fluctuating residuals
 

Hello,
I am simulating a cylinder(H-6cm,D-4cm) with an inlet on the top surface and outlet on the curved surface. the conditions i use are
mass flow inlet-0.04kg/s
outflow
mesh tri/Pave
residuals-1e-6
However, i get flat residuals after 1e-4 and the solution does not converge for a second order scheme. but for a first order scheme it does converge. how can i make the second order solution converge below 1e-4.