Flow conditioners serve to reduce the developing length between pipe fittings and flow meters and to create the fully developed standard flow condition within short developing distances. This has been used in industrial settings as means for metering errors reduction and elimination. The authors undertook a research project to predict the flow development downstream different flow conditioners to optimize their performance in reducing flow distortion and the attainment of the standard fully developed condition within shorter distances. The tested flow conditioners were the Etoile and the tube bundle, described by the standards ISO 5167, and other plate-type flow conditioners. The present paper will discuss only the results obtained for the Etoile flow conditioner, with its standard geometry and other proposed design settings. Powerful Computational Flow Dynamics techniques have been used to predict the flow development downstream the flow conditioners.