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1.
Several situations in which a spherical bubble experiences a lift force are examined, especially through the use of computational results obtained by solving the full Navier–Stokes equations. The lift force is computed over a wide range of Reynolds number for the case of pure shear flow, pure strain and solid body rotation. Using these results, the validity of asymptotic solutions derived in the limit of low Reynolds number or inviscid flow is discussed. A general expression of the lift force valid for low to moderate shears is proposed. It is shown that for such shears, the lift force in a complex flow can be predicted by superposing the results obtained in pure strain flow and solid body rotation flow. Finally, the interaction force experienced by two bubbles rising side-by-side is studied. The computational results reveal that, at variance with the predictions of potential theory, the sign of this force changes when the Reynolds number or the separation distance between the bubbles decreases below a critical value. All these results are discussed in terms of vorticity. The respective role played by the vorticity generated at the bubble surface and by the one that is eventually present in the unperturbed flow is emphasized. 相似文献
2.
O. A. Vlasova V. G. Kozlov N. V. Kozlov 《Journal of Applied Mechanics and Technical Physics》2018,59(2):219-228
The dynamics of a heavy cylindrical body in a liquid-filled horizontal cylindrical cavity with a time-varying rotation rate is experimentally investigated. The body is near the cavity boundary under a centrifugal force and undergoes solid-body rotation together with the liquid and the cavity at a fixed rotation rate. The dependence of the body dynamics on the amplitude and frequency of modulation of the rotation rate is investigated. It is found that at a critical amplitude of modulation (at definite frequency), the heavy body repulses from the cavity boundary and comes into a steady state at some distance from the wall. It is found that the average lift force (repulsive one) is generated by the azimuthal oscillation of the body in the rotating frame of reference and manifests itself at a distance comparable to the thickness of the viscous boundary layer. In the experiments, we observed azimuthal drift of the body due to asymmetric azimuthal oscillations of the body. In the limit of high frequency of the rotation rate modulation, the dependence of the lift force coefficient on the gap between the body and the wall is determined. 相似文献
3.
An airfoil with a cavity traps a vortex; the lift increases but the vortex shows great receptivity to upstream disturbances.
A simple potential flow model confirms that the vortex stability basin is of a reduced extent. In this paper we present a
control technique stabilizing the vortex position based on a potential flow model. The actuators are sources/sinks at the
wall and the suction/blowing law is obtained by the adjoint optimization method.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
可变形儒可夫斯基翼型非定常气动力的研究 总被引:1,自引:0,他引:1
对于翼面变形法向运动速度远小于来流速度的儒可夫斯基机翼,将解析解和离散涡方法相结合计算变形机翼的流场及非定常气动力,较详细地分析了变形机翼升力系数的准定常计算方法的误差来源,并给出修正方法.计算结果显示脱落涡尾迹对升力系数和机翼绕流环量的影响很小,变形机翼升力系数准定常计算方法的误差丰要来源于流体非定常运动引起的虚拟质量力,该非定常附加升力仅与当前时刻飞行姿态及翼犁形状和变形速率有关,与具体的变形历史过程无关,变形机翼的升力近似等于准定常计算结果叠加上相应的虚拟质量力. 相似文献
5.
对于翼面变形速度远小于来流速度情况下的儒可夫斯翼型亚音速绕流问题,通过仿射变换将可压缩流动转换成不可压缩流动,将解析解和离散涡方法相结合计算变形机翼的不可压缩流动速度场,再利用逆变换得到变形机翼的亚音速流动速度场,进而分析非定常气动力特性,建立变形机翼的准定常升力系数和非定常附加升力系数在可压缩和不可压缩两种状态下的简单近似对应关系。计算结果显示变形机翼的非定常气动升力近似等于准定常计算结果叠加上虚拟质量力导致的非定常附加升力,该非定常附加升力随翼型变形速率呈线性关系,由机翼当前时刻飞行姿态、翼型及其变形速率确定,与具体变形历史过程无关。低来流马赫数时虚拟质量力导致的非定常效应显著,高亚音速流动时准定常升力起主导作用。同时还分析了不同马赫数下机翼往复变形过程中升力的变化特性,指出尽管高亚音速变形机翼的气动升力近似等于准定常气动升力,但不能忽视非定常附加升力的影响,非定常附加升力将导致完成往复变形需要外界输入正比于Ma∞/[(1-Ma2∞)]的功。 相似文献
6.
