scholarly journals Investigation of Rayleigh–Taylor turbulence and mixing using direct numerical simulation with experimentally measured initial conditions. I. Comparison to experimental data

2009 ◽  
Vol 21 (1) ◽  
pp. 014106 ◽  
Author(s):  
Nicholas J. Mueschke ◽  
Oleg Schilling
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Initial Conditions

Direct Numerical Simulation of Partial Fuel Stratification Assisted Lean Premixed Combustion for Assessment of Hybrid G-Equation/Well-Stirred Reactor Model

2021 ◽  
Author(s):  
Chao Xu ◽  
Muhsin Ameen ◽  
Pinaki Pal ◽  
Sibendu Som
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Initial Conditions ◽  
Operating Conditions ◽  
Premixed Combustion ◽  
Lean Premixed Combustion ◽  
Fuel Stratification ◽  
Stirred Reactor ◽  
Lean Premixed ◽  
Flame Structures

Abstract Partial fuel stratification (PFS) is a promising fuel injection strategy to stabilize lean premixed combustion in spark-ignition (SI) engines. PFS creates a locally stratified mixture by injecting a fraction of the fuel, just before spark timing, into the engine cylinder containing homogeneous lean fuel/air mixture. This locally stratified mixture, when ignited, results in complex flame structure and propagation modes similar to partially premixed flames, and allows for faster and more stable flame propagation than a homogeneous lean mixture. This study focuses on understanding the detailed flame structures associated with PFS-assisted lean premixed combustion. First, a two-dimensional direct numerical simulation (DNS) is performed using detailed fuel chemistry, experimental pressure trace, and realistic initial conditions mapped from a prior engine large-eddy simulation (LES), replicating practical lean SI operating conditions. DNS results suggest that conventional triple flame structures are prevalent during the initial stage of flame kernel growth. Both premixed and non-premixed combustion modes are present with the premixed mode contributing dominantly to the total heat release. Detailed analysis reveals the effects of flame stretch and fuel pyrolysis on the flame displacement speed. Based on the DNS findings, the accuracy of a hybrid G-equation/well-stirred reactor (WSR) combustion model is assessed for PFS-assisted lean operation in the LES context. The G-equation model qualitatively captures the premixed branches of the triple flame, while the WSR model predicts the non-premixed branch of the triple flame. Finally, potential needs for improvements to the hybrid G-equation/WSR modeling approach are discussed.

scholarly journals Direct Numerical Simulation of separated turbulent flow in axisymmetric diffuser

2021 ◽  
Vol 2103 (1) ◽  
pp. 012214
Author(s):  
A S Stabnikov ◽  
D K Kolmogorov ◽  
A V Garbaruk ◽  
F R Menter
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Turbulent Flow ◽  
Turbulence Model ◽  
Eddy Viscosity ◽  
Separated Flow ◽  
Model Improvement ◽  
Good Agreement

Abstract Direct numerical simulation (DNS) of the separated flow in axisymmetric CS0 diffuser is conducted. The obtained results are in a good agreement with experimental data of Driver and substantially supplement them. Along with other data, eddy viscosity extracted from performed DNS could be used for RANS turbulence model improvement.

Combined Experimental and Numerical Study for Multiple Microchannel Heat Transfer System

2010 ◽  
Author(s):  
Jingru Zhang ◽  
Yogesh Jaluria ◽  
Tiantian Zhang ◽  
Li Jia
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Steady State ◽  
Numerical Model ◽  
Initial Conditions ◽  
Numerical Study ◽  
Numerical Models ◽  
Three Dimensional ◽  
Variation Versus ◽  
Heat Transfer System

Multiple microchannel heat sinks for potential use for electronic chip cooling are studied experimentally and numerically to characterize their thermal performance. The numerical simulation is driven by experimental data, which are obtained concurrently, to obtain realistic, accurate and validated numerical models. The ultimate goal is to design and optimize thermal systems. The experimental setup was established and liquid flow in the multiple microchannels was studied under different flow rates and heat influx. The temperature variation versus time was recorded by thermocouples, from which the time needed to reach steady state was determined. Temperature variations under steady state conditions were compared with three-dimensional steady state numerical simulation for the same boundary and initial conditions. The experimental data served as input parameters for the validation of the numerical model. In case of discrepancy, the numerical model was improved. A fairly good agreement between the experimental and simulation results was obtained. The numerical model also served to provide input that could be employed to improve and modify the experimental arrangement.

Direct numerical simulation of laminar and turbulent Bénard convection

1982 ◽  
Vol 119 ◽  
pp. 27-53 ◽  
Author(s):  
Günther Grötzbach
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Aspect Ratio ◽  
Direct Numerical Simulation ◽  
Plane Channel ◽  
Infinite Plane ◽  
Transition Range ◽  
Bénard Convection ◽  
Benard Convection ◽  
Rayleigh Numbers

The TURBIT-3 computer code has been used for the direct numerical simulation of Bénard convection in an infinite plane channel filled with air. The method is based on the three-dimensional non-steady-state equations for the conservation of mass, momentum and enthalpy. Subgrid-scale models of turbulence are not required, as calculations with different grids show that the spatial resolution of grids with about 322 × 16 nodes provides sufficient accuracy for Rayleigh numbers up to Ra = 3·8 × 105. Hence this simulation model contains no tuning parameters.The simulations start from nearly random initial conditions. This has been found to be essential for calculating flow patterns and statistical data insensitive to grid parameters and agreeing with experimental experience. The numerical results show the theoretically predicted ‘skewed varicose’ instability at Ra = 4000. Warm and cold ‘blobs’ are identified as causing temperature-gradient reversals for all the high Rayleigh numbers under consideration. The calculated wavelengths and the corresponding flow regimes observed in the transition range confirm the stability maps determined theoretically. In the turbulent range the wavelengths agree qualitatively with low-aspect-ratio experiments. Accordingly, the Nusselt numbers lie at the upper end of the scatter band of experimental data, as these also depend on the aspect ratio. Appropriately normalized, the velocity and temperature fluctuation peaks are independent of the Rayleigh number. The vertical profiles agree largely with experimental data and, especially in case of temperature statistics, exhibit comparable or less scatter.

