Moment-order selection based on dominant flow direction

Investigate how to select and conserve different orders of moments according to the dominant flow direction in the sparse entropic quadrature method.

Background

The numerical experiments conserve all moments up to a prescribed total order, using the same moment-order set for the full three-dimensional distribution and for the one-dimensional flow problems considered. This uniform choice may be inefficient or inaccurate when the flow has a distinguished direction, because different velocity components can contribute unequally to the relevant nonequilibrium effects.

The paper explicitly leaves unresolved the question of whether and how moment conservation should vary with the dominant flow direction. Resolving it could provide a more adaptive moment hierarchy and potentially reduce the computational cost while retaining accuracy for anisotropic rarefied-gas flows.