An Average Passage Closure Model for General Meshes

Abstract

Use of the average passage equations for simulating the steady flow in multistage tarbomachinery has been limited in practice to H-type meshes with a “pure” or “strict” character in which pitchwise mesh lines have no axial or radial variation. This requirement is due to the original implementation of the model for the deterministic component of the Adamczyk stress tensor which closes the average passage equations. Such meshes can be highly distorted, especially near blunt leading edges or around highly staggered airfoils. A more general implementation of the closure model is developed which permits the use of general meshes of varying topology and character and exploits the conservation properties of the underlying CFD algorithm. The derivation of the new implementation is based on the FAS multigrid forcing function construction and is identical to the original implementation when applied to pure H-meshes. An isolated cascade simulation is presented which demonstrates a typical improvement in accuracy when non-pure H-meshes are employed. Also, results for a two and one half stage research turbine are presented which employed the new closure implementation and show some of the other benefits of using more general grids, namely improved convergence rate and reduced computation times.