Zhang Qiaogen

Experimental Studies of the Enhanced Heat Transfer from a Heating Vertical Flat Plate by Ionic Wind

The effects of the ionic wind on the heat transfer rate from a heated vertical flat plate are described. The ionic wind is induced by three different types of discharge, corona discharge, dielectric barrier discharge (DBD) and dc glow discharge. The heat transfer coefficients for the heated copper plate under free convection conditions with and without an ionic wind are obtained by measuring the temperature and the heating power of the copper plate. It has been proved that the convective heat transfer coefficients increase by several times with the help of the ionic wind. With the ionic wind induced by a uniform dc glow discharge, the heat transfer coefficient of the heated copper plate is highly enhanced compared with those induced by a corona discharge or DBD. With the use of DBD, the breakdown voltage is increased significantly, which is helpful in avoiding a breakdown when heat transfer is enhanced by the ionic wind. In addition, it makes the application of the ionic wind much safer.

Experimental Investigation on the Characteristics of Sliding Discharge Plasma Aerodynamic Actuation

A new electrical discharge called sliding discharge was developed to generate plasma aerodynamic actuation for flow control. A microsecond-pulse high voltage with a DC component was used to energize a three-electrode actuator to generate sliding discharge. The characteristics of plasma aerodynamic actuation by sliding discharge were experimentally investigated. Discharge morphology shows that sliding discharge is formed when energized by properly adjusting microsecond-pulse and DC voltage. Compared to dielectric barrier discharge (DBD), the plasma extension of sliding discharge is quasi-diffusive and stable but longer and more intensive. Results from particle image velocimetry (PIV) test indicate that plasma aerodynamic actuation by sliding discharge can induce a ‘starting vortex’ and a quasi-steady ‘near-wall jet’. Body force induced by plasma aerodynamic actuation is about the order of mN, which is stronger than that induced by single DBD. It is inferred that microsecond-pulse sliding discharge may be more effective to generate large-scale plasma aerodynamic actuation, which is very promising for improving aircraft aerodynamic characteristics and propulsion efficiency.

Experimental Study on the Velocity and Efficiency Characteristics of a Serial Staged Needle Array-Mesh Type EHD Gas Pump

The ionic wind has good application prospects in the fields of air flow control and heat transfer enhancement. The key for successful applications is how to improve the velocity and how to increase the active area of the ionic wind. This paper designed a needle array-mesh type electrohydrodynamic (EHD) gas pump. The use of needle array electrode where corona discharge started simultaneously could enlarge the active area. The velocity of the ionic wind could increase by placing several single-stage ionic wind generators in series appropriately, called as serial staged generator. The maximum average flow velocity of 16.1 m/s and volumetric flow of 303.5 L/min were achieved at the outlet of a 25-stage gas pump and the conversion efficiency was approximately 2.2%.

Study on the Noise-Level Calculation Method for Capacitor Stacks in HVDC Converter Station

The capacitor stack is one of main acoustic noise sources in the high-voltage dc (HVdc) converter station. It is necessary and important to estimate the noise level of capacitor stacks before an HVdc converter station is constructed. In this paper, based on the analysis of capacitor noise generation mechanisms, the relationship between the vibration speed and sound pressure level of the capacitor is identified. The equation which can be used to calculate the noise level of capacitor stacks is derived. By applying mechanical force on the capacitor tank, the frequency-response function of the capacitor tank vibration is acquired. And then the noise level of capacitor stacks is calculated and compared with the measurement data. The results show that the noise level of the capacitor stack can be predicted effectively with the proposed calculation method.

