City Research Online

Abstract

Oil-free positive displacement machines are used in various industries where presence of oil in the process is prohibited. Due to the lack of cooling, they experience high temperatures and thermal growth of rotors and casing. Therefore, clearances between rotors and casing are increased to avoid contact. It is important to minimise operational clearances but retain reliable operation. This requires numerical methods able to calculate leakage flows accurately. A recent PIV measurement revealed that leakage flows in radial gap of roots blower are sensitive to rotor speed. This research is aimed to perform a numerical study to evaluate various grid generation and modelling techniques for estimation of leakage flows and comparing results with data obtained by Particle Imaging Velocimetry measurements. This study considered 2D static mesh with moving wall boundary condition, 2D unsteady dynamic layering mesh and full 3D deforming rotor grid model. Additionally, to accurately replicate the shape of the rotor tip and gap size, a deforming 3D grid with filleted tip and hybrid gap model was developed. CFD model also included change in air density due to the seeding required for PIV.

Velocity magnitude and profiles in clearances, discharge flow and gas temperature predictions were validated against experimental data. Full 3D grid with hybrid gap, 5% smoke seeding and axial gap size of 80µm agree more with experimental data than simplified models. Discharge flow and temperature deviations from experiment were within 7%. The validated model had captured leakage flows accurately and can be applied to various rotor profile shapes.

Publication Type:	Article
Additional Information:	© 2025 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Publisher Keywords:	Leakage flow, Roots Blower, PIV, SCORG, Radial gap, Deforming Rotor Grid, Smoke Seeding
Subjects:	T Technology > TJ Mechanical engineering and machinery T Technology > TL Motor vehicles. Aeronautics. Astronautics
Departments:	School of Science & Technology School of Science & Technology > Engineering
SWORD Depositor:	Symplectic Administrator

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