Unsteady Simulations for an Advanced-Louver Cooling Scheme

2008 ◽  
Author(s):  
Chad X.-Z. Zhang ◽  
Sung In Kim ◽  
Ibrahim G. Hassan
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Flat Plate ◽  
Flow Velocity ◽  
Detached Eddy Simulation ◽  
Computer Cluster ◽  
Vortical Structures ◽  
Eddy Simulation ◽  
Mainstream Flow ◽  
Adiabatic Effectiveness

The performance of a louver cooling scheme on a flat plate was analyzed using Detached Eddy Simulation. It was assumed that the louver cooling scheme was tested in a wind tunnel with the mainstream flow velocity of 20 m/s, equivalent to a Reynolds number of 16200 based on the jet diameter. Turbulence closure was achieved by a Realizable k-ε based DES turbulence model. Solutions of two blowing ratios of 0.5 and 1 were successfully obtained by running parallel on 16 nodes on a computer cluster. The instantaneous flow fields were found to be highly unsteady and oscillatory in nature. It is shown that the fluctuations in the adiabatic effectiveness are mainly caused by the spanwise fluctuation of the coolant jet and the unsteady vortical structures created by the interaction of the jet and the mainstream.

Characterization of the Surface Curvature Effect Using LES for a Single Round Impinging Jet

2017 ◽  
Author(s):  
Pierre Aillaud ◽  
Florent Duchaine ◽  
Laurent Gicquel ◽  
Sheddia Didorally
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Temporal Distribution ◽  
Impinging Jet ◽  
Ambient Air ◽  
Surface Curvature ◽  
Flow Topology ◽  
Reference Case ◽  
Vortical Structures ◽  
Eddy Simulation

In this paper, wall resolved Large Eddy Simulation is used to study the effect of the surface curvature for two impinging jet configurations. The reference case is a single round jet impinging on a flat plate at a Reynolds number (based on the bulk velocity Ub and the pipe diameter D) Re = 23 000 and for a nozzle to plate distance H = 2D. The results on this configuration have been previously analyzed and validated against experimental results. This paper compares for the same operating point, the flat plate impingement to an impinging jet on a concave hemispherical surface with a relative curvature d/D = 0.089 where d is the concave surface diameter. Mean and Root Mean Square (RMS) quantities are compared to highlight differences and similarities between the two cases. In addition high order statistic such as Skewness of the temporal distribution of wall heat flux is analyzed. Probability density functions (PDF) are also built to further characterize the effect of surface curvature. It is shown that the surface curvature has a destabilizing effect on the vortical structures present in such a flow leading to a modification of the wall heat transfer compared to the flat plate case. The flow topology in the concave case is dominated by a large toroidal stationary vortex. This vortex generates a natural confinement that causes the increase of the mean temperature of the ambient air around the jet. The main effect is the reduction of the capacity of the vortical structures to enhance heat transfer. Finally, the confinement effect combined with the destabilization due to the concave curvature lead to an alleviation of the secondary peak in the Nusselt distribution and a reduction of the heat transfer at the wall.

Detailed Investigation of Detached-Eddy Simulation for the Flow Past a Circular Cylinder at Re=3900

2012 ◽  
Vol 232 ◽  
pp. 471-476 ◽  
Author(s):  
Rui Zhao ◽  
Chao Yan
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Flow Structures ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Flow Past ◽  
Large Eddy ◽  
Mesh Resolution ◽  
Physical Phenomena

The flow past a circular cylinder at a subcritical Reynolds number 3900 was simulated by the method of detached-eddy simulation (DES). The objective of this present work is not to investigate the physical phenomena of the flow but to study modeling as well as numerical aspects which influence the quality of DES solutions in detail. Firstly, four typical spanwise lengths are chosen and the results are systematically compared. The trend of DES results along the span increment is different from previous large-eddy simulation (LES) investigation. A wider spanwise length does not necessary improve the results. Then, the influence of mesh resolution is studied and found that both too coarse and over refined grids will deteriorate the performance of DES. Finally, different orders of numerical schemes are applied in the inviscid fluxes and the viscous terms. The discrepancies among different schemes are found tiny. However, the instantaneous flow structures produced by 5th order WENO with 4th order central differencing scheme are more abundant than the others. That is, for the time-averaged quantities, the second-order accurate schemes are effective enough, whereas the higher-order accurate methods are needed to resolve the transient characteristics of the flow.

