Abstract
Modelling and performance calculation of screw machines with large helix angles such as a single and multiphase screw pumps by use of Computational Fluid Dynamics is challenging. The numerical procedures explained in literature are based on the 3D numerical meshes generated by series of 2D transverse cross sections which allows mesh to either follow the helix or be perpendicular to the rotor axis. This allows generating a conformal mesh. However, if the rotor helix angle is large, the cell skewness becomes prohibitively large which introduces errors in numerical simulation. The paper firstly attempts to generalize the generation method of rotor profiles with emphasis on producing a normal rack and rotors profiles. Then it introduces the method which uses series of 2D numerical meshes in the planes normal to each of the rotors and rack in order to decompose the working domain in two sub-domains. By this means it is possible to achieve 3D numerical mesh with extended capability of mesh refinement in clearances and alignment of the mesh to the main and leakage flows. However, special treatment is required to provide conformal interface between two moving meshes and with the casing. It is expected that it will greatly benefit accuracy and ease of performance calculation using a number of CFD solvers. In addition it is expected that it will allow generation of various different screw machine configurations like single screw machines or machines with conical rotors.
Highlights
Single and twin screw machines are positive displacement rotary machines comprising a meshing pair of rotors contained in a casing, which together form a working chamber whose volume depends on the angle of rotation
Published under licence by IOP Publishing Ltd a method using a rack defined in the normal plane to design the twin screw rotor profiles was proposed by him[5]
This paper proposes use of a normal rack in order to separates flow domains of the male and female rotors
Summary
Single and twin screw machines are positive displacement rotary machines comprising a meshing pair of rotors contained in a casing, which together form a working chamber whose volume depends on the angle of rotation. Published under licence by IOP Publishing Ltd a method using a rack defined in the normal plane to design the twin screw rotor profiles was proposed by him[5] The advantage of this method is that the normal circular pitch is same for main and gate rotor as the helix angle varies. There are three different mathematical methods for rotor profiles generation, namely, generation from a given main or gate rotor profile curve, generation from a meshing line and generation from a specifying rack on the transverse or normal plane.
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