Free surface problem in electrohydrodynamics

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Discussion Overview

The discussion revolves around the free surface problem in electrohydrodynamics, specifically addressing the relationship between bulk charge density in an electrified fluid and the potential existence of surface charge. Participants explore theoretical implications, mathematical relationships, and the behavior of electric fields in and around the fluid.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that a constant charge density within the fluid may lead to a surface charge, while others question this assumption and suggest that the bulk charge does not intrinsically produce a surface charge.
  • There is a discussion about the necessity of calculating electric displacement fields on either side of the fluid interface to determine surface charge implications.
  • Some participants argue that the electric field is different inside and outside the medium, with discontinuities related to surface charge, while others assert that in certain cases, such as a uniformly charged sphere, the electric field remains continuous at the surface.
  • One participant mentions connecting Euler equations with Maxwell's equations to analyze the resulting shape of the free surface, indicating a complex interplay between fluid dynamics and electromagnetic fields.
  • There is a suggestion that fluid motion could lead to the generation of surface charge, depending on the governing equations of the fluid.
  • Some participants express uncertainty about whether surface charge can be ignored in their specific problems, with conditions such as small perturbations from equilibrium being considered.
  • References to magnetohydrodynamics (MHD) literature are made, highlighting the relevance of finite-conductivity charged fluids with free surfaces in related research.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether a surface charge necessarily arises from a bulk charge density. Multiple competing views exist regarding the relationship between bulk charge, surface charge, and the behavior of electric fields.

Contextual Notes

Participants note that the assumptions regarding charge distribution and fluid motion may affect the conclusions drawn about surface charge. The discussion also highlights the complexity of the problem, with references to different scenarios and mathematical approaches that may yield varying results.

  • #31
renormalize said:
So do you agree that the authors meant to write ##\nabla## and that their eq.(2) is therefore not nonsense?
I don't know. It's certainly something that I'm not going to be concerned about when I deal with variable charge density, although I am curious where the term ##\rho_{v}\mathbf{u}## comes from. That would couple the variable charge density very nicely.
 

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