User defined nodal displacement of numerical mesh for analysis of screw machines in FLUENT

N Basha,S Rane,A Kovacevic

doi:10.1088/1757-899x/604/1/012012

Abstract

Growing demands to reduce energy consumption are driving researchers towards in-depth analysis of positive displacement machines. Twin screw compressors are amongst the most common types of positive displacement machines. These machines have inherently complex geometry due to intricate rotor profiles used. As the details of the internal flows are difficult to obtain experimentally, Computational Fluid Dynamics (CFD) offers a good alternative for evaluation of internal flow patterns. However, implementation of CFD is challenging due complex deforming geometries.In this paper, a customised grid generator SCORGTM developed by authors is used to generate numerical meshes for commercially available solver ANSYS FLUENT. FLUENT is an unstructured solver which offers flexibility of using both segregated and coupled solution algorithms. Segregated algorithms are generally faster which results in shorter product development time. Interface with FLUENT is implemented by performing User Defined Nodal Displacements (UDND) of grids generated by SCORG in a parallel framework. For this purpose, SCORG and UDND are coupled and extended to work with FLUENT’s parallel architecture. The developed code is compiled within the solver. The oil free air screw compressor with ‘N’ profile rotors and 3/5 lobe combination is modelled for 8000 RPM and 6000 RPM. Finally, the predicted performance values with FLUENT are compared to previously calculated CFX predictions and experimental results. FLUENT requires shorter solution time to obtain same accuracy of CFX.

Highlights

Compressed air accounts for a mean 10% of the global industrial electric energy consumptions and this share may reach 20% if commercial and residential needs are included [1][2]
Conclusion & future work Oil free twin screw air compressor is modelled in FLUENT by using an interface with customised grid generator SCORGTM
- This study has demonstrated that the segregated algorithm in FLUENT is three times faster than the coupled CFX solver for the same case

Summary

Introduction

Compressed air accounts for a mean 10% of the global industrial electric energy consumptions and this share may reach 20% if commercial and residential needs are included [1][2]. Computational Fluid Dynamics (CFD) has been gaining an increasing popularity as a tool for design improvement within screw compressors as experimental measurements with these machines is challenging due its complex and deforming geometry. With unstructured cell-centred solvers like cell numbers are updated when mesh is loaded in FLUENT For this reason, along with commercial grid generators User Defined Nodal Displacements (UDND) have to be used to transition the nodes with the time step. 2.1 Motion of customised grids with FLUENT solver UDND is used along with customised grid generators to create a set of grids representing nodal locations for each time step These are done prior to numerical flow calculation to guarantee that there is conservation of space and equations (‘Node Mapping’).

Parallelisation

Results and discussion

Conclusion & future work