Near-Field Behavior of an Evaporating Multisize Spray in a Non-Uniform Flow Field

In this paper we examine how the unsteady flow field radiated from an oscillating body is altered from the result of acoustic theory as the direct consequence of disturbances propagating through the non-uniform flow produced by the presence of the body. Taking the specific example of an oscillating airfoil placed in supersonic flow and having the contour of a parabolic arc, we derive a closed-form representation for the unsteady flow field in terms of the confluent hypergeometric function. The analytical expression reveals explicitly that, though the body shape has a negligible effect in the near field, it inextricably affects the unsteady flow at a large distance, both in its amplitude and phase, and substantially modifies the results of acoustic theory. In addition, we display the relation of this solution to the ‘fundamental solution’ and the other salient physical features connected with disturbances propagating through non-uniform flow. The present results recover Whitham's rule in the limit of zero frequency of oscillation and also include, as another special case, the unsteady solution for a wedge obtained by Carrier and Van Dyke.

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Instability wave models for the near-field fluctuations of turbulent jets

Journal of Fluid Mechanics ◽

10.1017/jfm.2011.401 ◽

2011 ◽

Vol 689 ◽

pp. 97-128 ◽

Cited By ~ 172

Author(s):

K. Gudmundsson ◽

Tim Colonius

Keyword(s):

Flow Field ◽

Large Scale ◽

Microphone Array ◽

Near Field ◽

Turbulent Jets ◽

Instability Wave ◽

Mean Flow ◽

Velocity Fluctuations ◽

The Mean ◽

Scale Structures

AbstractPrevious work has shown that aspects of the evolution of large-scale structures, particularly in forced and transitional mixing layers and jets, can be described by linear and nonlinear stability theories. However, questions persist as to the choice of the basic (steady) flow field to perturb, and the extent to which disturbances in natural (unforced), initially turbulent jets may be modelled with the theory. For unforced jets, identification is made difficult by the lack of a phase reference that would permit a portion of the signal associated with the instability wave to be isolated from other, uncorrelated fluctuations. In this paper, we investigate the extent to which pressure and velocity fluctuations in subsonic, turbulent round jets can be described aslinearperturbations to the mean flow field. The disturbances are expanded about the experimentally measured jet mean flow field, and evolved using linear parabolized stability equations (PSE) that account, in an approximate way, for the weakly non-parallel jet mean flow field. We utilize data from an extensive microphone array that measures pressure fluctuations just outside the jet shear layer to show that, up to an unknown initial disturbance spectrum, the phase, wavelength, and amplitude envelope of convecting wavepackets agree well with PSE solutions at frequencies and azimuthal wavenumbers that can be accurately measured with the array. We next apply the proper orthogonal decomposition to near-field velocity fluctuations measured with particle image velocimetry, and show that the structure of the most energetic modes is also similar to eigenfunctions from the linear theory. Importantly, the amplitudes of the modes inferred from the velocity fluctuations are in reasonable agreement with those identified from the microphone array. The results therefore suggest that, to predict, with reasonable accuracy, the evolution of the largest-scale structures that comprise the most energetic portion of the turbulent spectrum of natural jets, nonlinear effects need only be indirectly accounted for by considering perturbations to the mean turbulent flow field, while neglecting any non-zero frequency disturbance interactions.

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Towards Investigation of External Oil Flow From a Journal Bearing in an Epicyclic Gearbox

Volume 7A: Structures and Dynamics ◽

10.1115/gt2017-63451 ◽

2017 ◽

Author(s):

Martin Berthold ◽

Hervé Morvan ◽

Colin Young ◽

Richard Jefferson-Loveday

Keyword(s):

