共查询到18条相似文献,搜索用时 78 毫秒
1.
2.
3.
翼型绕流的电磁力控制 总被引:3,自引:0,他引:3
将表面包覆电磁激活板的翼型,按一定的攻角,置于流动的弱电介质溶液中,电磁激活板可产生作用于流体的切向电磁力(Lorentz力),从而改变流体边界层的结构. 在转动水槽中,对翼型绕流及电磁力控制下的绕流形态进行了实验研究. 结果表明,未加电磁力时,前缘涡的脱落点是不确定的,与流场具体条件有关,而后缘涡仅在尖角处脱落. 前缘涡与后缘涡相互影响,并周期性的脱体,在尾部形成涡街. 施加电磁力后,当力的方向与流动方向相同时,可以在一定程度上抑制分离,消除涡街,其效果与减小攻角类似. 加反向电磁力时,则相当于加大攻角,在翼型体的背风面形成涡街. 相似文献
4.
电磁力可有效对流体流动进行控制,增升减阻,抑制流动分离,制约其推广应用的瓶颈为控制效率问题.为提高其控制效率,基于翼型绕流的电磁力控制,对电磁力增升减阻的控制效率问题进行数值研究. 根据能量守恒定律,推导电磁力控制能耗的比,基于升力和阻力计算节省能量. 定义电磁力的控制效率为能量节省与电磁力控制所需能耗的比值,研究不同工况下电磁力增升减阻的控制效率. 发现在控制开始阶段,电磁力能量主要消耗在增加边界层流体的动能上,电磁力控制效率非常低,但电磁力控制效率会随着电磁力工作时间的增长而增加;电磁力控制效率随着来流速度的增加呈指数下降;通过增加电磁力激活板的输入能量可增强电磁力的控制效果,但无法明显增加其控制效率. 相似文献
5.
6.
在雷诺数Re=200的情况,利用Maxwell方程直接数值计算表面包覆电极与磁极圆柱体产生的电磁力分布,将其加入到动量方程中,在各种电磁力作用参数和电磁极宽度的组合下,对表面覆盖电磁极圆柱体在弱电解质中的绕流场结构及其升阻力特性进行了数值模拟与分析.结果表明,当电磁极宽度较小时,圆柱体绕流场的分离点越容易接近后驻点,而电磁力对总阻力的影响并不明显,但对压差和摩擦阻力均有明显影响.当电磁极宽度较大时,圆柱体尾部区域越容易产生射流现象,而且总阻力随电磁力作用参数和电磁极宽度增大而减小.在电磁力尚不足以完全抑制周期性涡脱落的情况下,升力幅值随电磁力作用参数增大而减小,但随电磁极宽度则先减小后略有增加,升力脉动频率则均随电磁力作用参数和电磁极宽度增大而增加.研究表明,电磁力可以有效地改善圆柱体绕流场结构,达到减小圆柱体阻力并抑制其脉动升力之目的,因此是圆柱型结构的一种有效流动控制手段. 相似文献
7.
包覆电磁场激活板的圆柱尾迹的数值研究 总被引:19,自引:3,他引:19
利用电磁场作用于电介质溶液的Lorentz力可以控制溶液的流动.对置于弱电介质溶液中,包覆电磁场激活板的圆柱周围的绕流进行数值研究,讨论了电磁场激活板的安装位置,激活方式等对圆柱尾迹的影响. 相似文献
8.
9.
亚临界状态下的圆柱绕流,背后卡门涡街旋涡脱落的频率与来流速度、圆柱直径有关,具体关系式为流体力学中一个有关不定常流动的相似参数—Strouhal数等于一个常数.用热线风速仪(或压力传感器)进行测量,并经微机采样和FFT运算,从功率谱可分析旋涡脱落的频率.文中验证了在亚临界范围内Strouhal数为常数的事实. 相似文献
10.
11.
Control of cross flow in the three-dimensional boundary layer using space-periodic body force action
A. P. Kuryachii 《Fluid Dynamics》2009,44(2):233-239
The possibility of attenuation of the cross flow in the three-dimensional incompressible laminar boundary layer on a sideslipping wing under the action of body force sources simulating the time-average forces generated by a surface electric discharge is estimated. The effect of the distance between the sources and the sideslip angle of the wing on the cross flow velocity is investigated for the source intensity observed experimentally. 相似文献
12.
