Dear friends, I am trying to simulate flow over a blunt body (hypersonic flow problem), flow over an airfoil (supersonic flow problem) and flow over an automobile (subsonic case)... I am using UPWIND scheme for all the three problems... IS THAT OK?? In what type of problems we can use HIGH RESOLUTION scheme???

what is that advection scheme?? I have not heard of that before..

Thanks in advance...

The high resolution scheme is described in the documentation. It is essentially a second order advection scheme. Upwind (first order) advection does not usually reproduce reality well, but its increased stability can help you arrive at better state for initial conditions to obtain convergence for a higher order advection scheme.

Best practice guidelines recommend using second-order advection wherever possible except in the case of turbulence models, where second-order advection schemes usually will not converge.

The upwind scheme may be ok for comparing the performance of 2 similar designs (to see if a change in a car fender results in less drag), but it probably won't accurately reproduce measured integral quantities (like pressure drops and drag force), let alone local flow properties.