This work demonstrates the possibility of broadband manipulation of instability waves in high-Reynolds-number subsonic turbulent jets using a closed-loop feedback reactive control system. Experiments were conducted across Mach numbers from 0.23 to 0.7, corresponding to Reynolds numbers from 2.2 & times; 105 to 6.5 & times; 105. The control system incorporated a high-frequency dielectric barrier discharge plasma actuator installed near the nozzle lip, a real-time signal processor, and two near-field microphones. The control law was designed in spectral space using a particle swarm optimization algorithm, informed by a preliminary linear single-input-single-output (SISO) system identification procedure. Although the total energy reduction was limited by the waterbed effect and distributed instability wave generation, a band-limited reduction of 1-2 dB within a Strouhal number range of Delta S & planckh; approximate to 0.25 was achieved, depending on the cost function and microphone positions.

A study was conducted on the influence of forced gas convection in the discharge zone on the power dissipated in the surface barrier discharge and the dynamics of ion-current charging of the barrier surface. It has been demonstrated that due to convective cooling of the discharge zone, a decrease in the power dissipated in the discharge is observed, which can reach 50

A closed-loop control was implemented to mitigate stationary cross-flow instability vortices in the boundary layer of a swept wing. Control was achieved using a multichannel plasma actuator and a flow velocity sensor based on a particle image velocimetry system. The optimal control strategy was determined using a gradient descent method, which minimized the root mean square of the steady velocity modulation. The excitation of the boundary layer by a single section of barrier discharge was investigated, with key actuator characteristics, such as linearity limits and noise levels, measured during the experiment. The system's performance was evaluated in a wind tunnel experiment, with various roughness patterns used to force the initial vortices. For isolated roughness elements, substantial transition delay was achieved.

The article presents the results of studying the stationary mode of cross-flow instability excited by a plasma actuator based on dielectric barrier discharge in a three-dimensional boundary layer on a swept plate with an induced pressure gradient. It is shown that the actuator generates an instability mode of a given wavelength with an initial amplitude of up to 2% of the free-stream velocity, while the signal-to-noise ratio is no greater than 15%. As a result of a parametric study, a family of growth curves of the excited instability mode was obtained as a function of the parameters of the voltage supplying the discharge. It is shown that the initial amplitude of stationary cross-flow vortices generated by the actuator in the studied range of parameters depends quadratically on the overvoltage at the electrodes and linearly on frequency, which coincides with a similar dependence for the actuator thrust.

In this work, a parametric study of the flow induced during the movement of an arc channel in a transverse constant magnetic field in initially still air is carried out. The analysis of the flow structure, integral energy and kinematic characteristics of the arc acceleration process is carried out. Instantaneous velocity fields in the induced flow were experimentally obtained for the range of discharge current amplitudes from 8 to 160 A and pulse durations from 40 to 380 mu s. A parametric study of the flow structure in the wake behind the arc is carried out by the method of two-dimensional numerical simulation in the MHD approximation. In the particular case of a single-mode current pulse, the shape of the current pulse is optimized to maximize the gas momentum in the near-wall region. It is shown that similar conditions for the balance of local acceleration, convective acceleration and viscous forces are observed for the problem of flow past an arc and a cylinder for regimes with a conditionally steady vortex shedding in the wake. In this case, the coincidence of the vortex shedding frequency occurs when the characteristic scale of the streamlined body is chosen equal to half the height of the thermal cavity. (c) 2022 Elsevier Ltd. All rights reserved.

The pulse electric arc discharge in an external magnetic field is studied as a vortex generator in the subsonic boundary layer. A pulsed Ampere force induces a hairpin vortex near the wall; its structure depends on the relative direction of arc propagation and external flow velocity. The data presented in this article were obtained from parametric studies of vortex characteristics and their effects on the boundary layer profile at various actuator momentum coefficients (Cμ=1−30) and vortex sizes relative to the boundary layer thickness (D/δ=0.5−1.2). Also, the control of turbulent boundary layer separation on a bump at a flow velocity up to 50 m/s was attempted. An average shift of the separation line by 15% of the bump height was obtained at a flow velocity of 50 m/s and a total momentum coefficient of 0.6%.

For a jet located near the wing, instability waves present in jet mixing layer scatter on the wing trailing edge, leading to additional noise generation. In this article, the possibility of reducing this noise by active cancellation of natural instability waves has been experimentally studied. The active control system consists of near-field microphones from which the feedback signal is taken, a data processing module for signal filtering, and a high-frequency dielectric barrier discharge plasma actuator. Decrease in pressure perturbations in the near field of a turbulent jet associated with axisymmetric instability waves in a narrow frequency band was demonstrated. It was shown that this reduction leads to a corresponding noise decrease in the far field.

