Large Eddy Simulation of Ducted Propulsors in Crashback

Flow around Propeller 4381 with duct is computed with the large eddy simulation methodology during crashback condition. A non-dissipative robust numerical algorithm developed by Mahesh et al. (2004) for unstructured grids is used. The ducted propeller without stator blades is solved in a rotating frame of reference. The flow is computed up to about 86 revolutions at the advance ratio J=-0.7 and Re=480,000 based on the propeller diameter. These preliminary results are discussed. The simulation shows that the evolutions of the thrust and torque are highly unsteady and have low frequency fluctuations. The computed mean values of the unsteady load are more negative as compared to the experimental results. Absence of the stator blades is thought to be responsible. The unsteady loads on the duct are also measured. Even though the effect of the duct on KT and KQ are not very large, that on the side force is significant. The effect of viscous force on the total unsteady loads is considered and the results indicate that the pressure load is dominant. The computed circumferential average of mean and RMS of velocity are compared to experimental results. Pressure distributions on blade surfaces and duct surface are also discussed.