Discharge coefficient calculation method of landing gear shock absorber and its influence on drop dynamics

Oleo-damping performance is a key factor affecting the landing gear buffer performance, while the flow discharge coefficient determines buffer damping force. For improving the calculation precision of discharge coefficient estimation method in aircraft design manual, a model for discharge coefficient is established based on pipeline fluid mechanics and damping orifice structure, and a numerical calculation is performed. Computational fluid dynamics (CFD) analysis is also conducted for damping orifice structure using the commercial software FLUNET. The simulation result of damping orifice discharge coefficient correlates well with the theoretical result. On this basis, landing gear drop dynamic response are calculated with the numerical analysis method using obtained discharge coefficient and compared with experimental results. Furthermore, the influences of current discharge coefficient estimation method and simulation method are analyzed and compared on the hydraulic force and the ground reaction force. The study demonstrates that the poor precision of discharge coefficient estimation method in aircraft design manual leads to more than 30 % differences between the drop dynamic estimation results and the experimental results. The method of CFD simulation or theoretical analysis can improve the calculation precision of discharge coefficient by about 17 %.