Experimental study of wall boundary conditions for large-eddy simulation

An experimental investigation was conducted to study the wall boundary cond ition for large-eddy simulation (LES) of a turbulent boundary layer at R-th eta = 3500. Most boundary condition formulations for LES require the specif ication of the instantaneous filtered wall shear stress field based upon th e filtered velocity field at the closest grid point above the wall. Three c onventional boundary conditions are tested using simultaneously obtained fi ltered wall shear stress and streamwise and wall-normal velocities, at loca tions nominally within the log region of the flow. This was done using arra ys of hot-film sensors and x-wire probes. The results indicate that models based on streamwise velocity perform better than those using the wall-norma l velocity, but overall significant discrepancies were found for all three models. A new model is proposed which gives better agreement with the shear stress measured at the wall. The new model is also based on the streamwise velocity but is formulated so as to be consistent with 'outer-flow' scalin g similarity of the streamwise velocity spectra. It is therefore expected t o be more generally applicable over a larger range of Reynolds numbers at a ny first-grid position within the log region of the boundary layer.