An increase in fuel efficiency and efficiency of combustion processes in power plants is discussed based on the data of physical and computational experiments.Two systems for ignition of a fuel mixture are considered, one of which uses a multipoint pulsed spark discharge, and the other uses a multipoint streamer discharge. A comparative assessment of the energy efficiency of each approach to the ignition of the air/fuel mixture is carried out, and conclusions are drawn about their effectiveness and prospects for use.
Development of models and methods of modelling and simulation of the mechanisms of noise generation in jet streams plays an important role in various engineering applications due to strict requirements for noise produced by different industrial devices as well as the possibilities of using sound in technological processes. The computational tools of numerical simulation of gas dynamics and aeroacoustics processes in supersonic jet flows are considered, and noise sources and noise generation mechanisms in supersonic jets are discussed. The approach to numerical simulation is based on large-eddy simulation technique allowing to resolve eddy structures in the flowfield and to predict noise generation more accurately compared to the existing tools. The results obtained show the structure of under- and over-expanded supersonic jets and could be used to calculate sources of noise in supersonic flows.
Интерес к разработке моделей и методов, направленных на изучение механизмов генерации шума в струйных течениях, объясняется постоянно ужесточающимися требованиями по шуму, производимому различными промышленными устройствами. Рассматриваются модели, лежащие в основе вычислительной газовой динамики и аэроакустики, а также интегральные методы расчета шума в дальнем поле и особенности численной реализации соответствующих математических моделей. Возможности разработанных средств численного моделирования демонстрируются на примере расчета шума, генерируемого сверхзвуковыми недорасширенными струями. Обсуждается влияние перепада давления на структуру струи, а также распределения газодинамических и акустических характеристик. Представленные средства численного моделирования задач вычислительной газовой динамики и вычислительной аэроакустики представляют собой инструменты решения исследовательских и инженерных задач, а также служат основой разработки новых методов и вычислительных алгоритмов. The interest in the development of models and methods focused on the study of mechanisms of noise generation in jets is explained by tightening requirements imposed on the noise produced by various industrial devices. The models of computational fluid dynamics and aeroacoustics, the integral methods of farfield noise calculation, and the numerical implementation of the corresponding mathematical models are considered. The capabilities of the developed numerical simulation tools are demonstrated by the solution of practical problems related to the noise generation by supersonic underexpanded jets. The effect of the nozzle pressure ratio on the jet structure and the distribution of gasdynamic and acoustic characteristics is discussed. The developed tools for the numerical solution of problems in the computational fluid dynamics and computational aeroacoustics can be considered as the tools for solving various research and engineering problems and as the basis for the development of new methods and numerical algorithms.
The calculation of noise generated by a jet of viscous compressible gas flowing out from a conical nozzle is considered. The calculations used the implicit version of the LES (Implicit LES, ILES), in which the role of the subgrid turbulence model performs numerical dissipation used finite-difference scheme. The distributions of the gas-dynamic and acoustic characteristics of the jet upon changing the conditions of its outflow are discussed. The analysis of the modal composition of the received noise is carried out and the correspondence between the features of the received directionality of the noise is determined by its various components and sources. The numerical simulation results are compared with the available experimental and calculated data.
The study considers the operation of an unmanned aerial vehicle in hovering mode over a flat landing platform. As a propulsion system, impellers are used, which are a system of a propeller rotating inside an air ring. The air ring is a body of revolution with an aerodynamic profile in cross section. The paper investigates the effect of unsteady interaction of vortex flows with the design of an aircraft by two alternative numerical methods, one of which is vortex-resolving. Numerical calculations are performed using the traditional turbulence modeling approach based on the averaged Navier-Stokes equations (RANS, Reynolds Averaged Navier-Stokes), where the turbulence is assumed to be isotropic, and the eddy-resolving Large Eddy Simulation method. The main feature of the latter is as follows: a turbulent flow is represented as the superposition of the motion of large-scale and small-scale turbulences. After discretizing the flow using a filtering operation, large-scale turbulence, which depends directly on the boundary conditions, is solved from the full Navier-Stokes equations. Small-scale turbulence has isotropic properties and is modeled similarly to semi-empirical RANS methods. The technique allows one to accurately calculate the vortex structure of any flow directly from the equations of motion using relatively low computing power, in contrast to the RANS models, which simulate the flow using a simplified mathematical model and can provide satisfactory accuracy only for a limited range of problems. The results indicate that eddy-resolving methods for modeling turbulence, in contrast to the methods based on averaged Navier-Stokes equations, make it possible to estimate the effect of aperiodic perturbations on the design of aircraft arising from the interaction of large eddies with each other and with the underlying surface. Such phenomena are accompanied by side impacts of a shock nature on the impeller rings, which can lead to loss of aircraft stability. Under conditions of a small propeller step, the use of an air ring results in a significant increase in the air flow passing through the rotor rotation loop, an increase in thrust due to the creation of flow circulation around the airfoil of the ring, and a decrease in the power on the propeller. Even though the effect of using an air ring disappears with a large incoming flow, this design is considered very promising for use on aircraft with vertical takeoff and landing. This mode of operation is the most energy-consuming and determines the greatest requirements for the lifting force of the power plant. The results of this work have demonstrated that numerical methods based on averaging the Navier-Stokes equations and the use of classical turbulence models of the k-ω or k-ε type, which are widely used in numerical modeling of propellers, in takeoff and landing modes fail to detect aperiodic unsteady phenomena associated with the interaction of large eddies, in contrast to eddy-resolving methods for modeling turbulence.
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