Large eddy simulation of turbulent horizontal buoyant jets

Ghaisas, Niranjan S.; Shetty, Dinesh A.; Frankel, Steven

doi:10.1080/14685248.2015.1008007

Cited by 24 publications

(15 citation statements)

References 44 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…To aid entrainment of the ambient fluid into the vortex ring and improve the numerical stability, a small co-flow of U co = 0.01U 0 is imposed with zero turbulence intensity. Negative streamwise velocity at the outflow plane can then be eliminated [38,39]. Furthermore, the no-slip and free-slip boundary conditions are applied at the nozzle wall and far field, respectively.…”

Section: Computational Setupmentioning

confidence: 99%

The Formation and Evolution of Turbulent Swirling Vortex Rings Generated by Axial Swirlers

Gan

Liu

2019

Flow Turbulence Combust

View full text Add to dashboard Cite

The present work investigates the formation process and early stage evolution of turbulent swirling vortex rings, by using planar Particle Image Velocimetry (PIV) and Large Eddy Simulation (LES). Vortex rings are produced in a piston-nozzle arrangement with swirl generated by 3D-printed axial swirlers in experiments. Idealised solid-body rotation is applied in LES to evaluate the effect of nozzle exit velocity profile in experiments. The Reynolds number (Re) based on the nozzle diameter D and the slug velocity U 0 in the nozzle is 20,000. The swirl number S generated ranges from 0 (zero-swirl vortex ring) and 1.1, covering the two critical swirl numbers previously identified in a swirling jet. Both PIV and LES results show that the formation number F decreases linearly as S increases, with the maximum F ≈ 2.6 at S = 0 (produced by the swirler with straight vanes) and minimum F = 1.9 at S = 1.1. The corresponding maximum attainable circulation in the nozzle axis parallel plane also diminishes with increasing S. Evolution of compact rings produced by a stroke ratio L/D = 1.5 reveals that circulation decay rate is largely proportional to S. The trajectory of the vortex core in the axial direction, hence the ring axial propagation velocity, decreases as S, while that in the radial direction and the radial propagation velocity, increase with S. An empirical scaling function is proposed to scale these variables.

show abstract

Section: Computational Setupmentioning

confidence: 99%

The Formation and Evolution of Turbulent Swirling Vortex Rings Generated by Axial Swirlers

Gan

Liu

2019

Flow Turbulence Combust

View full text Add to dashboard Cite

show abstract

“…Theorem 2.1. In the absence of the external forces and source terms (f = 0, p 0 = 0, f b = 0) and with homogeneous condition on the Dirichlet boundary (w = 0), and as δ → 0 in the open boundary condition (5), the scheme given by equations (20a)- (22) satisfies the relation…”

Section: Numerical Scheme and Discrete Energy Stabilitymentioning

confidence: 99%

“…Let us next consider how to implement the scheme represented by equations (20a)- (22), which are seemingly all coupled with one another. It is critical to realize the fact that the variables R(t), E[u], ξ and g(ξ) in these equations are but scalar-valued numbers, not field functions.…”

Section: Solution Algorithm and Implementation With High-order Spectrmentioning

confidence: 99%

A gPAV-based unconditionally energy-stable scheme for incompressible flows with outflow/open boundaries

Lin

Liu

Dong

2020

Computer Methods in Applied Mechanics and Engineering

View full text Add to dashboard Cite

We present an unconditionally energy-stable scheme for approximating the incompressible Navier-Stokes equations on domains with outflow/open boundaries. The scheme combines the generalized Positive Auxiliary Variable (gPAV) approach and a rotational velocity-correction type strategy, and the adoption of the auxiliary variable simplifies the numerical treatment for the open boundary conditions. The discrete energy stability of the proposed scheme has been proven, irrespective of the time step sizes. Within each time step the scheme entails the computation of two velocity fields and two pressure fields, by solving an individual de-coupled Helmholtz (including Poisson) type equation with a constant precomputable coefficient matrix for each of these field variables. The auxiliary variable, being a scalar number, is given by a well-defined explicit formula within a time step, which ensures the positivity of its computed values. Extensive numerical experiments with several flows involving outflow/open boundaries in regimes where the backflow instability becomes severe have been presented to test the performance of the proposed method and to demonstrate its stability at large time step sizes.

show abstract

“…where R is a chosen constant matrix satisfying the conditions to be specified below. Substitute these boundary conditions into (19), and the quadratic form becomes…”

Section: Energy-stable Boundary Conditions Based On a Quadratic Formmentioning

confidence: 99%

“…Backflow instability refers to the numerical instability caused by the un-controlled energy influx into the domain through the open/outflow boundary, often associated with strong vortices or backflows on such boundaries. A telltale symptom of this instability is that an otherwise stable computation blows up instantly when a vortex reaches the open/outflow boundary [11,13,35,19]. It is observed that usual measures such as increasing the mesh resolution or reducing the time step size do not help with this instability [12].…”

Section: Introductionmentioning

confidence: 99%

Energy-stable boundary conditions based on a quadratic form: Applications to outflow/open-boundary problems in incompressible flows

Yang

Dong

2019

Journal of Computational Physics

View full text Add to dashboard Cite

We present a set of new energy-stable open boundary conditions for tackling the backflow instability in simulations of outflow/open boundary problems for incompressible flows. These boundary conditions are developed through two steps: (i) devise a general form of boundary conditions that ensure the energy stability by re-formulating the boundary contribution into a quadratic form in terms of a symmetric matrix and computing an associated eigen problem; and (ii) require that, upon imposing the boundary conditions from the previous step, the scale of boundary dissipation should match a physical scale. These open boundary conditions can be re-cast into the form of a traction-type condition, and therefore they can be implemented numerically using the splitting-type algorithm from a previous work. The current boundary conditions can effectively overcome the backflow instability typically encountered at moderate and high Reynolds numbers. These boundary conditions in general give rise to a non-zero traction on the entire open boundary, unlike previous related methods which only take effect in the backflow regions of the boundary. Extensive numerical experiments in two and three dimensions are presented to test the effectiveness and performance of the presented methods, and simulation results are compared with the available experimental data to demonstrate their accuracy.

show abstract

Large eddy simulation of turbulent horizontal buoyant jets

Cited by 24 publications

References 44 publications

The Formation and Evolution of Turbulent Swirling Vortex Rings Generated by Axial Swirlers

The Formation and Evolution of Turbulent Swirling Vortex Rings Generated by Axial Swirlers

A gPAV-based unconditionally energy-stable scheme for incompressible flows with outflow/open boundaries

Energy-stable boundary conditions based on a quadratic form: Applications to outflow/open-boundary problems in incompressible flows

Contact Info

Product

Resources

About