Dielectric barrier discharges (DBDs) are characterized by electrical measurements interpreted on the basis of equivalent circuits. The concept of the simplest equivalent circuit of volume DBDs is expanded to surface DBDs (SDBDs); this was completed by taking into account the discharge expansion on the dielectric-gas interface. It is assumed, that this expansion is not limited by the dimension of the electrodes. This approach delivers an analytical relationship for the dissipated power as a function of the applied voltage amplitude. It applies to SDBDs with sufficiently long embedded electrodes and operated by sinusoidal high voltages. The obtained relations were validated by comparison with experimental data obtained from previous work devoted to SDBDs with 20 mm elongated electrodes operated in ambient air and for applied peak-to-peak voltages of up to 20 kV at 1 kHz frequency. The dependencies derived from the equivalent circuit agree well with experimentally recorded charge and dissipated energy.

Surface dielectric barrier discharges are investigated in order to explore the combined effects of barrier thickness and microstructure of the exposed electrode on the ion wind generation. Actuators with straight and structured high voltage electrodes with characteristic sizes of 200 and 250 µm and dielectric thicknesses of 0.5, 1 and 2 mm are compared. It is observed that: i) actuator efficiency of ion wind generation strongly depends on the applied voltage amplitude; ii) operation voltage depends on the dielectric thickness logarithmically; iii) electrode microstructure slightly increases the dynamic pressure (few percent in maximum), however the effect decreases with thicker dielectrics and smaller electrode structures; iv) the pattern of the most intensive discharge parts as well as the dielectric erosion repeats the regular structure of the electrodes down to 200 µm. Several identical samples are tested during different days to estimate the impact of the air humidity and the degradation of the dielectric. The microscale precision of the sample manufacture was accomplished by a commercial facility for printed circuit boards.

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The influence of localized nitrogen transpiration on second mode instabilities in a hypersonic boundary layer is experimentally investigated. The study is conducted using a 7 • half-angle cone with a length of 1100 mm and small nose bluntness at 0 • angle-of-attack. Transpiration is realized through a porous Carbon/Carbon patch of 44 × 82 mm located near the expected boundary layer transition onset location. Transpiration mass flow rates in the range of 0.05-1% of the equivalent boundary layer edge mass flow rate were used. Experiments were conducted in the High Enthalpy Shock Tunnel Göttingen (HEG) at total enthalpies around 3 MJ/kg and unit Reynolds numbers in the range of 1.4 ⋅ 10 6 to 6.4 ⋅ 10 6 m −1 . Measurements were conducted by means of coaxial thermocouples, Atomic Layer Thermopiles (ALTP), pressure transducers and high-speed schlieren. The present study shows that the most amplified second mode frequencies were shifted to lower values as nitrogen is transpired into the boundary layer. In some cases the instability amplitudes were found to be significantly reduced. The observed frequency reduction was verified to correlate with the change of the relative sonic line height in the boundary layer. The amplitude damping was observed to occur only until the most amplified frequencies were reduced to around 50% of their undisturbed values. When transpiration within this limit was performed shortly upstream of the natural boundary layer transition onset, a transition delay of approximately 17% could be observed.

Avoiding ice accumulation on aerodynamic components is of enormous importance to flight safety. Novel approaches utilizing surface dielectric barrier discharges (SDBDs) are expected to be more efficient and effective than conventional solutions for preventing ice accretion on aerodynamic components. In this work, the realization of SDBDs based on thin-film substrates by means of micro-electro-mechanical-systems (MEMS) technology is presented. The anti-icing performance of the MEMS SDBDs is presented and compared to SDBDs manufactured by printed circuit board (PCB) technology. It was observed that the 35 μm thick electrodes of the PCB SDBDs favor surface icing with an initial accumulation of supercooled water droplets at the electrode impact edges. This effect was not observed for 0.3 μm thick MEMS-fabricated electrodes indicating a clear advantage for MEMS-technology SDBDs for anti-icing applications. Titanium was identified as the most suitable material for MEMS electrodes. In addition, an optimization of the MEMS-SDBDs with respect to the dielectric materials as well as SDBD design is discussed.