Cancellation of the cross-flow vortices in a swept-wing boundary layer is attempted by plasma actuator array in numerical simulation. The response of the boundary layer to the stationary excitation by a single actuator section is measured experimentally and compared to the response obtained from the solution to the parabolized stability equations. A linear approach is shown to be held within the peak-to-peak magnitude of the stationary cross-flow vortices below 10% of the local potential flow velocity. Within the linear model, an optimal control strategy and a faster suboptimal one are developed to calculate voltage amplitude distribution across the electrodes, taking into account the forcing constraints. Simulation of the cancellation process is performed, showing up to a 20 dB reduction in the initial spanwise velocity modulation in the boundary layer. The minimal actuator resolution required for the successive implementation of the control is shown to be in the order of a quarter of the most amplified wavelength, or 3–4 displacement thickness of the boundary layer. Linear estimates predict up to a 150 mm (22% of flow acceleration region length) transition delay for an actuator momentum coefficient of 0.005%.

The results of hydrodynamic pressure fluctuations control by means of a dielectric barrier discharge plasma actuator in a rectangular cavity with sharp edges are presented. The study was carried out at the free flow velocity V=37 m/s. The discharge was organized near the leading edge of the cavity. The average energy of the discharge pulse was 0.03 J, its duration was 1 ms, and frequency modulation was implemented at the natural cavity resonant frequencies of 500, 817, 1317 Hz and at a high frequency of 2160 Hz which did not correspond to the natural resonant pressure peak. Pressure pulsations were measured with a Kulite pressure transducer. It is established that the discharge regime affects the pressure fluctuations in the cavity. The pressure amplitude at the downstream wall of the cavity can be either increased from 117 dB to 128 dB or decreased to 110 dB if, respectively, if either the dominant or higher modes are pumped by the discharge. The PIV visualization was organized in the phase-locked mode. The pressure spectrum corresponds to the magnitude of coherent structures in the shear layer of the cavity. Keywords: plasma actuator, cavity, active control, DBD, boundary layer, mixing layer, closed loop.

The results of hydrodynamic pressure fluctuations control by means of dielectric barrier discharge plasma actuator in a rectangular cavity with sharp edges are presented. The study was carried out at the free flow velocity V∞=37 m/s. The discharge was organized near the leading edge of the cavity. The average energy of the discharge pulse was 0.03 J, its duration was 1 ms, and frequency modulation was implemented at the natural resonant frequencies of 500, 817, 1317 Hz of the cavity and a high frequency of 2160 Hz, which did not correspond to the natural resonant pressure peak. Pressure pulsations were measured with a Kulite pressure transducer. It is established that the discharge regime affects the pressure fluctuations in the cavity. The pressure amplitude at the downstream wall of the cavity can be increased from 117 dB to 128 dB or decreased to 110 dB, respectively, if the dominant or higher modes are pumped by the discharge. The PIV visualization was organized in phase-locked mode. The pressure spectrum corresponds to the magnitude of coherent structures in the shear layer of the cavity.

An experimental and theoretical study has been performed to investigate the disturbances generated in a flat plate boundary layer by individual microdischarges in a dielectric barrier discharge plasma actuator. It has been shown that disturbances in the near field downstream of the actuator can be interpreted as non-stationary streaky structures, which are transformed into a fan of growing Tollmien–Schlichting waves away from the actuator. It has been found that the length of the transition zone dominated by disturbances of the first type is anomalously great and reaches a value of the order of 100 boundary layer displacement thicknesses. This should be taken into account when analyzing parasitic stochastic disturbances produced by plasma actuators used to control laminar-turbulent transition.

Mechanism of hydrodynamic noise generation in a subsonic flat plate boundary layer by a barrier discharge plasma actuator is described. The origin of the pulsations is an inscintric unsteadiness of the discharge structure caused by wandering of the microdischarges. Statistics of discharge wandering is obtained from discharge light emission. Propagation of the disturbances in a slightly unstable Blasius boundary layer is studied both experimentally and numerically. It is demonstrated that the discharge-induced noise can be modeled as a sum of delta-correlated localized boundary layer forcing events, with each event represented by the region of longitudinal and transversal force. Discharge-induced disturbances in the boundary layer undergo three main stages as they move downstream: streak-like structures in the near field, oblique wave fans, and eventually a plane Tollmien–Shllichting wave. A simple statistical model, describing the dependency of the pulsations power on actuator driving frequency and voltage, is proposed.