Abstract: Based on the Ringleb Flow, for which there exists analytical solution, a numerical tool named Ringleb Machine is developed to test the accuracy of algorithms of CFD. The affection that boundary procession exerts on the solution of the field is discussed. Result of our calculation shows that:1) Accompanying with a 2nd order field algorithm, a 2nd order boundary algorithm can lead to much more accurate solution than a 1st order one.2) To raise the accuracy of the solution,it's not enough to simply use a highe...