Increasing demands for high-performance screw pumps in oil and gas as well as other applications require deep understanding of the fluid flow field inside the machine. Some important influence factors on the performance are difficult to observe by experiments. However, it is possible to study such effects using well validated computational fluid dynamics (CFD) models.
The novel structured numerical mesh consisting of a single computational domain for moving screw pump rotors allows 3-D CFD simulation of such machines possible. The mesh is generated by the unique grid generation software SCORG.
It was integrated with the commercial CFD solver STAR-CCM+ by user defined functions (UDF) for manipulation of predefined numerical grids in order to obtain pressure and velocity fields within the machine. This allowed calculation of instantaneous mass flow rates, rotor torque, local pressure field, velocity field and other performance indicators including the indicated power.
A calculation model for the bearing friction losses was introduced to account for mechanical losses. Different turbulence models were applied and compared.
The CFD model was validated by comparing the numerical results with experimental data. Validation includes comparison of mass flow rates, shaft power and efficiency under variety of speeds and discharge pressure. It has been found that the predicted results match well with the measurements. The results showed that increase in viscosity brings increase in the mass flow rate and higher volumetric efficiency, while it also leads to increased rotor torque and power consumption at the same time.
The analysis presented in this paper contributes to better understanding of the working process inside the screw pump and offers a good reference to improve design and optimise such machines. In future this model will be used for analysis of cavitating flows and determining performance of other multiphase screw pumps.