When the light wave propagates through the hypersonic flow field,the aero-optic distortion happens.It is necessary to recognize the vortex structure for studying the light propagation model.A new vortex structure recognition method is proposed in this paper.Firstly,the refractive index field,which is transformed from the turbulent density field,is changed to gray scale images with abundant texture information equivalently.Then,wavelet transform is performed to decompose these images and the entropy values of the wavelet base coefficients are calculated.Comparing the entropy value to a given threshold,the modules with lower entropy are considered to be the large-scale vortex modules while those with higher entropy are small-scale vortex modules.The computer simulation results show that the proposed method is valid to recognize the vortex structures.This paper provides basis for investigation on the optics propagation model in terms of the turbulence vortex structures. 相似文献
Garlic (Allium sativum L) bulb explants produced undifferentiated white globular callus when grown on MS medium having 2,4-dichlorophenoxy-acetic acid (2,4-D) and Kinetin (Kn). Such callus when grown on medium having indole-3-yl-acetic acid (IAA) and/or Kn developed into the differentiating callus which had comparatively more allicin than that of undifferentiated callus. The effect of sucrose, NH/NO ratios and hormone concentrations on growth and allicin development in the callus was investigated. There was a significant increase in allicin development in callus when grown for up to 4 weeks on medium (a) having sucrose at 3% and 5% levels; (b) having NH and NO ratios at 2:1 and 1;1; and (c) with Kn alone at a concentration of 0.5 mg litre?1, which produced a tenfold increase in allicin content. 相似文献
Particle image velocimetry (PIV) is increasingly used to investigate unsteady velocity fields instantaneously. For the first time the PIV technique allows the recording of a complete velocity field in a plane of the flow within a few microseconds. The PIV technique thereby provides information about unsteady flow fields which is difficult to obtain with other experimental techniques. The short acquisition times and fast availability of data reduce the operational time, and hence cost, in large scale wind tunnels and test facilities.
At DLR a variety of PIV systems for use in industrial wind tunnels has been developed in the past decade. The flexibility of these portable systems is illustrated by presenting several results of recent PIV applications. More recently the original photographic means of PIV image recording has been partially replaced by high resolution electronic imaging which can provide PIV data nearly on-line. Images recorded by either system use the same multiple-pass, cross-correlation analysis software, whose algorithms are briefly described. Several examples of actual applications are given: the flow issuing from a jet nozzle was imaged by a specially developed high-speed video camera at close proximity. A high resolution dual-frame digital camera was applied in the study of helicopter rotor aerodynamics and wake vortex measurements of an airplane model. Further, large image sequences exceeding 100 PIV recordings provided detailed information on the structure of a turbulent boundary layer. 相似文献