Flow Field ◽

Journal Bearing ◽

Numerical Models ◽

Flow Behavior ◽

Phase Interface ◽

Journal Bearings ◽

Field Behavior ◽

Oil Flow ◽

Inlet Conditions ◽

Near Wall

High loads and bearing life requirements make journal bearings the preferred choice for use in high power, epicyclic gearboxes in jet engines. In contrast to conventional, non-orbiting journal bearings in epicyclic star gearboxes, the kinematic conditions in epicyclic planetary arrangements are much more complex. With the planet gears rotating about their own axis and orbiting around the sun gear, centrifugal forces generated by both motions interact with each other and affect the external flow behavior of the oil exiting the journal bearing. This paper presents a literature and state-of-the-art knowledge review to identify existing work performed on cases similar to external journal bearing oil flow. In order to numerically investigate external journal bearing oil flow, an approach to decompose an actual journal bearing into simplified models is proposed. Later, these can be extended in a step-wise manner to allow key underlying physical phenomena to be identified. Preliminary modeling considerations will also be presented. This includes assessing different geometrical inlet conditions with the aim of minimizing computational requirements and different numerical models for near-wall treatment. The correct choice of near-wall treatment models is particularly crucial as it determines the bearing’s internal and external thermal behavior and properties. The findings and conclusions are used to create a three dimensional (3D), two-component computational fluid dynamic (CFD) sector model with rotationally periodic boundaries of the most simplistic approximation of an actual journal bearing: a non-orbiting representation, rotating about its own axis, with a circumferentially constant, i.e. concentric, lubricating gap. The inlet boundary conditions for simulating the external oil flow are generated by partly simulating the internal oil flow within the lubricating gap. In order to track the phase interface between the oil and the air surrounding the bearing, the Volume of Fluid (VoF) method is used. The quality of the CFD simulations of the domain of interest is not only dependent on the accuracy of the inlet conditions, but is also dependent on the computational mesh type, cell count, cell shape and numerical methods used. External journal bearing oil flow was simulated with a number of different mesh densities and the effect on the flow field behavior will be discussed. Two different operating temperatures, representing low and high viscosity oil, were used and their effect on the flow field behavior will also be assessed. In order to achieve the future objective of creating a design tool for routine use, key areas will be identified in which further progress is required. This includes the need to progressively increase the model fidelity to eventually simulate an orbiting journal bearing in planetary configuration with an eccentric, i.e. convergent-divergent, lubricating gap.

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On the formation of the counter-rotating vortex pair in transverse jets

Journal of Fluid Mechanics ◽

10.1017/s0022112001005894 ◽

2001 ◽

Vol 446 ◽

pp. 347-373 ◽

Cited By ~ 166

Author(s):

L. CORTELEZZI ◽

A. R. KARAGOZIAN

Keyword(s):

Flow Field ◽

Computational Study ◽

Near Field ◽

Three Dimensional ◽

Vortex Pair ◽

Transverse Jets ◽

Vortical Structures ◽

Jet In Crossflow ◽

Dynamical Generation ◽

Counter Rotating Vortex Pair

Among the important physical phenomena associated with the jet in crossflow is the formation and evolution of vortical structures in the flow field, in particular the counter-rotating vortex pair (CVP) associated with the jet cross-section. The present computational study focuses on the mechanisms for the dynamical generation and evolution of these vortical structures. Transient numerical simulations of the flow field are performed using three-dimensional vortex elements. Vortex ring rollup, interactions, tilting, and folding are observed in the near field, consistent with the ideas described in the experimental work of Kelso, Lim & Perry (1996), for example. The time-averaged effect of these jet shear layer vortices, even over a single period of their evolution, is seen to result in initiation of the CVP. Further insight into the topology of the flow field, the formation of wake vortices, the entrainment of crossflow, and the effect of upstream boundary layer thickness is also provided in this study.

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Mean-Flow Measurements in the Boundary Layer and Wake and Wave Field of a Series 60 CB = 0.6 Ship Model—Part 2: Scale Effects on Near-Field Wave Patterns and Comparisons with Inviscid Theory

Journal of Ship Research ◽

10.5957/jsr.1993.37.1.16 ◽

1993 ◽

Vol 37 (01) ◽

pp. 16-24

Author(s):

J. Longo ◽

F. Stern ◽

Y. Toda

Keyword(s):

Boundary Layer ◽

Flow Field ◽

Scale Effects ◽

Near Field ◽

Wave Profile ◽

Wave System ◽

Mean Flow ◽

Wave Elevation ◽

Wave Patterns ◽

Field Wave

Part 2 of this two-part paper presents additional results from a towing-tank experiment conducted in order to explicate the influence of wavemaking by a surface-piercing body on its boundary-layer and wake and provide detailed documentation of the complete flow field appropriate for validating computational methods. In Part 1 (Journal of Ship Research, Dec. 1992), wave profile, local and global wave-elevation, and mean-velocity and pressure field measurements for Froude numbers 0.16 and 0.316 for a 3.048 m Series 60 CB = 0.6 hull form are presented and discussed to point out the essential differences between the flows at low and high Froude number and to assess the nature of the interaction between wavemaking and the boundary layer and wake. In Part 2, scale effects on the near-field wave patterns are examined through wave profile and local and global wave-elevation measurements for 1.829 and 3.048 m models and Froude numbers 0.316, 0.3, and 0.25. The bow-wave amplitude and divergence angle are larger and the stern waves smaller for the smaller model. The latter scale effect is well known, but the former one is a new and unexpected result. Also, comparisons are made between the experimental results and those from a wavy inviscid-flow method, which provides an evaluation of the capabilities of the computational method. Although the computations predict the gross features of the wave system and velocity and pressure fields, they do not simulate the complex details of either the wave system or the flow field, especially close to the hull and wake centerplane.

