Towards In-Flight Applications? A Review on Dielectric Barrier Discharge-Based Boundary-Layer Control

This study describes an active flow control concept that uses counterflowing jets to significantly modify external flowfields and strongly disperse the shock waves of supersonic and hypersonic vehicles to reduce aerothermal loads and wave drag. The potential aerothermal and aerodynamic benefits of the concepts were investigated by conducting experiments on a 2.6%-scale Apollo capsule model in Mach 3.48 and 4.0 freestreams in a trisonic blowdown wind tunnel, as well as pretest computational fluid dynamics analyses of the flowfields, with and without counterflowing jets. The model employed three sonic and two supersonic (with design Mach numbers of 2.44 and 2.94) jet nozzles with exit diameters ranging from 0.25 to 0.5 in. The schlieren images were consistent with the pretest computational fluid dynamics predictions, showing a long penetration mode jet interaction at low jet flow rates of 0.05 and 0.1 Ib m /s, whereas a short penetration mode jet was revealed at higher flow rates. The long penetration mode jet appeared to be almost fully expanded and was unsteady, with the bow shock becoming so dispersed that it was no longer discernible. High-speed camera schlieren data revealed the bow shock to be dispersed into striations of compression waves, which suddenly coalesced to a weaker bow shock with a larger standoff distance as the flow rate reached a critical value. Heat transfer results showed a significant reduction in heat flux, even giving negative heat flux for some short penetration mode interactions, indicating that the flow wetting the model had a cooling effect, instead of heating, which could significantly impact thermal protection system requirements and design. The findings suggest that high-speed vehicle design and performance can benefit from the application ofcounterflowing jets as an active flow control.

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Dynamics of Shock Dispersion and Interactions in Supersonic Freestreams with Counterflowing Jets

Forebody shock control devices for drag and aero-heating reduction: A comprehensive survey with a practical perspective

In the current study, selective forcing of cross-flow instability modes evolving on a swept wing at is achieved by means of spanwise-modulated plasma actuators, positioned near the leading edge. In the perspective of laminar flow control, the followed methodology holds on the discrete roughness elements/upstream flow deformation (DRE/UFD) approach, thoroughly investigated by e.g. Saric et al. (AIAA Paper 1998-781, 1998), Malik et al. (J. Fluid Mech., vol. 399, 1999, pp. 85-115) and Wassermann & Kloker (J. Fluid Mech., vol. 456, 2002, pp. 49-84). The possibility of using active devices for UFD provides several advantages over passive means, allowing for a wider range of operating numbers and pressure distributions. In the present work, customised alternating current dielectric barrier discharge plasma actuators have been designed, manufactured and characterised. The authority of the actuators in forcing monochromatic stationary cross-flow modes at different spanwise wavelengths is assessed by means of infrared thermography. Moreover, quantitative spatio-temporal measurements of the boundary layer velocity field are performed using time-resolved particle image velocimetry. The results reveal distinct steady and unsteady forcing contributions of the plasma actuator on the boundary layer. It is shown that the actuators introduce unsteady fluctuations in the boundary layer, amplifying at frequencies significantly lower than the actuation frequency. In line with the DRE/UFD strategy, forcing a sub-critical stationary mode, with a shorter wavelength compared to the naturally selected mode, results in less amplified primary vortices and related fluctuations, compared to the critical forcing case. The effect of the forcing on the flow stability is further inspected by combining the measured actuators body force with the numerical solution of the laminar boundary layer and linear stability theory. The simplified methodology yields fast and computationally cheap estimates on the effect of steady forcing (magnitude and direction) on the boundary layer stability.

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Conditioning of cross-flow instability modes using dielectric barrier discharge plasma actuators

The influence of steady energy addition into the flow by a low-voltage DC-arc discharge located upstream of conically nosed and spherically blunted bodies was investigated experimentally in the Ludwieg-Tube Facility at Mach 5. The results include drag force measurements and shadowgraph flow visualizations. The flow-field structure, arising due to the bow-shock/heated-wake interaction, as well as the bow-shock intensity and heating power effects on the drag reduction is analyzed in this paper. The results demonstrate the existence of an optimum heating rate, providing a maximum effectiveness of energy addition and showing distinct drag reductions up to 70% dependent on test conditions and model geometries.

