Distribution of Acoustic Power Spectra for an Isolated Helicopter Fuselage

The broadband aerodynamic noise can be studied, assuming isotropic flow, turbulence and decay. Proudman’s approach allows practical calculations of noise based on CFD solutions of RANS or URANS equations at the stage of post processing and analysis of the solution. Another aspect is the broadband acoustic spectrum and the distribution of acoustic power over a range of frequencies. The acoustic energy spectrum distribution in isotropic turbulence is non monotonic and has a maximum at a certain value of Strouhal number. In the present work the value of acoustic power peak frequency is determined using a prescribed form of acoustic energy spectrum distribution presented in papers by S. Sarkar and M. Y. Hussaini and by G. M. Lilley. CFD modelling of the flow around isolated helicopter fuselage model was considered using the HMB CFD code and the RANS equations

Simulation of flow around oscillating rotor blade section with aeroelastic flap

Flows around rotor blade sections equipped with active flaps with a degree of freedom in the flap deflection angle are considered in this paper. Results for oscillating flaps are presented. The resultant flap motion was found to couple with the unsteady air loads for cases of blade section in oscillatory translation

Exploring the detached-eddy simulation for main rotor flows

This paper applies the Detached-Eddy Simulation (DES) method to resolve a larger part of the flow spectrum around rotor blades in hover and forward flight. A comparison between DES and Unsteady Reynolds–Averaged Navier–Stokes simulation was carried out for the case of a forward flying rotor suggesting that DES has great potential for rotor applications

CFD simulation of helicopter rotor flow based on unsteady actuator disk model

Actuator Disks (AD) can provide characterizations of rotor wakes while reducing computational expense associated with modeling the fully resolved blades. This work presents an unsteady actuator disk method based on surface circulation distribution combined with empirical data, blade element theory and rotor momentum theory. The nonuniform circulation distribution accounts for 3D blade load effects, and in particular, tip loses. Numerical simulations were conducted for the isolated pressure sensitive paint model rotor blade in hover and forward flight using the HMB3 CFD solver of Glasgow University. Validation of CFD results in comparison with published numerical data was performed in hover, for a range of blade pitch angles using fully turbulent flow and the k-ω SST model. In forward flight, the vortex structures predicted using the unsteady actuator disk model showed configurations similar to the ones obtained using fully resolved rotor blades. Despite the reduced grid cells number, the CFD results for AD models captured well the main vortical structures around the rotor disk in comparison to the fully resolved cases

Numerical simulation of aeroacoustics of hovering helicopter rotor

The specifics of the problem of estimating the noise of a hovering rotor, allows for some simplification of the Ffowcs Williams-Hawkins (FW-H) equation. Most published works dedicated to helicopter tonal noise estimates use the far-field formulation. This paper estimates the aeroacoustic emissions of a helicopter rotor in hover, for observers placed at different distances using the FW-H equation, including near-field and far-field terms. The blade pressure distribution is obtained from numerical simulations with the RANS equations. To demonstrate this approach, the near- and far-field contributions are analyzed for the model-scale UH-1H main helicopter rotor. For the numerical simulations, the HMB solver of Glasgow University and the ANSYS Fluent13 commercial solver are used. As the rotor blade behaviour is characterized by a complex motion in the computer program it is assumed that the blade is seen in as a rotating rigid body. The most commonly used mathematical model of the FW-H equation corresponds to the classical impermeable formulation. In this case, the source surface corresponds to the blade surface. Then, the acoustic pressure (based on the FW-H 1A formulation) is modified with empirical adjustments, based on the radiation Mach number. This was applied for the near- or far-field thickness noise depending on the rotor-observer distance

Two ground-state modifications of quantum-dot beryllium

Exact electronic properties of a system of four Coulomb-interacting two-dimensional electrons in a parabolic confinement are reported. We show that degenerate ground states of this system are characterized by qualitatively different internal electron-electron correlations, and that the formation of Wigner molecule in the strong-interaction regime is going on in essentially different ways in these ground states.Comment: 5 pages, incl 5 Figures and 2 Table

Statistics of extinction and survival in Lotka-Volterra systems

We analyze purely competitive many-species Lotka-Volterra systems with random interaction matrices, focusing the attention on statistical properties of their asymptotic states. Generic features of the evolution are outlined from a semiquantitative analysis of the phase-space structure, and extensive numerical simulations are performed to study the statistics of the extinctions. We find that the number of surviving species depends strongly on the statistical properties of the interaction matrix, and that the probability of survival is weakly correlated to specific initial conditions.Comment: Previous version had error in authors. 11 pages, including 5 figure

Проблемы современного общества и этнический сепаратизм в Северо-Восточной Индии

This article deals with the issue of North-Eastern India, its current social and economic problems in the context of long-term demonstrations of the ethnic separatism. The main aim of the research implies systematic analysis and identification of key factors and reasons perpetuating separatism in NER as well as resource search which determines Indian strategy in solving this problem. The first part of the article is devoted to separatism peculiarities in the region which remains withdrawn and underexplored in many respects. Apart from this, the author provides a quite detailed analysis of negative mentality of the certain part of NER population which justifiably reproaches New Delhi for “discrimination” and inability to solve many problems of the region. Then the author paid the detailed attention to these problems of NER modern society (ethnic, demographic, economic, transport, social etc.) as well as measures undertaken by the Indian government for its settlement.Речь в данной статье идет о Северо-Восточной Индии, о современных проблемах ее социально-экономического развития в условиях, связанных с многолетними проявлениеми этнического сепаратизма. Основная цель работы - системный анализ и выявление ключевых факторов и причин, способствующих сохранению сепаратизма в СВИ, а также поиск ресурсов, определяющих стратегию Индии в решении проблемы. Первая часть статьи посвящена особенностям сепаратизма в регионе, который во многих отношениях остается закрытым и мало изученным. Кроме того, весьма подробно анализируются негативные умонастроения определенной части населения СВИ, которое не без оснований упрекает Дели в «дискриминации» и неспособности решить многочисленные проблемы региона. В дальнейшем автор уделил подробное внимание этим проблемам современного общества СВИ (этнические, демографические, экономические, транспортные, социальные и так далее) и мерам, которые предпринимает индийское правительство по их решению

Aerodynamic optimization of helicopter rear fuselage

An optimization process for the rear helicopter fuselage is presented using Genetic Algorithms and Kriging surrogate models. Shape parameterization is carried out with the super ellipse technique employed for the well-known ROBIN fuselage. The simulations were based on the RANS equations solved using the HMB CFD code. It is shown that a decrease of fuselage drag around 2.5% is possible without compromising the structure and the functionality of the design. Combined with an optimization of the helicopter skids, benefits of up to 4.6% were possible. The demonstrated method can be applied to fuselages of any shape during the initial design phase

Ground state energies of quantum dots in high magnetic fields: A new approach

We present a new method for calculating ground state properties of quantum dots in high magnetic fields. It takes into account the equilibrium positions of electrons in a Wigner cluster to minimize the interaction energy in the high field limit. Assuming perfect spin alignment the many-body trial function is a single Slater determinant of overlapping oscillator functions from the lowest Landau level centered at and near the classical equilibrium positions. We obtain an analytic expression for the ground state energy and present numerical results for up to N=40.Comment: 4 pages, including 2 figures, contribution to the Proceedings of EP2DS-14, submitted to Physica