Intake Ground Vortex Prediction Methods

Abstract

For an aircraft turbofan engine in ground operations or during the takeoff run, a ground vortex can occur that is ingested and could adversely affect the engine performance and operation. The vortex characteristics depend on the ground clearance, the intake flow capture ratio, and the relative wind vector. It is a complex flow for which there is currently very little appropriate quantitative preliminary design information. These aspects are addressed in this work, where a range of models are developed to provide a method for estimating the key metrics, such as the formation boundary and the ground vortex size and strength. Three techniques are presented that use empirical, analytical, and semiempirical approaches. The empirical methods are primarily based on a large data set of modelscale experiments that quantitatively measure the ground vortex characteristics for a wide range of configurations. These include the effects of intake ground clearance, approaching boundary-layer thickness, intake Mach number, and capture velocity ratio. Overall, the models are able to predict some of the key measured behaviors, such as the velocity ratio for maximum vortex strength. With increasing empiricism for key subelements of the model construction, an increasing level of agreement is found with the experimental results. Overall, the three techniques provide a relatively quick and easymethod in establishing the important vortex characteristics for a given headwind configuration, which is of significant use from a practical engineering perspective.