流变学流体的蠕动传输:食道中食物块的运动模型

研究食道中蠕动传输的流体力学.对任意的波形和任意的管道长度,建立起流变学流体蠕动传输的数学模型.用粘性流体的Ostwald-de Waele幂定律,描述非Newton流体的流动特性.解析公式化模型,详细且精确地给出食物块在食道中蠕动传输相关的一些重要性质.分析中应用了润滑理论,本研究特别适合于Reynolds数不大的情况.将食道看作环形的管道,通过食道壁周期性的收缩来传输食物块.就单个波和周期性收缩一组波的传播,研究与传输过程有关变量的变化,如压力、流速、食物颗粒轨迹以及流量等.局部压力的变化,对流变指数n有着高度的敏感性.研究结果清晰地表明,食物块在食道中蠕动传输时,Newton流体或流变学流体构成的连续流体,以组合波传播比大间隔单波传播,传输效率要高得多.     

Maxwell流体在震荡的矩形输送管道中的流动

分析了不可压缩Maxwell流体在震荡矩形截面管道中的非稳定流动问题.利用Fourier变换和Laplace变换作为数学工具,提出了问题的解,该解可以看成稳态解和暂态解之和.大倍数时,暂态消失,解可以表示为稳态解.在极限情况的案例中给出了Newton流体的解.当震荡频率不存在时,得到了Maxwell流体在震荡矩形截面管道中流动问题的解.最后,以图形形式给出不同参数时,矩形管道正弦震荡达到稳态所需要的时间.同时,分别描绘了x和y变化时的速度曲线.     

Jeffrey流体流过有限长圆柱管时磁流体动力学的蠕动流

研究Jeffrey流体流过有限长管道时的蠕动流.在外加磁场作用时,流体呈导电性.分析是在长波长和低Reynolds数近似假设下完成.得到了压力梯度、体积流量、平均体积流量和局部壁面剪应力的表达式.研究了松弛时间、延迟时间和Hartman数,对压力、局部壁面剪应力以及蠕动泵机械效率的影响.还研究了回流现象,调查了沿管道壁波数非整倍数时的传播情况,研究有限长管道传播的内在特性.     

化学反应对高对流Maxwell流体在多孔面上作MHD流动和传质的影响

研究导电的高对流Maxwell流体在多孔表面上,作计及物质化学反应时的MHD流动及其传质.将非线性的偏微分控制方程及其相应的边界条件,变换为非线性的常微分方程,并利用Kel-ler-Box法进行数值求解.用图形给出了各种物理参数对流动和传质特性的影响,并对结果进行了讨论.可以看到,化学反应阶次提高了扩散边界层的厚度;还可以看到,传质率强烈地依赖于Schmidt数和反应率参数.此外,在特例情况下得到了以往文献中可供利用的结果.     

应用逐次Taylor级数线性化法在多孔伸展界面上求解高对流Maxwell流体的磁流体动力学流动

研究不可压缩的高对流Maxwell(UCM)流体,在多孔伸展界面上作磁流体动力学(MHD)的边界层流动.利用相似变换将控制的偏微分方程,变换为非线性常微分方程.采用逐次Taylor级数线性化方法(STLM)求解该非线性问题.对所显现的参数完成速度分量的计算,介绍了表面摩擦因数的数值结果,并分析了问题所显现参数的变化.     

四阶流体在一个倾斜有局部滑移的非对称通道中作有热交换的蠕动流

分析研究滑移和热交换对四阶流体作磁流体动力学蠕动流的影响.首先建立模型的控制方程,然后在长波长的假设下,采用标准的摄动法近似值求解;给出的解包括:流函数、速度、压力梯度、温度和热交换系数的显式表达式;分析了滑移参数增大时泵输送性质的变化,及其潴留现象.进而对所出现的变化参数,得到了温度分布曲线和热交换系数;讨论了这些参数对所考虑流动特性的影响;并与以往发表的无滑移情况相比较,结果基本一致.     

Chebyshev谱方法研究非稳态Maxwell流体在轴向余弦振荡圆柱上的斜驻点流动北大核心CSCD

研究了非稳态Maxwell流体斜撞击轴向余弦振荡圆柱的斜驻点流动.首先,基于斜驻点流动特性,在柱面坐标系下求得关于压力的二阶常微分方程,对压强进行修正,建立了非稳态Maxwell流体在振荡圆柱上斜驻点流动的边界层模型.接着,合理的相似变换将模型转化,使用Chebyshev谱方法求得模型的数值解.结果表明,在贴近圆柱表面的流体随着圆柱体做周期性运动;圆柱的曲率越大越会使在同一时刻同一位置处的流体质点的速度越大;相反,非稳态参数及流体的记忆特性也会在更靠近圆柱壁面处阻碍流体流动.     

