diff --git a/docs/src/navier_stokes/ns.md b/docs/src/navier_stokes/ns.md index f29e5266..cb668f98 100644 --- a/docs/src/navier_stokes/ns.md +++ b/docs/src/navier_stokes/ns.md @@ -24,7 +24,7 @@ This approach can be combined with the multiphysics described in other pages to An initial attempt at solving the vorticity formulation of the inviscid incompressible Navier-Stokes momentum equation could be: -## Vorticity Formulation +## Vorticity Formulation (Incorrect) ```julia eq11_incorrect = @decapode begin @@ -38,7 +38,7 @@ end nothing # hide ``` -This formulation comes from the fact that you are treating `du` (vorticity) as the only state variable and computing the velocity field, which you need to advect vorticity along the flow with a linear solve of the exterior derivative `dā‚`. In other words, the velocity field is computed as the pseudo-inverse of the differential operation that computes curl. +This incorrect formulation does not use a stream function, but rather tries to compute the velocity field via a linear solve of the exterior derivative `dā‚`. In other words, the velocity field is computed as the pseudo-inverse of the differential operation that computes curl. ## Initial Conditions @@ -55,7 +55,7 @@ The following plots are shown from directly above the north pole of the sphere. ![Plot of Taylor Vortex initial conditions](taylor_ics.png) -### Numerical Solutions (Incorrect formulation) +### Numerical Solutions (Incorrect Formulation) This formulation is very unstable for both sets of initial conditions, failing approximately 0.4% of the way into the simulation. @@ -73,9 +73,9 @@ max u=NaN ā”Œ Warning: Instability detected. Aborting ``` -## Streamfunction-Poisson Formulation +## Stream Function / Poisson Problem Formulation (Correct) -There are cohomological reasons why the above model formulation produces low-quality simulations. The variable **X** is physically required to be in the kernel of $\Delta$, but that isn't guaranteed by the model formulation above. To fix this, you can use the solve for the stream-function by introducing a Laplacian solve as part of the update law. +There are cohomological reasons why the above model formulation produces low-quality simulations. The variable of interest is physically required to be in the kernel of $\Delta$, but that isn't guaranteed by the model formulation above. To fix this, you can use the solve for the stream function by introducing a Laplacian solve as part of the update law. Due to the equation $$du = -\Delta\psi$$ we can solve for the stream function with a linear solve of the Laplacian.