The Tethys autonomous underwater vehicle (AUV) is a 110 kg vehicle designed for longrange, high-endurance operations. Performance goals include supporting a payload power draw of 8 W for a range of 1000 km at 1 m/s, and a power draw of 1 W for 4000 km at 0.5 m/s. Achieving this performance requires minimizing drag and maximizing propulsion efficiency. In this paper, we present the design of the propulsion system, explore the issues of propeller-hull interactions, and present preliminary test results of power consumption and efficiency. In recent underwater experiments, the propulsion system's power consumptions were measured in both Bollard pull tests and during the vehicle's flights. Preliminary results of power consumptions and efficiency are shown to be close to the theoretical predictions.
CFD methods have been employed to solve a number of efficiency, safety and operational problems related to the aerodynamics of rail cars and locomotives. This paper reviews three case studies: 1) numerical models were employed to quantify the drag characteristics of two external railcar features; namely, well car side-posts and inter-platform gaps. The effects of various design modifications on train resistance and fuel usage were evaluated. 2) An operational safety issue facing railroad operators is wind-induced tip-over. A study was completed using CFD and wind tunnel tests to develop a database of tip-over tendencies for a variety of car types within the Norfolk Southern fleet. The use of this database in the development of a speed restricting system for the Sandusky Bay Bridge is also discussed. 3) Another safety issue involves the behavior of diesel exhaust plumes in the vicinity of locomotive cabs. Numerical simulations were performed for a variety of locomotives operating under a number of ambient conditions (wind speed, wind direction). The concentration of diesel exhaust at the operator cab window was quantified. Where appropriate, the studies provide information on the correlation of the CFD results with previously collected wind tunnel and field data.
A numerical procedure has been developed for the design of duct elbows that exhibit minimum pressure loss. A two-dimensional potential flow modeling method is used to determine the ideal static pressure distribution for a given elbow geometry. A turbulent boundary layer separation criterion is then used to determine whether the ideal distribution can be obtained. Those elbow designs for which flow does not separate are shown to produce minimum pressure loss. The procedure is also shown to be effective in the design of turning vanes. The design method is confirmed by experiments with a 90 degree elbow within a square duct.
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