A NUMERICAL STUDY OF SAND SEPARATION APPLICABLE TO ENGINE INLET PARTICLE SEPARATOR SYSTEMS

Past experiences with helicopter operation in severe sand environments have demonstrated the need for substantial Inlet Particle Separator (IPS) system improvements. Sand ingestion causes severe performance degradation, excessive wear, increased maintenance and eventually premature failure of the engines. In order to extend the life of helicopter engines in severe sand environments, new and innovative IPS system concepts and technologies must be explored. To identify ways to improve current engine separator technologies a numerical study was conducted to investigate the viscous flow of air, laden with sand particles, in typical engine inlet geometries. In this study, the three-dimensional Navier-Stokes equations for air and the conservation equations in the Lagrangian framework for the sand particles were solved simultaneously. Several inlet geometries were analyzed and particle paths, scavenge efficiencies, and the resulting pressure drops under identical conditions for different geometries and sand particle sizes were compared. In solving the particle conservation equations in the Lagrangian framework, the particle rebound angles after each collision with the engine inlet walls were calculated based on the existing polynomials that were developed for typical inlet wall materials. Therefore, this study combines the most recent advances in viscous flow solutions with realistic rebound angles based on experimental data to shed some light on this very important issue in helicopter engine design. Major conclusions of this study were: a) Extremely fine sand particles (below 10 microns in diameter) follow the air path and thus proved to be especially problematic and b) Optimization of the inlet path geometry and manipulation of particle paths can improve scavenge efficiencies for larger size sand particles. This improvement, however, is often at the expense of higher overall engine inlet pressure drops.