounded by Lau. Based on our observations, we propose that tearing, ‘slippage’ and fractional and partial pairings are responsible for the observed radial variation of structure passage frequency, and the causes of the different coherent structures educed by Bruun on the high- and low-speed sides of the mixing layer and for Yule's failure in educing a coherent structure on the low-speed side of the layer.

scholarly journals ELECTRIC CONDUCTIVITY OF Sb/Se THIN FILM MICRO-SCALE STRUCTURES

2011 ◽  
Vol 48 (1) ◽  
pp. 62-68 ◽  
Author(s):  
O. Shiman ◽  
V. Gerbreder ◽  
E. Sledevsky ◽  
A. Bulanov
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Electric Conductivity ◽  
Crystalline State ◽  
Large Scale ◽  
Structural Model ◽  
Electrical Characteristics ◽  
Micro Scale ◽  
Scale Structures ◽  
Film Change

ELECTRIC CONDUCTIVITY OF Sb/Se THIN FILM MICRO-SCALE STRUCTURESResearch into the phase change transition (PCT) from amorphous to crystalline state in chalcogenide glass semiconductors is often more associated with large-scale samples. The authors present a micro-scale structural model of the Sb/Se thin films. They have also extended the investigations of photo- and thermo-stimulated inter-diffusion and PCT effects between two adjacent layers. The results show that the optical and electrical characteristics of such a film change simultaneously. It has been found that the electric conductivity of the films increases 3 times during a PCT process.

Aero-Optical Effects of Mc=0.5 Supersonic Mixing Layer

2014 ◽  
Vol 989-994 ◽  
pp. 863-866
Author(s):  
Li Feng Tian ◽  
Shi He Yi ◽  
Yang Zhu Zhu ◽  
Yu Xin Zhao ◽  
Lin He
Keyword(s):  
Large Scale ◽  
Near Field ◽  
Mixing Layer ◽  
Wavefront Aberration ◽  
Spatiotemporal Resolution ◽  
Large Scale Structures ◽  
Supersonic Mixing ◽  
Optical Effects ◽  
Supersonic Mixing Layer ◽  
Scale Structures

Supersonic turbulent mixing layer requires high spatiotemporal resolution of measuring techniques to study its aero-optical effects. However, the spatiotemporal resolution of existing techniques is not high enough. NPLS-WT (NPLS based wavefront technique) is a new aero-optics measuring technique developed in 2010. Its time resolution is 6ns, and spatial resolution and time correction resolution can reach up to micrometers and 200ns respectively. NPLS-WT was used in this paper to study aero-optical effects induced by Mc=0.5 supersonic mixing layer. The fine wavefront aberration information is revealed by the OPD of high resolution. The results show that the wavefront in near field is not sensitive to the resolution, and large-scale structures play a dominant role on the wavefront in near field. The cumulative effects analysis show us that the density difference between large-scale structures and free stream is the main reason to wavefront aberration, and the larger the vortex is, the more obvious the effect to wavefront aberration is.

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