Onto Quantifying Unsteady Propulsion Characteristics Using Momentum and Energy Control Volume Assessments

Abstract

This effort presents a novel approach to interrogate efficiency for unsteady, undulating propulsion using variable momentum and energy conservation (VMEC) assessments. These integral approaches utilize large amounts of data from computational fluid dynamics (CFD) to address present difficulties associated with separating thrust from drag associated with propelling bodies as well as potentially resolve issues associated with defining a nonzero efficiency for a body in self-propulsion. Such a fundamental issue is addressed through strategic control volume assessments of the momentum and energy conservation equations. In this work, the Method of Manufactured Solutions (MMS) is used to verify the integral-based evaluation approach and better quantify output. The MMS results indicate the method is valid and that one can separate work associated with lift and drag from the energy budget. This separation procedure provides a means to separate propulsive and drag forces. The effort then studies previously validated CFD simulations of heaving and pitching foils to provide insight associated with separating axial forces into their thrust and drag components for highly complex systems. The effort then presents a new efficiency metric that can obtain nonzero efficiencies in self-propulsion. Overall, the results indicate that energy-based assessments provide insight that is a step forward toward isolating loss from propulsive mechanisms and developing proper metrics of efficiency.