For the modeling of high speed propulsion systems, there are at least two major categories of models, with several subdivisions in each category. One major category is characterized by computational fluid dynamics (CFD) and is highly accurate. CFD models can have millions of states, give a very complete view of the internal flow field, and run much slower than real-time on most computers. The other major category of models is used by control engineers for design and analysis of control systems. These models typically have on the order of ten to one hundred states, run near real-time, and capture the fundamental dynamics required for controller design. To provide improved control models particularly for these high speed systems, methods are needed that use the CFD techniques but yield models that are appropriate for both control analysis and design. The goal of this paper is to present/discuss some of the tools being developed to create an interdisciplinary technology bridge between the CFD and control disciplines.
The NASA Lewis Research Center (LeRC) and the Arnold Engineering Development Center (AEDC) have developed a closely coupled computer simulation system that provides a one dimensional, high frequency inlet / engine numerical simulation for aircraft propulsion systems. The simulation system, operating under the LeRC-developed Application Portable Parallel Library (APPL), closely coupled a supersonic inlet with a gas turbine engine. The supersonic inlet was modeled using the Large Perturbation Inlet (LAPIN) computer code, and the gas turbine engine was modeled using the Aerodynamic Turbine Engine Code (ATEC). Both LAPIN and ATEC provide a one dimensional, compressible, time dependent flow solution by solving the one dimensional Euler equations for the conservation of mass, momentum, and energy. Source terms are used to model features such as bleed flows, turbomachinery component characteristics, and inlet subsonic spillage while unstarted. High frequency events, such as compressor surge and inlet unstart, can be simulated with a high degree of fidelity. The simulation system was exercised using a supersonic inlet with sixty percent of the supersonic area contraction occurring internally, and a GE J85-13 turbojet engine.
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