Development of shock wave and vortex structures in unsteady jets

Golub, V. V.

doi:10.1007/bf01415825

Cited by 20 publications

(21 citation statements)

References 3 publications

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“…Similar type of tip vortex formation was also noticed in [53] for an under-expanded nitrogen jet, albeit with the vortices shifted noticeably further downstream compared to the hydrogen jets of the current study. This could be associated with the higher nozzle exit velocity of hydrogen (~1300 m/s) compared to that of nitrogen (~330 m/s).…”

Section: Transient Shock Dynamics and Jet Developmentsupporting

confidence: 85%

“…For this condition the methane jet exited from the nozzle with a velocity of U 1 ≈450 m/s which was much closer to that of nitrogen in [53] than hydrogen here. Similarly to [53], Figure 8 reveals that, unlike hydrogen, the methane jet exhibited a relatively smaller initial flow recirculation which consequently formed the jet tip vortices after the Mach disk location. The temporal intervals in Figures 5-8 are based on t 0 which was ~3 times larger for the methane jet than that of hydrogen.…”

Section: Transient Shock Dynamics and Jet Developmentmentioning

confidence: 71%

“…a wider Mach disk would be formed [8]. The fluctuating nature of the Mach disk dimensions (before its settlement at a final semi-steady location), has been attributed to the fluctuating behaviour of the upstream flow of the Mach reflection [14,53].…”

Section: Transient Shock Dynamics and Jet Developmentmentioning

confidence: 99%

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Gas dynamics and flow characteristics of highly turbulent under-expanded hydrogen and methane jets under various nozzle pressure ratios and ambient pressures

Hamzehloo

Aleiferis

2016

International Journal of Hydrogen Energy

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The current study used large eddy simulations to investigate the sonic and mixing characteristics of turbulent under-expanded hydrogen and methane jets with various nozzle pressure ratios issued into various ambient pressures including elevated conditions relevant to applications in direct injection gaseous-fuelled internal combustion engines. Due to the relatively low density of most gaseous fuels such as hydrogen and methane, DI requires high injection pressures to achieve suitable mass flow rates for fast in-cylinder fuel delivery and rapid fuel-air mixing. Such pressures typically form an under-expanded fuel jet past the nozzle exit. Test cases of hydrogen injection with nozzle pressure ratio (NPR) of 10 issued into quiescent air with pressure P ∞ ≈1, 5 and 10 bar were simulated. Direct comparison between hydrogen and methane jets with NPR=8.5 and P ∞ ≈1 was also made. The effect of ambient pressure on features of transient development of the nearnozzle shock structure and tip vortices (vortex ring) was investigated. It was observed that at constant NPR, higher ambient pressure resulted in slightly faster formation of the Mach reflection and shorter Mach disk settlement time. Different mechanisms were observed between hydrogen and methane with regards to transient formation of their initial tip vortex rings. It was found that the initial transient tip vortices of hydrogen jets may also contribute to the flow instabilities at the boundary of the intercepting shock and, unlike for methane, promote fuel-air mixing before the Mach reflection. It was also shown that the nearnozzle shock structure was only affected by NPR regardless of the ambient pressure. Furthermore, no flow recirculation zone was found just downstream of the Mach disk, a finding comparable to all previous experimental investigations. Also, it was observed that a locally richer mixture was created for jets with higher NPR or with higher ambient pressure at constant NPR. Based on the results of the current study, correlations were proposed for the shock cell spacing and jet tip penetration of highly under-expanded jets issued from millimetre-size circular nozzles.

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Section: Transient Shock Dynamics and Jet Developmentsupporting

confidence: 85%

Section: Transient Shock Dynamics and Jet Developmentmentioning

confidence: 71%

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Gas dynamics and flow characteristics of highly turbulent under-expanded hydrogen and methane jets under various nozzle pressure ratios and ambient pressures

Hamzehloo

Aleiferis

2016

International Journal of Hydrogen Energy

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“…44 This causes the diameter of the vortex loop to be innately larger at higher Mach numbers, as shown in Figure 16(a). Compared to the smaller nozzle (see Figure 8(a)), the variation in vortex loop diameter at different Reynolds numbers is more pronounced for the larger nozzle.…”

