Numerical Simulation on Rigid Foreign Object Exclusion in the Turboprop Engine Intake System With a Bypass Duct

Abstract

By considering the exclusion characteristics of foreign objects in a new intake system with a bypass duct for turboprop engines, two kinds of common rigid foreign objects, the grains, and metal pieces, are modeled based on airworthiness standards and reference reports. On the assumption that only a perfect elastic collision occurs without any structural damage to the objects or intake walls, a numerical method based on single high-fidelity computational fluid dynamics (CFD) and dynamic unstructured mesh techniques to simulate the 6DOF motion and impacts of the rigid foreign objects is presented. A practical used intake system with a bypass duct is employed to validate the method. According to the tolerance size of the intake, two spherical grains with the radius of 0.037 m and 0.0555 m and a regular hexahedron aluminum metal piece with the dimension of 0.20 m×0.11 m×0.01 m are built to test the exclusion ability of the intake and analyze their effects on the intake performance. The simulation results indicate that, in the cases of a symmetrical flow field, geometry, and initial states, all the rigid foreign objects will move in the intake without lateral motions. The spherical grains without an initial angular velocity only translate in the intake, and the small one finally enters into the bypass duct after four impacts, while the larger one flies into the inner part of the engine after six impacts. The larger grain can lead to a more apparent loss on the intake performance due to the greater shielding effect on the flow field, and the maximum decrements of the total pressure recovery coefficient and mass flow can reach to 2% and 4.1%, respectively; the total pressure distortion rate increases 116%. A coupled motion of translation and rotation occurs for the regular hexahedron aluminum piece, and after four impacts on the intake, it finally excludes to the outer space of the nacelles from the bypass duct. Compared to the spherical grains, the aluminum piece has more significant actions on the intake performance. The maximum losses of the total pressure recovery coefficient and mass flow can be 2.3% and 1.54%, respectively, while the distortion rate increases 518%. Although the numerical method in this study is simple and ideal, it can help researchers to obtain quick and effective evaluation results in the initial design stage of the new intake system with a bypass duct for the turboprop engine to improve the design efficiency and level.