PIV mapping of pressure and velocity fields in the plane magnetohydrodynamic Couette flow

TL;DR

This paper introduces a novel experimental method combining PIV and finite difference solving to map velocity and pressure fields simultaneously in magnetohydrodynamic Couette flow, revealing insights into flow transition behavior.

Contribution

It presents the first implementation of pressure PIV in MHD flow, enabling simultaneous measurement of velocity and pressure fields in a transparent electrolyte under magnetic influence.

Findings

First experimental velocity and pressure profiles in MHD Couette flow.

Identification of near-wall anisotropic perturbations during flow transition.

Demonstration of a new measurement technique for MHD flows.

Abstract

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.