Evaluation and Characterization of Fluid Dynamics in an Annular Flume
The overarching goal of this effort was to design a flow generation and flow straightening system in an annular flume to investigate whether this tank is a suitable testing facility to study sediment transport. The necessary flow field was generated by two 40 [lb.] thrust motors at incremental settings producing flow velocities from 15 [cm/s] to 35 [cm/s]. Flow straighteners then reduced turbulence and straightened the flow downstream for data collection. Three-dimensional velocity measurements were collected at various designated locations downstream using a 3D velocimeter. These readings were used to determine whether the flume was producing the necessary flow field needed to study sediment transport.
An analytic momentum balance was performed to size the flow generators for a range of desired flow conditions. The formulation included both friction due to wall and flow straighteners. This analytic model yielded a necessary maximum power output of 1/8 [HP] which correlates to an output thrust of 45 [Ibf] for a flow velocity of 55 [cm/s]. Numerical simulations of the flow field were conducted to evaluate the flow straightener performance and predict the optimum sampling location. These simulations indicated a 1.5 [in] diameter tube in a honeycomb array was the model that resulted in the least amount of frictional loss. Also it was found that at a 15° arc radius the flow straighteners performed the best at straightening the downstream flow.
Next, the flow generation and straightening system was constructed. 2 Minn Kota 40 [lb.] thrust motors were purchased from www.cabelas.com. These motors were mounted to the flume using supplies from the Chase Ocean Engineering building. Flow straighteners were constructed in a honeycomb style using rendered measurements taken from the analytic model. This tube array was then placed 45 degrees from the outboard motors. Proper measurements were taken into consideration if the flow straighteners had to be moved up or down stream.
Finally, the velocity field within flume was measured to evaluate the flume performance and hydrodynamic sampling regime. A mounting system was constructed using supplies from the Chase Ocean Engineering building. An angle iron was bolted to the mounting system and fitted with 2 parallel horizontal slots to allow for translation from inner flume wall to outer flume wall. A Vectrino II velocimeter was the instrument used to record the flow velocity. Both x and y flow velocities were recorded along with 2 estimates in the z direction. Using these recordings the data was then exported to Matlab for further investigation. Upon analysis it was determined that an annular flume is an acceptable facility to study sediment transport. An optimal testing location was found to be 12 [ft] from the flow straighteners along the outer flume wall.
Available from the National Sea Grant Library (use NHU number to search) or NH Sea Grant
- Evaluation and characterization of fluid dynamics in an annular flume (2013). Brett Goldman and Stephen Collister. Graduate student advisors: Emily Carlson and Charlie Watkins. Advisor: Diane Foster.