Unsteady Multiphase Simulation of Oleo-Pneumatic Shock Absorber Flow

The internal flow in oleo-pneumatic shock absorbers is a complex multiphysics problem combining the interaction between highly unsteady turbulent flow and multiphase mixing, among other effects. The aim is to present a validated simulation methodology that facilitates shock absorber performance pred...

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Bibliographic Details
Published in:Fluids (Basel) 2024-03, Vol.9 (3), p.68
Main Authors: Sheikh Al-Shabab, Ahmed A., Grenko, Bojan, Silva, Paulo A. S. F., Antoniadis, Antonis F., Tsoutsanis, Panagiotis, Skote, Martin
Format: Article
Language:English
Subjects:
Analysis
Boundary conditions
Bubbles
computational fluid dynamics
Design
Drop tests
Energy dissipation
Geometry
Hydraulics
Internal flow
landing gear
Landing of aircraft
Multiphase
multiphysics
Orifice meters
Orifices
Performance prediction
Shear layers
Shock absorbers
Simulation
turbulence modelling
Turbulent flow
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Summary:The internal flow in oleo-pneumatic shock absorbers is a complex multiphysics problem combining the interaction between highly unsteady turbulent flow and multiphase mixing, among other effects. The aim is to present a validated simulation methodology that facilitates shock absorber performance prediction by capturing the dominant internal flow physics. This is achieved by simulating a drop test of approximately 1 tonne with an initial contact vertical speed of 2.7 m/s, corresponding to a light jet. The flow field solver is ANSYS Fluent, using an unsteady two-dimensional axisymmetric multiphase setup with a time-varying inlet velocity boundary condition corresponding to the stroke rate of the shock absorber piston. The stroke rate is calculated using a two-equation dynamic system model of the shock absorber under the applied loading. The simulation is validated against experimental measurements of the total force on the shock absorber during the stroke, in addition to standard physical checks. The flow field analysis focuses on multiphase mixing and its influence on the turbulent free shear layer and recirculating flow. A mixing index approach is suggested to facilitate systematically quantifying the mixing process and identifying the distinct stages of the interaction. It is found that gas–oil interaction has a significant impact on the flow development in the shock absorber’s upper chamber, where strong mixing leads to a periodic stream of small gas bubbles being fed into the jet’s shear layer from larger bubbles in recirculation zones, most notably in the corner between the orifice plate and outer shock absorber wall.
ISSN:2311-5521
2311-5521
DOI:10.3390/fluids9030068