We present the first simultaneous mapping of two-dimensional, time-dependent velocity and pressure fields in a plane Couette flow pervaded by a transverse magnetic field. While electromagnetic forces are strongest in fluids of high electric conductivity such as liquid metals, their opacity excludes optical optical measurement methods. We circumvent this difficulty using a transparent electrolyte (Sulfuric acid), whose weaker conductivity is offset by higher magnetic fields. We describe an experimental rig based on this idea, where the Couette flow is entrained by a tape immersed in sulfuric acid and positioned flush onto the bore of large superconducting magnet, so that most of the flow is pervaded by a sufficiently homogeneous transverse magnetic field. Velocity and pressure fields are obtained by means of a bespoke PIV system, capable of recording the fluid's acceleration as well as its velocity. Both fields are then fed into a finite difference solver that extracts the pressure field from the magnetohydrodynamic governing equations. This method constitutes the first implementation of the pressure PIV technique to an MHD flow. Thanks to it, we obtain the first experimental velocity and pressure profiles in an MHD Couette flows and show that the transitional regime between laminar and turbulent states is dominated by near-wall, isolated, anisotropic perturbations.

中文翻译：

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平面磁流体动力学库埃特流中压力和速度场的 PIV 映射

我们首次同时绘制了横向磁场弥漫的平面 Couette 流中的二维、时间相关速度和压力场。虽然电磁力在液态金属等高导电性流体中最强，但它们的不透明度不包括光学光学测量方法。我们使用透明电解质（硫酸）规避了这一困难，其较弱的导电性被较高的磁场抵消。我们描述了一个基于这个想法的实验装置，其中 Couette 流被一条浸在硫酸中的胶带夹带，并与大型超导磁体的孔齐平放置，因此大部分流都被足够均匀的横向磁场所渗透。速度场和压力场是通过定制的 PIV 系统获得的，能够记录流体的加速度及其速度。然后将两个场都输入到有限差分求解器中，该求解器从磁流体动力学控制方程中提取压力场。该方法构成了对 MHD 流的压力 PIV 技术的首次实施。由于它，我们获得了 MHD Couette 流中的第一个实验速度和压力分布，并表明层流和湍流状态之间的过渡状态由近壁、孤立、各向异性扰动主导。