Effects of steady flow heating by arc discharge upstream of non-slender bodies

Numerical research of the gas pressure influence on a conduction current in a dielectric barrier discharge (DBD), the average volumetric force acting on gas from the discharge, and the power of heat release in the discharge is carried out for aerodynamic applications. The calculations are implemented with use of the earlier proposed boundary problem about the DBD generation near a flat dielectric plate. This problem statement takes into account such factors as the finite thickness of the exposed electrode, finite rates of desorption and the recombination of charged particles on the dielectric surface, and the electric field induced by a superficial charge. Represented are the results of numerical modeling of the incompressible Poiseuille and Couette flows under the time-averaged transverse force impact of DBD actuators placed along the main flow. The possibility of significant influence of an additional transfer of the main flow momentum due to the cross-flow (induced by actuators) on the structure and the characteristics of the considered shear flows is demonstrated.

Modeling of dielectric barrier discharge actuators at various gas pressures and estimation of their influence on shear flows

Experiments on the effect of corona discharge on the drag of a supersonic streamlined body are reported. The discharge is generated with an amplitude modulated, high frequency (13.6- 16MHz) supply, by means of a single- electrode generator of capacitive type. The tests were conducted in the T-l 13 wind tunnel at TsAGI at static pressures from 100 to 260Torr and a Mach number of 2. Drag was measured on an external elecno-mechanic balance that was relatively immune to the power supply noise. The aerodynamic models were streamlined with drag factors from 0.09 to 0.13. The maximum drag reduction was 6% : at'a propulsive efficiency near 1. This occurred

Influence of a corona discharge on the supersonic drag of an axisyjwmetric body

Theoretical approach to assessment of a possibility of laminar flow control on an infinite span swept wing owing to volumetric force and heat impact of plasma actuators is presented. The proposed approach includes numerical modeling of dielectric barrier discharge actuators, calculation of inviscid flow over a given airfoil, calculation of compressible boundary layer spatially modulated in spanwise direction, numerical solution of linear stability problem for stationary modes of cross-flow-type instability. Calculations have been performed for one set of parameters describing plasma actuators and airflow parameters corresponding to cruise flight conditions. Estimation of minimal force impact necessary for noticeable influence on cross-flow-type instability is obtained.

Attenuation of Cross-Flow-Type Instability in Compressible Boundary Layer by Means of Plasma Actuators

Features of numerical modeling of a dielectric barrier discharge

The numerical simulation of spatial-periodic systems of electrogasdynamic actuators (plasma actuators), using the dielectric barrier discharge (DBD) for a volumetric force impact on a gas flow was carried out. Both the typically used design of actuators and the advanced design with an additional screening electrode are considered. The mathematical model of the dielectric barrier discharge in air was formulated in the drift-diffusion approximation without accounting for convective transfer of the charged particles. The following volumetric reactions are taken into consideration, namely, the ionization of nitrogen and oxygen by electron impacts, the attachment of electrons to oxygen, the detachment of electrons from negative ions, and the ion-ion and the electron-ion recombination. The two types of boundary conditions were considered at the open dielectric surface, namely, the model of instantaneous recombination and the model of finite rates of recombination and electron desorption. The numerical simulation both for the typical and for the advanced actuator systems was done with the same set of problem parameters. It was shown that the advanced scheme provides the better energy efficiency of the system of DBD actuators. It was also found that the main integral characteristics of the DBD actuator weakly depend on the type of boundary conditions used on the dielectric surface. The new simplified design of a system of DBD actuators was proposed.

Vladimir Vladimirovich Skvortsov

Papers

Modeling of dielectric barrier discharge actuators at various gas pressures and estimation of their influence on shear flows

Influence of a corona discharge on the supersonic drag of an axisyjwmetric body

Attenuation of Cross-Flow-Type Instability in Compressible Boundary Layer by Means of Plasma Actuators

Features of numerical modeling of a dielectric barrier discharge

About increase of efficiency of plasma multi-actuator system for boundary layer control