Which averaging technique will best characterize performance in CFD flow fields where distortion is observed?

Three-dimensional flow fields typically have some degree of distortion in the flow properties and flow profiles across a given cross section. These distortions can be quite significant in localized regions, for example at the exit plane of a radial compressor impeller. Because most designers are interested in averaged values of performance, the question often arises as to what averaging technique is the best to use.