Non-Intrusive Ground Force Decomposition Applied to Turbofans—Part II: Filtered Rayleigh Scattering Application

Abstract This study applies an innovative control volume analysis method combined with filtered Rayleigh scattering (FRS) to perform force measurements in the exhaust flow of a Honeywell TFE731-2 turbofan engine at Virginia Tech’s TurboLab. A particle swarm optimization technique was employed to locate the best fit between the modeled and measured FRS spectra, resulting in a total force measurement of 8995.56 N with a 0.13% deviation from the force balance measurement of 9007 N. To separate the core and bypass flow streams, the Townsend approximation was applied to identify the dividing streamline as the location of the peak shear stress within the mixing layer. A turbulent shear stress mixing length model was used to approximate the maximum shear stress location at the peak of the squared axial velocity gradient. This approach resulted in a core force of 4085.22 N and a bypass force of 4910.34 N. The bypass ratio was experimentally determined to be 2.53, with an error of 2.3% compared to the manufacturer’s value of 2.60. Uncertainty quantification, which incorporates random, bias, and control volume sources, resulted in uncertainties of approximately 0.25% for total force, 11% for core force, and 9% for bypass force, with higher uncertainties of the decomposed force attributed to boundary definition errors. In general, this work demonstrates the successful integration of FRS and control volume analysis for accurate force decomposition in complex exhaust environments and laid the ground work for in-flight measurement development.