Effects of Prandtl number and a new instability mode in a plane thermal plume

Lakkaraju, Rajaram; Alam, Meheboob

doi:10.1017/s0022112007008610

Cited by 6 publications

(4 citation statements)

References 18 publications

(32 reference statements)

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“…It can also not be ruled out that nonlinear effects alter the threshold of global instability (Couairon & Chomaz 1997). The influence of the Prandtl number has not been investigated in this study, but it has been shown by Lakkaraju & Alam (2007) that the instability behaviour of planar plumes undergoes qualitative changes as P r is varied far from unity.…”

Section: Discussionmentioning

confidence: 92%

Global stability of buoyant jets and plumes

2017

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The linear global stability of laminar buoyant jets and plumes is investigated under the low-Mach-number approximation. For Richardson numbers in the range $10^{-4}\leqslant Ri\leqslant 10^{3}$ and density ratios $S=\unicode[STIX]{x1D70C}_{\infty }/\unicode[STIX]{x1D70C}_{jet}$ between 1.05 and 7, only axisymmetric perturbations are found to exhibit global instability, consistent with experimental observations in helium jets. By varying the Richardson number over seven decades, the effects of buoyancy on the base flow and on the instability dynamics are characterised, and distinct behaviour is observed in the low-$Ri$ (jet) and in the high-$Ri$ (plume) regimes. A sensitivity analysis indicates that different physical mechanisms are responsible for the global instability dynamics in both regimes. In buoyant jets at low Richardson number, the baroclinic torque enhances the basic shear instability, whereas buoyancy provides the dominant instability mechanism in plumes at high Richardson number. The onset of axisymmetric global instability in both regimes is consistent with the presence of absolute instability. While absolute instability also occurs for helical perturbations, it appears to be too weak or too localised to give rise to a global instability.

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Section: Discussionmentioning

confidence: 92%

Global stability of buoyant jets and plumes

2017

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“…where σ k denotes the turbulent Prandtl coefficient in the kinetic equation k [35]; σ ε is the turbulent Prandtl coefficient of dissipation rate in the ε equation; µ t is the turbulence viscosity; G k is the turbulence kinetics generated from the average speed gradient; and G b is the turbulence kinetics generated from buoyancy. Furthermore,…”

Section: Of 16mentioning

confidence: 99%

An Innovative Design of Regional Air Conditioning to Increase Automobile Cabin Energy Efficiency

Yang

Chen

et al. 2019

Energies

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With the goal of increasing energy efficiency and passenger comfort in an automobile cabin, we developed a regional air-conditioning design to control cold air in specific regions, and an air management strategy that can keep air circulation when the car engine cuts out. According to computational simulations, an air velocity of 2 m/s was adopted, which could form an independent flow field space in the cabin with a temperature gap of 7 °C according to the user’s needs. The designed regional air-conditioning and circulation system could create independent flow field spaces with temperature differences. Inlet air volume demand was also reduced by 60% and blower power by 53 W. In addition, the cabin ventilation system led air exchange rate reached 89% per hour. In 20 min of exposure under sun, the system could lower the cabin temperature by 12.3 °C.

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“…§ § Typical values of Pr are ∼ 10 − 2 for liquid metals, ∼ 1 for air, ∼ 10 for water, and ∼ 10 21 for Earth's mantle .…”

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confidence: 99%

mentioning

confidence: 99%

Unstructured finite element method for the solution of the Boussinesq problem in three dimensions

Smethurst

Silvester

Mihajlović

2013

Numerical Methods in Fluids

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SUMMARY We present a numerical method for the monolithic discretisation of the Boussinesq system in three spatial dimensions. The key ingredients of the proposed methodology are the finite element discretisation of the spatial part of the problem using unstructured tetrahedral meshes, an implicit time integrator, based on adaptive predictor–corrector scheme (the explicit second‐order Adams–Bashforth method with the implicit stabilised trapezoid rule), and a new preconditioned Krylov subspace solver for the resulting linearised discrete problem. We test the proposed methodology on a number of physically relevant cases, including laterally heated cavities and the Rayleigh–Bénard convection. Copyright © 2013 John Wiley & Sons, Ltd.

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Effects of Prandtl number and a new instability mode in a plane thermal plume

Cited by 6 publications

References 18 publications

Global stability of buoyant jets and plumes

Global stability of buoyant jets and plumes

An Innovative Design of Regional Air Conditioning to Increase Automobile Cabin Energy Efficiency

Unstructured finite element method for the solution of the Boussinesq problem in three dimensions

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