Effectiveness of Central Swirlers in the Thermal Uniformity of Jet-in-Crossflow Mixing

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Tarek Elgammal ◽  
Ryoichi S. Amano
Keyword(s):  
Mixture Fraction ◽  
Prolate Spheroid ◽  
Dimensionless Numbers ◽  
Eddy Motion ◽  
Eddy Simulation ◽  
Jet In Crossflow ◽  
Hot Air ◽  
The Difference ◽  
High Reynolds ◽  
Les Model

The present paper introduces the analysis-led-design concept in attaining the thermal homogeneity at the exit section of a mixing chamber. Staggered holes (SH) chamber type is representing jet-in-crossflow (JICF) where cold air is injected radially into an axially flowing hot air with a different velocity. Streamlined body of prolate-spheroid shape is fitted in the center of the chamber, and equipped with swirl generating fins (Swirlers). Numerical simulations were first run to predict the flow and energy fields and assess the performance of seven cases representing distinct swirlers setting (shape, dimension, and number). An unsteady turbulent condition was adopted considering high Reynolds number (Re) at the boundaries and large eddy simulation (LES) model for solving the eddy motion in the domain. Afterward, experimental measurements worked on validating the numerical results through proving the effectiveness of the recommended swirler design. Graphical and tabulated results showed the difference between the mixing patterns in thermal dimensionless numbers (normalized mixture fraction and uniformity factor), and consideration of total pressure drop was taken. All swirling designs enhanced the mixing process by generating substantial central swirl besides the small eddies formed from the jet interaction. Numerically, average uniformity improvement achieved in all cases studied was 46%, while the recommended geometry (football with four short rectangular swirlers, F4SR) is 16% better than plain football (FB), but loses pressure by 17%. Upon experimentation, F4SR had almost the same positive outcomes against plain football and SH by 24% and 47%, respectively. Finally, F4SR acts well at lower Re.

Accuracy Verification of the Turbulent Flame LES Model by a Methane/Air Burner Flame

2015 ◽  
Author(s):  
Murase Kagenobu ◽  
Oshima Nobuyuki ◽  
Takahashi Yusuke
Keyword(s):  
Laminar Flame ◽  
Mixture Fraction ◽  
Turbulent Flame ◽  
Counter Flow ◽  
Flamelet Model ◽  
Eddy Simulation ◽  
Partially Premixed Combustion ◽  
Large Eddy ◽  
Burner Flame ◽  
Les Model

This paper focuses on the numerical simulation of Sandia National Laboratories “the piloted methane/air burner flame D.” Large Eddy Simulation and 2-scalar flamelet approach are applied for the turbulent and partially premixed combustion field, which is expressed by the LES filtered equations of scalar G for tracking the flame surfaces and mixture fraction of a fuel and an oxidizer. The flamelet data consists of temperature, specific volume and laminar flame speed are calculated by the detail chemical reaction with GRI-Mech 3.0. Two kinds of flamelet data are validated; one is “equilibrium flamelet data” calculated by 0-dimensional equilibrium solution based on equilibrium model; the other is “diffusion flamelet data” calculated by 1-dimensional counter flow solution based on laminar flamelet model. Consequently, the “diffusion flamelet data” gives better result in this type of combustion field.

Large Eddy Simulation of Vaporizing Sprays Considering Multi-Injection Averaging and Grid-Convergent Mesh Resolution

2013 ◽  
Author(s):  
P. K. Senecal ◽  
E. Pomraning ◽  
Q. Xue ◽  
S. Som ◽  
S. Banerjee ◽  
...  
Keyword(s):  
Adaptive Mesh Refinement ◽  
Mixture Fraction ◽  
Adaptive Mesh ◽  
Dynamic Structure ◽  
Ensemble Averaging ◽  
Eddy Simulation ◽  
Modeling Methodology ◽  
Large Eddy ◽  
Minimum Number ◽  
Les Model

A state-of-the-art spray modeling methodology, recently presented by Senecal et al. [1, 2], is applied to Large Eddy Simulations (LES) of vaporizing sprays. Simulations of non-combusting Spray A (n-dodecane fuel) from the Engine Combustion Network are performed. An Adaptive Mesh Refinement (AMR) cell size of 0.0625 mm is utilized based on the accuracy/runtime tradeoff demonstrated by Senecal et al. [2]. In that work it was shown that grid convergence of key parameters for non-evaporating and evaporating sprays was achieved for cell sizes between 0.0625 and 0.125 mm using the Dynamic Structure LES model. The current work presents an extended and more thorough investigation of Spray A using multi-dimensional spray modeling and the Dynamic Structure LES model. Twenty different realizations are simulated by changing the random number seed used in the spray sub-models. Multi-realization (ensemble) averaging is shown to be necessary when comparing to local spray measurements of quantities such as mixture fraction and gas-phase velocity. Through a detailed analysis, recommendations are made regarding the minimum number of LES realizations required for accurate prediction of Diesel sprays. Finally, the effect of a spray primary breakup model constant on the results is assessed.

