Investigation of the energy carrying outer layer structures in adverse pressure gradient flows

Spatio-temporal energy spectra are analyzed from a direct numerical simulation of a non-equilibrium adverse pressure gradient (APG) turbulent boundary layer (TBL) spanning Re_θ =1500-8200 and shape factor H = 1.4 − 3. The temporal data at two streamwise positions corresponding to small (H = 1.6) and large (H = 2.5) velocity defects are used to obtain the spatio-temporal spectra. The increase in the mean velocity defect has several effects on the energy carrying outer layer structures. The turbulent activity in the inner layer is attenuated. The energy moves away from the wall to the outer layer. The streamwise and spanwise wavelengths of the energy carrying outer layer structures decrease with increasing velocity defect.