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 Study of Flow and Heat Transfer in Swirling and Non-Swirling Impinging Jets on a Semi-Cylinder Concave Target

2021 ◽  
Vol 11 (15) ◽  
pp. 7167
Author(s):  
Liang Xu ◽  
Xu Zhao ◽  
Lei Xi ◽  
Yonghao Ma ◽  
Jianmin Gao ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Wall Temperature ◽  
Target Surface ◽  
Impinging Jets ◽  
Small Scale ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Large Eddy

Swirling impinging jet (SIJ) is considered as an effective means to achieve uniform cooling at high heat transfer rates, and the complex flow structure and its mechanism of enhancing heat transfer have attracted much attention in recent years. The large eddy simulation (LES) technique is employed to analyze the flow fields of swirling and non-swirling impinging jet emanating from a hole with four spiral and straight grooves, respectively, at a relatively high Reynolds number (Re) of 16,000 and a small jet spacing of H/D = 2 on a concave surface with uniform heat flux. Firstly, this work analyzes two different sub-grid stress models, and LES with the wall-adapting local eddy-viscosity model (WALEM) is established for accurately predicting flow and heat transfer performance of SIJ on a flat surface. The complex flow field structures, spectral characteristics, time-averaged flow characteristics and heat transfer on the target surface for the swirling and non-swirling impinging jets are compared in detail using the established method. The results show that small-scale recirculation vortices near the wall change the nearby flow into an unstable microwave state, resulting in small-scale fluctuation of the local Nusselt number (Nu) of the wall. There is a stable recirculation vortex at the stagnation point of the target surface, and the axial and radial fluctuating speeds are consistent with the fluctuating wall temperature. With the increase in the radial radius away from the stagnation point, the main frequency of the fluctuation of wall temperature coincides with the main frequency of the fluctuation of radial fluctuating velocity at x/D = 0.5. Compared with 0° straight hole, 45° spiral hole has a larger fluctuating speed because of speed deflection, resulting in a larger turbulence intensity and a stronger air transport capacity. The heat transfer intensity of the 45° spiral hole on the target surface is slightly improved within 5–10%.

Very Large Eddy Simulation of Passive Drag Control for a D-Shaped Cylinder

2013 ◽  
Vol 135 (10) ◽  
Author(s):  
Xingsi Han ◽  
Siniša Krajnović
Keyword(s):  
Large Eddy Simulation ◽  
Flow Control ◽  
Control Problem ◽  
Bluff Body ◽  
Numerical Study ◽  
Numerical Results ◽  
Complex Flow ◽  
Local Disturbance ◽  
Eddy Simulation ◽  
Large Eddy

The numerical study reported here deals with the passive flow control around a two-dimensional D-shaped bluff body at a Reynolds number of Re=3.6×104. A small circular control cylinder located in the near wake behind the main bluff body is employed as a local disturbance of the shear layer and the wake. 3D simulations are carried out using a newly developed very large eddy simulation (VLES) method, based on the standard k − ε turbulence model. The aim of this study is to validate the performance of this method for the complex flow control problem. Numerical results are compared with available experimental data, including global flow parameters and velocity profiles. Good agreements are observed. Numerical results suggest that the bubble recirculation length is increased by about 36% by the local disturbance of the small cylinder, which compares well to the experimental observations in which the length is increased by about 38%. A drag reduction of about 18% is observed in the VLES simulation, which is quite close to the experimental value of 17.5%. It is found that the VLES method is able to predict the flow control problem quite well.

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.

Large Eddy Simulation of Heat Transfer Over In-Line Flat-Tube Array in Laminar and Turbulent Flows

2017 ◽  
Author(s):  
Salar Taghizadeh ◽  
Sumanta Acharya ◽  
Kong Ling ◽  
Yousef Kanani ◽  
Xuan Ge
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Numerical Study ◽  
Numerical Models ◽  
Leading Edge ◽  
Flat Tube ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy

This study presents a transient three-dimensional numerical study on fluid flow and heat transfer of flat-tube array using large eddy simulation (LES) covering both laminar and turbulent flow regimes. The simulations were performed in a rectangular region containing only one tube with periodic conditions specified on all boundaries. A staggered flat-plate array was first studied, and an existing solution was used for validation purpose. The numerical models were then applied to an in-line array composed of flat tubes with an aspect ratio of 0.25 and fixed tube spacings. By varying the in-flow velocity, the tube array was studied over a wide range of Reynolds number (600–12000). Temperature, velocity, and turbulent kinetic energy distributions as well as the interactions between them are presented and analyzed. Furthermore, the local heat transfer rate was analyzed along the various parts of the tube (leading edge, flat-top and wake or trailing-edge regions). Heat transfer correlation for each region of the tube and the entire tube array is proposed.

Experimental and Large Eddy Simulation Study for Visualizing Complex Flow Phenomena of Gas Turbine Internal Blade Cooling Channel with No Bend

2021 ◽  
pp. 1-19
Author(s):  
Farah Nazifa Nourin ◽  
Ryoichi S. Amano
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Complex Flow ◽  
Pressure Drops ◽  
Two Circular Holes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Circular Holes

Abstract In this study, the internal cooling channel was investigated without any bend. Smooth surfaces and dimpled surfaces were investigated using the different combinations of connecting circular and rectangular holes. The computations were performed using the Large Eddy Simulation (LES) model for Reynolds (Re) numbers from 10,000 to 50,000. A total of six different connecting holes were investigated with a smooth and dimpled surface. A partial spherical dimple with two circular holes showed the highest heat transfer, but it has a higher pressure loss penalty. Even though the Leaf dimple with the rectangle indicated a low heat transfer because of low-pressure drops, it represents the highest efficiency at higher Reynolds numbers.

scholarly journals LARGE EDDY SIMULATION OF AN ELLIPTIC JET INJECTED INTO A SUPERSONIC CROSSFLOW

2012 ◽  
Vol 19 ◽  
pp. 109-113
Author(s):  
GUO-LEI WANG ◽  
XI-YUN LU
Keyword(s):  
Large Eddy Simulation ◽  
Vortex Pair ◽  
Horseshoe Vortex ◽  
Mach Disk ◽  
Spanwise Direction ◽  
Complex Flow ◽  
Transverse Jet ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Features

A transverse jet issuing from an elliptic injector into a supersonic crossflow has been investigated using large eddy simulation. The complex flow structures and the relevant flow features are analyzed to exhibit the evolution of shock structures, vertical structures and jet shear layer. A horseshoe vortex is formed in the upstream of the jet and the shock structures exhibit small fluctuations due to the flow interaction. The kidney-shaped counter-rotating vortex pair dominates the flow field in the downstream of the jet. The elliptic jet spreads rapidly in the spanwise direction and then the axis-switching phenomenon occurs. Intense turbulent fluctuations are identified behind the Mach disk because of the large velocity gradients.

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.

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