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Добірка наукової літератури з теми "Axisymmetric subsonic flow structure"

Автор: Grafiati

Опубліковано: 30 травня 2022

Оновлено: 31 травня 2022

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Статті в журналах з теми "Axisymmetric subsonic flow structure"

Hatta, N., R. Ishii, and H. Fujimoto. "Numerical Analysis of Gas-Particle Two-Phase Subsonic Freejets." Journal of Fluids Engineering 114, no. 3 (September 1, 1992): 420–29. http://dx.doi.org/10.1115/1.2910048.

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This paper describes a numerical analysis of gas-droplet two-phase subsonic free jets in the axisymmetric system. Thermal coupling through heat transfer to droplets, as well as momentum coupling through aerodynamic drag responsible for droplet motion, is taken into account in the present numerical model. The Navier-Stokes equations for a gas-phase interacting with particle phase are solved by a time-dependent difference technique and the particle-phase is solved by a discrete particle cloud model. The jet flow structures of mixture composed of air and water-droplets with 1 μm, 5 μm, and 30 μm, respectively, in diameter are calculated with a single particle size. Some of significant characteristics for the two-phase subsonic free jets are pointed out, in particular, focusing upon the effect of particle size on the flow structure.

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Li, Songqi, and Lawrence S. Ukeiley. "Experimental investigation of the fluctuating static pressure in a subsonic axisymmetric jet." International Journal of Aeroacoustics 20, no. 3-4 (April 13, 2021): 196–220. http://dx.doi.org/10.1177/1475472x211004854.

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Measuring the fluctuating static pressure within a jet has the potential to depict in-flow sources of the jet noise. In this work, the fluctuating static pressure of a subsonic axisymmetric jet was experimentally investigated using a 1/8” microphone with an aerodynamically shaped nose cone. The power spectra of the fluctuating pressure are found to follow the -7/3 scaling law at the jet centerline with the decay rate varying as the probe approaches the acoustic near field. Profiles of skewness and kurtosis reveal strong intermittency inside the jet shear layer. By applying a continuous wavelet transform (CWT), time-localized footprints of the acoustic sources were detected from the pressure fluctuations. To decompose the fluctuating pressure into the hydrodynamic component and its acoustic counterpart, two techniques based on the CWT are adopted. In the first method the hydrodynamic pressure is isolated by maximizing the correlation with the synchronously measured turbulent velocity, while the second method originates from the Gaussian nature of the acoustic pressure where the separation threshold is determined empirically. Similar results are obtained from both separation techniques, and each pressure component dominates a certain frequency band compared to the global spectrum. Furthermore, cross-spectra between the fluctuating pressure and the turbulent velocity were calculated, and spectral peaks appearing around Strouhal number of 0.4 are indicative of the footprint of the convecting coherent structures inside the jet mixing layer.

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Saxer-Felici, H. M., A. P. Saxer, A. Inderbitzin, and G. Gyarmathy. "Prediction and Measurement of Rotating Stall Cells in an Axial Compressor." Journal of Turbomachinery 121, no. 2 (April 1, 1999): 365–75. http://dx.doi.org/10.1115/1.2841323.

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This paper presents a parallel numerical and experimental study of rotating stall cells in an axial compressor. Based on previous theoretical and experimental studies stressing the importance of fluid inertia and momentum exchange mechanisms in rotating stall, a numerical simulation using the Euler equations is conducted. Unsteady two-dimensional solutions of rotating stall behavior are obtained in a one-stage low subsonic axial compressor. The structure and speed of propagation of one fully developed rotating stall cell together with its associated unsteady static pressure and throughflow field distributions are presented. The numerical capture of a stalled flow region starting from a stable high-flow operating point with an axisymmetric flow distribution and evolving at a reduced mass flow operating point into a rotating stall pattern is also discussed. The experimental data (flow visualization, time-averaged and unsteady row-by-row static pressure measurements) acquired in a four-stage water model of a subsonic axial compressor cover a complete characteristic line ranging from high mass flow in the stable regime to zero throughflow. Stall inception is presented together with clearly marked different operating zones within the unstable regime. For one operating point in the unstable regime, the speed of propagation of the cell as well as the static pressure spikes at the front and rear boundaries of the rotating stall cell are compared between computations, measurements, and an idealized theory based on momentum exchange between blade rows entering and leaving the stalled cell. In addition, the time evolution of the pressure trace at the rotor/stator interface is presented. This study seems to support the assumption that the cell structure and general mechanism of full-span rotating stall propagation are essentially governed by inertial effects and momentum exchange between the sound and stalled flow at the cell edges.

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Afsar, Mohammed Z., Adrian Sescu, and Stewart J. Leib. "Modelling and prediction of the peak-radiated sound in subsonic axisymmetric air jets using acoustic analogy-based asymptotic analysis." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 377, no. 2159 (October 14, 2019): 20190073. http://dx.doi.org/10.1098/rsta.2019.0073.

