Matching Items (3)
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- All Subjects: Aerospace Engineering
- Genre: Masters Thesis
- Creators: Dahm, Werner J.A.
Description
Reynolds-averaged Navier-Stokes (RANS) simulation is the industry standard for computing practical turbulent flows -- since large eddy simulation (LES) and direct numerical simulation (DNS) require comparatively massive computational power to simulate even relatively simple flows. RANS, like LES, requires that a user specify a “closure model” for the underlying turbulence physics. However, despite more than 60 years of research into turbulence modeling, current models remain largely unable to accurately predict key aspects of the complex turbulent flows frequently encountered in practical engineering applications. Recently a new approach, termed “autonomic closure”, has been developed for LES that avoids the need to specify any prescribed turbulence model. Autonomic closure is a fully-adaptive, self-optimizing approach to the closure problem, in which the simulation itself determines the optimal local, instantaneous relation between any unclosed term and the simulation variables via solution of a nonlinear, nonparametric system identification problem. In principle, it should be possible to extend autonomic closure from LES to RANS simulations, and this thesis is the initial exploration of such an extension. A RANS implementation of autonomic closure would have far-reaching impacts on the ability to simulate practical engineering applications that involve turbulent flows. This thesis has developed the formal connection between autonomic closure for LES and its counterpart for RANS simulations, and provides a priori results from FLUENT simulations of the turbulent flow over a backward-facing step to evaluate the performance of an initial implementation of autonomic closure for RANS. Key aspects of these results lay the groundwork on which future efforts to extend autonomic closure to RANS simulations can be based.
ContributorsAhlf, Rick (Author) / Dahm, Werner J.A. (Thesis advisor) / Wells, Valana (Committee member) / Huang, Huei-Ping (Committee member) / Arizona State University (Publisher)
Created2017
Description
The Vortex-lattice method has been utilized throughout history to both design and analyze the aerodynamic performance characteristics of flight vehicles. There are numerous different programs utilizing this method, each of which has its own set of assumptions and performance limitations. This thesis highlights VORLAX, one such solver, and details its historic and modernized performance characteristics through a series of code improvements and optimizations. With VORLAX, rapid synthesis and verification of aircraft performance data related to wing pressure distributions, stability and control, and Federal Regulation compliance can be quickly and accurately obtained. As such, VORLAX represents a class of efficient yet largely forgotten computational techniques that allow users to explore numerous design solutions in a fraction of the time that would be needed to use more complex, full-fledged engineering tools. In the age of modern computers, one hypothesis is that VORLAX and similar “lean” computational fluid dynamics (CFD) solvers have preferential performance characteristics relative to expensive, volume grid CFD suites, such as ANSYS Fluent. By utilizing these types of programs, tasks such as pre- and post-processing become trivially simple with basic scripting languages such as Visual Basic for Applications or Python. Thus, lean engineering programs and methodologies deserve their place in modern engineering, despite their wrongfully decreasing prevalence.
ContributorsSouders, Tyler Jeffery (Author) / Takahashi, Timothy T. (Thesis advisor) / Herrmann, Marcus (Thesis advisor) / Dahm, Werner J.A. (Committee member) / Arizona State University (Publisher)
Created2021
Description
This work uses Arizona State University’s (ASU) newly developed high-speed vehicle stability and control screening methodologies to reverse-engineer famous United States Air Force (USAF) flight tests from the 1950s and 1960s. This thesis analyzes the root cause of Chuck Yeager's fateful 1953 supersonic spin in the Bell X-1A to become the "Fastest Man Alive". This thesis then takes a look back at Neil Armstrong's inadvertent atmospheric skip in the North American X-15 and his subsequent hypersonic flight months later. The fundamental flying qualities assessment shown in this work begins with calculating rigid-body frequencies and damping ratios of an aircraft to Military Standard (MIL) requirements, and uses these to create a full, classical stability and control analysis of a high-speed vehicle. Through reverse engineering the flight envelopes and missions for the above aircraft, it appears that the near-disasters of each flight were due to a confluence of then overlooked, yet fundamental, aerodynamic instabilities.
ContributorsLorenzo, Will (Author) / Takahashi, Timothy T (Thesis advisor) / Dahm, Werner J.A. (Committee member) / Grandhi, Ramana V (Committee member) / Arizona State University (Publisher)
Created2023