The use of conditioned axial flow impellers to generate a current in test tanks

• A novel experimental arrangement is described.
• Wake evolution is measured from a conditioned axial flow impeller.
• Results will aid the design of combined wave and current test tanks.
• Data gathered here should enable the development of numerical models.
• Turbulence and velocity are measured using an Acoustic-Doppler Velocimeter (ADV).

It is necessary to build a new generation of current and wave testing tanks to simulate more realistic sea conditions. Methods for wave generation and absorption are well established but those for current generation in this context are less established. One means of producing a current is by using an axial flow impeller. Unfortunately an impeller introduces into the flow unsteady velocities with high shear, strong turbulent fluctuations and hub effects, alongwith the useful thrust. In the experiment presented here honeycomb flow conditioning placed immediately downstream of the impeller is used to reduce the turbulence present in the flow. An Acoustic-Doppler Velocimeter (ADV) is used to measure three velocity components at a rate sufficient to characterise turbulence. A novel experimental arrangement using brush seals allows the ADV to penetrate the duct without compromising the integrity of the duct. A large number of point measurements were used to construct velocity profiles at various positions downstream of the honeycomb. Three different impeller speed settings were tested to investigate wake evolution. The results presented will aid the development of numerical models and increase understanding of the flow downstream of a conditioned impeller.