Fluid Dynamics - The results of investigation of oscillations of an airfoil on an elastic hinge that performs transverse sinusoidal oscillations in the free stream of a viscous incompressible fluid... 相似文献
7.
S. A. Takovitskii 《Fluid Dynamics》2003,38(6):933-941
A solution of the problem of optimization of an airfoil in a supersonic flow is proposed. A symmetric airfoil with minimum wave drag for a given longitudinal cross-sectional area is constructed within the framework of a local analysis of variations of the shape with respect to the exact solution for a wedge and a rhombus. Analytic dependences representing the shape of the airfoil and its drag are found. The solution obtained is tested numerically within the framework of the Euler model. 相似文献
8.
The inviscid transonic flow past a symmetric airfoil having a curvature minimum in the middle is numerically investigated. It is shown that at zero angle of attack both symmetric and asymmetric steady-state flow patterns can exist on a certain freestream Mach number range Mmin < Mmax. On this range, the asymmetric flows are stable against small perturbations, whereas the symmetric flows are stable only if M does not coincide with a singular Mach number at which small variations in M or can result in flow restructuring. 相似文献
9.
本文用FLUENT软件模拟了结冰后NACA 0012翼型周围流场的变化,并与结冰前NACA 0012翼型的气动性能进行了对比.工作中首先以未结冰的NACA 0012翼型(干净翼型)为标准模型进行了数值验证计算,再以经过检验的方法计算结冰模型,并与结冰风洞试验数据进行了对比.本文计算攻角为0°~20°,温度为250.37K,雷诺数为2,400,000,冰型为圆形坚冰.通过对比升力阻力性能,发现与干净翼型相比,结冰翼型的最大升力系数大约减少了50%,阻力系数增加了约65%,失速攻角降低了4°.结冰后翼型提前失速是造成气动性能恶化的主要原因. 相似文献
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11.
A. N. Khrabrov 《Fluid Dynamics》2005,40(3):474-485
The linear problem of the time-dependent inviscid flow past a thin symmetric airfoil with a control on its trailing edge deflected in accordance with an arbitrary law is considered. The aerodynamic loads on the airfoil are calculated. The intensity of the vortex wake shed from the airfoil is determined by numerically solving a Volterra integral equation of the first kind. Questions of the mathematical modeling of the time-dependent aerodynamic loads in a form convenient for the joint solution of the problems of aerodynamics and flight dynamics are also considered. The results of the modeling are compared with the numerical solutions obtained.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, 2005, pp. 157–169.Original Russian Text Copyright © 2005 by Khrabrov. 相似文献
12.
A locally monodisperse air-supercooled water drop flow past an airfoil is studied. The influence of the viscous boundary layer on the force exerted on the drops by the carrier gas and the effect of deformation of the drops on (i) their trajectories, (ii) the water mass flux density over the airfoil surface, and (iii) the wetted-surface length are considered. The effect of an airfoil electrostatic field on the dynamics of charged atmospheric drops is estimated. The role of the governing parameters, i.e. the airfoil angle of attack, the radius of the undisturbed spherical drop, and the drop charge is investigated.The possible origins of the discrepancy between the numerical and experimental results of foreign researchers are indicated. 相似文献
13.
A. V. Bunyakin 《Fluid Dynamics》2001,36(4):602-607
An algorithm for eliminating flow separation in the nose region of a symmetric airfoil section at nonzero angle of incidence is proposed. Below the separation-prone region of the section, to increase the critical angle of incidence, a vortex cell with a cylinder rotating inside is located. The shape of the vortex cell and the precise location of the cylinder are so chosen as to create the same pressure gradient in the mixing layer as in the external flow. 相似文献
14.
A discrete model of an elastic pendulum with a follower force is studied. This model is an inverted mathematical two-link pendulum with viscoelastic hinges. It is shown that divergent bifurcations are possible for some absolute values of the follower force and the stiffness of the restraint of the pendulum's upper end. As a result, the vertical position of the equilibrium becomes unstable and two new nonvertical stable equilibrium states (fork bifurcation) occur. 相似文献
15.
