Search results

1 – 10 of over 11000
Article
Publication date: 1 January 1992

J.I. RAMOS

A domain‐adaptive technique which maps the unknown, time‐dependent, curvilinear geometry of annular liquid jets into a unit square is used to determine the steady state…

Abstract

A domain‐adaptive technique which maps the unknown, time‐dependent, curvilinear geometry of annular liquid jets into a unit square is used to determine the steady state mass absorption rate and the collapse of annular liquid jets as functions of the Froude, Peclet and Weber numbers, nozzle exit angle, initial pressure and temperature of the gas enclosed by the liquid, gas concentration at the nozzle exit, ratio of solubilities at the inner and outer interfaces of the annular jet, pressure of the gas surrounding the liquid, and annular jet's thickness‐to‐radius ratio at the nozzle exit. The domain‐adaptive technique yields a system of non‐linearly coupled integrodifferential equations for the fluid dynamics of and the gas concentration in the annular jet, and an ordinary differential equation for the time‐dependent convergence length. An iterative, block‐bidiagonal technique is used to solve the fluid dynamics equations, while the gas concentration equation is solved by means of a line Gauss‐Seidel method. It is shown that the jet's collapse rate increases as the Weber number, nozzle exit angle, temperature of the gas enclosed by the annular jet, and pressure of the gas surrounding the jet are increased, but decreases as the Froude and Peclet numbers and annular jet's thickness‐to‐radius ratio at the nozzle exit are increased. It is also shown that, if the product of the inner‐to‐outer surface solubility ratio and the initial pressure ratio is smaller than one, mass is absorbed at the outer surface of the annular jet, and the mass and volume of the gas enclosed by the jet increase with time.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 2 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 1 July 1956

In an arrangement for deflecting a propulsive jet forwardly for braking purposes the jet reversal is effected by moving a series of curved blades at the rear end of the jet

Abstract

In an arrangement for deflecting a propulsive jet forwardly for braking purposes the jet reversal is effected by moving a series of curved blades at the rear end of the jet pipe to intercept the jet stream. As shown in FIG. 1 the jet pipe 10 terminates in an opening in the upper surface 12 of a delta‐wing, the deflecting blades 17 being mounted to form a grille 14 which is normally housed forwardly of the jet discharge opening, but which is movable rearwardly by an electric motor 33 and rack‐and‐pinion gearing 27, 28 into a position where it extends across the discharge opening to reverse the jet. FIG. 2 shows a modification in which the jet is divided into two streams by a wedge shaped vane 109 to discharge through openings 107, 108 in the upper and lower wing surfaces respectively, deflexion of the streams being effected by upper and lower grilles 102, 103. In addition the vane 109 may be rotated about a pivot 140 to deflect the whole of the jet through the upper or lower wing outlet. A similar effect may be obtained without the use of a bifurcated jet pipe by modifying the arrangement according to FIG. 1 to include a downwardly directed branch of the jet pipe 10 opening in the undersurface of the wing and controlling the flow of the jet through this branch by hinged flaps at the junction of the main and branch pipes, and in the undersurface of the wing, respectively. In the case of a circular jet pipe 40, FIG 3, the rear portion of the pipe is cut off along oblique planes 41, 42, and the cut‐away portions occupied by curved vanes 43, 44 hinged about a rear transverse axis 45. The vanes 43, 44 are surrounded by curved blade grills 46, 47 which in turn are enclosed by external plates 51, 52. To effect reversal of the jet the closure plates 51, 52 are first slid forwardly clear of the grilles 46, 47, and jacks 55, 56 are then operated to move the grilles 46, 47 and the tail portion 53 of the jet pipe forwardly, thus causing the vanes 41, 42 to pivot about the axis 45 to obstruct the jet pipe and cause the jet to escape through the grilles 46, 47.

Details

Aircraft Engineering and Aerospace Technology, vol. 28 no. 7
Type: Research Article
ISSN: 0002-2667

Article
Publication date: 19 April 2013

Saeed Fathi, Phill Dickens and Richard Hague

The purpose of this paper is to present the findings on jet array instabilities of molten caprolactam. Initial investigations showed that although a suitable range of…

Abstract

Purpose

The purpose of this paper is to present the findings on jet array instabilities of molten caprolactam. Initial investigations showed that although a suitable range of parameters was found for stable jetting, there were cases where instabilities occurred due to external sources such as contamination.

