INTERACTION BETWEEN 2 CLOSELY SPACED AZIMUTHING THRUSTERS

To assist in predicting the performance of omni-directional propelled vehicles a series of experiments has been conducted to measure the int eraction between two closely spaced ducted azimuthing thrusters. The t hrusters were tested below a shallow draft ground board in a towing ta nk at a spacing of approximately 2 propeller diameters. Measurements w ere made of forces acting on a single thruster for a range of operatin g conditions and similarly on two thrusters for a range of relative po sitions. The results show that forces from the trailing thruster are h eavily affected by interaction, particularly due to impingement of the race from the leading thruster, whereas forces from the leading thrus ter remain essentially unaffected despite its proximity to the trailin g thruster. A semi-empirical mathematical model suitable far simulatio n of omni-directional vehicle dynamics is presented. The model is base d on the trajectory of the race from the leading thruster derived from momentum considerations with additional empirical relations to accoun t for other more minor flow effects. Comparison of the predicted and m easured results show satisfactory agreement.