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The turbulent drag reduction technique proposed by Keefe[4, 5] is studied for the first time by direct numerical simulation in the turbulent channel flow geometry at a Reynolds number of Rτ =180, based on the friction velocity of the stationary-wall case and the half channel height. The actuator consists of arrays of flush-mounted discs which rotate at constant angular velocity. For a fixed maximum disc tip velocity, drag reduction can be achieved when the disc diameter is larger than a threshold, while below this threshold the drag increases. We find a maximum drag reduction of 23%. The net power saved, computed by taking into account the power spent to activate the discs against the fluid viscous resistance, is found to be positive and reach 10%. We estimate the disc-flow parameters required for flows of technological interest and discuss possible future implementations based on micro-electromagnetic motors and micro-air turbines.
Author(s):
Pierre Ricco
The University of Sheffield
United Kingdom
Stanislav Hahn
Honeywell Turbo Technologies
Czech Republic