**3.4 Summary**

288 Hydrodynamics – Advanced Topics

the case of the O radical, the density profile of Fig. 11 was averaged along the radial direction until rd=50µm and drawn in Fig. 16 with the magenta color. The light blue color curve represents the O radical profile obtained with the Fluent Software when the specific source term profile SOc(z) is injected between a pin and the cathode plane in the simulation

In the following results, the complete simulation of the successive discharge and postdischarge phases involves 10 neutral chemical species (N, O, O3, NO2, NO, O2, N2, N2 (A3∑u+), N2 (a'1∑u-) and O2 (a1∆g)) reacting following 24 selected chemical reactions. The pin electrodes are stressed by a DC high voltage of 7.2kV. Under these experimental conditions the current pulses appear each 0.1ms (i.e. with a repetition frequency of 10KHz). It means that the previous described source terms are injected every 0.1ms during laps time td or tp and only locally inside the micro-plasma filament located between each pin and the plane.

Pictures in Fig. 17 show the cartography of the temperature and of the ozone density after 1ms (i.e. after 10 discharge and post-discharge phases). One, two, three or four pins are stressed by the DC high voltage. Pictures (a) show that for the mono pin case, the lateral air flow and the memory effect of the previous ten discharges lead to a wreath shape of the

**(a)**

**(a)**

**(b)**

**(c)**

**(c)**

**(d)**

The lateral air flow is fixed with a neutral gas velocity of 5m.s-1.

space distribution of both the temperature and the ozone density.

**T (°K)**

300

Fig. 17. Temperature and ozone density profile at 1ms i.e. after ten discharge and postdischarge phases. The number of high voltage pin is respectively (a) one, (b) two, (c) three

The temperature and the ozone maps are very similar. Indeed, both radical and energy source terms are higher near the pin (i.e. inside the secondary streamer area expansion as it was shown in section 3.2). Furthermore, the production of ozone is obviously sensitive to the gas temperature diminution since it is mainly created by the three body reaction *OO M O M* + +→ + 2 3 (having a reaction rate inversely proportional to gas temperature).

0

0.20

0.51

0.91

1.12

1.73

1.32

2.03

x 10<sup>22</sup>

**O3 (m-3 )** 

305

313

323

333

341

338

351

conditions of Fig. 14.

**(d)** 

and (d) four. The lateral air flow is 5m.s-1.

**(a)** 

**(b)** 

**(c)** 

The complete simulation of all the complex phenomena that are triggered by microdischarges in atmospheric non thermal plasma was found to be possible not as usually done in the literature only for 0D geometry but also in multidimensional geometry. In DC voltage conditions, a specific first order electro-hydrodynamics model was used to follow the development of the primary and secondary streamers in mono pin-to-plane reactor. The simulation results reproduce qualitatively the experimental observations and are able to give a full description of micro-discharge phases. Further works, already undertaken in small dimensions or during the first instants of the micro-discharge development (Pancheshnyi 2005, Papageorgiou et al. 2011 ), have to be achieved in 3D simulation in order to describe the complex branching structure for pulsed voltage conditions. Nevertheless, the micro-discharge phase simulation gives specific information about the active species profiles and density magnitude as well as about the energy transferred to the background gas. All these parameters were introduced as initial source terms in a more complete hydrodynamics model of the post-discharge phase. The fist obtained results show the ability of the Fluent software to solve the physico-chemical activity triggered by the micro-discharges.