Section: Resultsmentioning

confidence: 99%

Shock wave-induced vortex loops emanating from nozzles with singular corners

et al. 2010

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The focus of the current study is to examine experimentally the diffracted shock wave pattern and the consequent vortex loop formation, propagation, and decay from nozzles having singular corners.Non-intrusive qualitative and quantitative techniques: schlieren, shadowgraphy, and particle image velocimetry (PIV) are employed to analyse the induced flow fields. Eye-shaped nozzles were used with the corner joints representing singularities. The length of the minor axes are a = 6 and 15 mm, with the major axis b = 30 mm for both cases. The experiments are performed for flow Reynolds numbers in the range 0.8 ×10 5 and 4.6 ×10 5 . Air is used in both driver and driven sections of the shock tube.

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“…[1][2][3] Also, because of many important physical phenomena, the starting flow fields of supersonic jets have been studied previously. 4,5 Moreover, interaction of the starting flow fields of supersonic jets with rigid bodies are found in many areas of aerospace and mechanical engineering; however there are not many works reported in this field. This paper focuses on unsteady supersonic flows and is concerned with the development of a simple implicit pressure correction method for computing compressible fluids and extending it to the ability of handle supersonic axisymmetric flows, which contain strong shocks.…”

Section: Introductionmentioning

confidence: 99%

Simulation of the Supersonic Starting Jet Flow Interactions with a Rigid Body

Azizian¹

2017

AAOAJ

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The interaction of starting flow fields of an axisymmetric supersonic under-expanded jet with the cross section of a cylinder is simulated. To achieve this goal, an implicit pressure correction algorithm based on a finite volume method on a collocated grid for simulation of compressible flows is presented. A two dimensional test problem, the supersonic flow through a wind tunnel with a step, is simulated and the numerical outcomes agree very well with previous results. Then, the method is extended to axisymmetric flows and validated for a supersonic circular jet flow. Finally, the proposed method is used to analyze the concerned problem. To describe the evolution of the starting flow fields, the Mach number, pressure, density and temperature contours evolutions through time are investigated. Also, the evolution of total force and temperature distribution on the cylinder cross section surface are studied during the collision of mushroom head of supersonic jet with the surface of cylinder. Keywordswhere γ is the ratio of specific heats, and by using this equation in energy equation (eq. 3), the number of variables are reduced.In the aforementioned governing equations, the conservation forms are used that the fluxes of mass, momentum and energy into and out of the control volume, themselves become important dependent variables rather than just the primitive variables. This is due to the fact that there are discontinuities in primitive variables across the shock; however, the fluxes are constant across the shock wave. 9To non-dimensionalization, the reference variables are used as follow:Where , r r u ρ and L are reference velocity, density and length, respectively. In this way, the non-dimensional governing equations are: AlgorithmThe variables are collocated in space at the center of control volumes. Moreover, the numerical method is implicit in time. The governing equations can be discretized by integrating over a control volume and using the Gauss theorem as follows:. . . .where the superscripts denote the time steps. Also, the subscripts c,v and face represent the values at the center of control volumes and the values that located on the control volume surfaces, respectively.Here, V and face A determine the volume and surface area of the control volumes. Furthermore, i g is the momentum in the direction of i and N u is the face normal velocity, which is acquired by projection and nor that interpolation. 10To find the values on the control volume surfaces, which there are in the convection term of the governing equations, the following scheme is used:Where Q can be each of the terms on the control volume surfaces. At the vicinity of discontinuity w i takes the value of +1 and -1 depends on the flow direction, but in the rest of the domain it takes the value of zero.Adapted from the researches of Hou & Mahesh, 10,11 the algorithm is based on a pressure-correction method, which the face normal velocities are projected to satisfy a constraint on the divergence that is determined by the energy equation. Thi...

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Development of shock wave and vortex structures in unsteady jets

Cited by 20 publications

References 3 publications

Gas dynamics and flow characteristics of highly turbulent under-expanded hydrogen and methane jets under various nozzle pressure ratios and ambient pressures

Gas dynamics and flow characteristics of highly turbulent under-expanded hydrogen and methane jets under various nozzle pressure ratios and ambient pressures

Shock wave-induced vortex loops emanating from nozzles with singular corners

Simulation of the Supersonic Starting Jet Flow Interactions with a Rigid Body

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