Health effects from low-frequency noise and infrasound in the general population: Is it time to listen? A systematic review of observational studies.

Plasma actuators operating in atmospheric air can induce a body force through collisions between electrically charged particles and neutral air molecules by an externally applied electric field. The fast response and the simple structure make the plasma actuator a promising option in aerospace applications. In this work, experiments were performed with several alternative current excited plasma (streamwise and spanwise) actuators to control flow-induced noise from a cavity. It was found that the streamwise actuator induced three-dimensional variations in the shear layer. The spanwise actuator, however, has little influence on the global flow field. As a result, the streamwise actuator is more effective than the spanwise actuator in cavity noise attenuation.

/pdf/streamwise-and-spanwise-plasma-actuators-for-flow-induced-50gyxknycl.pdf

Streamwise and spanwise plasma actuators for flow-induced cavity noise control

In this article the use of plasma actuation for noise control is reviewed. This research follows the tradition of Geoffrey Lilley who conducted the first experiment relevant to aircraft noise, controlling jet noise by disrupting the helical mode of noise radiation. Advances in electronics, control theory, manufacture process, and diagnostic tools now allow more sophisticated control methods to be developed. In addition to propulsive system noise, airframe noise has now become equally important in defining the overall aircraft noise. Plasma actuation represents a novel method to control aircraft noise, worthy of research and development. Advantages of the approach include simplicity, absence of mechanical moving parts, and fast response. Cases studied in this article demonstrated that the method can be used to attenuate both tonal and more importantly broadband noise radiated by typical aircraft components. The limits and constraints of the methods are also discussed.

/pdf/plasma-actuators-for-noise-control-16nl0oej69.pdf

Plasma actuators for noise control

Plasma actuators operating in atmospheric air were employed to modify aerodynamic flow over a bluff body. The model consisted of a cylinder and a torque link that was installed on the lee side of the cylinder. The objective was to reduce the broadband noise that is mainly generated by the impingement of the cylinder wake on the torque link. The plasma actuators were configured to produce dielectric barrier discharges, through which the flow separation from the cylinder was enhanced by the externally imposed body force. As a result the flow-structure interaction between the wake and the torque link was reduced, leading to the attenuation of broadband noise. The noise and flow control performance with the plasma actuators were studied in an anechoic chamber facility as well as in a wind tunnel facility by examining sound pressure and mean flow field respectively. With the current plasma actuators, it was found that there was 1 dB reduction in overall sound pressure level at a free stream speed of 30 m/s, and the wake speed impinging on the torque link was reduced. A possible solution to improve the broadband noise attenuation performance is discussed at the end of this paper.

Bluff Body Noise and Flow Control with Atmospheric Plasma Actuators

Objective: This entire study has two parts. Study I aimed to develop a psychological assessment scale and the study II aimed to investigate the effects of LFN (low frequency noise) on the psychological responses in humans, using the scale developed in the study I. Background: LFN is known to have a negative impact on the functioning of humans. The negative impact of LFN can be categorized into two major areas of functioning of humans, physiological and psychological areas of functioning. The physiological impact can cause abnormalities in threshold, balancing and/or vestibular system, cardiovascular system and, hormone changes. Psychological functioning includes cognition, communication, mental health, and annoyance. Method: 182 college students participated in the study I in development of a psychological assessment scale and 42 paid volunteers participated in the study II to measure psychological responses. The LFN stimuli consisted of 12 different pure tones and 12 different 1 octave-band white noises and each stimulus had 4 different frequencies and 3 different sounds pressure levels. Results: We developed the psychological assessment scale consisting of 17 items with 3 dimensions of psychological responses (i.e., perceived physical, perceived physiological, and emotional responses). The main findings of LFN on the responses were as follows: 1. Perceived psychological responses showed a linear relation with SPL (sound pressure level), that is the higher the SPL is, the higher the negative psychological responses were. 2. Psychological responses showed quadric relations with SPL in general. 3. More negative responses at 31.5Hz LFN than those of 63 and 125Hz were reported, which is deemed to be caused by perceived vibration by 31.5Hz. "Perceived vibration" at 31.5Hz than those of other frequencies of LFN is deemed to have amplified the negative psychological response. Consequently there found different effects of low frequency noise with different frequencies and intensity (SPL) on multiple psychological responses. Conclusion: Three dimensions of psychological responses drawn in regard to this study differed from others in the frequencies and SLP of LFN. Negative psychological responses are deemed to be differently affected by the frequency, SPL of the LFN and "feel vibration" induced by the LFN. Application: The psychological scale from our study can be applied in quantitative psychological measurement of LFN at home or industrial environment. In addition, it can also help design systems to block LFN to provide optimal conditions if used the study outcome, .i.e., the relations between physical and psychological responses of LFN.

/pdf/low-frequency-noise-and-it-s-psychological-effects-3i059xsafq.pdf

Low Frequency Noise and It's Psychological Effects

It is expected that with the projected increase in air travel aeroacoustics research will be very critical in meeting increasingly stringent aircraft noise certification standards. In the United States aeroacoustics research has steadily progressed toward enhanced safety, noise benefits and lower costs. This report provides a brief summary of selected recent aeroacoustics activity in the US. Four topics of great interest to the aerospace industry are: (1) Advanced Subsonic Technology (AST) for future subsonic aircraft, (2) High Speed Research (HSR) for future supersonic commercial aircraft, (3) Rotorcraft noise control efforts, and (4) Weapons bay and other noise control applications for the military. Examples of good progress in the areas of jet, fan, airframe and helicopter noise as well as liner design and weapons bay noise suppression are provided herein. In the next few years we look forward to seeing major strides in noise reduction technology and our ability to predict situations of aeroacoustics i...

Recent aeroacoustics research in the United States

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Recent aeroacoustics research in the United States