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91.
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93.
采用水平移动射流方法模拟移动动量源,实验研究了该移动动量源在密度分层流体中生成准二维偶极子涡街的机理,分析了偶极子涡街的演化特性. 在系列实验基础上,获得了移动动量源在密度分层流体中能够演化为偶极子涡街的(Re,Fr)组合条件. 对不同的Re取值,获得了偶极子涡街无因次形成时间及其无因次涡街平均波长倒数与Fr之间的相关关系,表明它们不依赖于Re数,而与Fr近似为幂指数关系.
关键词:
分层流体
移动动量源
偶极子涡街
涡街形成时间 相似文献
94.
Mitri FG 《Ultrasonics》2011,51(4):496-502
Background and motivation
Generalized Bessel vortex beams are regaining interest from the standpoint of acoustic scattering and radiation force theories for applications in particle rotation, mixing and manipulation. Other possible applications may include medical and nondestructive imaging. To manipulate heavy particles in a host medium, a minimum threshold of the incident sound field intensity is required at relatively high wave amplitudes such that nonlinear wave propagation occurs and the generation of harmonics may be detected. Thus, predictions of the harmonics generation become crucial from the standpoint of experimental design, and the present analysis should assist in the development of more complete models related to the (nonlinear) scattering and radiation forces under such circumstances. The purpose of this research is to construct a theoretical model for the second-harmonic pressure generation associated with a category of non-diffracting Bessel vortex beams known as high-order Bessel vortex beams of fractional typeα (HOBVBs-Fα).Method
The weakly nonlinear wave propagation of a HOBVB-Fα is investigated based on Lighthill’s formalism. Analytical solutions up to the second-order level of approximation are derived and discussed. Closed-form solutions are obtained, which are expressed as a function of first-order quantities available from the classical linear theory. Lateral profiles of the HOBVB-Fα are computed and compared.Results and conclusion
The results show that the beam’s width reduces and becomes narrower, the side-lobes decrease in magnitude, and the hollow region diameter (or null in magnitude) increases as the order of nonlinearity increases. Furthermore, the nonlinearity of the medium preserves the non-diffracting feature of the beam’s second-harmonic generation within the pre-shock range. 相似文献95.
96.
97.
Longitudinal vortices disrupt the growth of the thermal boundary layer, thereby the vortex generators producing the longitudinal vortices are well known for the enhancement of heat transfer in compact heat exchangers. The present investigation determines the heat transfer characteristics with secondary flow analysis in plate fin triangular ducts with delta wing vortex generators. This geometrical configuration is investigated for various angles of attack of the wing i.e. 15°, 20°, 26° and 37° and Reynolds numbers 100 and 200. The constant wall temperature boundary condition is used. The solution of the complete Navier Stokes equation and the energy equation is carried out using the staggered grid arrangement. The performance of the combination of triangular secondary fins and delta wing with stamping on slant surfaces has also been studied. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
98.
99.
Régis Brugiere et Pierre Lucasson 《辐射效应与固体损伤》2013,168(1):55-57
The nature of the electron bombarded aluminium electrical recovery process has been studied by combining quenches with irradiations. Measured Frenkel pair formation rates per incident electrons as well as annealing kinetics emphasize the role of impurity interstitial trapping. 相似文献
100.
Three-dimensional turbulent offset jets were investigated using a particle image velocimetry technique. The measurements were performed at three different exit Reynolds numbers and for four offset heights. The results in the early region of flow development clearly show significant effects of Reynolds number and offset height on the decay of maximum mean velocity and growth of the shear layer. On the contrary, the decay and spread rates were found to be nearly independent of offset height at larger downstream distances. The decay rates of 1.18 ± 0.03 as well as the spread rates of 0.055 ± 0.001 and 0.250 ± 0.005 obtained, respectively, in the wall-normal and lateral directions fall in the range of values reported in previous studies. The locations of the maximum mean velocities increased nearly linearly with streamwise distance in the self-similar region. Analysis from two-point velocity correlations revealed substantially larger structures in the outer layer and self-similar region than in the inner layer and developing region. It was also observed that the hairpin vortices in the inner regions of the wall jets are inclined at angles of 11.2° ± 0.6°, which are in good agreement with reported values in boundary layer studies. 相似文献