Shane B. Coogan

Validation and Rules-of-Thumb for Computational Predictions of Liquid Slosh Dynamics

During flight, the sloshing of liquid propellant onboard the vehicle can have significant effects on vehicle stability due to the large amount of propellant mass. Because of the stability effect, propellant sloshing is included in the guidance, navigation and control (GNC) analysis to account for the dynamics of the propellant sloshing motion. Typically, the sloshing propellant is simplified either as a mechanical system in the form of a swinging pendulum or as a spring-mass system. In either case, the important parameters governing the dynamics of the system are the mass, natural frequency, and damping ratio. The sloshing parameters of frequency and damping of the slosh system are dependent on the type of propellant, tank geometry, and the liquid level in the tank. The parameters are typically derived from the large amount of experimental data currently available for conventional tank shapes. Unconventional tank shapes, however, require either experimental or computational work to develop new sloshing parameters. Because of the cost of experimental slosh testing, it may be preferred to use computational fluid dynamics (CFD) solvers to predict sloshing dynamics. While previous studies have shown the applicability of CFD to predict sloshing parameters, a consistent methodology to conduct sloshing simulations has not yet been reported. Specifically, there is currently no guidance in the literature for selecting the necessary physics in the simulation, nor is there a suggestion for a starting point of the computational grid resolution. In this paper, the CFD solver FLOW-3D is used to simulate propellant sloshing in oblate spheroidal and cylindrical tanks. The slosh frequency and damping factor predicted with the simulations are validated with experimental data for a range of propellant fill levels and with and without tank baffles. The required physics for sloshing simulations are discussed and rules-of-thumb are presented to provide a starting point for defining the computational grid resolution.

Case Study: Dynamic Analysis of a Novel Vertical Axis Wind Turbine

An analytical model was developed for the dynamic evaluation of a novel vertical axis wind energy system. This study was conducted early on in the design process, so the goal was to create a low level tool to determine if the concept was feasible, to perform initial sizing of the turbine, to better understand the behavior of the unique furling mechanisms, and to predict the performance. In order to prevent damage at high rotational speeds, the novel concept integrates passive mechanisms into a drag driven vertical axis wind turbine with the intention that blades furl out of the wind once a critical wind speed is reached, and passively reopen. Established wind turbine aeroelastic codes were unable to represent this unique system, therefore, a standalone analytical model was developed in Python. A Lagrangian approach was taken to represent the interactions of the system’s degrees of freedom. To complete the model, mathematical representations of the furling mechanisms and interaction of the wind on the blades was developed. Basic structural calculations were also included to determine the initial size of the primary mechanical components. This case study focuses on the development of the low-level dynamic model and shares several results of the expected behavior.Copyright

Design of a Small Scale Gas Turbine for a Hybrid Propulsion System

As part of the Great Horned Owl (GHO) program Southwest Research Institute© (SwRI©) has developed a small, lightweight gas-turbine generator to provide power for an electric or hybrid electric Unmanned Aerial Vehicle (UAV). This original design for a fuel-to-electricity component of a hybrid propulsion system was designed, built and tested at the SwRI facility in San Antonio, TX. The design is based on a patented SwRI gas-turbine configuration and went through five major design iterations leading to the final configuration. The design iterations of the gas generator were driven by aggressive targets for weight, size and performance that were part of program requirements. The design of the GHO machine evolved from the initial concept based on lessons learned from previous testing at SwRI and considerations to improve manufacturability and operability. Improvements to the design were also incorporated to meet performance goals and increase life of hot section parts.This machine is low-cost and simple to operate and in addition to the original design intent of fuel-to-electricity use in a hybrid propulsion system can be used as a technology demonstration platform. SwRI plans to use the GHO machine in projects such as instrumentation development, as a test bed for new technologies such as ceramic or additive manufactured parts and for use as a component in a hardware-in-the-loop system.Copyright

Design of a Micromix Fuel Injector for High Temperature Hybrid Concentrated Solar Power Plants

The hybrid air Brayton concentrated solar power plant (CSP) combines a natural gas fired combustor in series with a traditional CSP system. The combination boosts turbine inlet temperature above the receiver temperature and reduces output variability. However, a combustor operating in this mode must tolerate an inlet air temperature equal to the solar receiver outlet temperature, which is expected to be as much as 1,000°C for next generation designs. High inlet temperature hybrid combustors must achieve low NOx emissions in spite of the increased risk for autoignition and flashback. In addition, the hybrid injector must be able to adjust to the variability inherent to the solar source. The design of a multibank micromix injector that meets these challenges is described with emphasis on its NOx and CO emissions characteristics.Copyright