Very Large Eddy Simulation of Flow and Heat Transfer in a Pulsating Impinging Jet

2020 ◽  
Author(s):  
Fangyuan Liu ◽  
Junkui Mao ◽  
Xingsi Han ◽  
Zhaoyang Xia
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Large Eddy Simulation ◽  
Impinging Jet ◽  
Core Region ◽  
Wall Jet ◽  
The Core ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Pulsating Jets

Abstract The steady impinging jets applied in turbomachine have been comprehensively studied but the pulsating jets still need to be further researched. The flow field and heat transfer characteristics of pulsating impinging jet impinging on a flat plate have been simulated using the improved very large eddy simulation established with SST k–ω model. Two time-mean Reynolds numbers (6,000 and 23,000) in the conditions of frequency = 10Hz and steady state at the constant jet–to–surface distance (6D) were considered. The velocity, vortices, and Nusselt number distributions on the plate surface were investigated to emphasize on the vortex structures in the flow and its relation to the heat transfer. The investigation has revealed the advantage of the improved very large eddy simulation for predicting the dynamical generating process of flow structures in pulsating jets. Calculated results showed pairs of vortices were organized and induced from the jet exit, and propagated along with the jet region periodically. The vortices grew with the entrainment towards the ambient fluid and resulted in accelerated interaction in the wall jet region. Meanwhile, the vortices had strong interaction with the core region and weakened velocity in the core region. Results showed that the time–mean local Nusselt number of pulsating jet was lower in the stagnation region at both investigated Re numbers but not reduced in the wall jet region.

Large Eddy Simulation of a Forced Turbulent Jet Impacting on a Semi-Cylinder

2013 ◽  
Author(s):  
Z. Li ◽  
L. Khezzar ◽  
N. Kharoua
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Large Eddy Simulation ◽  
Stagnation Region ◽  
Eddy Simulation ◽  
Wall Structures ◽  
Large Eddy ◽  
Target Wall ◽  
Circular Target ◽  
Plane Jet

This study is devoted to a forced turbulent plane jet emerging from a slot rectangular nozzle impinging on a semi-cylindrical surface using large eddy simulation. Both forced and unforced cases are considered. The Reynolds number, based on the slot velocity and width, was 5600. The LES simulations were validated using published experimental results and contrasted against RANS models. The study is performed for a slot-to-surface distance equal to twice the nozzle width and considers two forcing frequencies equal to 400 and 800 Hz. The jet was excited using a sinusoidal inlet velocity profile at several harmonics of the preferred mode and the flow and heat transfer characteristics were analyzed. The phase averaged Nusselt number exhibited several peaks along the semi-circular target plane. Increases above the steady unforced jet values of heat transfer rates were obtained in the stagnation region and decreases were observed in the wall jet region. The fluctuations in the phase averaged surface Nusselt number are explained in terms of the interaction of organized shear layer structures with induced target wall structures.

Numerical Study of Heat Transfer in a Row of Cylinders by 2D Large Eddy Simulation

2019 ◽  
Author(s):  
Andreas Stengaard Thorstensen ◽  
Andreas Krogh ◽  
Bjørn Christian Dueholm ◽  
Sebastian Bækkel Højte ◽  
Signe Birkebæk Thomasen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Large Eddy Simulation ◽  
Local Time ◽  
Numerical Study ◽  
Heat Transfer Analysis ◽  
Spanwise Direction ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Large Eddy

Abstract Complex flow structures arise as fluids are forced to flow across cylinder rows at moderate Reynolds numbers. In this study a numerical heat transfer analysis of 12 cylinders in an inline configuration is performed using Large Eddy Simulation (LES). The LES is conducted to get a better understanding of changes in the time averaged Nusselt number, 〈Nu〉, and local time averaged Nusselt number, 〈Nuθ〉, for each cylinder in the cylinder row. The simulations are performed at Re = UD/v = 10,000 and Pr = 0.71 with isothermal cylinders and a constant and uniform inflow temperature. The results show that the time averaged Nusselt number increases slightly between the first and second cylinder due to increased turbulent velocity fluctuations. Beyond the second cylinder, the time averaged Nusselt number decreases until it reaches a near constant value after the fifth cylinder. For all 12 cylinders the local time averaged Nusselt number around the surface is highest at the stagnation point. The first cylinder in the row has the same distribution as the reference simulation conducted for a single cylinder. From the second cylinder and onwards a larger part of the overall heat transfer is in the spanwise direction compared to the first- and reference cylinder.

scholarly journals Large-Eddy Simulation and Conjugate Heat Transfer in a Round Impinging Jet

2014 ◽  
Author(s):  
Francis Shum-Kivan ◽  
Florent Duchaine ◽  
Laurent Gicquel
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Large Eddy Simulation ◽  
Unsteady Flow ◽  
Conjugate Heat Transfer ◽  
Wall Jet ◽  
Hybrid Strategy ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Features

This study addresses and evaluates the use of high fidelity Large Eddy Simulation (LES) for the prediction of Conjugate Heat Transfer (CHT) of an impinging jet at a Reynolds number of 23 000, a Mach number of 0.1 and for a nozzle to plate distance of H/D = 2. For such simulations mesh point localization as well as the turbulent model and the numerical scheme are known to be of primary importance. In this context, a compressible unstructured third order in time and space LES solver is assessed through the use of WALE sub-grid scale model in a wall-resolved methodology. All simulations discussed in this document well recover main unsteady flow features (the jet core development, the impinging region, the deviation of the flow and the wall jet region) as well as the mean statistics of velocity. Convergence of the wall mesh resolution is investigated by use of 3 meshes and predictions are assessed in terms of wall friction and heat flux. The meshes are based either on full tetrahedral cells or on a hybrid strategy with prism layers at the wall and tetrahedral elsewhere. The hybrid strategy allows reaching good discretization of the boundary layers with a reasonable number of cells. Unsteady flow features retrieved in the jet core, shear layer, impinging region and wall jet region are analyzed and linked to the unsteady and mean heat flux measured at the wall. To finish, a LES based CHT computation relying on the finer grid is used to access the plate temperature distribution. Nusselt number profiles along the plate for the isothermal and the coupled cases are also provided and compared.

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