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.

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