Abstract
A computational study was conducted on flows over an NACA0015 airfoil with dielectric barrier discharge (DBD) plasma. The separated flows were controlled by a DBD plasma actuator installed at the 5% chord position from the leading edge, where operated AC voltage was modulated with the duty cycle not given a priori but dynamically changed based on the flow fluctuations over the airfoil surface. A single-point pressure sensor was installed at the 40% chord position of the airfoil surface and the DBD plasma actuator was activated and deactivated based on the strength of the measured pressure fluctuations. The Reynolds number was set to 63,000 and flows at angles of attack of 12 and 16 degrees were considered. The three-dimensional compressible Navier–Stokes equations including the DBD plasma actuator body force were solved using an implicit large-eddy simulation. Good flow control was observed, and the burst frequency proven to be effective in previous fixed burst frequency studies is automatically realized by this approach. The burst frequency is related to the characteristic pressure fluctuation; our approach was improved based on the findings. This improved approach realizes the effective burst frequency with a lower control cost and is robust to changing the angle of attack.
Highlights
Flow separation control is an important topic of fluid dynamics and has been studied for many years
The separated flows were controlled by the dielectric barrier discharge (DBD) plasma actuator, where the alternating current (AC) voltage was modulated with the duty cycle not given a priori, but dynamically changed based on the measured pressure fluctuations given by the point sensor
To verify the effectiveness of this approach, three-dimensional compressible Navier–Stokes equations with the DBD plasma actuator body force terms were solved by implicit large-eddy simulations
Summary
Flow separation control is an important topic of fluid dynamics and has been studied for many years. The authors’ group conducted both experimental and computational investigations on the relationship between burst frequencies and flow control authority and showed that higher non-dimensional burst frequencies, such as 6 to 10, are much more effective under certain conditions, and identified that such frequencies are closely related to the instability of the separation shear layer [22,23,24,25] They identified three important flow structures: induced weak jets, two-dimensional vortex flow structures, and small disturbances in the burst actuation, which were key for robust flow control in burst actuation [26,27]. The effectiveness of the method is discussed based on high-fidelity computations using large-eddy simulations (LES) with the actuator-induced body force added This method may be considered as a control system which optimizes the time-dependent burst frequencies with the measured unsteady pressure data over the airfoil surface. Application to the case at a higher angle of attack highlighted the robustness of one of the approaches presented here
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