The electrohydrodynamic body force produced in an asymmetric surface dielectric barrier discharge is widely utilized in flow control applications. The mechanism of body force production has a key role in the performance of plasma actuators. In this paper, a novel supplementary theory of body force production, named 'nonlinear force', is described as a new interesting component of total body force. This force is distinct from the well-known body force with a Coulomb origin, and also acts through a different mechanism. The theory of nonlinear force shows that it is unidirectional and pushes all particles towards the lower electrode irrespective of the charge sign and variations in electric field polarity.
Dielectric barrier discharge plasma actuators have attracted a lot of attention to use as new technologies for active flow control. In this paper, an experimental investigation of a single unsteady plasma actuator driven by two simultaneous sinusoidal high voltages is carried out. The aerodynamic performance of this plasma actuator is investigated for flow control of a wind turbine blade. Leading edge separation control at Reynolds number of 0.26×106 and in a wide range of angles of attack including linear, stall, and post-stall regions is considered as the test case. The momentum imparted by the plasma actuator to flow is investigated via measuring induced electric wind velocity, which represents that the induced velocities in the steady mode, with vmax≅5 m/s, are higher than that of the unsteady mode. The important aspect of exciting the unsteady dielectric barrier discharge plasma actuator in this new approach is improving its efficiency through increasing the authority of momentum addition to flow and reducing the minimum input power for discharge ignition relative to its typical grounded structure. This can be very important practically in flow control applications where the amount of consumed energy is a substantial factor in determining the actuator's efficiency. The obtained aerodynamic results reveal that the unsteady plasma actuator has the best operation in post-stall angles of attack, which is of great importance for operation characteristics of wind turbine blades. The power spectral density of pressure time series illustrates that the unsteady plasma actuator affects the flow through instabilities of the separation layer and vortex shedding structure.
In this study, ZnO was doped with 0.01% Mn and it is grown on p-Si by the sol-gel spin-coating method. Obtained the thin film was studied that to understand the effect of 0.01% Mn-doping ratio on the optical and electrical properties of ZnO structure. In this context, first, the morphological structure of the thin film was studied with the use of atomic force microscopy (AFM). The surface structure was obtained homogeneous, and roughness and fiber size were calculated between 27.2-33.6 and 0.595-0.673 nm, respectively. Second, the optical properties were characterized via ultravioletvisible (UV-Vis) spectrophotometry. Third, the effect of light intensity on junction properties of the photodiode was studied. The current-voltage (I-V) of the photodiode was measured under dark and at the different intensities of illumination. Obtained results showed that the current of photodiode was increased with the intensity of illumination from 6.41 9 10 -7 to 5.32 9 10 -4 A. These results indicate that photocurrent under illumination is higher than the dark current. After that, the other parameters of the photodiode such as barrier height and ideality factor were determined from forwarding I-V plots using the thermionic emission model that the barrier height and the ideality factor were found 0.74 eV and 5.3, respectively. On the other hand, the capacitance-voltage (C-V) was measured at the different frequencies. The C-V characteristic shown that C-V characteristic of the photodiode was changed depends on increasing frequency. In addition, the interface density (D it ) value was decreased by increasing frequency too. Similarly, the serial resistance of the photodiode was also decreased by increasing frequency. Received all these results indicated that Mn-doped ZnO thin film sensitive to light and due to this property, it can be used for different optoelectronic applications as a photodiode and photosensor.
In the present research, the performance of the electrohydrodynamic force in an asymmetric surface dielectric barrier discharge actuator has been investigated at different bias voltages. The effects of DC, AC plus DC (DC-offset), and sinusoidal bias voltages on the force generation have been studied through measuring the electric wind velocity profiles, surface potential, and electric field. The results showed that applying DC and DC-offset biases to the lower electrode instead of connecting it to the ground in a typical case increased the charge deposition on the dielectric surface and consequently reduced the electrohydrodynamic force generation. This effect was also observed in case of exchanging these voltages with AC sinusoidal voltage of the upper electrode. In addition, as a new idea, two-phase shifted AC voltage was applied to the electrodes and the resulting changes have been studied. The obtained results at 180 • phase difference were very noticeable and showed 46% improvement in the maximum velocity of the induced flow relative to the grounded electrode with the same input power. Using this technique, a certain wind velocity can be obtained at relatively lower voltages and input powers compared to the conventional case of grounding the lower electrode. Such a capability is significant in aerodynamic applications, where applying large values of the high voltages may disturb the operational systems.
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