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This paper uses asymptotic analysis within the generalized acoustic analogy formulation (Goldstein 2003 JFM 488 , 315–333. ( doi:10.1017/S0022112003004890 )) to develop a noise prediction model for the peak sound of axisymmetric round jets at subsonic acoustic Mach numbers (Ma). The analogy shows that the exact formula for the acoustic pressure is given by a convolution product of a propagator tensor (determined by the vector Green's function of the adjoint linearized Euler equations for a given jet mean flow) and a generalized source term representing the jet turbulence field. Using a low-frequency/small spread rate asymptotic expansion of the propagator, mean flow non-parallelism enters the lowest order Green's function solution via the streamwise component of the mean flow advection vector in a hyperbolic partial differential equation. We then address the predictive capability of the solution to this partial differential equation when used in the analogy through first-of-its-kind numerical calculations when an experimentally verified model of the turbulence source structure is used together with Reynolds-averaged Navier–Stokes solutions for the jet mean flow. Our noise predictions show a reasonable level of accuracy in the peak noise direction at Ma = 0.9, for Strouhal numbers up to about 0.6, and at Ma = 0.5 using modified source coefficients. Possible reasons for this are discussed. Moreover, the prediction range can be extended beyond unity Strouhal number by using an approximate composite asymptotic formula for the vector Green's function that reduces to the locally parallel flow limit at high frequencies. This article is part of the theme issue ‘Frontiers of aeroacoustics research: theory, computation and experiment’.

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Pokora, C. D., and J. J. McGuirk. "Stereo-PIV measurements of spatio-temporal turbulence correlations in an axisymmetric jet." Journal of Fluid Mechanics 778 (July 30, 2015): 216–52. http://dx.doi.org/10.1017/jfm.2015.362.

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Stereoscopic three-component particle image velocimetry (3C-PIV) measurements have been made in a turbulent round jet to investigate the spatio-temporal correlations that are the origin of aerodynamic noise. Restricting attention to subsonic, isothermal jets, measurements were taken in a water flow experiment where, for the same Reynolds number and nozzle size, the shortest time scale of the dynamically important turbulent structures is more than an order of magnitude greater that in equivalent airflow experiments, greatly facilitating time-resolved PIV measurements. Results obtained (for a jet nozzle diameter and velocity of 40 mm and $1~\text{m}~\text{s}^{-1}$, giving $\mathit{Re}=4\times 10^{4}$) show that, on the basis of both single-point statistics and two-point quantities (correlation functions, integral length scales) the present incompressible flow data are in excellent agreement with published compressible, subsonic airflow measurements. The 3C-PIV data are first compared to higher-spatial-resolution 2C-PIV data and observed to be in good agreement, although some deterioration in quality for higher-order correlations caused by high-frequency noise in the 3C-PIV data is noted. A filter method to correct for this is proposed, based on proper orthogonal decomposition (POD) of the 3C-PIV data. The corrected data are then used to construct correlation maps at the second- and fourth-order level for all velocity components. The present data are in accordance with existing hot-wire measurements, but provide significantly more detailed information on correlation components than has previously been available. The measured relative magnitudes of various components of the two-point fourth-order turbulence correlation coefficient ($R_{ij,kl}$) – the fundamental building block for free shear flow aerodynamic noise sources – are presented and represent a valuable source of validation data for acoustic source modelling. The relationship between fourth-order and second-order velocity correlations is also examined, based on an assumption of a quasi-Gaussian nearly normal p.d.f. for the velocity fluctuations. The present results indicate that this approximation shows reasonable agreement for the measured relative magnitudes of several correlation components; however, areas of discrepancy are identified, indicating the need for work on alternative models such as the shell turbulence concept of Afsar (Eur. J. Mech. (B/Fluids), vol. 31, 2012, pp. 129–139).

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Schmidt, Oliver T., Aaron Towne, Georgios Rigas, Tim Colonius, and Guillaume A. Brès. "Spectral analysis of jet turbulence." Journal of Fluid Mechanics 855 (September 21, 2018): 953–82. http://dx.doi.org/10.1017/jfm.2018.675.

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Informed by large-eddy simulation (LES) data and resolvent analysis of the mean flow, we examine the structure of turbulence in jets in the subsonic, transonic and supersonic regimes. Spectral (frequency-space) proper orthogonal decomposition is used to extract energy spectra and decompose the flow into energy-ranked coherent structures. The educed structures are generally well predicted by the resolvent analysis. Over a range of low frequencies and the first few azimuthal mode numbers, these jets exhibit a low-rank response characterized by Kelvin–Helmholtz (KH) type wavepackets associated with the annular shear layer up to the end of the potential core and that are excited by forcing in the very-near-nozzle shear layer. These modes too have been experimentally observed before and predicted by quasi-parallel stability theory and other approximations – they comprise a considerable portion of the total turbulent energy. At still lower frequencies, particularly for the axisymmetric mode, and again at high frequencies for all azimuthal wavenumbers, the response is not low-rank, but consists of a family of similarly amplified modes. These modes, which are primarily active downstream of the potential core, are associated with the Orr mechanism. They occur also as subdominant modes in the range of frequencies dominated by the KH response. Our global analysis helps tie together previous observations based on local spatial stability theory, and explains why quasi-parallel predictions were successful at some frequencies and azimuthal wavenumbers, but failed at others.

