An experimental study validating the conditions necessary to prevent the formation and ingestion of aero-inlet vortices

Abstract

The race to create aircraft engines that push the boundaries of efficiency leads to the creation of engines that are not only larger in size, but have lower ground clearances as well. Under certain flow conditions, a surface to inlet vortex may form. These vortices could potentially damage the engine through increased instability, wear and even compressor stall. However, the most damaging effect is the ingestion of foreign objects that are lifted by these vortices.

These vortices form only under certain conditions. Studies conducted in the past have revealed the existence of three vortex regions separated by two threshold lines. In order to verify the results obtained through running computational fluid dynamic (CFD) simulations, a physical experimental set up has been designed. A scaled model nacelle was placed in a water tunnel, with the ability to vary the parameters such as ground clearance and velocity ratio. Results obtained through video recordings have been processed, analyzed and a plot of Vi/Vo against H/D yielded a graph of three distinct vortex formation regions; no vortex, unsteady vortex and steady vortex.

The experimental results for the headwind configuration showed that at lower Reynolds number, the vortex threshold line was lowered, thereby supporting the trend proposed by Ho and Jermy, where the Reynolds number affects the vortex formation threshold. The experiment gave further insight into the vortex formation mechanism, where the direction of spin of a vortex formed could be due the location of the vortex with respect to the engine inlet.