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11.
昆虫拍翼方式的非定常流动物理再探讨 总被引:5,自引:0,他引:5
基于提出的理论模化方法来探讨昆虫拍翼方式的非定常流动物理. 以悬停飞行为
例,通过对拍翼运动的分析,不仅解释了昆虫利用高频拍翼的方式为何能够克服低雷诺数带
来的气动局限性(St \gg 1/Re),而且还指出高升力产生和调节的3个流动
控制因素:(1) 由于拍翼的变速运动即时引起了流体动力响应,这种附加惯性效应
可产生瞬时的高升力; (2) 保持前缘涡不脱离翼面有助于减少升力的下降;
(3) 增大后缘涡的强度并加速其脱离后缘能够有效地提高升力. 相似文献
12.
I. V. Sturova 《Journal of Applied Mechanics and Technical Physics》2006,47(1):71-78
The effect of initial disturbances and unsteady external loading on an elastic beam of finite length which floats freely on
the surface of an ideal incompressible fluid is studied in a linear treatment. The fluid flow is considered potential. The
beam deflection is sought in the form of an expansion in the eigenfunctions of beam vibrations in vacuum with time-dependent
amplitudes. The problem reduces to solving an infinite system of integrodifferential equations for unknown amplitudes. The
memory functions entering this system are determined by solving the radiation problem. The beam behavior is studied for various
loads with and without allowance for the weight of the fluid. The effect of fluid depth on beam deformation was determined
by comparing with the previously obtained solutions of the unsteady problem for a beam floating in shallow water.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 1, pp. 85–94, January–February, 2006. 相似文献
13.
H. Pascal 《International Journal of Heat and Fluid Flow》1988,9(4):381-388
In this paper the conditions for the existence of self-similar solutions of the equations governing unsteady flows through a porous medium are presented and discussed. The first two sections deal with the case of non-Newtonian fluids of power-law behavior; the third section analyzes the case of non-Darcy gas flows. The boundary and initial conditions occuring currently in a large class of fluid mechanics problems, of practical interest in engineering, are considered. 相似文献
14.
本文报告了明渠非定常水流垂向结构的实验研究,通过 LDV 激光测速,我们给出了非定常水流的速度削面,湍流度,Eulerian质量输运速度的垂向分布。实验结果表明:在非定常周期很长时非定常流动的速度剖面,湍流强度及其粗糙度的影响基本上与定常流动相一致,当非定常流动为纯往复流动时,存在一个逆时针方向的环流,这种环流有利于底部的质量输运。 相似文献
15.
This experimental investigation deals with transition phenomena of a separated boundary layer under unsteady inlet flow conditions.
The main purpose of this investigation is to understand the influence of the rotor-stator interaction in turbomachinery on
the subsequent, highly loaded boundary layer. The research project is divided into two phases. In the first phase, which has
been completed recently, only the variation of mean velocity caused by upstream blades was simulated in the experiments while
the free-stream turbulence intensity was retained at a constant low level. The experiments are carried out in an Eifel-type
wind tunnel to investigate the laminar separated boundary layer of a flat plate under oscillating inlet conditions. The adverse
pressure gradient, similar to that of turbomachines, is generated by the contoured upper wall. The unsteadiness is produced
by a rotating flap located downstream of the test section. The reduced frequency, the amplitude and the mean Reynolds number
are varied to simulate the conditions prevailing in turbomachines. In addition to the Kelvin–Helmholtz instability of the
separated shear layer, a lower frequency instability was observed. This is frequently referred to as `free shear layer flapping'
and results in two distinctly different ways of re-attachment, depending primarily on the Reynolds number. For low momentum
thickness Reynolds numbers at the separation point, large-scale vortices locked to the frequency of the unsteady main flow
are identified. They originate nearly at the top of the separation bubble and are ejected downstream. A fully turbulent boundary
layer develops after these vortices mix out. For higher Reynolds numbers, transition is completed within a short length of
the free shear layer and there-attachment region. The characteristic momentum thickness Reynolds number separating these two
regimes in unsteady flow is about 125. The Strouhal number (reduced frequency) does not appear to have any significant effect.
Based on the experimental results, this behaviour is discussed in some detail.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
本文对动失速型非定常分离涡结构的控制方法,在低速风洞中应用相平均测压技术进行了实验研究。在二元平板模型中部安装一作俯仰振荡的扰流板产生动失速型分离涡,在其上游安装另一用作控制的小扰流板。实验结果表明,应用前置的振荡小扰流板可影响并改变动失速分离涡的强度和对流特性。在最有利的控制相位下,涡吸力峰可降低48%,涡对流时间可以推迟0.19周期。对于间歇式振荡扰流板,采用相位提前控制方式比相位滞后控制方式更有效。 相似文献
17.
P.M. Ligrani R. Van Den Braembussche M. Roustan 《International Journal of Heat and Fluid Flow》1983,4(2):103-106
Results from an experimental study of flow behaviour at the inlet of a vaneless diffuser of a centrifugal compressor are presented. Measurements from a crossed hot-wire probe are given for operating points having inlet flow coefficients ranging from 0.006 to 0.019 at different Reynolds numbers. Instantaneous, time-averaged, and phase-averaged absolute velocity and flow angle at the diffuser inlet are deduced from the hot-wire signals after correction for mean density variations. These results show how flow behaviour varies in stable, rotating stall and surge regimes of compressor operation 相似文献
18.
19.
L. A. Nazarov L. A. Nazarova V. M. Fomin N. P. Ryashentsev A. N. Ryashentsev A. V. Solov'ev 《Journal of Applied Mechanics and Technical Physics》2006,47(1):109-115
A laboratory study including physical modeling of filtration processes in porous beds with similarity criteria satisfied is
performed. It is demonstrated that weak dynamic actions on stressed host rock blocks can initiate repacking of the system
of blocks, leading to an increase in pressure in the productive bed and in oil recovery.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 1, pp. 131–138, January–February, 2006. 相似文献
20.
On Solutions of Some Non-Linear Differential Equations Arising in Newtonian and Non-Newtonian Fluids
Mohyuddin M. R. Hayat T. Mahomed F. M. Asghar S. Siddiqui A. M. 《Nonlinear dynamics》2004,35(3):229-248
Some steady as well as unsteady solutions of the equations of motion for an incompressible Newtonian and non-Newtonian (second-grade)
fluids are obtained by applying different methods including the Lie symmetry group method. The flows considered are axially
symmetric with the swirling motion, and the governing equations for second-grade fluid flow have been modeled. Expressions
for streamlines, velocity and vorticity components are constructed explicitly in each case. Exact analytical solutions in
second-grade fluid are obtained and compared with the corresponding viscous solutions. 相似文献