CFD simulation of the unsteady performance of contra-rotating propellers

As part of a series study on the CFD modeling of contra-rotating propeller performances, a simulation method for the unsteady interaction between forward and aft propellers is presented in this paper by using the sliding mesh model. Numerical simulations are carried out for two sets of CRPs with different combinations of blade numbers and operating in open -water condition. The time-averages of predicted unsteady thrust and torque are compared with their experimental counterparts. The effect of unsteadiness in forward-aft blade interaction is investigated through comparison of results obtained from the quasi-steady multiple reference frame and unsteady sliding mesh models. It is found that the unsteady model yields more accurate time-averages and fluctuation amplitudes in both thrust and torque because it takes into account the impingement of the forward propeller's trailing vortex on the aft propeller.