Numerical modelling of twin-screw pumps based on computational fluid dynamics

Abstract

modelling of twin-screw pumps based on computational fluid dynamics. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, doi: 10.1177/0954406216670684 This is the accepted version of the paper.This version of the publication may differ from the final published version. Permanent AbstractIncreasing 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. Important effects on the performance such as dynamic losses, influence of the leakage gaps, presence and extent of cavitation are difficult to observe by experiments. However, it is possible to study such effects using well validated CFD (computational fluid dynamics) models. The novel structured numerical mesh consisting of a single computational domain for moving screw pump rotors was developed to allow 3-D CFD simulation of such machine possible. Based on Finite Volume Method (FVM), the instantaneous mass flow rates, rotor torque, local pressure field, velocity field and other performance indicators including the indicated power were predicted. A calculation model for the bearing friction losses was introduced to account for mechanical losses. The geometry of the inlet and outlet passages and piping system are taken into consideration to evaluate their influences on the pressure distribution and shaft power. The paper also shows the influence of rotor clearances on the pump performance. The CFD model was validated by comparing the numerical results with the measured performance obtained in the experimental test rig through the comprehensive experiment performed for a set of discharge pressures and rotational speeds. 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 also showed that that the radial clearances have larger influence on the mass flow rate than the interlobe clearance. The correct design of the flow passages within the screw pump plays significant role in minimizing required power consumption. 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 terms of clearance selection, shape of the ports, piping system etc. In future this model will be used for analysis of cavitating flows and determining performance of other multiphase screw pumps.

Rotor profile design and numerical analysis of 2–3 type multiphase twin-screw pumps

“…The CFD calculation with the A-type rotors has been validated by experiment in the prior publication by the authors [21], in order to confirm the accuracy and applicability of this numerical method for performance prediction of screw pumps. Figure 13 Rotor torque under different rotation Angle Figure 13 shows the rotor torque of screw pump with A, D1 and D2 profiles under the same discharge pressure.…”

“…The size of the numerical mesh for all three cases is shown as Table 3. The grid independence for this calculation model has already been investigated in another publication [21]. Figure 11 Polyhedral mesh of suction and discharge ports …”

Numerical investigation of cavitation in twin-screw pumps

“…Performance prediction of the liquid pump analysed in this paper was validated for a single phase calculation in previous publication by the authors [35]. It included validation of internal and integral parameters as well as the grid independency study and comparison of different turbulence modes.…”

“…The grid independency study for this calculation model has already been performed in another publication [35]. …”

“…Handling of the mesh generated by SCORG in STAR-CCM+ solver is managed by use of the UDF made specially for handling conformal rotor mesh and it will be described later in the paper. This method has been validated by experiment in single-phase CFD modelling of screw pump [35][36]. This paper is aimed to study the flow characteristics of twin-screw pumps under cavitating conditions.…”