Numerical Simulation of Turbulent Transport and Structures in Temporally Developing Plane Mixing Layers

2013 ◽  
Vol 367 ◽  
pp. 57-62
Author(s):  
Thangam Natarajan
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Computational Model ◽  
Simulation Study ◽  
Initial Conditions ◽  
Turbulent Transport ◽  
Turbulence Models ◽  
Mixing Layers ◽  
Turbulent Structures

The investigation on the sensitivity of the flows to the initial conditions was carried with varying grid resolutions, turbulence models and perturbations. The Direct Numerical Simulation study of Pantano and Sarkar [1] was taken as the reference study and the computational model used in this study was built with a similar configuration of theirs except for the perturbations used. Important results were arrived pertaining to the effect of initial conditions on the turbulent properties and the turbulent structures of the flow.

Direct numerical simulation of stationary homogeneous stratified sheared turbulence

2012 ◽  
Vol 696 ◽  
pp. 434-467 ◽  
Author(s):  
D. Chung ◽  
G. Matheou
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Large Scale ◽  
Initial Conditions ◽  
Similarity Theory ◽  
Stationary Flow ◽  
Stratified Turbulence ◽  
Diapycnal Diffusivity ◽  
Turbulence Analysis ◽  
Theory Framework

AbstractUsing direct numerical simulation, we investigate stationary and homogeneous shear-driven turbulence in various stratifications, ranging from neutral to very stable. To attain and maintain a stationary flow, we throttle the mean shear so that the net production stays constant for all times. This results in a flow that is characterized solely by its mean shear and its mean buoyancy gradient, independent of initial conditions. The method of throttling is validated by comparison with experimental spectra in the case of neutral stratification. With increasing stratification comes the emergence of vertically sheared large-scale horizontal motions that preclude a straightforward interpretation of flow statistics. However, once these motions are excluded, simply by subtracting the horizontal average, the underlying flow appears amenable to the standard methods of turbulence analysis. It is shown that a direct acknowledgement of the confining influence of the periodic simulation box can lead to a meaningful physical interpretation of the large scales. Once an appropriate confinement scale is identified, many features, including horizontal spectra, flux–gradient relationships and length scales, of stratified sheared turbulence can be readily understood, both qualitatively and quantitatively, in terms of Monin–Obukhov similarity theory. Finally, the similarity-theory framework is used to interpret the scaling of the vertical diapycnal diffusivity in stratified turbulence.

Direct numerical simulation of the droplet deformation in the external flow at various Reynolds and Weber numbers

2020 ◽  
Author(s):  
Anna Zotova ◽  
Yuliya Troitskaya ◽  
Daniil Sergeev ◽  
Alexander Kandaurov
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Reynolds Number ◽  
Direct Numerical Simulation ◽  
Software Package ◽  
Weber Number ◽  
Deformation Mode ◽  
Stationary Flow ◽  
External Flow ◽  
Droplet Deformation

<p>A lot of experimental works is devoted to studying behaviour of a droplet in the flow of the external medium. It is shown in [1] that mode of the deformation of droplet in the stationary flow is affected by the Weber number and the Reynolds number. The authors distinguish two types of the droplet deformation in the external flow: the dome-shaped deformation and the bowl-shaped one.</p><p>Using the Basilisk software package, direct numerical simulation of the process of deformation of liquid drop in the gas stream was carried out. We examined the problem of the following geometry: a drop of liquid with diameter of 5 mm was placed in the gas stream at the speed of 30 m/s. The density of liquid and gas correspond to the density of water and air, the viscosity of liquid is equal to the viscosity of water. The viscosity of gas and the surface tension at the interface between liquid and gas are determined by the set values of the Reynolds (50 - 3000) and the Weber (2 - 30) numbers. Two main modes of the drop deformation were observed: the dome-shaped deformation and the bowl-shaped one, there is a transitional deformation mode between them. The map of deformation modes is constructed for comparison with the experimental data available in the literature. It was found that the dependence of the Weber number corresponding to the transition from one deformation mode to another on the Reynolds number is well described by the power law proposed in the literature.</p><p> </p><p>This work was supported by the RFBR projects 19-05-00249, 18-35-20068, 18-55-50005, 18-05-60299, 20-05-00322 (familiarization with the Basilisk software package) and the Grant of the President No. MK-3184.2019.5, work on comparison with experimental data was supported by the RSF project No. 18-77-00074, carrying out numerical experiment was supported by the RSF project No. 19-17-00209, A.N. Zotova is additionally supported by the Ministry of Education and Science of the Russian Federation (Government Task No. 0030-2019-0020). The authors are grateful to the FCEIA employee: UNR - CONICET (Rosario, Rep. Argentina) Dr. Ing. César Pairetti.</p><p>[1] Hsiang, L.-P., Faeth, G. M., Int. J. Multiphase Flow 21(4), 545-560 (1995).</p>

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