The nonlinear harmonic method (NLH) and its extension to the modeling of the clocking effects can simulate the unsteady flows in multistage machines at drastically reduced CPU costs.
The blade row interactions that are reproduced are those between adjacent rotors and stators and also between successive rotors or successive stators. At an additional level of complexity, it appears that in stator1 / rotor / stator2 configurations the amplitude of the perturbation associated with a blade passing frequency (BPF) in a row is not only created by the adjacent row but is also modified in space by the interaction of the periodic disturbances coming from the other two rows. For instance, the spatial modes of the periodic disturbance in stator2 are provoked not only by the interaction with the adjacent rotor but also by an additional interaction with the periodic flow coming from stator1.
The present paper introduces a method that enables the identification of these modes for a general configuration row1 / row2 / row3. Any row can be a stator or a rotor and the time-varying disturbances are not only produced by the interaction with the adjacent row but also with the other rows. In particular, this is validated and illustrated for the calculation of the unsteady effects provoked in contra-rotating open rotors (CROR) by the engine pylon. Results are also shown for stator/rotor/stator configurations that shows the effects of clocking on the time harmonics.