Final technical rept. June-Sep 78,
GENERAL ELECTRIC CO CINCINNATI OHIO AIRCRAFT ENGINE GROUP
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The variable cycle engines now being studied for preliminary engine-aircraft design have greatly increased the complexity of engine modeling, control element design, and cycle calculation relative to the simpler turbofan and turbojet engines which preceeded them. The production of engine data is the major computations cost element in mission studies and optimization investigations this problem can become even more severe in the future unless improvements in cycle calculations and component modeling techniques are developed and introduced now. The current method of obtaining balanced cycle data points is to use the simultaneous Newton-Raphson iteration method. The partial derivatives are obtained by numerical differentiation. This report documents the results obtained by calculating the partial drivatives from analytical expressions obtained by differentiating a cycle deck. Examples illustrating both the method of obtaining the analytical derivatives as well as setting up the control logic are given. A cost comparison was carried out between two engine simulations using numerical derivatives and the same pair of engine simulations using analytical derivatives. A data matrix consisting of the same 411 operating points was used for each of the engine simulation comparisons.
- Jet and Gas Turbine Engines