LES of cavitating flow inside a Diesel injector including dynamic needle movement

Örley, Felix; Hickel, Stefan; Schmidt, Steffen J.; Adams, Nikolaus A.

doi:10.1088/1742-6596/656/1/012097

Cited by 6 publications

(6 citation statements)

References 9 publications

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“…They conclude that RANS can predict cavitation with a reasonably acceptable accuracy in an operating condition with high pressure difference, whereas it fails to predict the cavitation at a lower pressure difference. It is worth mentioning the recent work of Ö rley et al, 22 who employed an LES framework with cut-cell immersed boundary method and a barotropic fluid, including the effect of non-condensable gas, for the simulation of a nine-hole diesel injector to obtain timeresolved information on cavitating or turbulent flow structures in the injector sac, orifices and jets.…”

Section: Introductionmentioning

confidence: 99%

Performance of turbulence and cavitation models in prediction of incipient and developed cavitation

Koukouvinis

Naseri

Gavaises

2016

International Journal of Engine Research

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The aim of the current paper is to assess the impact of turbulence and cavitation models on the prediction of Diesel injector nozzle flow. Two nozzles are examined, an enlarged one, operating at incipient cavitation and an industrial injector tip operating at developed cavitation. The turbulence model employed include the RNG k-ε, Realizable k-ε and k-omega SST RANS models, linear pressure-strain Reynolds Stress Model and the WALE Large Eddy Simulation model. The results indicate that all RANS and the Reynolds stresses turbulence models have failed to predict cavitation inception, due to their limitation to resolve adequately the low pressure existing inside vortex cores, which is responsible for cavitation development in this particular flow configuration. Moreover, RANS models failed to predict unsteady cavitation phenomena in the industrial injector. On the other hand, the WALE LES model was able to predict incipient and developed cavitation, while also capturing the shear layer instability, vortex shedding and cavitating vortex formation. Furthermore, the performance of two cavitation methodologies is discussed within the LES framework. In particular, a barotropic model and a mixture model based on the asymptotic Rayleigh-Plesset equation of bubble dynamics have been tested. The results indicate that although the solved equations and phase change formulation is different in these models, the predicted cavitation and flow field were very similar at incipient cavitation conditions. At developed cavitation conditions standard cavitation models may predict unrealistically high liquid tension, so modifications may be essential. It is also concluded that accurate turbulence representation is crucial for cavitation in nozzle flows.

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Section: Introductionmentioning

confidence: 99%

Performance of turbulence and cavitation models in prediction of incipient and developed cavitation

Koukouvinis

Naseri

Gavaises

2016

International Journal of Engine Research

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“…The current study treats primevally cases of hydrodynamic cavitation, where flow is often treated as isothermal; 1,48,49 however, the assumption that thermal effects play a role is followed even in cases of cavitating flows inside diesel injector nozzles. 2,33,50,51…”

Section: Governing Equationsmentioning

confidence: 99%

“…The IB methodology is particularly relevant for these cases as it allows the modeling of the flow field at zero lift, where the needle remains closed. Numerous numerical works are focused on these flows, which accommodate the movement with either complete remeshing the domain 1 or cell layer addition and inflation 2 or interpolating between girds of different resolution but same cell count; 82 only few studies employ cut-cell IB methods, [29][30][31][32][33] which however do not permit the needle to fully close but rather demand a minimum lift of about 8%, 29 2%-4%, 30 or 1.5%. 31 Cut-cell methods could be an alternative option, though the Cartesian background geometry would necessitate an excessive amount of cells for describing small needle/needle seat gaps.…”

Section: Cavitation In a Diesel Injector With Needle Movementmentioning

confidence: 99%

“…Battistoni et al, 29 Zhao et al, 30 as well as Örley et al [31][32][33] employed cut-cell IB methodologies on the numerical study of cavitation inception in diesel injectors with moving needle. The recent works of Huang et al 34 and Park et al 35 on cavitation induced by the motion of underwater projectiles, and Xu et al 36,37 on cloud cavitation around blunt bodies followed a cut-cell approach as well.…”

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confidence: 99%

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A direct forcing immersed boundary method for cavitating flows

