Some aspects of modeling compressor behavior in gas turbine performance calculations

Performance calculation procedures for gas turbine engines are usually based on the performance characteristics of the engine components, and especially the turbo components are of major interest. In this paper methods of modelling compressors irt gas turbine performance calculations ai-e discussed. The basic methodologies based on Mach number similarity are summarized briefly including some second order effects. Under extreme engine partload conditions, as So, example subidle or windmilling, the operating points irt the compressor map are located in a region which is usually ii at covered by rig tests. In addition the parameters usually used in compressor maps are no longer appropriate. For these operating conditions a method is presented to extrapolate compressor maps towards very low spool speed down to the locked rotor. Instead of the efficiency more appropriate parameters as for example specific work or specific torque are suggested. A compressor map prepared with the proposed methods is presented and discussed. As another relevant topic the performance modelling of fans for lore bypass ratio turbofans is cover ed. Due to the flow splitter downstream of such a fan the core and bypass sri-sam may be throttled independently during engine operation and bypass ratio becomes a third independent parameter in the map. Because testing a fan on the rig for various bypass ratios is a very costly task, a simplified method has been developed Lc which accounts for the effects of bypass ratio.