Indirectly Measuring the Thrust of Air Jets via Momentum-Flow-Rate Estimation

Experiments were conducted to determine if velocity and temperature measurements in subsonic, model-scale air jets could provide accurate estimates of the thrust they produced. Three different nozzles were used: one round and two different 10-lobed nozzles. All had approximately the same exit area. The thrust was directly measured using a thrust stand. Corresponding velocity and temperature measurements (obtained using particle-image velocimetry and thermocouple probe surveys) were used to estimate the momentum carried by the jet, which was then related to its thrust via the integral form of the conservation of momentum. The thrust estimated via flow measurements was relatively accurate for round nozzles, but less so for lobed nozzles. Potential explanations for this observation are provided.