**4.1 Test model and experimental setup**

The experimental study was performed in the Icing Research Tunnel available at Aerospace Engineering Department of Iowa State University (i.e., ISU-IRT). As shown schematically in **Figure 5**, ISU-IRT is a research-grade, multi-functional icing research tunnel with a test section of 2.0 m in length × 0.4 m in width × 0.4 m in height and four transparent side walls. It has the capacity of generating a maximum wind speed of 60 m/s in the test section and an airflow temperature down to −25°C. An array of eight pneumatic atomizer/spray nozzles are installed at the entrance of the contraction section of ISU-IRT to inject micro-sized water droplets (10 ~ 100 μm in size) into the airflow. By manipulating the pressure and flow rate supplied to the atomizer/spray nozzles, the liquid water content (*LWC*) in ISU-IRT is adjustable (i.e., *LWC* ranging from 0.1 g/m3 to 5.0 g/m3 ). In summary, ISU-IRT can be used to simulate various atmospheric icing phenomena over a range of icing conditions (i.e., from dry *rime* to wet *glaze* ice conditions). In the present study, a typical glaze icing condition was generated in ISU-IRT with the freestream airflow velocity of *U*∞ = 40 m/s, temperature of *T*∞ = −5°C and liquid water content level (LWC) of LWC = 1.0 g/m3 .

**Figure 5** also gives the schematic of the airfoil/wing model used in the present study, which has a NACA0012 airfoil profile in the cross section and a chord length of 150 mm (i.e., *C* = 150 mm). A resistive electrical film heater (*i.e.*, Kapton® Polyimide Film insulated heater), which was selected due to its outstanding operational performance among the electrical film heaters available on the market, was

### *An Experimental Investigation on the Thermodynamic Characteristics of DBD Plasma… DOI: http://dx.doi.org/10.5772/intechopen.100100*

embedded over one side of the airfoil surface. The electric film heater consists of an etched foil element of 0.013 mm thickness that is encapsulated between two layers of 0.05 mm Polyimide Film and 0.025 mm FEP adhesive tape. The coverage area of the film heater is 50.8 mm × 101.6 mm. A DC power source was used to power the electrical film heater for the anti−/de-icing operation during the experiments.

A DBD plasma actuator was embedded over the other half surface of the airfoil/ wing model for a side-by-side comparison of the anti−/de-icing methods. The DBD plasma actuator consist of four encapsulated electrodes and five exposed electrodes, with the same electrode thickness of about 70 μm. Three layers of Kapton film (*i.e.*, 130 μm for each layer) were integrated to serve as the dielectric barrier to separate the encapsulated electrodes from the exposed electrodes. Ranging from the airfoil leading-edge to about 27% chord length downstream, four encapsulated electrodes were distributed evenly over the airfoil model with a separation distance of 3.0 mm. The length of the encapsulated electrodes was about 350 mm, and the width was 10.0 mm (except the one at the leading edge which was 5.0 mm). As reported by Waldman and Hu [48], since most of the ice would accrete around the leading edge of the airfoil/wing model, the width of the first encapsulated electrode was reduced to 5.0 mm in order to generate more plasma discharges near the airfoil leading-edge for a successful anti−/de-icing operation in the region, while the encapsulated electrodes were attached symmetrically around the leading edge of airfoil model. The exposed electrodes (*i.e.*, 96 mm in length and 3.0 mm in width) were placed right above the encapsuled electrodes with zero overlap between the exposed and encapsulated electrodes. The DBD plasma actuator were wired to a high-voltage AC power supply (Nanjing Suman Co., CTP-2000 K), which is capable of providing a maximum 30 kV peak-to-peak sinusoidal voltage with a center frequency of 10 kHz. During the experiments, while the AC current applied to the plasma actuator was measured by using a high response current probe (Pearson Electronics, Inc., Pearson 2877), the high-amplitude voltage was measured by using a high voltage probe (*i.e.*, P6015A from Tektronix). The electric voltage supplied to the electrodes was manipulated with a variable voltage transformer at a constant frequency of 10 kHz. In order to quantitatively compare the anti−/de-icing performance of the DBD plasma actuator against the electrical film heater under the pre-selected icing conditions, the applied power (i.e., in the term of the applied power density, *P*d) to the DBD plasma actuator was adjusted to be same as that applied to the electrical film heater.

During the experiments, in addition to use a high-speed, high-resolution camera (PCO Tech, Dimax) with a 60 mm lens (Nikon, 60 mm Nikkor f/2.8) to record the dynamic ice accreting or anti−/de-icing process over the airfoil surface, an infrared (IR) thermal imaging system (FLIR A615) was also used to map the surface temperature of the ice accreting airfoil surface via an infrared window (i.e., FLIR IR Window-IRW-4C with optic material of Calcium Fluoride) flush mounted on the top wall of the ISU-IRT test section. An in-situ calibration was performed to validate the IR thermal imaging results against the measured surface temperature data with a high-accuracy RTD probe. The measurement uncertainty for the IR thermal imaging system was found to be within ±0.5°C. The high-speed video camera and the IR thermal imaging system were connected to a digital delay generator (Berkeley Nucleonics, model 575) that synchronized the timing between the two systems.
