Second-Law Methods for the Analysis & Design of Hypersonic Vehicles

Recent efforts to use the second law of thermodynamics to develop entropy-based or exergy-based approaches for multidisciplinary analysis of flight vehicles have introduced the possibility of defining a true "common currency" for vehicle performance that is valid for virtually any subsystem or physical mechanism. Using these concepts, a new performance auditing methodology for flight vehicles based on the laws of thermodynamics has been developed. This includes the theoretical development of performance auditing methodologies based on vehicle-based exergy loss (which is different from exergy losses in stationary systems), and an implementation of these methodologies using a multidisciplinary analysis and optimization system. The exergy concepts are applied to the external aerodynamics, propulsion system, and thermal heating of a hypersonic vehicle for performance auditing throughout a flight trajectory. Important relationships between minimum fuel and minimum loss trajectories have been developed, and it has been shown in an application that the minimum fuel and minimum loss trajectories are essentially identical for a class of point-to-point missions. The techniques and software developed in this project provide a unique framework for understanding vehicle performance and the relative magnitudes of various loss mechanisms, which is expected to lead to better understanding of how to improve overall vehicle performance. The second-law techniques have been implemented into an existing multidisciplinary analysis and optimization system for hypersonic vehicles: the Integrated Hypersonic Aeromechanics Tool (IHAT). New capabilities have been added to the IHAT system to allow calculation of second-law loss metrics (e.g., exergy loss rates) for different subsystems and due to different physical mechanisms. The techniques have been applied to the aerodynamic, propulsion, and thermal heating subsystems of a generic waverider vehicle. Over a typical mission, the total exergy loss due to different physical mechanisms and components of the aerodynamic, propulsion, and thermal heating systems are calculated. Critical variables for total exergy loss of a hypersonic waverider vehicle are identified through parametric studies. These variables are then optimized for minimum total exergy loss for given flight conditions.