V. P. Zamuraev A. P. Kalinina 《Journal of Applied Mechanics and Technical Physics》2005,46(5):664-669
The possibility of controlling the aerodynamic characteristics of airfoils with the help of local pulsed-periodic energy addition into the flow near the airfoil contour at transonic flight regimes is considered. By means of the numerical solution of two-dimensional unsteady equations of gas dynamics, changes in the flow structure and wave drag of a symmetric airfoil due to changes in localization and shape of energy-addition zones are examined. It is shown that the considered method of controlling airfoil characteristics in transonic flow regimes is rather promising. For a zero angle of attack, the greatest decrease in wave drag is obtained with energy addition at the trailing edge of the airfoil.__________Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 5, pp. 60–67, September–October, 2005. 相似文献
16.
The effects of an accelerating freestream from a nonzero velocity on the transitional separation bubble characteristics were investigated quantitatively. Hot wire anemometry was used to determine the boundary layer velocity profile repsonse to the acceleration at selected chordwise locations on a Wortmann FX 63-137 airfoil at 7 ° angle of attack. Both positive and negative accelerations were studied from base chord Reynolds number of 100,000 and 150,000, respectively. The purpose of this experiment was to verify the trends witnessed in previous research concerning a sinusoidally oscillating freestream velocity by uncoupling the accelerating and decelerating boundary layer effects. The experimental results indicate that as a result of a freestream acceleration, the separation bubble position shifts in the direction opposite to the chordwise direction it would move for a quasi-steady velocity change. The transition location was more responsive to the acceleration than was the separation position. This supports the oscillating freestream experiment conclusions.This research was supported by the U.S. Navy Office of Naval Research under contract N00014-83-K-0239 相似文献
17.
The results of investigating the shape of an electric arc carrying an electric current of less than 100 A and exposed to an air, nitrogen, or argon stream at a stream velocity of from zero to 20 m/s, when the interelectrode gap is less than 20 mm, are reported. The shape of the arc is qualitatively investigated as a function of the gas type, blowing velocity, and interelectrode gap. It is shown that an arc burning in a channel with insulated walls is much more stable under these conditions than an arc with the same parameters burning in free space. 相似文献
18.
A. V. Kashevarov A. L. Stasenko 《Journal of Applied Mechanics and Technical Physics》2018,59(4):645-652
The process of airfoil icing caused by incidence of ice crystals is considered. A physicomathematical model of motion of spheroidal crystals in the gas flow and their interaction with the body is formulated. The model takes into account the non-spherical particle orientation with respect to the velocity vector of the gas flow. It is assumed that the particle impact onto the body surface leads to partial destruction of the particle under the action of normal and tangential stresses, and some part of the particle mass remains in the vicinity of the impact point. An inviscid flow around the airfoil with a time-dependent shape is calculated by the method of approximate conformal mapping. 相似文献
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20.
M. Breuer 《Flow, Turbulence and Combustion》2018,101(2):433-456
The present paper is concerned with numerical investigations on the effect of inflow turbulence on the flow around a SD7003 airfoil. At a Reynolds number Rec =?60,000, an angle of attack α =?4° and a low or zero turbulence intensity of the oncoming flow, the flow past the airfoil is known to be dominated by early separation, subsequent transition and reattachment leading to a laminar separation bubble with a distinctive pressure plateau. The objective of the study is to investigate the effect of inflow turbulence on the flow behavior. For this purpose, a numerical methodology relying on a wall-resolved large-eddy simulation, a synthetic turbulence inflow generator and a specific source term concept for introducing the turbulence fluctuations within the computational domain is used. The numerical technique applied allows the variation of the free-stream turbulence intensity (TI) in a wide range. In order to analyze the influence of TI on the arising instantaneous and time-averaged flow field past the airfoil, the present study evaluates the range 0% ≤ TI ≤?11.2%, which covers typical values found in atmospheric boundary layers. In accordance with experimental studies it is shown that the laminar separation bubble first shrinks and finally completely vanishes for increasing inflow turbulence. Consequently, the aerodynamic performance in terms of the lift-to-drag ratio increases. Furthermore, the effect of the time and length scales of the isotropic inflow turbulence on the development of the flow field around the airfoil is analyzed and a perceptible influence is found. Within the range of inflow scales studied decreasing scales augment the receptivity of the boundary layer promoting an earlier transition. 相似文献