Dear all,
I see that in order to solve the Navier Stokes equations with Fenics, see for example here,
a function space of order 2 is used for the velocity and one of order 1 for the pressure
V = VectorFunctionSpace(mesh, 'P', 2)
Q = FunctionSpace(mesh, 'P', 1)
Changing the order of these spaces may make the algorithm yield the wrong solution. May you please give me some references explaining why these orders 2+1 are chosen?