Ilya Popov

Flow Separation Control on Airfoil With Pulsed Nanosecond Discharge Actuator

An experimental study of flow separation control with a nanosecond pulse plasma actuator was performed in wind-tunnel experiments. The discharge used had a pulse width of 12 ns and rising time of 3 ns with voltage up to 12 kV. Repetition frequency was adjustable up to 10 kHz. The first series of experiments was to measure integral effects of the actuator on lift and drag. Three different airfoil models were used, NACA-0015 with the chord of 20 cm, NLF-MOD22A with the chord of 60 cm and NACA 63-618 with the chord of 20 cm. Different geometries of the actuator were tested at flow speeds up to 80 m/s. In stall conditions the significant lift increase up to 20% accompanied by drag reduction (up to 3 times) was observed. The critical angle of attack shifted up to 5–7 degrees. The relation of the optimal discharge frequency to the chord length and flow velocity was proven. The dependence of the effect on the position of the actuator on the wing was studied, showing that the most effective position of the actuator is on the leading edge in case of leading edge separation. In order to study the mechanism of the nanosecond plasma actuation experiments using schlieren imaging were carried out. It shown the shock wave propagation and formation of large-scale vortex structure in the separation zone, which led to separation elimination. PIV diagnostics technique was used to investigate velocity field and quantitative properties of vortex formation. In flat-plate still air experiments small scale actuator effects were investigated. Measured speed of flow generated by actuator was found to be of order of 0.1 m/s and a span-wise nonuniformity was observed. The experimental work is supported by numerical simulations of the phenomena. The formation of vortex similar to that observed in experiments was simulated in the case of laminar leading edge separation. Model simulations of free shear layer shown intensification of shear layer instabilities due to shock wave to shear layer interaction.

Non-equilibrium plasma ignition for internal combustion engines

High-voltage nanosecond gas discharge has been shown to be an efficient way to ignite ultra-lean fuel air mixtures in a bulk volume, thanks to its ability to produce both high temperature and radical concentration in a large discharge zone. Recently, a feasibility study has been carried out to study plasma-assisted ignition under high-pressure high-temperature conditions similar to those inside an internal combustion engine. Ignition delay times were measured during the tests, and were shown to be decreasing under high-voltage plasma excitation. The discharge allowed instant control of ignition, and specific electrode geometry designs enabled volumetric ignition even at high-pressure conditions.

Experimental Study and Numerical Simulation of Flow Separation Control with Pulsed Nanosecond Discharge Actuator

Active flow separation control with a nanosecond pulse plasma actuator, which is essentially a simple electrode system on the surface of an airfoil, introducing lowenergy gas discharge into the boundary layer, with little extra weight and no mechanical parts, was performed in wind-tunnel experiments on various airfoil models. In stall conditions the significant lift increase up to 30% accompanied by drag reduction (up to 3 times) was observed. The critical angle of attack shifted up to 5–7 degrees. Schlieren imaging show the shock wave propagation and formation of large-scale vortex structure in the separation zone, which led to separation elimination. The experimental work is supported by numerical simulations of the phenomena. The formation of vortex similar to that observed in experiments was simulated in the case of laminar leading edge separation. Model simulations of free shear layer show intensification of shear layer instabilities due to shock wave to shear layer interaction. The mechanism of flow control by nanosecond plasma discharge is based on extra vorticity created by the shock wave, which is produced from the layer of the hot gas. This hot gas in generated during the fast thermalisation process, in which up to 60% of the discharge energy is converted to heat in less than 1 µs [1]. This phenomenon gives an opportunity for nanosecond discharge actuator to be effective at high velocities [2, 3]. The current work continues studying the performance of nanosecond plasma actuator. A series of wind tunnel experiments was carried out with different actuator layouts at flow velocities up 80 m/s at various airfoils with chords up to 1.5 m and spans up to 5 m. A numerical model was developed to prove the shock wave mechanism of actuator operation. 2. Experiment In the present work, a linear actuator was used [4]. The actuator consisted of a base layer of insulator attached onto the surface of the airfoil, a covered electrode, an interelectrode layer of insulation and an exposed electrode. In the majority of the cases, exposed electrode was ground, and the high-voltage electrode was covered one. High-voltage nanosecond pulses were provided by three different nanosecond pulsers, which were capable of producing pulses of up to 50 kV with rising time of 3-15 ns and duration from 10 to 50 ns at repetition frequencies up to 10 kHz. Low-speed experiments was carried out in open jet wind tunnel using the NACA0015 airfoil with the chord of 20 cm and span about 75 cm. The tunnel was equipped with an

Numerical Simulations of Disturbances in Shear Flows Introduced by NS-DBD Plasma Actuators

Present paper describes results of a numerical study of instabilities introduced into shear flows by nanosecond dielectric barrier discharge (NS-DBD) plasma actuators using a laminar boundary layer as an example. Numerical study is done using compressible Navier-Stokes equations and a thermal model of the NS-DBD actuator. The results of the numerical simulation of NS-DBD (nanosecond dielectric barrier discharge) plasma actuator in laminar boundary layer on a flat plate are compared to the results of the experiment. The results are found to be in good agreement in terms of wavelength, wave speed and shape. The results of the comparison indicate that the proposed thermal model is suitable for predicting phenomenology of disturbances in the laminar boundary layer produced by NS-DBD plasma actuators. The disturbance is also compared to the Tollmien-Schlichting waves predicted by linear stability theory. Simulations demonstrate that the primary effect of the NS-DBD actuator is excitation of the T-S waves.

On-Board Plasma Assisted Fuel Reforming

It is well known that the addition of gaseous fuels to the intake manifold of diesel engines can have significant benefits in terms of both reducing emissions of hazardous gases and soot and improving fuel economy. Particularly, the addition of LPG has been investigated in numerous studies. Drawbacks, however, of such dual fuel strategies can be found in storage complexity and end-user inconvenience. It is for this reason that on-board refining of a single fuel (for example, diesel) could be an interesting alternative. A second-generation fuel reformer has been engineered and successfully tested. The reformer can work with both gaseous and liquid fuels and by means of partial oxidation of a rich fuel-air mix, converts these into syngas: a mixture of H2 and CO. The process occurs as partial oxidation takes place in an adiabatic ceramic reaction chamber. High efficiency is ensured by the high temperature inside the chamber due to heat release. Thus, efficient thermal insulation is crucial to maintain said temperature. Heat recuperation from the reformer exhaust also improves the thermal efficiency. The prototype yields up to 20% of H2 (80% of the theoretical maximum) and 22% of CO with all kinds of fuels tested, including automotive diesel fuel. Efficient thermal insulation allows to keep the dimensions below 40 cm in any direction for a full burning power of 10-30 kW while outer wall of the reformer is exposed to air at normal temperature.