【摘要】 电化学法可用来测量流体流过固壁时,壁面上的剪应力[1]。在拟稳态假定下,电极表面的传质速率 N 与壁面上剪应力τ_w 的关系式可写成N=β(τ_w/μ)1/3 (1)式中μ为流体粘度,β在给定的测量体系中为一常数。当流体流动随时间变化时,上述关系是否适用,对于测量非稳态流动系统的壁面剪应力是至关重要的。小幅度(<10%)速度扰动可用线性化法[2]研究电极的响应,但当速度扰动幅度大时,需直接求解非稳态的二维浓度场方程。本文用数值计算方法,计算了幅值为0.3.0.5和0.7时电极表面附近的浓度场分布。结果表明在幅值小于50%范围内,与线性化法基本一致,但当幅值进一步加大后,电极的响应与外加的扰动波形有所偏离。更多还原

【Abstract】 Electrochemical method can be used to measure shear stress on the-wall when fluid flows over the wall.In pseudosteady state,the mass transter rate N on the surface of the electrode is related to the wall shear sterss τ_wby, N=β（τ_w/μ）^1/3 where μ is the viscosity,and β is a constant for a given system.If the flow changes with time,it is important to know whether Equation （1） is still app- licable for the measurement of the wall shear stress at unsteady state.The electrode response to a small amplitude （<10%） of flow oscillation was ana- lyzed with the linear theory.However,for large amplitude of flow osci- llation,an unsteady mass balance equation in two dimensions has to be solved. This study presents the results of a numeriacal calculation of concentra- tion profiles near the surface of the electrode for three amplitudes:0.3, 0.5,0.7,respectively.For the amplitude less than 0.5,the calculated resu- lts are in good agreement with the linearized method.But,the response of the electrode deviates from the wave form of the imposed oscillation when the amplitude is larger than 0.5.更多还原