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SIMON, FRANCK, SEBASTIEN DECK, PHILIPPE GUILLEN, PIERRE SAGAUT, and ALAIN MERLEN. "Numerical simulation of the compressible mixing layer past an axisymmetric trailing edge." Journal of Fluid Mechanics 591 (October 30, 2007): 215–53. http://dx.doi.org/10.1017/s0022112007008129.

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Numerical simulation of a compressible mixing layer past an axisymmetric trailing edge is carried out for a Reynolds number based on the diameter of the trailing edge approximately equal to 2.9 × 106. The free-stream Mach number at separation is equal to 2.46, which corresponds to experiments and leads to high levels of compressibility. The present work focuses on the evolution of the turbulence field through extra strain rates and on the unsteady features of the annular shear layer. Both time-averaged and instantaneous data are used to obtain further insight into the dynamics of the flow. An investigation of the time-averaged flow field reveals an important shear-layer growth rate in its initial stage and a strong anisotropy of the turbulent field. The convection velocity of the vortices is found to be somewhat higher than the estimated isentropic value. This corroborates findings on the domination of the supersonic mode in planar supersonic/subsonic mixing layers. The development of the shear layer leads to a rapid decrease of the anisotropy until the onset of streamline realignment with the axis. Due to the increase of the axisymmetric constraints, an adverse pressure gradient originates from the change in streamline curvature. This recompression is found to slow down the eddy convection. The foot shock pattern features several convected shocks emanating from the upper side of the vortices, which merge into a recompression shock in the free stream. Then, the flow accelerates and the compressibility levels quickly drop in the turbulent developing wake. Some evidence of the existence of large-scale structures in the near wake is found through the domination of the azimuthal mode m = 1 for a Strouhal number based on trailing-edge diameter equal to 0.26.

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Baqui, Yamin B., Anurag Agarwal, André V. G. Cavalieri, and Samuel Sinayoko. "A coherence-matched linear source mechanism for subsonic jet noise." Journal of Fluid Mechanics 776 (July 6, 2015): 235–67. http://dx.doi.org/10.1017/jfm.2015.322.

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We investigate source mechanisms for subsonic jet noise using experimentally obtained datasets of high-Reynolds-number Mach 0.4 and 0.6 turbulent jets. The focus is on the axisymmetric mode which dominates downstream sound radiation for low polar angles and the frequency range at which peak noise occurs. A linearized Euler equation (LEE) solver with an inflow boundary condition is used to generate single-frequency hydrodynamic instability waves, and the resulting near-field fluctuations and far-field acoustics are compared with those from experiments and linear parabolized stability equation (LPSE) computations. It is found that the near-field velocity fluctuations closely agree with experiments and LPSE computations up to the end of the potential core, downstream of which deviations occur, but the LEE results match experiments better than the LPSE results. Both the near-field wavepackets and the sound field are observed directly from LEE computations, but the far-field sound pressure levels (SPLs) obtained are more than an order of magnitude lower than experimental values despite close statistical agreement of the near hydrodynamic field up to the potential core region. We explore the possibility that this discrepancy is due to the mismatch between the decay of two-point coherence with increasing distance in experimental flow fluctuations and the perfect coherence in linear models. To match the near-field coherence, experimentally obtained coherence profiles are imposed on the two-point cross-spectral density (CSD) at cylindrical and conical surfaces that enclose near-field structures generated with LEEs. The surface pressure is propagated to the far field using boundary value formulations based on the linear wave equation. Coherence matching yields far-field SPLs which show improved agreement with experimental results, indicating that coherence decay is the main missing component in linear models. The CSD on the enclosing surfaces reveals that the application of a decaying coherence profile spreads the hydrodynamic component of the linear wavepacket source on to acoustic wavenumbers, resulting in a more efficient acoustic source.

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Chen, Li-Wei, Guo-Lei Wang, and Xi-Yun Lu. "Numerical investigation of a jet from a blunt body opposing a supersonic flow." Journal of Fluid Mechanics 684 (August 30, 2011): 85–110. http://dx.doi.org/10.1017/jfm.2011.276.

