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German, Brian J.

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Author: German, Brian J. × Start date: 2000 × End date: 2009 ×

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    A Riemannian Geometric Mapping Technique for Identifying Incompressible Equivalents to Subsonic Potential Flows
    (Georgia Institute of Technology, 2007-04-05) German, Brian J.
    This dissertation presents a technique for the solution of incompressible equivalents to planar steady subsonic potential flows. Riemannian geometric formalism is used to develop a gauge transformation of the length measure followed by a curvilinear coordinate transformation to map a subsonic flow into a canonical Laplacian flow with the same boundary conditions. The method represents the generalization of the methods of Prandtl-Glauert and Karman-Tsien and gives exact results in the sense that the inverse mapping produces the subsonic full potential solution over the original airfoil, up to numerical accuracy. The motivation for this research was provided by the analogy between linear potential flow and the special theory of relativity that emerges from the invariance of the wave equation under Lorentz transformations. Whereas elements of the special theory can be invoked for linear and global compressibility effects, the question posed in this work is whether other techniques from relativity theory could be used for effects that are nonlinear and local. This line of thought leads to a transformation leveraging Riemannian geometric methods common to the general theory of relativity. The dissertation presents the theory and a numerical method for practical solutions of equivalent incompressible flows over arbitrary profiles. The numerical method employs an iterative approach involving the solution of the incompressible flow with a panel method and the solution of the coordinate mapping to the canonical flow with a finite difference approach. This method is demonstrated for flow over a circular cylinder and over a NACA 0012 profile. Results are validated with subcritical full potential test cases available in the literature. Two areas of applicability of the method have been identified. The first is airfoil inverse design leveraging incompressible flow knowledge and empirical data for the potential field effects on boundary layer transition and separation. The second is aerodynamic testing using distorted models.
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    An Evaluation of Green Propellants for an ICBM Post Boost Propulsion System
    (Georgia Institute of Technology, 2000-11) German, Brian J. ; Branscome, Ewell Caleb ; Frits, Andrew P. ; Yiakas, Nicholas C. ; Mavris, Dimitri N.
    Propellant toxicity is a major concern in storing, maintaining, and transporting strategic missiles. Many low toxicity green propellants have been developed which hold the potential of increasing the safety and lowering the operation and support costs of liquid-fuelled strategic missile propulsion systems. This study evaluates several green propellants for use in a notional next-generation post-boost propulsion system (PBPS). The mission and physical dimensions for this PBPS were defined by the requirements of the current Minuteman III propulsion system rocket engine (PSRE). Possible propellants were initially screened in terms of toxicity, performance, and technical feasibility for the PBPS application with a multi-attribute ranking method based on an overall evaluation criterion (OEC). Promising propellants were identified, and candidate PBPS concepts were developed and sized for each of these propellants. These concepts were evaluated in terms of weight, cost, and technical risk to determine which concepts, and hence propellants, show the most promise for the application. Probabilistic techniques were employed to explore the effects of uncertainty in the propellant performance and structural weight estimates. The results indicate that high-test peroxide (HTP) combined with either an ethanol-based nontoxic hypergolic miscible fuel (NHMF) or competitive impulse non-carcinogenic hypergol (CINCH) is a very viable propellant solution.