Analytical study of the effects of wind tunnel turbulence on turbofan rotor noise

The influence of tunnel turbulence on turbofan rotor noise was carried out to evaluate the effectiveness of the NASA Ames 40 by 80 foot tunnel in simulating flight levels of fan noise. A previously developed theory for predicting rotor/turbulence interaction noise was refined and extended to include first-order effects of inlet turbulence anisotropy. This theory was then verified by carrying out extensive data/theory comparisons. The resulting model computer program was then employed to carry out a parametric study of the effects of fan size, blade number, and operating line on rotor/turbulence noise for outdoor test stand. NASA Ames wind tunnel, and flight inlet turbulence conditions. A major result of this study is that although wind tunnel rotor/turbulence noise levels are not as low as flight levels they are substantially lower than the outdoor test stand levels and do not mask other sources of fan noise

Jet Noise Suppression

The objectives of this chapter are to review and summarize the jet noise suppression technology, to provide a physical and theoretical model to explain the measured jet noise suppression characteristics of different concepts, and to provide a set of guidelines for evolving jet noise suppression designs. The underlying principle for all jet noise suppression devices is to enhance rapid mixing (i.e., diffusion) of the jet plume by geometric and aerothermodynamic means. In the case of supersonic jets, the shock-cell broadband noise reduction is effectively accomplished by the elimination or mitigation of the shock-cell structure. So far, the diffusion concepts have predominantly concentrated on jet momentum and energy (kinetic and thermal) diffusion, in that order, and have yielded better noise reduction than the simple conical nozzles. A critical technology issue that needs resolution is the effect of flight on the noise suppression potential of mechanical suppressor nozzles. A more thorough investigation of this mechanism is necessary for the successful development and design of an acceptable noise suppression device for future high-speed civil transports

Assessment of the Noise Reduction Potential of Advanced Subsonic Transport Concepts for NASA's Environmentally Responsible Aviation Project

Aircraft system noise is predicted for a portfolio of NASA advanced concepts with 2025 entry-into-service technology assumptions. The subsonic transport concepts include tube-and-wing configurations with engines mounted under the wing, over the wing nacelle integration, and a double deck fuselage with engines at a mid-fuselage location. Also included are hybrid wing body aircraft with engines upstream of the fuselage trailing edge. Both advanced direct drive engines and geared turbofan engines are modeled. Recent acoustic experimental information was utilized in the prediction for several key technologies. The 301-passenger class hybrid wing body with geared ultra high bypass engines is assessed at 40.3 EPNLdB cumulative below the Stage 4 certification level. Other hybrid wing body and unconventional tube-and-wing configurations reach levels of 33 EPNLdB or more below the certification level. Many factors contribute to the system level result; however, the hybrid wing body in the 301-passenger class, as compared to a tubeand- wing with conventional engine under wing installation, has 11.9 EPNLdB of noise reduction due to replacing reflection with acoustic shielding of engine noise sources. Therefore, the propulsion airframe aeroacoustic interaction effects clearly differentiate the unconventional configurations that approach levels close to or exceed the 42 EPNLdB goal

Break-taking behaviour pattern of long-distance freight vehicles based on GPS trajectory data

This paper focuses on the break-taking behaviour pattern of long-distance freight vehicles, providing a new perspective on the study of behaviour patterns and simultaneously providing a reference for transport management departments and related enterprises. Based on Global Positioning System (GPS) trajectory data, we select stopping points as break-taking sites of long-distance freight vehicles and then classify the stopping points into three different classes based on the break-taking duration. We then explore the relationship of the distribution of the break-taking frequency between the three single classifications and their combinations, on the basis of the break-taking duration distribution. We find that the combination is a Gaussian distribution when each of the three individual classes is a Gaussian distribution, contrasting with the power-law distribution of the break-taking duration. Then we experimental analysis the distribution of the break-taking durations and frequencies, and find that, for the durations, the three single classifications can be fitted individually by an Exponential distribution and together by a Power-law distribution, for the frequencies, both the three single classifications and together can be fitted by a Gaussian distribution,so that can validate the above theoretical analysis. Key words: break-taking behaviour, long-distance freight vehicle, statistical analysi