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AbstractNumerical investigation of a sonic jet from a blunt body opposing a supersonic flow with a free stream Mach number ${M}_{\infty } = 2. 5$ was carried out using large-eddy simulation for two total pressure ratios of the jet to the free stream, i.e. $\mathscr{P}= 0. 816$ and 1.633. Results have been validated carefully against experimental data. Various fundamental mechanisms dictating the flow phenomena, including shock/jet interaction, shock/shear-layer interaction, turbulent shear-layer evolution and coherent structures, have been studied systematically. Based on the analysis of the flow structures and features, two typical flow states, i.e. unstable and stable states corresponding to the two values of $\mathscr{P}$, are identified and the behaviours relevant to the flow states are discussed. Small-scale vortical structures mainly occur in the jet column, and large-scale vortices develop gradually in a recirculation region when the jet terminates through a Mach disk and reverses its orientation as a conical free shear layer. The turbulent fluctuations are enhanced by the rapid deviation of the shear layer and the interaction with shock waves. Moreover, the coherent structures of the flow motion are analysed using the proper orthogonal decomposition technique. It is found that the dominant mode in the cross-section plane exhibits an antisymmetric character for the unstable state and an axisymmetric one for the stable state, while statistical analysis of unsteady loads indicates that the side loads can be seen as a rotating vector uniformly distributed in the azimuthal direction. Further, we clarify a feedback mechanism whereby the unsteady motion is sustained by the upstream-propagating disturbance to the Mach disk through the recirculation subsonic region and downstream propagation in the conical shear layer. Feedback models are then proposed which can reasonably well predict the dominant frequencies of the two flow states. The results obtained in this study provide physical insight into the understanding of the mechanisms relevant to the opposing jet/supersonic flow interaction.

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Bogey, Christophe. "On noise generation in low Reynolds number temporal round jets at a Mach number of 0.9." Journal of Fluid Mechanics 859 (November 27, 2018): 1022–56. http://dx.doi.org/10.1017/jfm.2018.864.

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Two temporally developing isothermal round jets at a Mach number of 0.9 and Reynolds numbers of 3125 and 12 500 are simulated in order to investigate noise generation in high-subsonic jet flows. Snapshots and statistical properties of the flow and sound fields, including mean, root-mean-square and skewness values, spectra and auto- and cross-correlations of velocity and pressure, are presented. The jet at a Reynolds number of 12 500 develops more rapidly, exhibits more fine turbulent scales and generates more high-frequency acoustic waves than the other. In both cases, however, when the jet potential core closes, mixing-layer turbulent structures intermittently intrude on the jet axis and strong low-frequency acoustic waves are emitted in the downstream direction. These waves are dominated by the axisymmetric mode and are significantly correlated with centreline flow fluctuations. These results are similar to those obtained at the end of the potential core of spatially developing jets. They suggest that the mechanism responsible for the downstream noise component of these jets also occurs in temporal jets, regardless of the Reynolds number. This mechanism is revealed by averaging the flow and pressure fields of the present jets using a sample synchronization with the minimum values of centreline velocity at potential-core closing. A spot characterized by a lower velocity and a higher level of vorticity relative to the background flow field is found to develop in the interfacial region between the mixing layer and the potential core, to strengthen rapidly and reach a peak intensity when arriving on the jet axis, and then to break down. This is accompanied by the growth and decay of a hydrodynamic pressure wave, propagating at a velocity which, initially, is close to 65 per cent of the jet velocity and slightly increases, but quickly decreases after the collapse of the high-vorticity spot in the flow. During that process, sound waves are radiated in the downstream direction.

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Дисертації з теми "Axisymmetric subsonic flow structure"

Фесенко, Ксения Владимировна. "Метод расчетно-теоретического исследования структуры течения и характеристик ступеней центробежных нагнетателей". Thesis, Национальный аэрокосмический университет им. Н. Е. Жуковского "Харьковский авиационный институт", 2015. http://repository.kpi.kharkov.ua/handle/KhPI-Press/17150.

