is it possible to apply more than one cell in zeroGradient or groovyBC internalField?
 

at my run the cells that are neighbours to outlet boundary show a high value for pressure and velocity that is unrealistic.I guess it can be from one cell getting in zeroGradient and also first order interpolation in internalField utility.
can a second order interpolation be used?how or any hint is appreciated.
thanks.

Usually higher order interpolation tends to make that kind of problem worse.

What is usually the problem in such cases is using a plain zeroGradient condition and having backflow at the outlet. Either extend the outlet to eliminate backflow or use the inletOutlet-condition (or something similar) to have a Dirichlet-conditon for faces where flow comes back in