Stavropoulos-Vasilakis

Rodríguez

Kyriazis

et al. 2021

Numerical Methods in Fluids

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In the current study, an immersed boundary method for simulating cavitating flows with complex or moving boundaries is presented, which follows the discrete direct forcing approach. Although the immersed boundary methods are widely used in various applications of single phase, multiphase, and particulate flows, either incompressible or compressible, and numerous alternative formulations exist, to the best of the authors' knowledge, a handful of computational works employ such methodologies on cavitating flows. The herein proposed method, following previous works of the author's group, tries to fill this gap and to solidify the development of a computational tool of a simple formulation capable to tackle complex numerical problems of cavitation modeling. The method aims to be used in a wide range of applications of industrial interest and treat flows of engineering scales. Therefore, a validation of the method is performed by numerous benchmark test-cases, of progressively increasing complexity, from incompressible low Reynolds number to compressible and highly turbulent cavitating flows. K E Y W O R D Scavitation, diesel injector, direct forcing, immersed boundary method, turbulence modeling INTRODUCTIONWithin the framework of computational fluid dynamics, applications of industrial interest often refer to flows in complex geometries or around moving bodies; their simulation may be numerically challenging and computationally expensive. Many cases of cavitating flows fall into that category. For example, cavitation formation in diesel injector nozzles with moving needle, gear pumps, or propellers mounted under ship hauls, refer to problems with moving geometrical parts and include different geometrical features with wide range of length scales and topological features that impose severe constraints in mesh generation. The conventional strategy of generation of boundary-conforming grids for such problems, may become demanding and time consuming. When the numerical simulation involves moving parts with large displacements, common conformal grid strategies result in remeshing of the entire domain in every time-step, 1 or deforming the grid and adding or removing cell-layers when a desired cell size is reached. 2 In the case of marine propellers, to accommodate their rotational motion, either the entire computational domain would be rotated accordingly, 3 or a multi-region mesh would be used, which lets the part of the grid that conforms with the propeller blades to slide with regards to the global domain. 4 Another approach of over-set grids 5 (also known as Chimera grids), employs multiple overlapping 3092

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“…The resulting mass flow rate, as well as the liquid jets emerging from the orifices, showed noticeable sensitivity to the needle off-axis motion. A cut-cell based immersed boundary method for modelling the needle motion, without considering the effect of wobble was presented by Ö rley et al 16,36 with a primary focus on the developed turbulent structures. Moreover, all aforementioned studies have not considered the compressibility of the phases and they assumed needle motion in the axial direction only.…”

Section: Introductionmentioning

confidence: 99%

Numerical simulation of fuel dribbling and nozzle wall wetting

Gavaises

Murali-Girija

Rodríguez

et al. 2021

International Journal of Engine Research

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The present work describes a numerical methodology and its experimental validation of the flow development inside and outside of the orifices during a pilot injection, dwelt time and the subsequent start of injection cycle. The compressible Navier-Stokes equations are numerically solved in a six-hole injector imposing realistic conditions of the needle valve movement and considering in addition a time-dependent eccentric motion. The valve motion is simulated using the immersed boundary method; this allows for simulations to be performed at zero lift during the dwelt time between successive injections, where the needle remains closed. Moreover, the numerical model utilises a fully compressible two-phase (liquid, vapour) two-component (fuel, air) barotropic model. The air’s motion is simulated with an additional transport equation coupled with the VOF interface capturing method able to resolve the near-nozzle atomisation and the resulting impact of the injected liquid on the oleophilic nozzle wall surfaces. The eccentric needle motion is found to be responsible for the formation of strong swirling flows inside the orifices, which not only contributes to the breakup of the injected liquid jet into ligaments but also to their backwards motion towards the external wall surface of the injector. Model predictions suggest that such nozzle wall wetting phenomena are more pronounced during the closing period of the valve and the re-opening of the nozzle, due to the residual gases trapped inside the nozzle, and which contribute to the poor atomisation of the injected fluid upon re-opening of the needle valve in subsequent injection events.

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LES of cavitating flow inside a Diesel injector including dynamic needle movement

Cited by 6 publications

References 9 publications

Performance of turbulence and cavitation models in prediction of incipient and developed cavitation

Performance of turbulence and cavitation models in prediction of incipient and developed cavitation

A direct forcing immersed boundary method for cavitating flows

Numerical simulation of fuel dribbling and nozzle wall wetting

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