  The goal of this dissertation is to investigate the PANS model capabilities
in providing significant improvement over RANS predictions at slightly higher
computational expense and producing LES quality results at significantly lower
computational cost. The objectives of this study are: (i) investigate the model
fidelity at a fixed level of scale resolution (Generation1-PANS/G1-PANS) for
smooth surface separation, (ii) Derive the PANS closure model in regions of
resolution variation (Generation2-PANS/G2-PANS), and (iii) Validate G2-PANS
model for attached and separated flows. The separated flows considered in this
study have been designated as critical benchmark flows by NASA CFD study group.
  The key contributions of this dissertation are summarized as follows. The
turbulence closure model of varying resolution, G2-PANS, is developed by
deriving mathematically-consistent commutation residues and using energy
conservation principles. The log-layer recovery and accurate computation of
Reynolds stress anisotropy is accomplished by transitioning from steady RANS to
scaled resolved simulations using the G2-PANS model. Finally, several
smooth-separation flows on the NASA turbulence website have been computed with
high degree of accuracy at a significantly reduced computational effort over
LES using the G1-PANS and G2-PANS models.