Computational Study of a Target Fluidic Flowmeter

2010 ◽  
Author(s):  
Andrzej F. Nowakowski ◽  
Franck C. G. A. Nicolleau ◽  
S. M. Muztaba Salim
Keyword(s):  
Reynolds Number ◽  
Computational Study ◽  
Numerical Technique ◽  
Three Dimensional ◽  
Boundary Layer Separation ◽  
Structure Design ◽  
Design Parameters ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Wide Range

The computational studies on the flow structure, design and performance of a target fluidic flowmeter have been carried out. The computational challenge was to find a universal approach to study a wide range of flow regimes. To this end the Detached Eddy Simulation (DES) approach for unsteady flows was applied. The numerical technique enabled to accurately reproduced three dimensional flow structures in a target fluidic flowmeter. The signal analysis of the obtained results was conducted for a range of Reynolds numbers from laminar case up to 4000. The results show that a number of factors such as meter geometry and aspect ratio can influence the performance of the flow meter significantly. A minimum Reynolds number constraint for the measurements to be accurate was evaluated for various design parameters. The significance of using knife edges which influence boundary layer separation was also established. The experimental data, which were obtained for a prototype of flowmeter setup were used to validate numerical tools in the important area of low Reynolds number flows.

Merging Near-Wall RANS Models With LES for Separating and Reattaching Flows

2006 ◽  
Author(s):  
Suad Jakirlic´ ◽  
Bjo¨rn Kniesner ◽  
Sanjin Sˇaric´ ◽  
Kemal Hanjalic´
Keyword(s):  
Reynolds Number ◽  
Equation Model ◽  
Navier Stokes ◽  
Model Parameters ◽  
Wall Region ◽  
Detached Eddy Simulation ◽  
Rans Model ◽  
Eddy Simulation ◽  
Moderate Reynolds Number ◽  
Near Wall

A method of coupling a low-Reynolds-number k–ε RANS (Reynolds-Averaged Navier-Stokes) model with Large-Eddy Simulation (LES) in a two-layer Hybrid LES/RANS (HLR) scheme is proposed in the present work. The RANS model covers the near-wall region and the LES model the remainder of the flow domain. Two different subgrid-scale (SGS) models in LES were considered, the Smagorinsky model and the one-equation model for the residual kinetic energy (Yoshizawa and Horiuti, 1985), combined with two versions of the RANS ε equation, one governing the “isotropic” (ε˜; Chien, 1982) and the other the “homogeneous” dissipation rate (εh; Jakirlic and Hanjalic, 2002). Both fixed and self-adjusting interface locations were considered. The exchange of the variables across the interface was adjusted by smoothing the turbulence viscosity either by adjusting the RANS model parameters, such as Cμ (Temmerman et al., 2005), or by applying an additional forcing at the interface using a method of digital-filter-based generation of inflow data for spatially developing DNS and LES due to Klein et al. (2003). The feasibility of the method was illustrated against the available DNS, fine- and coarse grid LES, DES (Detached Eddy Simulation) and experiments in turbulent flow over a backward-facing step at a low (Yoshioka et al., 2001) and a high Re number (Vogel and Eaton, 1985), periodic flow over a series of 2-D hills (Fro¨hlich et al., 2005) and in a high-Re flow over a 2-D, wall-mounted hump (Greenblat et al, 2004). Prior to these computations, the method was validated in a fully-developed channel flow at a moderate Reynolds number Rem ≈ 24000 (Abe et al., 2004).

Numerical investigation of vortex-induced vibration of an elastically mounted circular cylinder with One-degree of freedom at high Reynolds number using different turbulent models

2018 ◽  
Vol 233 (2) ◽  
pp. 443-453 ◽  
Author(s):  
Niaz Bahadur Khan ◽  
Zainah Ibrahim
Keyword(s):  
Reynolds Number ◽  
Flow Direction ◽  
Cross Flow ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Flow Around Cylinder ◽  
Reynolds Averaged Navier Stokes ◽  
Turbulent Models

This study presents numerical investigation for flow around cylinder at Reynolds number = 104 using different turbulent models. Numerical simulations have been conducted for fixed cylinder case at Reynolds number = 104 and for cylinder free to oscillate in cross-flow direction, at Reynolds number O (104), mass–damping ratio = 0.011 and range of frequency ratio wt = 0.4–1.4 using two-dimensional Reynolds-averaged Navier–Stokes equations. In the literature, the study has been conducted using detached eddy simulation, large eddy simulation and direct numerical simulation which are comparatively expensive in terms of computational cost. This study utilizes the Reynolds-averaged Navier–Stokes shear stress transport k-ω and realizable k-ε models to investigate the flow around fixed cylinder and flow around cylinder constrained to oscillate in cross-flow direction only. Hydrodynamic coefficients, vortex mode shape and maximum amplitude ( Ay/ D) extracted from this study are compared with detached eddy simulation, large eddy simulation and direct numerical simulation results. Results obtained using two-dimensional Reynolds-averaged Navier–Stokes shear stress transport k-ω model are encouraging, while realizable k-ε model is unable to capture the entire response branches. In addition, broad range of “lock-in” region is observed due to delay in capturing the transition from upper to lower branch during two-dimensional realizable k-ε analyses.

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