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Диссертация на соискание ученой степени кандидата технических наук по специальности 05.05.16 – турбомашины и турбоустановки. – Национальный технический университет "Харьковский политехнический институт", Харьков, 2015 г. В диссертации разработан метод расчетно-теоретического исследования структуры течения и характеристик ступеней центробежных нагнетателей с радиальными лопатками рабочих колес, который позволяет определять в широком диапазоне режимов работы суммарные характеристики и структуру осредненного в окружном направлении сжимаемого дозвукового течения в проточной части, включая межлопаточные каналы. Для учета вязких эффектов использованы обобщенные полуэмпирические зависимости, используемые при анализе течения в центробежных нагнетателях. Данный метод расчета позволяет учитывать геометрические особенности радиальных рабочих колес с лопатками, образованными цилиндрическими и коническими поверхностями, безлопаточных и лопаточных диффузоров, обратных направляющих аппаратов. На основе предложенного метода разработан программный комплекс AxCB, который позволяет проводить численный анализ двумерного дозвукового течения в ступенях центробежных нагнетателей, определять поля газотермодинамичних параметров потока газа и суммарные характеристики ступеней, а также их отдельных элементов. Верификация разработанного метода расчета показала удовлетворительную точность согласования результатов численных исследований течений в криволинейных каналах, рабочих колесах, отдельных элементах и ступенях в целом с данными экспериментальных исследований, а также с аналитическим решением. С помощью предложенного метода и ПК AxCB проведено исследование влияния различных геометрических параметров проточной части и лопаточных венцов на структуру течения и суммарные характеристики ступеней ЦБН, а именно формы средней линии и величины геометрического угла выхода лопатки РК, формы меридиональных обводов проточной части и величины геометрического угла лопатки на входе в ЛД, а также различных вариантов исполнения диффузора ступени. На основании выполненного детального анализа предложено усовершенствование геометрических параметров трех ступеней ЦБН с целью повышения их основных параметров. Ступень "А" усовершенствована путем изменения формы средней линии, а также величины конструктивного угла лопатки на выходе из РК, что привело к увеличению коэффициента политропического напора и расширении рабочей зоны характеристики нагнетателя. Модернизация ступени "Б" заключалась в коррекции формы меридиональных обводов проточной части и величины конструктивного угла лопатки на входе в ЛД, что привело к улучшению согласования работы РК и ЛД. После проведения расчетов ряда вариантов проточной части ступени "В", отличающихся используемым диффузором и шириной проточной части, были даны рекомендации по совершенствованию суммарных характеристик ступени, что при-вело к увеличению коэффициента политропического напора и КПД.
Thesis for scientific degree of the Candidate of Sciences (Engineering) on the special-ty 05.05.16 – Turbomachinery and Turboplants. – National Technical University "Kharkiv Politechnical Institute", Kharkov, 2015. The calculation and theoretical studies method of flow structure and characteristics of centrifugal blowers stages with impellers radial vanes was created. It allows determining summary characteristics and 2D flow structure of flow path including blade-to-blade channels in wide range of working regimes. To account for viscous effects generalized semiempirical dependences for centrifugal blowers were used. The proposed method allows taking into account the geometric features of radial impeller with blades that formed by cylindrical and conical surfaces, vaneless and vaned diffusers, reverse guide vanes and gas-path curvilinear contours. The software package AxCB was developed, which allows carrying out the verification of the calculation method. It showed satisfactory accuracy of flow numerical investigation results in the stages with experimental and analytical data. With the proposed method and software package AxCB studies were undertook which dealt with influence of different geometric parameters of flow path and blade rows on the flow structure and stages summary characteristics. On the basis of a detailed analysis modernization of three centrifugal blower stages was proposed to improve their basic parameters or expand the characteristic working area.

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Фесенко, Ксенія Володимирівна. "Метод розрахунково-теоретичного дослідження структури течії та характеристик ступенів відцентрових нагнітачів". Thesis, НТУ "ХПІ", 2015. http://repository.kpi.kharkov.ua/handle/KhPI-Press/17148.

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Дисертація на здобуття наукового ступеня кандидата технічних наук за фахом 05.05.16 – турбомашини та турбоустановки. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2015 р. В дисертації розроблено метод розрахунково-теоретичного дослідження структури течії та характеристик ступенів відцентрових нагнітачів з радіальними лопатками робочих коліс, який дозволяє визначати в широкому діапазоні режимів роботи сумарні характеристики та структуру осередненої у коловому напрямку стисливої дозвукової течії в проточній частині, включаючи міжлопаткові канали. Для врахування в'язких ефектів використані узагальнені напівемпіричні залежності, що використовуються для розрахунку відцентрових нагнітачів. Запропонований метод дозволяє врахувати геометричні особливості радіальних робочих коліс з лопатками, що образовані циліндричними або конічними поверхнями, лопаткових і безлопаткових дифузорів, зворотних направляючих апаратів та криволінійних обводів проточних частин, а також оцінювати узгодженість їх сумісної роботи. За допомогою розробленого програмного комплексу AxCB проведено верифікацію методу розрахунку, яка показала задовільну точність зіставлення результатів числових досліджень течій в ступенях ВЦН з даними експериментальних досліджень та з аналітичним рішенням. Проведено дослідження впливу геометричних параметрів проточної частини і лопаткових вінців на структуру течії і сумарні характеристики ступенів ВЦН. На підставі виконаного детального аналізу запропоновано удосконалення геометричних параметрів трьох ступенів ВЦН з метою підвищення їх напору, ККД або розширення робочої зони характеристики.
Thesis for scientific degree of the Candidate of Sciences (Engineering) on the special-ty 05.05.16 – Turbomachinery and Turboplants. – National Technical University "Kharkiv Politechnical Institute", Kharkov, 2015. The calculation and theoretical studies method of flow structure and characteristics of centrifugal blowers stages with impellers radial vanes was created. It allows determining summary characteristics and 2D flow structure of flow path including blade-to-blade channels in wide range of working regimes. To account for viscous effects generalized semiempirical dependences for centrifugal blowers were used. The proposed method allows taking into account the geometric features of radial impeller with blades that formed by cylindrical and conical surfaces, vaneless and vaned diffusers, reverse guide vanes and gas-path curvilinear contours. The software package AxCB was developed, which allows carrying out the verification of the calculation method. It showed satisfactory accuracy of flow numerical investigation results in the stages with experimental and analytical data. With the proposed method and software package AxCB studies were undertook which dealt with influence of different geometric parameters of flow path and blade rows on the flow structure and stages summary characteristics. On the basis of a detailed analysis modernization of three centrifugal blower stages was proposed to improve their basic parameters or expand the characteristic working area.

