Evaluating Propulsor Mechanical Flow Power in Powered Aircraft Wind Tunnel Experiments

This paper describes a methodology for evaluating propulsor mechanical flow power on a 1:11 scale, electrically powered, wind tunnel model of a boundary layer ingesting (BLI) aircraft. The use of a full aircraft aerodynamic configuration precluded direct in-situ measurements of the mechanical flow power, a key metric for BLI aircraft performance. The measured electrical power thus had to be converted to flow power through two sets of supporting experiments. The first set of experiments were flow power measurements with the propulsor in a small wind tunnel which replicates the incoming flow conditions of the powered wind tunnel test. The second set were motor calibration experiments that allowed the motor losses and aerodynamic inefficiencies to be determined separately, giving insight into the motor and the aerodynamic operating point of the propulsor. Using this combined approach, the measurements of electrical power were converted to mechanical flow power with an experimental uncertainty of less than 1%.