放/吸热流体在两个充满多孔材料的竖直平行板之间作不稳定的自然对流

在一个由两块无限竖直平行板组成的管道中,充满着多孔的介质材料,使用Darcy模型(Brinkman模型的推广)的动量方程,连同能量方程,计算不可压缩、粘性、放/吸热流体在该管道中的不稳定自然对流,即Couette流动.流动是由于边界平板有不对称的加热,以及作加速运动所引起.选用合理的无量纲参数,对控制方程进行简化,通过Laplace变换进行解析求解,得到闭式的速度和温度分布曲线解,随后导出表面摩擦力和传热率.发现在竖直管道中的不同剖面,流体的流动及温度分布曲线随着时间而增加,且在运动平板附近更高.特别是,流体的速度和温度随着平板间距的增加而增加,但是,表面摩擦力和热传导率随着平板间距的增加而减小.     

Peristaltic mechanism of a Maxwell fluid in an asymmetric channel

The peristaltic flow of a Maxwell fluid in an asymmetric channel is studied. Asymmetry in the flow is induced by taking peristaltic wave train of different amplitudes and phase. The viscoelasticity of the fluid is induced in the momentum equation. An analytic solution is obtained through a series of the wave number. The leading velocity term denotes the Newtonian result. The first and second order terms are the viscoelastic contribution to the flow. Expressions for stream function and longitudinal pressure gradient are obtained analytically. Numerical computations have been performed for the pressure rise per wavelength and discussed.     

微极流体蠕动泵经由滑移边界管道输送的Stokes流动

计及管道边界条件滑移的影响,研究微极流体蠕动泵,经由圆柱形管道输运的Stokes流动.壁面运动的控制方程为正弦波方程.使用润滑理论,得到了轴向速度、微转动向量、流函数、压力梯度、摩擦力和机械效率的解析数值解.用图形表示出构成参数,如像耦合参数、微极参数和表征蠕流泵特性的滑移参数、摩擦力和俘获现象的影响.数值计算表明,当耦合参数较大时,需要蠕动泵的压力更大,而微极参数和滑移参数正相反.俘获团块的大小随耦合参数和微极参数的减小而缩小,而随滑移参数的增大而缩小.     

内窥镜中Walter B流体的蠕动流

研究内窥镜中Walter B流体的蠕动流,在圆柱坐标系中建立问题的模型,目的是研究内窥镜对Walter B流体蠕动流的影响.以delta为摄动参数,使用正规的摄动法求出解析解.利用数值积分,求得压力增量和摩擦力的近似解析解.用图形给出了Walter B流体所显现参数的影响.     

Unsteady flow of a Maxwell fluid over a stretching surface in presence of chemical reaction

An analysis is presented for unsteady two-dimensional flow of a Maxwell fluid over a stretching surface in presence of a first order constructive/destructive chemical reaction. Using suitable transformations, the governing partial differential equations are converted to ordinary one and are then solved numerically by shooting method. The flow fields and mass transfer are significantly influenced by the governing parameters. Fluid velocity initially decreases with increasing unsteadiness parameter and concentration decreases significantly due to unsteadiness. The effect of increasing values of the Maxwell parameter is to suppress the velocity field. But the concentration is enhanced with increasing Maxwell parameter.     

Peristaltic flow of viscoelastic fluid with fractional Maxwell model through a channel

The paper presents the transportation of viscoelastic fluid with fractional Maxwell model by peristalsis through a channel under long wavelength and low Reynolds number approximations. The propagation of wall of channel is taken as sinusoidal wave propagation (contraction and relaxation). Homotopy perturbation method (HPM) and Adomian decomposition method (ADM) are used to obtain the analytical approximate solutions of the problem. The expressions of axial velocity, volume flow rate and pressure gradient are obtained. The effects of fractional parameters (α), relaxation time (λ₁) and amplitude (?) on the pressure difference and friction force across one wavelength are calculated numerically for different particular cases and depicted through graphs.     

Channel flow of a Maxwell fluid with chemical reaction

This work is concerned with the two-dimensional boundary layer flow of an upper-convected Maxwell (UCM) fluid in a channel with chemical reaction. The walls of the channel are porous. Employing similarity transformations the governing non-linear partial differential equations are reduced into non-linear ordinary differential equations. The resulting ordinary differential equations are solved analytically using homotopy analysis method (HAM). Expressions for series solutions are derived. The convergence of the obtained series solutions are shown explicitly. The effects of Reynold’s number Re, Deborah number De, Schmidt number Sc and chemical reaction parameter γ on the velocity and the concentration fields are shown through graphs and discussed.     

Peristaltic motion of a magnetohydrodynamic generalized second‐order fluid in an asymmetric channel

We investigate the peristaltic motion of a magnetohydrodynamic (MHD) generalized second‐order fluid in an asymmetric channel. The governing equations are first modeled and then numerically solved under the long wavelength approximation. Attention has been focused to analyze the shear‐thinning and shear‐thickening effects of the investigated non‐Newtonian fluid, the influence of the magnetic force on the flow, especially the trapping, pumping characteristics caused by the peristalsis of the walls. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2011