Flow Control under Constant Power Input

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Turbulent flows are present in many natural and technological processes and are characterized by larger energy losses due to friction drag between fluid and wall than their laminar counterparts. In order to enable efficient energy usage turbulent losses need to be minimized and the corresponding flow control research is one of the major topics in fluid mechanics. Much work in this field is presently based on direct numerical simulation (DNS). In preliminary work a novel DNS method was developed which is especially suited for investigating controlled flows in respect to their energy efficiency, because the energy input per time (power) can be prescribed.Existing DNS methods realize the flow through a duct by either prescribing a fixed volume flow rate or by imposing a fixed pressure gradient. The other component is a result of the simulation such that the time averaged values for flow rate and pressure gradient are the same for both techniques. If a drag reducing flow control technique is applied to either technique, the power input (energy input per time) into the flow, which is given by the product of flow rate and pressure gradient, changes. In the first case the power input decreases (constant flow rate at reduced pressure gradient) while it increases for the second case (increased flow rate at constant pressure gradient). As a result the influence of control techniques on turbulence properties can be interpreted in different ways. Reliable statements concerning changes in the energy dissipation mechanisms are basically not possible. Furthermore, for active control techniques, the power input required to drive the control has to be considered if the total energy requirement of the controlled flow is to be evaluated.In the present project we intend to further develop the novel DNS method based on a constant power input where this power input includes both, pumping and control power. This method will be used to revisit selected existing flow control techniques and analyze those in respect to their turbulence properties, with special focus on the dissipation mechanisms. In addition, they will be evaluated in respect to their energy efficiency and in comparison with results obtained with existing DNS methods.