Design/methodology/approach

The inkjet system consisted of a melt supply unit, filtration unit and printhead with pneumatic and thermal control. A start‐up strategy was developed to initiate the jetting trials. A digital microscope camera monitored the printhead nozzle plate to record the jet array stability within the recommended range of parameters from earlier research. The trials with jet instabilities were studied to analyse the instability behaviour.

Findings

It was found that instabilities occurred in three forms which were jet trajectory error, single jet failure and jet array failure. Occasionally, the jet with incorrect trajectory remained stable. When a jet failed, bleeding of melt from the nozzle due to the actuations influenced the adjacent jets initiating an array of jets to fail similar to falling dominos.

Originality/value

The research concept is novel and investigating the jet array instability behaviours could give an understanding on jetting reliability issues.

Article
Publication date: 1 June 1977

C.N. Jones

The literature on jets is extensive but scattered. A concise guide is needed, and this paper attempts (at the risk of over‐simplification) to summarise some of the…

Abstract

The literature on jets is extensive but scattered. A concise guide is needed, and this paper attempts (at the risk of over‐simplification) to summarise some of the available information, both theoretical and experimental (some of it obtained in the Department of Mechanical Engineering) on those jet properties which are important in engineering — velocity profile and decay, spread, entrainment and static pressure.

Details

Aircraft Engineering and Aerospace Technology, vol. 49 no. 6
Type: Research Article
ISSN: 0002-2667

Article
Publication date: 1 August 2004

L. Lin and X. Bai

Recent years have seen a rapid development of ink‐jet printing technology. This paper reviews the state‐of‐the‐art in ink‐jet printing technology and gives an overview of…

1220

Abstract

Recent years have seen a rapid development of ink‐jet printing technology. This paper reviews the state‐of‐the‐art in ink‐jet printing technology and gives an overview of ink‐jet printing into the immediate future. The focus is placed on various applications of jet printing technology. The potential of applying jetting technology in the conventionally surface coating dominated applications will also be explored.

Details

Pigment & Resin Technology, vol. 33 no. 4
Type: Research Article
ISSN: 0369-9420

Keywords

Article
Publication date: 5 March 2018

Kannan B.T. and Panchapakesan N.R.

This study aims to investigate the effects of nozzle momentum flux distribution on the flow field characteristics.

Abstract

Purpose

This study aims to investigate the effects of nozzle momentum flux distribution on the flow field characteristics.

Design/methodology/approach

The nozzle configuration consists of a central nozzle surrounded by four nozzles. All nozzles have the same diameter and constant separation between nozzles. OpenFOAM® is used for simulating the jet flow. Reynolds-averaged Navier-Stokes (RANS) equations are solved iteratively with a first-order closure for turbulence. Pitot-static tube with differential pressure transducer is used for mean velocity measurements. The comparison of computed results with experimental data shows similar trend and acceptable validation.

Findings

According to the results, the momentum flux distribution significantly alters the near field of multiple turbulent round jets. Highly non-linear decay region in the near field is found for the cases having higher momentum in the outer jets. As a result of merging, increased positive pressure is found in the mixing region. Higher secondary flows and wider mixing region are reported as a result of momentum transfer from axial to lateral directions by Reynolds stresses.

Research limitations/implications

The present study is limited to isothermal flow of air jet in air medium.

Social implications

Optimum momentum flux distribution in multijet injector of a combustor can reap better mixing leading to better efficiency and lesser environmental pollution.

Originality/value

As summary, the contributions of this paper in the field of turbulent jets are following: simulations for various momentum distribution cases have been performed. In all the cases, the flow at the nozzle exit is subsonic along with constant velocity profile. To simulate proper flow field, a large cylinder-type domain with structured grid is used with refinements toward the nozzle exit and jet axis. The results show that the non-linearity increases with increase in momentum of outer jets. Longer merging zones are reported for cases with higher momentum in outer nozzles using area-averaged turbulent kinetic energy. Similarly, wider mixing regions are reported using secondary flow parameter and visualizations.

