For future helicopter turbine engines, Turbomeca is working on compressors with increased overall pressure ratio based on centrifugal compressors with variable geometries. Increasing the overall pressure ratio helps cut specific fuel consumption (SFC). In turn, centrifugal compressors allow high pressure ratio without impacting weight or compactness. Variable geometries should help maintain a flat SFC curve.
In a presentation made at the European Rotorcraft Forum 2010 in Paris, Turbomeca research chief engineer Eric Seinturier insisted recent progress in simulation is enabling such advancements. This is all the more important as, when the pressure ratio increases, compressor efficiency becomes more sensitive to “local effects” such as leakages, surface quality defects, blade tip gaps, etc. Moreover, operability becomes an issue, with a greater risk of surge. Unsteady behavior can cause high-cycle fatigue. Hence the need for solid compressor aerodynamic simulation. A typical compressor steady simulation takes 10 hours to process. For unsteady simulation, this order of magnitude is ten times higher. Seinturier hinted that alternative numerical approaches are under development.
What’s at stake in turbines is predicting temperature. Increasing turbine inlet temperature allows to reduce the air flow needed for a given power. Therefore, the size of the compressor is minimized. Seinturier pointed out that temperature simulation should be very precise, since a 20-degree Celsius error on a component’s temperature can cut its life in half. (From December 2010 Rotorcraft Report)