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Deparis, Simone. "Numerical analysis of axisymmetric flows and methods for fluid-structure interaction arising in blood flow simulation /." [S.l.] : [s.n.], 2004. http://library.epfl.ch/theses/?display=detail&nr=2965.

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Bennington, Jeremy Lawrence. "Effects of Various Shaped Roughness Elements in Two-Dimensional High Reynolds Number Turbulent Boundary Layers." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/34907.

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Modeling the effects of surface roughness is an area of concern in many practical engineering applications. Many current roughness models to this point have involved the use of empirical 'constants' and equivalent sand grain roughness. These underdeveloped concepts have little direct relationship to realistic roughness and cannot predict accurately and consistently the flow characteristics for different roughness shapes. In order to aid in the development of turbulence models, the present research is centered around the experimental investigation of seven various shaped single roughness elements and their effects on turbulence quantities in a two-dimensional turbulent boundary layer.

The elements under scrutiny are as follows: cone, cone with spatial variations equal to the smallest sublayer structure length scale, cone with spatial variations equal to 2.5 times the smallest sublayer structure length scale, Gaussian-shaped element, hemisphere, cube aligned perpendicular to the flow (cube at 90°), and a cube rotated 45° relative to the flow. The roughness element heights, k+, non-dimensionalized by the friction velocity (U_tau) of the approaching turbulent boundary layer, are 145, 145, 145, 145, 80, 98, and 98 respectively. Analysis of a three-dimensional fetch of the same Gaussian-shaped elements described previously was also undertaken. In order to analyze the complex flow fields, detailed measurements were obtained using a fine-measurement-volume (50 micron diameter) three-velocity component laser-Doppler velocimetry (LDV) system.

The data reveals the formation of a horseshoe vortex in front of the element, which induces the downwash of higher momentum fluid toward the wall. This 'sweep' motion not only creates high Reynolds stresses (v^2, w^2, -uv) downstream of the element, but also leads to higher skin-friction drag. Triple products were also found to be very significant near the height of the element. These parameters are important in regards to the contribution of the production and diffusion of the turbulent kinetic energy in the flow. The 'peakiness' of the roughness element was found to have a direct correlation to the production of circulation, whereas the spatial smoothing does not have an immense effect on this parameter. The peaked elements were found to have a similar trend in the decay of circulation in the streamwise direction. These elements tend to show a decay proportional to (x/d)^-1.12, whereas the cube elements and the hemisphere do not have a common trend.

A model equation is proposed for a drag correlation common to all roughness elements. This equation takes into account the viscous drag and pressure drag terms in the calculation of the actual drag due to the roughness elements presence in the boundary layer. The size, shape, frontal and wetted surface areas of the roughness elements are related to one another via this model equation. Flow drawings related to each element are presented which gives rise to a deeper understanding of the physics of the flow associated with each roughness element.

Master of Science

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Kassab, Sadek Zakaria. "Turbulence structure in axisymmetric wall-bounded shear flow." 1986. http://hdl.handle.net/1993/15390.

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Книги з теми "Axisymmetric subsonic flow structure"

S, Ukeiley Lawrence, Lee Sang W, and Langley Research Center, eds. Aeroacoustic data for a high Reynolds number axisymmetric subsonic jet. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1999.

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A Numerical Investigation of Subsonic and Supersonic Flow Around Axisymmetric Bodies. Storming Media, 2001.

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Частини книг з теми "Axisymmetric subsonic flow structure"

Reichel, Th, M. Zechner, and H. Olivier. "Experiments in a Transonic Shock Tube at Subsonic Mach and High Reynolds Numbers." In Flow Modulation and Fluid—Structure Interaction at Airplane Wings, 105–22. Berlin, Heidelberg: Springer Berlin Heidelberg, 2003. http://dx.doi.org/10.1007/978-3-540-44866-2_6.

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Geropp, D., and A. Leder. "The Flow Structure in the Wake and Separated Region of Plane and Axisymmetric Bodies." In Notes on Numerical Fluid Mechanics (NNFM), 142–49. Wiesbaden: Vieweg+Teubner Verlag, 1993. http://dx.doi.org/10.1007/978-3-663-13986-7_20.