Details

Aircraft Engineering and Aerospace Technology, vol. 90 no. 2
Type: Research Article
ISSN: 1748-8842

Keywords

Article
Publication date: 1 May 1996

J.I. Ramos

This paper analyses numerically the effects of sinusoidal g—jitter onthe fluid dynamics of, and mass transfer in, annular liquid jets. It is shownthat the pressure and…

Abstract

This paper analyses numerically the effects of sinusoidal g—jitter on the fluid dynamics of, and mass transfer in, annular liquid jets. It is shown that the pressure and volume of the gases enclosed by the jet, the gas concentration at the jet’s inner interface, and the mass absorption rates at the jet’s inner and outer interfaces are sinusoidal functions of time which have the same frequency as that of the g—jitter. The amplitude of these oscillations increases and decreases, respectively, as the amplitude and frequency, respectively, of the g—jitter is increased. The pressure coefficient and the gas concentration at the jet’s inner interface are in phase with the applied g—jitter and the amplitude of their oscillations increases almost linearly with the amplitude of the g—jitter. The mass absorption rates at the jet’s inner and outer interfaces exhibit a phase lag with respect to the g—jitter.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 6 no. 5
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 1 January 1962

S. Pivko

A simplified method for estimating the aerodynamic properties of thin flapped aerofoils influenced by high velocity jet sheets is developed. It is assumed that the main…

Abstract

A simplified method for estimating the aerodynamic properties of thin flapped aerofoils influenced by high velocity jet sheets is developed. It is assumed that the main flow around the aerofoil does not influence the velocity distribution in the jet. Considering also the effect of the mixing with the surrounding air, a real jet is supposed to be replaced by an appropriate aerodynamic model, having a linear downstream distribution of velocity adopted on the basis of test data. Both thin aerofoil and the jet sheet are adequately replaced by vortex distributions,so that the lift and the pitching moment of the aerofoil influenced by the jet may be evaluated in the usual manner. Comparison with some available experimental results shows that the proposed semi‐empirical method gives good agreement with experiment.

Details

Aircraft Engineering and Aerospace Technology, vol. 34 no. 1
Type: Research Article
ISSN: 0002-2667

Article
Publication date: 2 May 2017

Andrzej Boguslawski, Artur Tyliszczak, Agnieszka Wawrzak and Karol Wawrzak

The purpose of the paper is to summarize recent achievements and suggest further research directions in numerical studies of round free jets with particular attention on…

Abstract

Purpose

The purpose of the paper is to summarize recent achievements and suggest further research directions in numerical studies of round free jets with particular attention on the influence of the inlet parameters (mean velocity, turbulence intensity, length and time scales) on the jet dynamics.

Design/methodology/approach

The large eddy simulation (LES) and direct numerical simulation (DNS) are regarded as accurate tools which can support expensive and requiring sophisticated measurements techniques experimental studies. In the paper, the authors present challenges and recent findings related to the LES and DNS of jet type flows in isothermal, heated, excited and reactive conditions.

Findings

LES of the isothermal jet allowed to identify the new jet instability mechanism leading to the self-sustained oscillations and to determine conditions required to trigger this phenomenon. Numerical simulation on the low-density round jet captured the phenomenon of absolute instability with a very good agreement with the experimental findings. LES/DNS of excited jet exhibited bifurcating and blooming jet and showed that the jet can be directly controlled by excitation frequency what is crucial issue also for flame shape control.

Originality/value

The paper shows complexity of seemingly simple jet type flow and proves that despite a huge interest in these flows and relatively deep knowledge on the jet dynamics there are still some open issues requiring further studies.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 27 no. 5
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 18 October 2018

S. Manigandan and Vijayaraja K.

The purpose of this paper is to present the results of mixing promotion and screech frequency of controlled elliptical supersonic jet.

Abstract

Purpose

The purpose of this paper is to present the results of mixing promotion and screech frequency of controlled elliptical supersonic jet.

Design/methodology/approach

Flow field characteristics of low-aspect-ratio elliptical jets are examined at over-expanded, under-expanded and correctly expanded conditions. The tabs are placed at elliptical jet exit along the major and minor axes.

Findings

The results show that the mixing done by the minor axis is superior to the tabs along major axis. At all pressure ratios, the content of jet noise and the frequency are high for the tabs along the major axis because of increase in the amplitude of screech frequency. Further the tabs along minor axis show a dominance of large-scale vertical structures. In under-expanded conditions, the shock cell shows the rapid change because of the presence of tabs. The tabs along minor axis are making the shock weaker, hence no evidence of axis switching.

Practical implications

To achieve the greater performance of jet, the authors need to reduce the potential core length of the issuing jet. This can be achieved by implementing different types of tabs at the exit of the nozzle.

Originality/value

The present paper represents the flow of controlled jet using inverted triangular tabs. By achieving the controlled jet flow, the performance of propulsion systems can be improved. This can be used in systems such as combustion chamber, missile’s noise reduction and thrust vector control.

Details

Aircraft Engineering and Aerospace Technology, vol. 90 no. 9
Type: Research Article
ISSN: 1748-8842

Keywords

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