Flow control of leading edge separation on airfoil using DBD plasma actuator

In the past, dielectric barrier discharge (DBD) plasma actuators have been shown to be capable of manipulating airflow by producing an electric wind in the boundary layer.Many researchers have investigated the potential of this device.Recently, many researchers have been studying about flow separation control with unsteady actuation.However, the effectiveness of the pulse-modulated drive is still not clearly described when angle of attack is high.Therefore, an investigation on the flow is studied when a plasma surface discharge is driven with pulse modulation both at the stall control condition and at high angle of attack condition.The purposes of this study are as follows:1) To study the effect of pulse-modulated drive of plasma actuator on the flow around the airfoil both at the stall control condition and at high angle of attack condition.2) To study the effect of amplitude modulated pulse modulation on the flow around the airfoil both at the stall control condition and at high angle of attack condition and to compare the improvement of lift coefficient C l between pulse modulation with amplitude modulation (PM+AM) and only pulse modulation (PM).In this study, the DBD plasma actuator is located at the leading edge of airfoil because this configuration had been found to be more effective at high angles of attack.The DBD plasma actuator is installed at x/c = 0.025 of a NACA 0015 airfoil with a 100-mm chord and 150-mm width.It is tested at Re ≈ 67,000 in an airflow of 10 m/s for lift force and hot-wire measurement.However, for flow visualization, the airfoil is tested in airflow of 5 m/s for better flow images.A high-voltage AC current is supplied to the exposed electrode while the encapsulated electrode is grounded.The base waveform is an 8-kHz sinusoidal wave, generated by a digital function generator.The signal is amplified by a high-voltage amplifier to give a peak-peak voltage of 6 kV.Unsteady actuation is performed by applying a low modulation frequency to the base wave.For the next stage of this study, an amplitude modulated pulse modulation is designed to have the same power consumption as pulse-modulated drive.Waveform of pulse modulation in addition to amplitude modulation is set to the same modulation frequency f M and the same base frequency f B as that for pulse modulation case.An amplitude modulated pulse modulation is Flow control of leading edge separation on airfoil using DBD plasma actuator Abstract iv applied to the DBD plasma actuator to investigate the lift coefficient C l improvement compared to pulse-modulated drive.The results are summarized as follows:1.In the case of no actuation, the stall occurs at α = 13.5° and when the actuator is driven at Duty = 100% the stall occurs at α = 15°.However, the application of ON-OFF control of the actuator is able to maintain the increment of the C l value.Furthermore, when St = 4.0, the lift coefficient is reduced sharply after reaching a maximum, while when St = 0.6, it falls gradually.For a high angle of attack (α = 18°) when the angle of attack exceeds the maximum C l , there is an optimum pulse length for effectively controlling the flow.2. Pulse-modulated drive is able to manipulate the behavior of the flow above the airfoil in the high angle of attack.When St = 0.6, a large vortex appears and covers almost the entire airfoil surface.When St = 4.0, however, a small-scale vortex structure forms near the leading edge and then diverges away from the wing surface.3. Setting St = 4.0 is an effective means of increasing the airfoil performance for the stall control condition (α = 16°).For the high angle of attack case, however, it was found that setting St = 0.6 increases the lift coefficient of the airfoil.4. The lift coefficient C l showed similar trends for both the PM and PM+AM cases at the same St values.When St = 4.0, C l decreased rapidly after reaching a maximum.However, when St = 0.6, C l decreased gradually.5. The PM+AM case improves the lift coefficient more effectively than the PM case at a high angle of attack (α = 18°), with minimal improvement under the stall control condition (α = 16°).6.An unsteady amplitude modulated signal stimulates vortex growth more for the PM+AM case than for the PM case, the former forces the flow closer to the wing which improves the lift coefficient.Flow control of leading edge separation on airfoil using DBD plasma actuator Acknowledgements v Flow control of leading edge separation on airfoil using DBD plasma actuatorTable of contents vi Table of contents List of Figures viii