Yasuaki KohamaDaiki Motegi 《Experimental Thermal and Fluid Science》1994,8(4):273-278
Boundary layers that develop over a body in fluid flow are in most cases three-dimensional owing to the spin, yaw, or surface curvature of the body. Therefore, the study of three-dimensional (3D) boundary-layer transition is essential to work in practical aerodynamics. The present investigation is concerned with the problem of 3D boundary layers over a yawed body. A yawed cylinder model that represents the leading edge portion of a swept wing and the mechanism of crossflow instability are investigated in detail using hot-wire velocimetry and a flow visualization technique. As a result, traveling disturbances having frequencies f1 and f2, which differ by about one order of magnitude, are detected in the transition region. The phase velocities and directions of travel of those disturbances are measured. Results for the low-frequency disturbance f1 show qualitative coincidence with results numerically predicted for a crossflow unsteady disturbance. Nameley, F1 travels nearly spanwise to the yawed cylinder and very close to the cylinder wall. The results for the high-frequency disturbance f2 good agreement with the existing experimental results. The 2 disturbance is found to be the high-frequency inflectional secondary instability that appears in 3D boundary layer transition in general. A two-stage transition process, where stationary crossflow vortices appear as the primary instability and a traveling inflectional disturbance is generated as a secondary instability, was observed. Secondary instability seems to play a major role in turbulent transition. 相似文献
13.
The effects of streaks on boundary layer transition depend on the initial amplitude of T-S waves introducedto excite the transition. This problem was studied in a flat-plate boundary layer in water tunnel byusing hydrogen bubble method. Three T-S wave initial amplitudes were tested. The results show thatboth narrow and wide-spacing streaks depress the transition excited by T-S waves with lower initialamplitude. However, when transition is excited by T-S waves of higher initial amplitude, thenarrow-spacing streaks depress the transition, while the wide-spacing streaks promote thetransition. Further the underlying mechanisms were also analyzed. 相似文献
14.
I. I. Lipatov 《Fluid Dynamics》2006,41(5):725-735
Local flows in a laminar boundary layer flowing over surface heating elements are investigated. Mathematical models of disturbed flows are constructed on the basis of an asymptotic analysis and the similarity parameters are determined. The time-dependent local heating regimes ensuring control of separation and flow stability in the boundary layer are studied. The results of a numerical and analytic analysis are obtained. 相似文献
15.
Residual Reynolds number effects in the established data for the velocity profile in turbulent boundary layers (and in pipe
or channel flows) are found to be remarkably large. We combine two eddy-viscosity models (with overlapping validity in the
inertial sublayer) and show (both analytically and numerically) that this enhancement (which involves a viscous correlation
length) arises from inner-outer sublayer interaction. 相似文献
16.
The importance of the lift force acting on the dispersed phase in the boundary layer of a laminar gas-particle dilute mixture
flow generated by a shock wave is investigated numerically. The particle phase is supposed to form a continuum and is described
by an Eulerian approach. The ability of the Eulerian model to simulate particle flows and the importance of the two-way coupling
are proven by comparison with experimental data as well as with the numerical results from schemes based on a Lagrangian approach.
The models used for the lift force are discussed through comparisons between numerical and experimental results found in the
literature. Some results about the formation of a dust cloud are numerically reproduced and show the major role of the lift
force. Simulations of two-dimensional two-phase shock tube flows are also performed including the lift force effects. Although
the wave propagation is weakly influenced by the lift force, the force modifies substantially the dynamics of the flow near
the wall.
Received 17 February 2000 / Accepted 30 November 2000 相似文献
17.
Axisymmetric turbulent boundary layers that develop around streamwise oriented long cylinder-like objects can be found in many applications, such as towed array sonars or marine seismic streamers. In many of these applications, turbulent fluctuations within the boundary layer flow can have a negative impact compared with laminar flow conditions. The aim of the present work is to design a surface modification that influences the turbulent boundary layer around a cylinder in axial flow in order to reduce turbulent fluctuations. To design the surface we consider recent findings regarding the turbulence damping effects of groove-like surface structures and combine these insights with the effect of convex transverse curvature on turbulence. We use large-eddy simulations to investigate the flow around a cylinder of modified design and around a reference circular cylinder. Both flows have a radius-based Reynolds number of . The modified design leads to a 20 % decrease in the average wall shear stress and results in local reductions in the turbulent intensities, Reynolds stress, the temporal velocity spectrum, and the turbulent dissipation rate. The analysis within the anisotropy-invariant space reveals a tendency towards flow relaminarization. However, the new design has no effect on turbulent pressure fluctuations. We provide suggestions on how to further improve the surface design to achieve even greater flow stabilization. 相似文献
18.
Rama Subba Reddy Gorla Frank Jankowski David Textor 《International Journal of Heat and Fluid Flow》1988,9(4):421-426
An analysis is presented to investigate the time-mean characteristics of the laminar boundary layer near an axisymmetric stagnation point when the velocity of the oncoming flow relative to the body oscillates. Different solutions are obtained for the small and high values of the reduced frequency parameter. The range of Reynolds number considered was from 0.01 to 100. Numerical solutions for the velocity functions are presented, and the wall values of the velocity gradients are tabulated. 相似文献