| Oleo-pneumatic shock absorbers are the most widely used form of shock absorber on aircraft landing gear,and the study of oil orifice damping characteristics is one of the key points in the study of landing gear shock absorber performance.At present,most studies of the damping characteristics of oil orifices are discussed by means of numerical simulations of single-phase flow computational fluid dynamics,ignoring the role of nitrogen in the study.In this paper,the oleo-pneumatic shock absorber model is simplified and the damping characteristics of the oleo-pneumatic shock absorber are investigated by means of numerical simulation of two-phase flow.Firstly,the basic working principle of the oleo-pneumatic shock absorber of the landing gear is disassembled and analyzed.The damping characteristics of the oil passing through the oil orifice are analyzed by the basic theory of fluid mechanics,and three different calculation methods for the flow coefficient of the damping orifice are solved.Combined with the twomass spring system of the shock absorber,the axial force composition and calculation model of the shock absorber are analyzed.Secondly,the flow characteristics of the internal flow field of the oleo-pneumatic shock absorber during the compression stroke are numerically simulated by means of two-phase flow numerical simulation.The effects of the initial nitrogen inflation pressure,the length of the oil orifice and the diameter of the oil orifice on the damping characteristics of the shock absorber are investigated.In particular,the numerical simulations were carried out using the dynamic mesh technique to simulate more realistically the boundary motion of the piston rod compression oil.To ensure that the dynamic mesh moves properly in the complex region,an unstructured mesh is used globally.In order to better capture the interface between the two phases,the CLSVOF method is used for the phase interface definition.Validation of the numerical simulation results by engineering estimation of the oil damping forces reveals that they are relatively close,with an maximum error of around 8%.Finally,a variable damping shock absorber model with variable section oil needles is built.The working principle is analyzed,and the oil damping force model of the variable damping shock absorber and the calculation model of the flow rate and flow coefficient when the oil needle is eccentric are determined.According to the two-phase flow numerical simulation method proposed in this paper,the oil flow characteristics and damping characteristics of variable damping shock absorber during compression are studied.Unlike the constant oil orifice shock absorber,the variable damping shock absorber with oil needle slowly increases the oil damping force during compression.Then,the models of different oil needle eccentricity values were numerically simulated and calculated,and through the analysis and calculation results,it was found that the eccentric value of the oil needle had a greater influence on the damping characteristics of the shock absorber. |
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