Development of a multi-dimensional wall-function approach for wall condensation

摘要

As a basis for the further development of a wall-function approach, the SETCOM (Separate Effect test for Condensation Modeling) facility is operated at Forschungszentrum Julich to gain an insight into the turbulent heat and mass transfer in the boundary layer during wall condensation. This data was applied on the one hand for a detailed validation of a resolved boundary layer (low-Re) CFD approach. On the other hand, the data has been post processed following the classical scaling approach based on the friction or shear velocity u(tau) (i.e. u(+) - y(+) or T+ - y(+)). It became obvious that a single dimensionless parameter y(+), which is a kind of Reynolds number, is not sufficient for describing flows including near wall buoyancy and wall normal mass transfer. For this reason, two additional new dimensionless parameters, the dimensionless gravity force and the dimensionless heat flux have been introduced to describe the wall boundary conditions by 3D surfaces instead of a 1D analytical correlation. These characteristic 3D maps, which are based on a combination of detailed experimental data and validated CFD results, are implemented numerically efficient for u(+), T+, Y-S(+) and turbulence (eta(t) via omega) by means of a non-equilibrium factor and an approximation by radial basis functions into an existing U-RANS model. Following a detailed discussion of the model derivation and implementation, the paper is concluded with exemplary discussion of current model assessment results.