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EFFICIENCY IMPROVEMENTS OF ELECTROMAGNETIC FLOW CONTROL

Evan Spong
School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney, Australia 2052

John Reizes
School of Mechanical and Manufacturing Engineering, UNSW-Sydney, Sydney 2052, Australia

Abstract

In turbulent flow heat transfer is controlled to a large degree by the intensity of the turbulence fluctuations in the near vicinity of a surface. Thus, the ability to adjust the turbulence intensity is a means of influencing heat transfer from a surface to a surrounding fluid. In the case of a weak electrically conducting fluid, such as seawater, the turbulence intensity can be controlled by subjecting the fluid to an electromagnetic field. This technique, known as Electro-magneto-hydro-dynamic (EMHD) flow control, has been shown to have promise as a means of reducing the turbulence intensity, and hence heat transfer, of turbulent boundary layers. Unfortunately EMHD flow control currently suffers from poor efficiency due to the high energy requirements of the electromagnetic field.
A numerical study has been conducted in which two means of improving the efficiency of EMHD flow control have been investigated. In the first part of the numerical study a new actuator design has been developed to provide a more efficient spatial distribution of the electromagnetic forces.
In the second part of the study the new actuator design has been coupled to an ideal flow sensor. A flow control subroutine, embedded in the numerical model, uses the velocity information from the ideal sensor to determine the appropriate actuating force to apply to the flow at each time step.
The new actuator design has been shown to be capable of successfully attenuating a sequence of artificial low speed streaks in a simplified model of a low Reynolds number turbulent boundary layer. Low speed streaks are known to be a precursor to the turbulence inducing ‘ejection-burst-sweep’ process so that a decrease in the number of low speed steaks would reduce the turbulence intensity of the flow. In doing so a potential solution to the poor efficiency of EMHD flow control has been offered by providing the means through which the expensive electromagnetic forces can be strategically and sparingly applied to the flow thereby reducing the total power requirements of EMHD flow control.

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