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Numerical predictions of near field behavior of variable density non-reacting turbulent round jets

International Journal of Heat and Mass Transfer ◽

10.1016/j.ijheatmasstransfer.2020.120201 ◽

2020 ◽

Vol 160 ◽

pp. 120201

Author(s):

Amel Elkaroui ◽

Amani Amamou ◽

Rim Ben Khalifa ◽

Nejla Mahjoub Said ◽

Mohamed Hichem Gazzah ◽

...

Keyword(s):

Near Field ◽

Variable Density ◽

Round Jets ◽

Numerical Predictions ◽

Field Behavior

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Numerical simulation of the non-uniform flow in a full-annulus multi-stage axial compressor with the harmonic balance method

Advances in Mechanical Engineering ◽

10.1177/1687814019897213 ◽

2020 ◽

Vol 12 (3) ◽

pp. 168781401989721 ◽

Cited By ~ 1

Author(s):

Haiou Sun ◽

Meng Wang ◽

Zhongyi Wang ◽

Song Wang ◽

Franco Magagnato

Keyword(s):

Flow Field ◽

Harmonic Balance ◽

Axial Compressor ◽

Harmonic Balance Method ◽

Internal Flow ◽

Uniform Flow ◽

Experimental Results ◽

Balance Method ◽

Operating Characteristics ◽

Multi Stage

To improve the understanding of unsteady flow in modern advanced axial compressor, unsteady simulations on full-annulus multi-stage axial compressor are carried out with the harmonic balance method. Since the internal flow in turbomachinery is naturally periodic, the harmonic balance method can be used to reduce the computational cost. In order to verify the accuracy of the harmonic balance method, the numerical results are first compared with the experimental results. The results show that the internal flow field and the operating characteristics of the multi-stage axial compressor obtained by the harmonic balance method coincide with the experimental results with the relative error in the range of 3%. Through the analysis of the internal flow field of the axial compressor, it can be found that the airflow in the clearance of adjacent blade rows gradually changes from axisymmetric to non-axisymmetric and then returns to almost completely axisymmetric distribution before the downstream blade inlet, with only a slight non-axisymmetric distribution, which can be ignored. Moreover, the slight non-axisymmetric distribution will continue to accumulate with the development of the flow and, finally, form a distinct circumferential non-uniform flow field in latter stages, which may be the reason why the traditional single-passage numerical method will cause certain errors in multi-stage axial compressor simulations.

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PREDICTION OF NOISE GENERATED BY A ROUND NOZZLE JET FLOW USING COMPUTATIONAL AEROACOUSTICS

Journal of Computational Acoustics ◽

10.1142/s0218396x11004365 ◽

2011 ◽

Vol 19 (03) ◽

pp. 291-316 ◽

Cited By ~ 23

Author(s):

ALI UZUN ◽

M. YOUSUFF HUSSAINI

Keyword(s):

Flow Field ◽

Near Field ◽

Internal Flow ◽

Jet Flow ◽

Computational Aeroacoustics ◽

Far Field ◽

Free Jet ◽

Grid Points ◽

Field Noise ◽

Inflow Conditions

This paper demonstrates an application of computational aeroacoustics to the prediction of noise generated by a round nozzle jet flow. In this study, the nozzle internal flow and the free jet flow outside are computed simultaneously by a high-order accurate, multi-block, large-eddy simulation (LES) code with overset grid capability. To simulate the jet flow field and its radiated noise, we solve the governing equations on approximately 370 million grid points using high-fidelity numerical schemes developed for computational aeroacoustics. Projection of the near-field noise to the far-field is accomplished by coupling the LES data with the Ffowcs Williams–Hawkings method. The main emphasis of these simulations is to compute the jet flow in sufficient detail to accurately capture the physical processes that lead to noise generation. Two separate simulations are performed using turbulent and laminar inflow conditions at the jet nozzle inlet. Simulation results are compared with the corresponding experimental measurements. Results show that nozzle inflow conditions have an influence on the jet flow field and far-field noise.

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