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"Ultrasonic homogenizing systems are able to produce particle-size and droplet-size distributions that approach those of piston homogenizers with a lower power re-quirement. In order to work, they must be fed a well-blended premix or a metered feed of the liquid components. The vibrating element is an extra maintenance item, espe-cially in heavy or abrasive service. Overall, they offer an attractive option when fixed-gap rotor/stator devices do not produce the required size distributions. 5. Homogenizer/Extruder Another high-pressure homogenizer/extruder with an adjustable valve having produc-tion capacities from 8 mL/hr to 12,000 LL/hr is available. A positive displacement pump produces pressures up to 30,000 psig. The manufacturer claims that no O-ring is used in the product pass and pump seal, and this homogenizer/extruder was approved by the U.S. Food and Drug Administration for pharmaceutical use [36]. At this writing, in-formation concerning the internal structure is not available. The apparatus is capable of producing fine emulsions and liposomal dispersions. Figure 36 shows a laboratory unit. 6. Microfluidizer Technologies A more recent invention to find wide use in specialized forms of dispersed system dosage forms is the microfluidizer. This device uses a high-pressure positive-displacement pump operating at a pressure of 500-20,000 psig, which accelerates the process flow to up to 500 m/min through the interaction chamber. The interaction chamber consists of small channels known as microchannels. The microchannel diameters can be as narrow as 50 urn and cause the flow of product to occur as very thin sheets. The configuration of these microchannels within the interaction chamber resembles Y-shaped flow streams in which the process stream divides into these microchannels, creating two separate microstreams. The sum of cross-sectional areas of these two microstreams is less than the cross-sectional area of the pipe before division to two separate streams. This nar-rowing of the flow pass creates an (axisymmetric) elongational flow to generate high Fig. 36 Emulsiflex-C5, a high-pressure homogenizer. (From Ref. 36.)." In Pharmaceutical Dosage Forms, 365–67. CRC Press, 1998. http://dx.doi.org/10.1201/9781420000955-54.

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Тези доповідей конференцій з теми "Axisymmetric subsonic flow structure"

Wang, Zhexuan, and Yiannis Andreopoulos. "Compressibility Effects in Turbulent Subsonic Jets." In ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/fedsm2003-45079.

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The behavior of compressible turbulent jets issuing in still air in the absence of shock waves has been investigated at three different subsonic Mach numbers, 0.3, 0.6 and 0.9. Helium, nitrogen and krypton gases were used to generate the jet flows and investigate the density effects on the structure of turbulence. Particle Image Velocimetry and high-frequency response pressure transducers were used to obtain velocity, Mach number inside the flow field. The decay of the Mach number at the centerline of the axisymmetric jets increases with increasing the initial Mach number at the exit of the flow for all jets. The decay of mean velocity at the centerline of the jets is also higher at higher exit Mach numbers. However, the velocity non-dimensionalized by the exit velocity seems to decrease faster at low exit Mach numbers suggesting a reduced mixing with increasing the exit flow Mach numbers. Helium jets were found to have the largest spreading rate among the three different gas jets used in the present investigation, while krypton had the lowest spreading rate. Total pressure fluctuations appear to decrease with increasing exit flow Mach numbers. Unusually high turbulence intensities were measured in helium jets issuing in still air.

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Saxer-Felici, H. M., A. P. Saxer, A. Inderbitzin, and G. Gyarmathy. "Prediction and Measurement of Rotating Stall Cells in an Axial Compressor." In ASME 1998 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/98-gt-067.

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This paper presents a parallel numerical and experimental study of rotating stall cells in an axial compressor. Based on previous theoretical and experimental studies stressing the importance of fluid inertia and momentum exchange mechanisms in rotating stall, a numerical simulation using the Euler equations is conducted. Unsteady 2-D solutions of rotating stall behavior are obtained in a one-stage low subsonic axial compressor. The structure and speed of propagation of one fully developed rotating stall cell together with its associated unsteady static pressure and throughflow field distributions are presented. The numerical capture of a stalled flow region starting from a stable high-flow operating point with an axisymmetric flow distribution and evolving at a reduced mass flow operating point into a rotating stall pattern is also discussed. The experimental data (flow visualization, time-averaged and unsteady row-by-row static pressure measurements) acquired in a four-stage water model of a subsonic axial compressor covers a complete characteristic line ranging from high mass flow in the stable regime to zero throughflow. Stall inception is presented together with clearly marked different operating zones within the unstable regime. For one operating point in the unstable regime, the speed of propagation of the cell as well as the static pressure spikes at the front and rear boundaries of the rotating stall cell are compared between computations, measurements and an idealized theory based on momentum exchange between blade rows entering and leaving the stalled cell. In addition, the time-evolution of the pressure trace at the rotor/stator interface is presented. This study seems to support the assumption that the cell structure and general mechanism of full-span rotating stall propagation are essentially governed by inertial effects and momentum exchange between the sound and stalled flow at the cell edges.

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Arthurs, David, and Samir Ziada. "Self-Sustained Oscillations of High Speed Impinging Planar Jets." In ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-30215.

