We study experimentally how plasma actuators operating on the basis of surface barrier high-frequency discharge affect jet noise characteristics. The results of investigations of air jets (100–200 m/s) have demonstrated that the studied plasma actuators have control authority over the noise characteristics of these jets. An actuator’s effect on the jet in the applied configuration is related to acoustic discharge excitation and to a large extent is similar to the well-known Vlasov-Ginevsky effect. It has been shown that jet excitation in the case of St ∼ 0.5 using the barrier-discharge plasma actuator leads to broadband amplification of jet sound radiation. The jet excitation in the case of St > 2 leads to broadband noise reduction if the action is sufficiently intensive.

In the modeling of the noise sources in turbulent jets two open questions are still remain. The first, what is the multipole type of the sources? The second, what kind of stochastic fields can be used for the noise source description. These issues are analyzed in this work. Two-point cross-correlation of the jet noise is used to determine the multipole type of sources. Modeling of the cross-correlation provides clear evidence in favor of the quadrupole type of the jet noise sources. In the context of the second issue the recently developed two-stage correlation model is tested on the basis of measurements of azimuthally decomposed jet noise. The results show a promising agreement in a wide range of parameters.

Compliance with environmental protection regulations, in particular, community noise requirements, constitutes one of the major obstacles for designing future supersonic civil aircraft. Although there are several noise sources that contribute to the total noise level of supersonic aircraft, it is the turbulent jet that appears most problematic; jet noise is a dominant noise source for low-to moderate- bypass-ratio engines, and at present there are no effective methods of jet noise reduction other than decreasing jet speed by increasing bypass ratio, which, in turn, is constrained by aerodynamic requirements for supersonic flight. The present study considers a concept of supersonic civil aircraft under the assumption that its total noise is determined by turbulent jets; it is shown that compliance of the supersonic aircraft with the current regulations for subsonic aircraft noise (Chapter 14 Volume I Annex 16 ICAO) would require the decreased jet speed that corresponds to a prohibitively high bypass ratio of aircraft engines. To enable jet noise reduction without necessarily increasing bypass ratio, a novel configuration of supersonic aircraft is proposed that meets the requirements of Chapter 14, thereby demonstrating that the norms of Chapter 14 are achievable for future supersonic civil aircraft with the use of existing technologies.

The aeroacoustic characteristics of a helicopter rotor are calculated by a new method, to assess its applicability in assessing rotor performance in hovering. Direct solution of the Euler equations in a noninertial coordinate system is used to calculate the near-field flow around the spinning rotor. The far-field noise field is calculated by the Ffowcs Williams–Hawkings (FW–H) method using permeable control surfaces that include the blade. For a multiblade rotor, the signal obtained is duplicated and shifted in phase for each successive blade. By that means, the spectral characteristics of the far-field noise may be obtained. To determine the integral aerodynamic characteristics of the rotor, software is written to calculate the thrust and torque characteristics from the near-field flow solution. The results of numerical simulation are compared with experimental acoustic and aerodynamic data for a large-scale model of a helicopter main rotor in an open test facility. Two- and four-blade configurations of the rotor are considered, in different hover conditions. The proposed method satisfactorily predicts the aerodynamic characteristics of the blades in such conditions and gives good estimates for the first harmonics of the noise. That permits the practical use of the proposed method, not only for hovering but also for forward flight.

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.