Water ingestion up to the saturation point reduces the compressor inlet temp. to near 'wet bulb' temp. The droplets then evaporate within the blade path, the adiabatic process causing the temp. to drop further. Since it takes less energy to compress cooler air, compressor work is saved. This translates to less load on the turbine, so the N1 increases.
This 'wet compression' process is used in some power stations to increase the efficiency of the combustion turbines.
Water ingestion beyond the saturation point (very heavy rain) results in water entering and evaporating in the N2 compressor and combustion sections. This results in reduction of the cycle temp. of the engine, reducing the work available to drive the N1 fan. Consequently, N1 decreases in this condition.
Last edited by Re-entry; 20th Mar 2007 at 08:17.