In a rotating positive-displacement compressor, such as a screw compressor, only a time dependent flow calculation is meaningful. The Arbitrary Lagrangean-Eulerean (ALE) formulation of the flow equations allows CFD with moving grids. Due to the complex movement of the rotors, a powerful grid manipulator is necessary. The algorithm presented in this paper moves the nodes of a block-structured grid based on the solution of a Laplace potential-equation ∇2φ = 0 in a two-dimensional section of the flow domain. The qualities of a Laplace solution for grid generation have been used in grid generators and manipulators since Winslow. The difference with this new algorithm is that now this solution is explicitly obtained on an unstructured grid to allow greater control over the movement of the grid. The grid manipulation algorithm is demonstrated on an oil-free screw compressor geometry. Results of this calculation confirm the applicability of this algorithm to such complex geometries.

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