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High speed impinging jets are frequently used in a variety of industrial applications including thermal and coating control processes. These flows are liable to the production of very intense narrow band acoustic tones, which are produced by a feedback mechanism between instabilities in the jet free shear layer which roll up to form large scale coherent structures, and pressure fluctuations produced by the impingement of these structures at the impingement surface. This paper examines tone generation of a high speed planar gas jet impinging normally on a flat, rigid surface. Experiments are performed over the complete range of subsonic and transonic jet flow velocities for which tones are generated, from U0 = 150m/s (M≈0.4) to choked flow (U0 = 343m/s, M = 1), and over the complete range of impingement distance for which tones occur. The effect of varying the jet thickness is also examined. The behavior of the planar impinging jet case is compared to that of the axisymmetric case, and found to be significantly different, with tones being excited at larger impingement distances, and at lower flow velocities. The Strouhal numbers associated with tone generation in the planar case are on average an order of magnitude lower than that of the axisymmetric case when using similar velocity and length scales. The frequency behavior of the resulting tones is predicted using a simple feedback model, which allows the identification of the various shear layer modes of the instabilities driving tone generation. Finally, a thorough dimensionless analysis is performed in order to quantify the system behavior in terms of the appropriate scales.

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Speth, Rachelle L., and Datta V. Gaitonde. "Near Field Pressure and Associated Coherent Structures of Excited Jets." In ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting collocated with the ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/fedsm2014-21186.

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Large Eddy Simulations (LES) were performed for Mach 0.9 and 1.3 cold jets to associate the structures of the shear layer with near field pressure fluctuations. The jets were excited by Localized Arc Filament Plasma Actuators (LAFPAs) arranged around the periphery of the nozzle with the axisymmetric (m = 0) mode. Excitation frequencies of St = fD/Uj = 0.05 to 0.25 (close to the column mode frequency) were computed for each Mach number. The St = 0.05 produces one pulse that propagates downstream without interacting with previously emitted pulses. This is referred to as the the impulse response. The St = 0.25 frequency exhibits subsequent pulse interactions. Simulation data for both Mach numbers was collected along three arrays at different radial locations. Strong agreement was found for the near field response to excitation and the mean center-line axial velocity between the subsonic simulations and the experiments. The experiment and simulations depict a large hydrodynamic wave downstream of the exit moving at the speed of convection near the shear layer consisting of a large peak followed by a large trough after the actuator pulse. For the highest excitation frequency, the interaction between structures yields an almost sinusoidal wave in the near field. These hydrodynamic waves are associated to the phase-averaged flow structure which includes a series of rollers and ribs and the associated dilatation field. The structure interactions from subsequent pulses results in a quasi-linear superposition of the impulse jet response (St = 0.05) to actuation. Auto-correlations and two-point correlations describe the development and interaction between adjacent structures in time and space.

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Valentich, Griffin, Rajan Kumar, Daniel Cuppoletti, Mark Alphonso, and Christopher Harris. "Flow Field Characteristics of Non-Axisymmetric High Subsonic Jets." In 52nd AIAA/SAE/ASEE Joint Propulsion Conference. Reston, Virginia: American Institute of Aeronautics and Astronautics, 2016. http://dx.doi.org/10.2514/6.2016-4969.

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Zhaomiao, Liu, and Li Jinhui. "Study on Flow Field Structure in Axisymmetric Radial Flow." In 2013 International Conference on Mechanical and Automation Engineering (MAEE). IEEE, 2013. http://dx.doi.org/10.1109/maee.2013.35.

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Mueller, Michael, Luis Bernal, Paul Miska, Peter Washabaugh, Tsung-Kuan Chou, Babak Parviz, Chungo Zhang, and Khalil Najafi. "Flow structure and performance of axisymmetric synthetic jets." In 39th Aerospace Sciences Meeting and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2001. http://dx.doi.org/10.2514/6.2001-1008.

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Little, Jesse, Marco Debiasi, and Mo Samimy. "Flow Structure in Controlled and Baseline Subsonic Cavity Flows." In 44th AIAA Aerospace Sciences Meeting and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2006. http://dx.doi.org/10.2514/6.2006-480.

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Eaton, A. R., and W. C. Reynolds. "Flow Structure and Mixing in a Motored Axisymmetric Engine." In SAE International Congress and Exposition. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 1989. http://dx.doi.org/10.4271/890321.

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Lasiecka, I., and J. T. Webster. "Long-time dynamics and control of subsonic flow-structure interactions." In 2012 American Control Conference - ACC 2012. IEEE, 2012. http://dx.doi.org/10.1109/acc.2012.6315219.

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Звіти організацій з теми "Axisymmetric subsonic flow structure"

Catalano, George D., Walter B. Sturek, and Sr. A Numerical Investigation of Subsonic and Supersonic Flow Around Axisymmetric Bodies. Fort Belvoir, VA: Defense Technical Information Center, September 2001. http://dx.doi.org/10.21236/ada398641.

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