A Repetitive Nanosecond Pulse Source for Generation of Large Volume Streamer Discharge

Using a unipolar pulse with the rise time and the pulse duration in the order of microsecond as the primary pulse, a nanosecond pulse with the repetitive frequency of several kilohertz is generated by a spark gap switch. By varying both the inter-pulse duration and the pulse frequency, the voltage recovery rate of the spark gap switch is investigated at different working conditions such as the gas pressure, the gas composition as well as the bias voltage. The results reveal that either increase in gas pressure or addition of SF6 to the air can increase the voltage recovery rate. The effect of gas composition on the voltage recovery rate is discussed based on the transferring and distribution of the residual space charges. The repetitive nanosecond pulse source is also applied to the generation of large volume, and the discharge currents are measured to investigate the effect of pulse repetition rate on the large volume streamer discharge.

Design of a Rogowski Coil with a Magnetic Core Used for Measurements of Nanosecond Current Pulses

A Rogowski coil is developed to detect the nanosecond pulse signals of the discharge current with a wide bandwidth of 800 kHz to 106 MHz and high sensitivity of 2.22 V/A. Performance tests show that the Rogowski coil has both excellent dynamic and static characteristics. Calibrating results and the comparison between the standard current shunt and the developed Rogowski coil for the measurement of nanosecond discharge pulses demonstrate that the developed Rogowski coil can reproduce the actual waveform of the discharge current accurately.

Plasma Sheet Actuator Driven by Repetitive Nanosecond Pulses with a Negative DC Component

A type of electrical discharge called sliding discharge was developed to generate plasma aerodynamic actuation for flow control. A three-electrode plasma sheet actuator driven by repetitive nanosecond pulses with a negative DC component was used to generate sliding discharge, which can be called nanosecond-pulse sliding discharge. The phenomenology and behaviour of the plasma sheet actuator were investigated experimentally. Discharge morphology shows that the formation of nanosecond-pulse sliding discharge is dependent on the peak value of the repetitive nanosecond pulses and negative DC component applied on the plasma sheet actuator. Compared to dielectric barrier discharge (DBD), the extension of plasma in nanosecond-pulse sliding discharge is quasi-diffusive, stable, longer and more intensive. Test results of particle image velocimetry demonstrate that the negative DC component applied to a third electrode could significantly modify the topology of the flow induced by nanosecond-pulse DBD. Body force induced by the nanosecond-pulse sliding discharge can be approximately in the order of mN. Both the maximum velocity and the body force induced by sliding discharge increase significantly as compared to single DBD. Therefore, nanosecond-pulse sliding discharge is a preferable plasma aerodynamic actuation generation mode, which is very promising in the field of aerodynamics.

Investigation on the Characteristics of Dielectric Barrier Surface Discharge Driven by Repetitive Nanosecond Pulses in Airflows

Recently, more and more attention has been drawn to nanosecond pulsed surface dielectric barrier discharge (NPSDBD) due to its potential applications in flow control. A study of the interaction between high-speed airflows and NPSDBD generated by different nanosecond waveforms is presented in this paper. The effects of airflows on the discharge characteristics, such as plasma morphology, discharge current, the inception voltage of discharge, are investigated at different pulse rise times and flow velocities. The results show that the NPSDBD sustained by pulses with a fast rise time (

Multichannel Discharge Characteristics of Gas Switch Gap in SF6-N2 or SF6-Ar Gas Mixtures Under Nanosecond Triggering Pulses

\sim 20

Study on Withstand Voltage Characteristics and Surface Electrical Field Distribution along Polluted Insulators

ns) is quasi-uniform, and relatively stable in the airflows. While the NPSDBD driven by pulses with a rise time more than 50 ns, it seems easier to be influenced by a flowing air of 60 m/s, with a filamentary pattern and a typical discharge current, which has two or more current peaks in the pulse front. In the case of pulses with slow rise time, the inception voltage of discharge increases with the flow velocity, but it almost remains constant in the case of fast rise time. In addition, the deposited energy of discharge generated by the pulses with slow rise time increases slightly with the influence of flowing air. The emission spectrum of NPSDBD is also examined. The variation of the emission spectrum with pulse waveforms is basically consistent with the different discharge behaviors driven by different pulse waveforms.