The residual is simply how tightly the linear solver has achieved, and the link of this to accuracy is complex. THe CFX advection schemes "Upwinding" and "High res" are both upwinding schemes, just "upwinding" is first order and "High res" is second order, and blending to first order where the flux limiter cuts in.Īnd finally, do not be confused into thinking that simulation error is proportional to the residual. I do not agree with Talita's comment - there is no such thing as a simulation where first order is more suited than second, any time you choose a first order scheme you are sacficising accuracy for easy convergence.
This results in slower and less tight convergence (as more little perturbations are present) but higher accuracy.
This means the flow has less artificial damping and therefore closer to the correct amount of damping. It contains far less numerical diffusion. High Res uses a second order scheme when possible and blends to a first order scheme to maintain boundedness. This means the flow is damped artifically more than it should be which results in easy and tight convergence, but inaccurate results. Upwinding is a first order scheme and contains lots of numerical diffusion. Better convergence with Upwind than High-Resolution advection scheme - CFD Online Discussion Forums
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