Probability density function ͑pdf͒ methods are extended to include modeling of wall-bounded turbulent flows. A pdf near-wall model is developed in which the generalized Langevin model is combined with an exact model for viscous transport. Then the method of elliptic relaxation is used to incorporate the wall effects without the use of wall functions or damping functions. Information about the proximity of the wall is provided only in the boundary conditions so that the model can be implemented without ad hoc assumptions about the geometry of the flow. A Reynolds-stress closure is derived from this pdf model, and its predictions are compared with DNS and experimental results for fully developed turbulent channel flow.

Probability density function (p.d.f.) methods are extended to include modelling of wall-bounded turbulent flows. A p.d.f. near-wall model is developed in which the generalized Langevin model is combined with a model for viscous transport. This provides exact treatment of viscous inhomogeneous effects, and enables consistent imposition of the no-slip condition in a particle framework. The method of elliptic relaxation is combined with additional boundary conditions and with the generalized Langevin model to provide an analogy for the near-wall fluctuating continuity equation. This provides adequate representation of the near-wall anisotropy of the Reynolds stresses. The model is implemented with a p.d.f./Monte Carlo simulation for the joint p.d.f. of velocity and turbulent frequency. Results are compared with DNS and experimental profiles for fully developed turbulent channel flow.

A mechanism is proposed for the generation of large-amplitude acoustically-driven streaming flows in which time-mean flow speeds are comparable to the instantaneous speed of fluid particles in a high-frequency sound-wave field. Motivated by streaming observed in high-intensity discharge (HID) lamps, two-dimensional flow of a density-stratified ideal gas in a channel geometry is analysed in the asymptotic limit of high-frequency acoustic-wave forcing. Predictions of streaming flow magnitudes based on classical arguments invoking Reynolds stress divergences originating in viscous boundary layers are orders of magnitude too small to account for the observed mean flows. Moreover, classical ‘Rayleigh streaming’ theory cannot account for the direction of the cellular mean flows often observed in HID lamps. In contrast, the mechanism proposed here, which invokes fluctuating baroclinic torques away from viscous boundary layers and thus is largely independent of viscous effects, can account both for the magnitude and the orientation of the observed streaming flows.

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A wall-function boundary condition is developed for the pdf/Monte Carlo method. Like traditional wall functions, this reproduces the logarithmic velocity profile and shear stress in equilibrium flow conditions. A constant-stress analysis for the pdf, and a linear-stress analysis for the first two moments of the pdf are developed as the basis for this wall-function approach. Stable and accurate boundary conditions are derived and demonstrated with fully-developed channel flow.