RELIABILITY OF 3RD-ORDER MOMENT PARAMETERIZATION FOR MODELS OF TURBULENT BOUNDARY-LAYER OVER GENTLE TOPOGRAPHY

An analysis is made of the transport equation of Reynolds shear stress , written in a streamline coordinate system, starting from the fields of first-and second-order moments of wind velocity, measured in a terr ain-following system over gentle topography, in order to verify the us ual parameterizations of third-order moments. The equation is split in to two parts: the first contains the terms which can be calculated dir ectly from measurements, the second involves the pressure-velocity cor relation considering the terms of rapid distortion, curvature and retu rn to isotropy and the transport of triple velocity-correlation modell ed assuming a flux-gradient approximation. Moreover, the error estimat es associated with both parts have been computed using a Monte Carlo t echnique which takes into account the experimental errors. This analys is is performed on mind tunnel data over a gently shaped two-dimension al valley and hill. The comparison between the measured and modelled p arts is good near the surface, whereas, at higher levels, where the pe rtubations induced by the topography are significant, there ape large zones generally characterized by streamlines with concave curvature in which the flux-gradient approximation used to compute the triple prod uct correlation cannot be applied.