Experimental study of confined coaxial jets in a non-axisymmetric co-flow

Larsson, I. A. Sofia; Lycksam, Henrik; Lundström, T. Staffan; Marjavaara, B. Daniel

doi:10.1007/s00348-020-03094-3

Cited by 16 publications

(4 citation statements)

References 25 publications

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“…It is known that the far-field equivalence ratio φ ∞ → 0 due to the absence of fuel in the free stream. Since the length of the inner potential core is less than d st for the velocity ratio (Larsson et al 2020), the centreline composition at the axial location (x = d st ) will not be pure fuel. Thus, the local centreline equivalence ratio is unknown and will be estimated in this section.…”

Section: Radial Variation Of the Local Equivalence Ratio ( φ)mentioning

confidence: 99%

Insights into the flame transitions and flame stabilization mechanisms in a freely falling burning droplet encountering a co-flow

Vadlamudi,

Aravind,

Basu

2023

J. Fluid Mech.

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The present study investigates the flame dynamics of a contactless burning fuel droplet under free fall subjected to a co-flow. The dynamic external relative flow established due to co-flow and droplet acceleration results in a series of droplet flame transitions. Different flame structures were observed, including a wake flame, reversed wake flame and enveloped flame. Following ignition, the droplet is allowed to fall through the central tube of a co-flow arrangement, and, at its exit, the droplet flame encounters the co-flow. The wake flame, which was established based on the droplet's instantaneous velocity of descent, encounters the abrupt relative velocity jump due to the co-flow. This causes the droplet flame to go through various transitions as it approaches equilibrium with the surrounding flow. Once it equilibrates, the droplet flame evolves in response to the instantaneous relative flow velocity. The droplet flame evolves by altering both its shape and the stabilization mechanism. Two stabilization mechanisms were identified for the droplet wake flame: edge-flame stabilization and bluff-body stabilization. The stabilization mechanism for different flame structures and the transition events have been theoretically analysed, and the relation between flame shape evolution and flow velocity has been determined based on the flow-field characteristics at the corresponding Re (Reynolds number) range. Furthermore, these correlations are employed in a mathematical formulation based on the spring–mass analogy, which predicts the droplet flame evolution after encountering the co-flow, including all the transition events.

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Section: Radial Variation Of the Local Equivalence Ratio ( φ)mentioning

confidence: 99%

Insights into the flame transitions and flame stabilization mechanisms in a freely falling burning droplet encountering a co-flow

Vadlamudi,

Aravind,

Basu

2023

J. Fluid Mech.

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“…Although stationary mixing declined in the streamwise direction, the rate of relative mixing varied according to the mixing tendency of the regimes. Many studies [51][52][53][54] have shown that the Reynolds number or velocity ratio affects the mixing of flow regimes. Thus, the MR is defined as the ratio of the Reynolds number at the outlet to that at the inlet for each control volume.…”

Section: Inlet Egrmentioning

confidence: 99%

Entropy generation rate analysis of turbocharger radial flow compressor in range from surge to choke

Altafi,

Mojaddam,

Bastankhah

2023

Proceedings of the Institution of Mechanical Engineers, Part A:

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This study compares the local losses of a radial compressor in the range from surge to choke considering shock phenomena, boundary layer separation, and mixing mechanisms. For this purpose, formulation of the local entropy generation rate (EGR) is added to the computational fluid dynamics (CFD) solver, which models the turbulent flow field of the compressor through the RANS approach. For validation, the numerical pressure rise curve of the compressor is compared with the experimental data. The results indicate that at the design point, the impeller, diffuser, and the volute account for approximately 50.8%, 30.0%, and 12.3% of the EGR, respectively, with approximately 5% in the impeller backspace, 1% in the diffuser cavity, and less than 0.5% in the inlet duct. Approaching the surge condition, local losses due to mixing and shock waves decline while boundary layer losses increase. Based on comprehensive analysis of the leading-edge boundary layer, the largest dead-air zone is found at the design point, resulting in a lower diffusion entrance loss and a higher mixing loss. Furthermore, the EGR variation in the diffuser channel is investigated by shedding light on mixing dynamics and classification of the channel flow regime into three different zones based on mixing ratio (MR). The outcomes show that the flow regime tends to mix more quickly at a higher MR, resulting in a slight decrease in EGR, which benefits compressor performance. We demonstrate that the mixing rate of flow regimes decreases in both the leading-edge boundary layer and the radial diffuser approaching the surge margin.

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“…The coaxial feeding of the aerosol and sheath gas in the downer produces a confined jet also referred to as Craya-Curtet jets. These kinds of jets have been addressed in different investigations and they are of relevance for certain industrial applications such as jet pumps or jet furnaces [35][36][37]. One of the main issues associated with these kinds of jets is the appearance of a region of reverse flow or recirculation as well as separation zones near the wall when the coaxial surrounding flow is sufficiently low.…”

Section: Mathematical Model 231 Governing Equationsmentioning

confidence: 99%

Particle Lagrangian CFD Simulation and Experimental Characterization of the Rounding of Polymer Particles in a Downer Reactor with Direct Heating

et al. 2021

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Polypropylene (PP) powders are rounded at different conditions in a downer reactor with direct heating. The particles are fed through a single central tube, while the preheated sheath gas is fed coaxially surrounding the central aerosol jet. The influence of the process parameters on the quality of the powder product in terms of particle shape and size is analyzed by correlating the experimental results with the flow pattern, residence time distribution of the particles and temperature distribution predicted by computational fluid dynamics (CFD) simulations. An Eulerian–Lagrangian numerical approach is used to capture the effect of the particle size distribution on the particle dynamics and the degree of rounding. The simulation results reveal that inlet effects lead to inhomogeneous particle radial distributions along the total length of the downer. The configuration of particle/gas injection also leads to fast dispersion of the particles in direction of the wall and to particle segregation by size. Broad particle residence time distributions are obtained due to broad particle size distribution of the powders and the particles dispersion towards the wall. Lower mass flow ratios of aerosol to sheath gas are useful to reduce the particle dispersion and produce more homogenous residence time distributions. The particles’ residence time at temperatures above the polymer’s melting onset is determined from the simulations. This time accounts for the effective treatment (rounding) time of the particles. Clear correlations are observed between the numerically determined effective rounding time distributions and the progress of shape modification on the particles determined experimentally.

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Experimental study of confined coaxial jets in a non-axisymmetric co-flow

Cited by 16 publications

References 25 publications

Insights into the flame transitions and flame stabilization mechanisms in a freely falling burning droplet encountering a co-flow

Insights into the flame transitions and flame stabilization mechanisms in a freely falling burning droplet encountering a co-flow

Entropy generation rate analysis of turbocharger radial flow compressor in range from surge to choke

Particle Lagrangian CFD Simulation and Experimental Characterization of the Rounding of Polymer Particles in a Downer Reactor with Direct Heating

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