Numerical analyses of high Reynolds number flow of high pressure fuel gas through rough pipes

In this paper, a CFD commercial code is used to evaluate the pressure drop through pipes in a stream of high pressure gas. Both hexahedral and tetrahedral grids are considered. Preliminarily, a grid sensitivity analysis is carried out by comparing CFD results with analytical results. Each grid is characterized by a different number and thickness of layers in order to investigate the behavior of the grid with respect to the boundary layer. Then, the model is validated by using a literature test case, in which high pressure gas flow through a rough pipe is experimentally studied. Moreover, various equations of state (i.e., constant properties, Ideal Gas and Redlich-Kwong equations) and boundary conditions (e.g., pressure, mass flow, etc.) are taken into consideration and compared. Finally, the model is used to extrapolate the behavior of gaseous fuels (i.e., natural gas, biogas and hydrogen-methane mixture) flowing at high pressure through pipes of different roughness. The analyses show that the radial depth of the prism layers on pipe wall has to be controlled to allow the correct resolution of the boundary layer. Moreover, the results highlight that the first element height of the prism layer should be high enough to avoid inconsistencies in the rough model application. At the same time, the grid used for calculations does not strongly influence the numerical results and hence tune of the first element height to perfectly fit the roughness is not always justified. The final analysis on the different gaseous fuels put into evidence the capability of the CFD analysis to determine the energy performance of fuel transportation in gas pipeline. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.