A Navier-Stokes solutions: Beltrami flow

casparov
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Question on viscosity with Beltrami flow
There are some known solutions for 3D Navier-Stokes such as Beltrami flow.
In the literature these Beltrami flow solutions are said to not take into account viscosity, however when I read the information on Beltrami flow, they do seem to involve (kinematic) viscosity:

From incompressible vorticity eq,

{\displaystyle {\frac {\partial {\boldsymbol {\omega }}}{\partial t}}+(\mathbf {v} \cdot \nabla ){\boldsymbol {\omega }}-({\boldsymbol {\omega }}\cdot \nabla )\mathbf {v} =\nu \nabla ^{2}{\boldsymbol {\omega }}+\nabla \times f,}


and because w and v are parallel,
{\displaystyle (\mathbf {v} \cdot \nabla ){\boldsymbol {\omega }}=({\boldsymbol {\omega }}\cdot \nabla )\mathbf {v} =0}
, yields a linear DE

{\displaystyle {\frac {\partial {\boldsymbol {\omega }}}{\partial t}}=\nu \nabla ^{2}{\boldsymbol {\omega }}+\nabla \times f.}

Which is satisfied with Beltrami flow. With nu the kinematic viscosity and f an external force.

Is the problem the linearization ?
Also, might the necessary viscosity also not be modelled through a suitable "external" force expression?

Can someone explain why Beltrami flows are considered inviscid solutions ?
 
Thread 'Direction Fields and Isoclines'

Thread 'Direction Fields and Isoclines'

I sketched the isoclines for $$ m=-1,0,1,2 $$. Since both $$ \frac{dy}{dx} $$ and $$ D_{y} \frac{dy}{dx} $$ are continuous on the square region R defined by $$ -4\leq x \leq 4, -4 \leq y \leq 4 $$ the existence and uniqueness theorem guarantees that if we pick a point in the interior that lies on an isocline there will be a unique differentiable function (solution) passing through that point. I understand that a solution exists but I unsure how to actually sketch it. For example, consider a...
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