Spatial-temporal and modal analysis of propeller induced ground vortices by particle image velocimetry

Abstract

During the ground operation of aircraft, there is potentially a system of vortices generated from the ground toward the propulsor, commonly denoted as ground vortices. Although extensive research has been conducted on ground vortices induced by turbofans which were simplified by suction tubes, these studies cannot well capture the properties of ground vortices induced by propellers, e.g. the flow phenomena due to intermittent characteristics of blade passing and the presence of slipstream of the propeller. Therefore, the investigation of ground vortices induced by a propeller is performed to improve understanding to these phenomena. The distributions of velocities in two different planes containing the vortices were measured by high frequency Particle Image Velocimetry (PIV). These planes are a wall-parallel plane in close proximity to the ground and a wall-normal plane upstream of the propeller. The instantaneous flow fields feature highly unsteady flow in both of these two planes. The spectral analysis is conducted in these two flow fields and the energetic frequencies are quantified. The flow fields are further evaluated by applying the Proper Orthogonal Decomposition (POD) analysis to capture the coherent flow structures. Consistent flow structures with strong contributions to the turbulent kinetic energy are noticed in the two planes.