Near-field sound radiation of fan tones from an installed turbofan aero-engine

The development of a distributed source model to predict fan tone noise levels of an installed turbofan aero-engine is reported. The key objective is to examine a canonical problem: how to predict the pressure field due to a distributed source located near an infinite, rigid cylinder. This canonical problem is a simple representation of an installed turbofan, where the distributed source is based on the pressure pattern generated by a spinning duct mode, and the rigid cylinder represents an aircraft fuselage. The radiation of fan tones can be modelled in terms of spinning modes. In this analysis, based on duct modes, theoretical expressions for the near-field acoustic pressures on the cylinder, or at the same locations without the cylinder, have been formulated. Simulations of the near-field acoustic pressures are compared against measurements obtained from a fan rig test. Also, the installation effect is quantified by calculating the difference in the sound pressure levels with and without the adjacent cylindrical fuselage. Results are shown for the blade passing frequency fan tone radiated at a supersonic fan operating conditio

Improved reference genome of Aedes aegypti informs arbovirus vector control

Female Aedes aegypti mosquitoes infect more than 400 million people each year with dangerous viral pathogens including dengue, yellow fever, Zika and chikungunya. Progress in understanding the biology of mosquitoes and developing the tools to fight them has been slowed by the lack of a high-quality genome assembly. Here we combine diverse technologies to produce the markedly improved, fully re-annotated AaegL5 genome assembly, and demonstrate how it accelerates mosquito science. We anchored physical and cytogenetic maps, doubled the number of known chemosensory ionotropic receptors that guide mosquitoes to human hosts and egg-laying sites, provided further insight into the size and composition of the sex-determining M locus, and revealed copy-number variation among glutathione S-transferase genes that are important for insecticide resistance. Using high-resolution quantitative trait locus and population genomic analyses, we mapped new candidates for dengue vector competence and insecticide resistance. AaegL5 will catalyse new biological insights and intervention strategies to fight this deadly disease vector

Open rotor broadband interaction noise

A theoretical model is presented for calculating the broadband noise produced by the interaction of an open rotor with the wake from either an upstream contra-rotating rotor or a stationary pylon. The model is used to investigate the dependence of the radiated noise on parameters such as pylon–rotor gap and the polar and azimuthal directivity of the noise field. A simple model is also presented which assumes that the unsteady loading on adjacent blades is uncorrelated. It is shown that the simple model can be used to calculate broadband interaction noise for most practical open rotor geometries

Counter-rotation propeller tip vortex interaction noise

Counter-rotation propeller tip vortex interaction noise occurs when tip vortices, shedfrom each of the upstream propeller blades, interact with the blades on the downstreampropeller. This paper describes two separate models for calculating the noise produced bythis interaction. The first model approximates each tip vortex as a helical vortex tube ofinfinite extent while the second is based on a previously published study and uses a twodimensionalapproximation to model the tip vortex interaction and represents the velocityfield induced by the tip vortices as a piecewise function for which the flow incident on thedownstream blade row must be calculated numerically. The unsteady loading on thedownstream propeller blades is determined from the incident flow predicted using either ofthe models and is used to calculate the radiated sound field using an analytic propeller noiseformul

Laminary boundary layer instability noise produced by an aerofoil

When a laminar boundary layer exists on the surface of an aerofoil up to the trailing edge, a tone or a number of tones are sometimes produced. These tones have been the subject of a number of investigations which have proposed a variety of different mechanisms regarding their production. This paper gives a brief overview of the previously proposed mechanisms and then describes the development of a theoretical model to estimate the tone frequencies. The model is validated against a number of well-known published experiments and also against the results of an experimental investigation undertaken by the authors. The model is compared with other models available for predicting laminar boundary layer instability noise and is shown to be accurate and robust. Unlike previous models, which are empirical, the model presented in this paper is purely theoretical and could be used to predict the frequency of laminar boundary layer instability noise produced by an arbitrary aerofoil.<br/

Effect of centerbody scattering on advanced open-rotor noise

Formulas for calculating the effect of centerbody scattering on the sound radiated from an advanced open rotor are presented. The effects of blade sweep and distributed blade loading are considered. Mach number effects are also implicitly included in the model. The work extends a previously published method and applies it to a practical situation in which scattering by the centerbody has a significant effect on the radiated sound field. Nomenclature B = number of blades on the propeller Bk = disturbance periodicity (number of disturbances per revolution) b = hub/centerbody radius, m c = chord length, m c0 = speed of sound, m:s 1 f = magnitude of f, Pa f = load per unit area (vector) exerted by the propeller ~f = blade on the air, P

Predicting the noise of an open rotor in a wind tunnel

A study of the impact of reverberation on cruise regime acoustic testing of contra-rotating open rotors in a wind tunnel is presented. Models for the rotor tone noise generated in closed cross-section wind tunnels are derived and used in the analysis. The models account for rectangular and circular cross-sections, rigid or impedance boundaries and, for the rectangular wind tunnel case, the rotor axis may be arbitrarily located within the tunnel (but aligned with the flow direction). These models are used to generate simple simulations of model-scale open rotor testing in two real wind tunnels suited to high-speed rotor testing – the Transonic Wind Tunnel in Bedford, UK and the S1MA wind tunnel in Modane, France. In the analysis, the effect of various modelling parameters on the reverberant noise field is investigated. It is shown that open rotor interaction tone noise may be particularly susceptible to the impact of reverberation and that for many tones the reverberant field may persist and contribute to a contaminated noise field, even for wind tunnels with acoustic treatments on the walls of the working section.</p

Effect of Centerbody Scattering on Advanced Open-Rotor Noise

In CDF we have observed several exclusive processes: 2-photon --> e+e- and --> mu+mu-, photon+pomeron --> J/psi and psi(2S), and pomeron+pomeron --> chi_c. The cross sections agree with QED, HERA photoproduction data, and theoretical estimates of gg --> chi_c with another gluon exchanged to screen the color. This observation of exclusive chi_c, together with earlier observations of exclusive dijets and exclusive 2-photon candidates, support some theoretical predictions for p+p --> p+H+p at the LHC. Exclusive dileptons offer the best means of precisely calibrating forward proton spectrometers