NH90 Main Gear Box fan oil cooling system.

 

The components to be analyzed are part of the oil cooling system used on the Main Gear Box of NH90 helicopter. Finite element analysis interested the fan body, the outlet flange and the fan wheel. The most severe environmental conditions that affect structural design are represented by forced response due to sinusoidal and random excitation. Operating loads experienced during a design life of 10000 hours are condensed into a series of tests, as for example, vibration endurance tests performed separately along each principal axis.

By using power spectral density functions and Rayleigh distribution for random vibrations, damping factors and natural frequencies of the component as well as amplitudes and frequencies of sinusoidal forcing functions, a load spectrum can be determined. The following step is to evaluate unit stresses at critical locations,  and apply the load spectrum in order to obtain  a stress spectrum in form of mean and alternating stress components. Finally, for each critical location the Cumulative Damage and Fatigue Life are evaluated through  Miner's approach.

Fan wheel and shaft are also designed in such a way that its critical speeds are far enough from the nominal rotational speed of the fan.