Numerical prediction of air core diameter, coefficient of discharge and spray cone angle of a swirl spray pressure nozzle

Datta, Amitava; Som, S. K.

doi:10.1016/s0142-727x(00)00003-5

Cited by 91 publications

(40 citation statements)

References 11 publications

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“…Inside the swirl chamber da/do = 0.47 ± 0.03 and was also almost independent of Re. Both findings are in accordance with several authors [10,18,19], who reported independent air core size for regimes of high Re. Instabilities, in the form of air core fluctuations, both in the axial and radial direction ( Figure 5) were observed at the top of the swirl chamber.…”

Section: Resultssupporting

confidence: 94%

Internal flow and air core dynamics in simplex and spill-return pressure-swirl atomizers

Malý

Janáčková

Jedelský

et al. 2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

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It is well known that the spray characteristics of pressure-swirl atomizers are strongly linked to the internal flow and that an unstable air core may cause instabilities in the spray. In this paper, a 10:1 scale transparent Plexiglas (PMMA) model of a pressure-swirl atomizer as used in a small gas turbine is introduced. The internal flow was examined using high-speed imaging, laser-Doppler anemometry and computational fluid dynamics tools. The experimental and numerical results were analysed and compared in terms of the air core morphology and its temporal stability. Two different liquids were used, Kerosene-type Jet A-1 represented a commonly used fuel while p-Cymene (4-Isopropyltoluene) matched the refractive index of the Plexiglas atomizer body. The internal flow characteristics were set using dimensionless numbers i.e. the Reynolds number and Froude number. The flow test conditions were limited to inlet Reynolds numbers from 750 to 1750. Two atomizers were examined to represent a Simplex and Spill-return (SR) geometries. In a comparative manner, the SR atomizer features a central passage in the rear wall of the swirl chamber. The main advantage of this concept is that the fuel is always supplied to the swirl chamber at a high pressure therefore providing good atomization over a wide range of the injection flow rate. However, the presence of the spill orifice strongly affects the internal flow even if the spill-line is closed. The air core in the Simplex atomizer was found fully developed and stable. The SR atomizer behaved differently, the air core did not form at all, and the spray was therefore unstable. KeywordsInternal flow dynamics, Pressure-swirl, transparent nozzle, CFD Introduction Pressure-swirl (PS) atomizers are used in many applications where a large surface area of droplets is needed or a surface must by coated by a liquid e.g. combustion, fire suspension or air conditioning. PS atomizers are easy to manufacture, reliable and provide good atomization quality. They convert the pressure energy of the pumped liquid into kinetic and surface energy of the resulting droplets. The pumped liquid is injected via tangential ports into a swirl chamber, where it gains a swirl motion, under which it leaves the exit orifice as a conical liquid sheet. The centrifugal motion of the swirling liquid creates a low-pressure zone in the centre of the swirl chamber and generate an air core along the centreline. The flow inside the atomizer is rather complex; it is two-phase with secondary flow effects. There is a strong link between internal flow conditions and the resulting spray characteristics, however, not all aspects of the internal flow are well understood. Before the advent of computational fluid dynamics, a number of authors attempted to describe the internal flow by relatively simple analytical approaches. One of the first was presented by Taylor [1] which focused on an inviscid analysis using Bernoulli's equation and the principle of maximal flow. Taylor derived an equation for the discharge coeffi...

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Section: Resultssupporting

confidence: 94%

Internal flow and air core dynamics in simplex and spill-return pressure-swirl atomizers

Malý

Janáčková

Jedelský

et al. 2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

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“…If this quantity is neglected, the energy balance yields an approximate value of v^, which, together with Uco above, determines the half-angle of the cone in terms of magnitudes evaluated at the end of the orifice as The approximation (3.1) is similar to approximations proposed by Datta & Som (2000), Yule & Chinn (2000) and Nouri-Borujerdi & Kebriaee (2012). The approximate cone half-angle (3.1) is shown in figure 3(d) as a function of the atomizer constant.…”

Section: Effect Of the Atomizer Constantmentioning

confidence: 89%

Quasi-cylindrical approximation to the swirling flow in an atomizer chamber

Higuera

Pereña

2014

J. Fluid Mech.

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A quasi-cylindrical approximation is used to analyse the axisymmetric swirling flow of a liquid with a hollow air core in the chamber of a pressure swirl atomizer. The liquid is injected into the chamber with an azimuthal velocity component through a number of slots at the periphery of one end of the chamber, and flows out as an annular sheet through a central orifice at the other end, following a conical convergence of the chamber wall. An effective inlet condition is used to model the effects of the slots and the boundary layer that develops at the nearby endwall of the chamber. An analysis is presented of the structure of the liquid sheet at the end of the exit orifice, where the flow becomes critical in the sense that upstream propagation of long-wave perturbations ceases to be possible. This analysis leads to a boundary condition at the end of the orifice that is an extension of the condition of maximum flux used with irrotational models of the flow. As is well known, the radial pressure gradient induced by the swirling flow in the bulk of the chamber causes the overpressure that drives the liquid towards the exit orifice, and also leads to Ekman pumping in the boundary layers of reduced azimuthal velocity at the convergent wall of the chamber and at the wall opposite to the exit orifice. The numerical results confirm the important role played by the boundary layers. They make the thickness of the liquid sheet at the end of the orifice larger than predicted by irrotational models, and at the same time tend to decrease the overpressure required to pass a given flow rate through the chamber, because the large axial velocity in the boundary layers takes care of part of the flow rate. The thickness of the boundary layers increases when the atomizer constant (the inverse of a swirl number, proportional to the flow rate scaled with the radius of the exit orifice and the circulation around the air core) decreases. A minimum value of this parameter is found below which the layer of reduced azimuthal velocity around the air core prevents the pressure from increasing and steadily driving the flow through the exit orifice. The effects of other parameters not accounted for by irrotational models are also analysed in terms of their influence on the boundary layers.

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“…An improved technique was used by Datta and Som [44] who assumed the air core to be cylindrical and estimated the air core diameter from pressure drop calculations. They predicted the air core diameter, coefficient of discharge and spray cone angle from the numerical computations of flow within the nozzle.…”

Section: Figurementioning

confidence: 99%

Trends in Comprehensive Modeling of Spray Formation

Tharakan

Mukhopadhyay

Datta

et al. 2013

International Journal of Spray and Combustion Dynamics

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Comprehensive modeling of spray formation in liquid fuel injectors involves modeling of (i) internal hydrodynamics of fuel injector (ii) break up of liquid sheet leading to primary and secondary atomization and (iii) prediction of size and velocity distributions of droplets in the spray. Comprehensive models addressing all the three aspects are rare though some work has been reported that incorporate two of the three aspects. However, significant volume of literature exists on the individual modules. In the present work, progress and current trends in the individual modules have been extensively reviewed and their implications on development of comprehensive models have been discussed. The unresolved issues and future research directions are also indicated.

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Numerical prediction of air core diameter, coefficient of discharge and spray cone angle of a swirl spray pressure nozzle

Cited by 91 publications

References 11 publications

Internal flow and air core dynamics in simplex and spill-return pressure-swirl atomizers

Internal flow and air core dynamics in simplex and spill-return pressure-swirl atomizers

Quasi-cylindrical approximation to the swirling flow in an atomizer chamber

Trends in Comprehensive Modeling of Spray Formation

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