Comparing the Effect of Duct Inlet Length on the Hydrodynamic Performance and Open Water Efficiency of a Pre-Swirl PumpJet Propulsion System with Experimental Method and Uncertainty Analysis

This study investigates the effect of duct inlet length on the hydrodynamic performance of a pre-swirl pump-jet system, focusing on open water efficiency through uncertainty analysis.To this end, five models with varying duct inlet lengths (0~0.1DRotor) were experimentally tested in the cavitation tunnel at Imam Khomeini Naval University in Noshahr.Sampled parameters included rotor thrust, combined duct and stator thrust, and rotor torque at eight advance ratios (J).Each measurement was repeated four times, and their averaged values were utilized in the calculations.Sensitivity analysis revealed that torque has a more significant impact on open-water efficiency compared to total thrust.Experimental test results demonstrated that the open water efficiency for all configurations reached a maximum at J=1.1.The L=0.1DR configuration exhibited the highest efficiency at 62.15%, representing a 5.15% improvement over the L=0DR configuration.The relative uncertainty of efficiency was below 5%, and the L=0.1DR configuration showed the smallest uncertainty range, indicating high experimental precision.Furthermore, an examination of the open water efficiency uncertainty range revealed that for advance ratios of 0.6, 1.1, and 1.4, the L=0.1DR configuration yielded the widest efficiency range.The upper bound of open water efficiency also belonged to the L=0.1DR configuration for other advance ratios.Therefore, based on the results of the conducted uncertainty analysis, the L=0.1DR configuration demonstrates improved open water efficiency performance compared to other configurations.This improvement is attributed to increased thrust resulting from better uniformity of the flow entering the stator and optimized angle of attack to the rotor blades.