Method and apparatus for detecting timing errors in a system oscillator

This invention is comprised of a method of detecting timing errors in a system oscillator for an electronic device, such as a power supply, includes the step of comparing a system oscillator signal with a delayed generated signal and generating a signal representative of the timing error when the system oscillator signal is not identical to the delayed signal. An LED indicates to an operator that a timing error has occurred. A hardware circuit implements the above-identified method

Some physical phenomena associated with the anxiety states and their relation to hyperventilation

The authors believe that there is a physiological background for the perseverance of an anxiety state as part of a psychoneurosis; that this background is produced by the constant presence of purely emotional disturbances; and that the resultant physiological state aggravates the psychic component to such a degree that a vicioris cycle is instituted, the symptoms of which are manifold. These symptoms increase the severity of the emotional tension ; and, if they are prolonged, permanent structural change with the production of organic clisease results. The mechanism is at first a repetition of attacks, from the stimulation by an emotion such as fear upon the sympathetic nervous system, which in turn becomes increasingly labile. The mechanism is perpetuated by the effects of the simulus on the system of self-defense, which is dispatched by the endocrine group. This reaction causes a state of hyperirritability to exist through the presence of tissue alkalosis, tissue liydremia, and tissue anoxemia; and results in a state of tetany which may be regional or generalized. The Symptoms of tetany, and allied rnanifestations such ac tachycardia, distended stomach and dilated urinary bladder, are enough to aggravate the neurosis because of the patient's fear of impending dissolution. Multiplication of impulses increases the bombardment of the sympathetic nervous system, making repetition of tlie reaction more easy at subsequent intervals. The cure is accomplished through elimination of tlie fear-impulse by psychotherapy. The symptoms may be alleviated medically, and by this rneans that part of the neurosis which is on the basis of anxiety concerning health may be eliminated. Because of the subjective and objective improvement in the patient's condition, contact for psychotherapy is more easily obtained. Medical treatment is directed toward preservation of the acid-base balance; toward decreasing the effect of adrenalin on the nerve-tissue by means of a known chemical antagonist; or toward converting the state of tone of the individual from extreme to moderate, whether parasympathic or sympathetic in type

On the generation and propagation of multiple pure tones inside turbofans at transonic regime

Whereas the sound radiated from the inlet of turbofans is mainly due to rotor-stator interactions in approach flight, the shock waves (or N-waves) emitted by the rotor at transonic rotation speeds can be a dominant noise source during takeoff and climb. The study of N-waves needs to take account of two main processes: (i) The generation of N-waves for a perfect rotor (where all blades are identical) and for a real rotor (considering small geometrical blade dispersion); (ii) The N-wave propagation through the inlet duct producing the blade passing harmonics for a perfect rotor, and the multiple pure tones (harmonics of the rotation frequency) for a real rotor. Several approaches have been investigated for the past forty years. This paper intends to cross-check the main methods by applying them to two modern turbofan demonstrators. Moreover, a prospective way of N-wave generation based on geometrical considerations is investigated thanks to test data related to pressure signal and blade stagger angle measurements during the engine rotation. This prediction overcomes some drawbacks of other methods. Moreover, it appears to be very efficient to build rotor blade orderings that reduce the sound pressure level of the multiple pure tones

Prediction of contra-rotating open rotor broadband noise in isolated and installed configurations

Broadband noise is a significant part of the noise emitted by contra-rotating open rotors. Several noise sources can contribute to the total broadband sound field, with the most dominant ones probably being trailing edge noise, rotor-wake interaction noise and pylon-wake interaction noise. This paper addresses the prediction of these noise sources using analytical models based on Amiet’s flat plate airfoil theory and also to empirical turbulence models, fed by input data extracted from steady and unsteady CFD RANS simulations. The models are assessed against wind tunnel tests of Rolls-Royce’s rig 145 (build 1) conducted at the DNW anechoic open jet test facility using Rolls-Royce blades and Airbus pylons. The study showed promising results in terms of the ability of the models to predict acoustic power spectrum shapes, peak frequencies and absolute levels. The effects of changes in thrust on broadband wake-interaction noise are well reproduced. However, the models significantly underestimate the effect of thrust on trailing edge noise and the effect of rotational velocity on pylon interaction noise