In the preliminary conceptional design phase of any new gas turbine project the design and off-design performance of many alternative configurations and cycles must be studied. The simulation results for the off-design cases depend very much on the component maps employed in the model. Especially important are the compressor maps, and when the pre-design study covers a wide range in pressure ratio, then the use of a consistent set of maps is essential for high quality simulation results. A statistical analysis of many compressor maps — taken from open literature and from the MTU in house data bank — was performed. In each map a reference point was defined which was employed to normalize it. Then, the topology of the normalized map was captured with three characteristic numbers that describe 1) the region where efficiency is highest, 2) the mass flow – speed relationship and 3) the shape of the speed lines. The characteristic numbers show in the statistic evaluation clear trends with reference pressure ratio. From these trends a new map scaling procedure was derived which describes the systematic change of the compressor map topology with design pressure ratio much better than the conventional map scaling method, which applies constant factors on pressure ratio or on specific work.

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 in gas turbine performance calculations are discussed. The basic methodologies based on Mach number similarity are summarized briefly including some second order effects. Under extreme engine partload conditions, as for example subidle or windmilling, the operating points in the compressor map are located in a region which is usually not 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 low bypass ratio turbofans is covered. Due to the flow splitter downstream of such a fan the core and bypass stream 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 which accounts for the effects of bypass ratio.

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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 in gas turbine performance calculations are discussed. The basic methodologies based on Mach number similarity are summarized briefly including some second order effects. Under extreme enginepartload conditions, as for example subidle or windmilling, the operating points in the compressor map are located in a region which is usually not 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 low bypass ratio turbofans is covered. Due to the flow splitter downstream of such a fan the core and bypass stream 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 which accounts for the effects of bypass ratio.