AVOCADO: A numerical code to calculate gas pressure distribution

Abstract A code for efficient and accurate gas pressure calculation named AVOCADO is described in this paper. The non-collisional gas flow is resolved at steady-state considering only the solid boundaries of the domain (gas–wall interaction), where the gas pressure is defined. The mutual interactions between elements of the three-dimensional discretized surfaces are evaluated in terms of fluxes considering the cosine law as scattering operator. A coefficient matrix, which describes the geometry of the model, is parallel computed using view factors; correction factors accounting for gas species and specified boundary conditions are then applied, before the degree of freedom inversion is carried out. The developed tool includes also an efficient BiCGstab (biconjugate gradient stabilized method) implementation for sparse matrix inversion, to solve the system of equations. This surface finite element method reduces the degrees of freedom of the linear system and allows for fast solution of gas pressure distributions in both well-detailed and complex geometries. Overall results and pressure distribution obtained with the application of the code on typical analytical cases are presented and discussed.