Fluids - boundary conditions for rotating sphere

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SUMMARY

The discussion focuses on the boundary conditions for a rotating sphere in a simple shear flow, specifically defined by the equations ui = EijkRjxk on the sphere and ui = G(x2 + c) at infinity. The standard formula for rotational velocity, expressed as v = ω x r or vi = εijkωjrk, is confirmed to apply, indicating that the fluid velocity at the sphere's surface matches the surface's velocity. The use of the Kronecker delta (dij) and the permutation symbol (Eijk) is also highlighted as essential components in the equations governing the system.

PREREQUISITES
  • Understanding of fluid dynamics principles
  • Familiarity with boundary condition concepts in fluid mechanics
  • Knowledge of vector calculus and rotational motion
  • Proficiency in tensor notation, specifically Kronecker delta and permutation symbols
NEXT STEPS
  • Study the application of boundary conditions in fluid dynamics simulations
  • Learn about the Navier-Stokes equations in relation to rotating bodies
  • Explore the implications of shear flow on rotating spheres
  • Investigate numerical methods for solving fluid dynamics problems involving complex geometries
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This discussion is beneficial for fluid dynamics researchers, mechanical engineers, and students studying rotational motion in fluids, particularly those interested in boundary condition applications and shear flow dynamics.

davcrai
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Homework Statement


A sphere under uniform rotation R, in a simple shear flow, given at infinity by
ui = G(x2 + c)deltai1
The centre of sphere is fixed at x2

Boundary conditions are ui = EijkRjxk on sphere,
and ui = G(x2 + c) at infinity


Homework Equations



dij is the kronecker delta
Eijk is the permutation symbol

The Attempt at a Solution



Just trying to understand the boundary condition on the sphere.
 
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hi davcrai! :smile:

ui = εijkRjxk is the standard formula for rotational velocity …

usually written v = ω x r, which is the same as vi = εijkωjrk :wink:

(in other words, the fluid velocity at the surface of the sphere is the same as the velocity of the surface, as one might expect)
 
Thanks
 

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