Inertial Particle Separator Multiphase Dynamics

The effects of sand and dust ingestion often limit the useful life of turbine engines operating in austere environments and efforts are needed to reduce the quantity of particulate entering the engine. Several Engine Air Particle Separation (EAPS) systems exist. In particular, Inertial Particle Separators (IPS) are of interest because they offer significant weight savings and are more compact. However, they do not yet provide separation efficiencies as high as that from barrier filter and vortex-tube separator technologies. In order to further improve the efficiency of IPS systems, an in depth study of the multiphase flow dynamics has been undertaken.

An experimental approach was chosen to fill the void of available data and provide useful information for model validation. A wind tunnel has been designed, constructed and tested to study the multiphase flow dynamics of an inertial particle separator. The experimental facility includes a rectangular test-section ideal for optical access, and is capable of reproducing full-scale flow and particle conditions seen in separator systems. Separation efficiencies were measured for A4 Coarse Test Dust over a range of operating conditions for several geometries. Results show that the separation efficiency is dependent on the scavenge flow split and strongly dependent on the outer surface geometry. Further separation efficiency tests where conducted using nominally sized 10um, 35um, and 120um glass spheres to eliminate the complexities of dust size, shape, and density that are present in Arizona Test Dust. A model was then created to determine the separation efficiency for particles of any given size.

Several flow visualization techniques were performed to determine the fluid and particle dynamics. Oil-streak flow visualization was utilized to characterize the flow along the walls of the IPS to determine the location of the recirculation zone and to verify that sidewall effects were minimal. Particle Image Velocimetry (PIV) was utilized to quantify the fluid flow field using small olive oil tracer particles. PIV was further utilized using 10um and 35um glass-spheres to determine the particle velocities in the IPS. Finally, high-speed video was used to capture the dynamics of the particle-fluid interactions. These experiments have shown the dynamic instabilities present in an IPS system that lead to lower separation efficiencies compared with other EAPS systems. The identification of these instabilities will help to improve future IPS designs. Also, the data collected during the course of this study provides the first reference of comparison for computational modeling of an IPS.