Modeling Fuel Spray Vapor Distribution With Large Eddy Simulation of Multiple Realizations

2014 ◽  
Author(s):  
P. K. Senecal ◽  
S. Mitra ◽  
E. Pomraning ◽  
Q. Xue ◽  
S. Som ◽  
...  
Keyword(s):  
Adaptive Mesh Refinement ◽  
Current Model ◽  
Mixture Fraction ◽  
Adaptive Mesh ◽  
Dynamic Structure ◽  
Ensemble Averaging ◽  
Eddy Simulation ◽  
Modeling Methodology ◽  
Large Eddy ◽  
Les Model

A state-of-the-art spray modeling methodology, recently presented by Senecal et al. [1, 2, 3], is applied to Large Eddy Simulations (LES) of vaporizing sprays. Simulations of non-combusting Spray H (n-heptane fuel) from the Engine Combustion Network are performed. Adaptive Mesh Refinement (AMR) cell sizes of 0.03125 mm to 0.25 mm are utilized to further demonstrate grid convergence of the Dynamic Structure LES model for diesel sprays. Twenty-eight different realizations are simulated by changing the random number seed used in the spray submodels. Multi-realization (ensemble) averaging, which has been shown to be necessary when comparing to local spray measurements, is performed. Global quantities such as liquid and vapor penetration are compared, as well as local mean mixture fraction and mixture fraction standard deviation. The results suggest that the current model does a reasonable job predicting the major features of the n-heptane spray when appropriate grid resolution is utilized.

scholarly journals Machine Learning Model of Dimensionless Numbers to Predict Flow Patterns and Droplet Characteristics for Two-Phase Digital Flows

2021 ◽  
Vol 11 (9) ◽  
pp. 4251
Author(s):  
Jinsong Zhang ◽  
Shuai Zhang ◽  
Jianhua Zhang ◽  
Zhiliang Wang
Keyword(s):  
Machine Learning ◽  
Learning Algorithms ◽  
Digital Microfluidics ◽  
Flow Patterns ◽  
Machine Learning Algorithms ◽  
Dimensionless Numbers ◽  
Two Phase ◽  
The Difference ◽  
Input Variables ◽  
Digital Microfluidic

In the digital microfluidic experiments, the droplet characteristics and flow patterns are generally identified and predicted by the empirical methods, which are difficult to process a large amount of data mining. In addition, due to the existence of inevitable human invention, the inconsistent judgment standards make the comparison between different experiments cumbersome and almost impossible. In this paper, we tried to use machine learning to build algorithms that could automatically identify, judge, and predict flow patterns and droplet characteristics, so that the empirical judgment was transferred to be an intelligent process. The difference on the usual machine learning algorithms, a generalized variable system was introduced to describe the different geometry configurations of the digital microfluidics. Specifically, Buckingham’s theorem had been adopted to obtain multiple groups of dimensionless numbers as the input variables of machine learning algorithms. Through the verification of the algorithms, the SVM and BPNN algorithms had classified and predicted the different flow patterns and droplet characteristics (the length and frequency) successfully. By comparing with the primitive parameters system, the dimensionless numbers system was superior in the predictive capability. The traditional dimensionless numbers selected for the machine learning algorithms should have physical meanings strongly rather than mathematical meanings. The machine learning algorithms applying the dimensionless numbers had declined the dimensionality of the system and the amount of computation and not lose the information of primitive parameters.

Simulating flow separation from continuous surfaces: routes to overcoming the Reynolds number barrier

2009 ◽  
Vol 367 (1899) ◽  
pp. 2885-2903 ◽  
Author(s):  
Michael Leschziner ◽  
Ning Li ◽  
Fabrizio Tessicini
Keyword(s):  
Reynolds Number ◽  
Turbulent Flows ◽  
Major Elements ◽  
Wall Layer ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Rans Models ◽  
High Reynolds ◽  
Near Wall

This paper provides a discussion of several aspects of the construction of approaches that combine statistical (Reynolds-averaged Navier–Stokes, RANS) models with large eddy simulation (LES), with the objective of making LES an economically viable method for predicting complex, high Reynolds number turbulent flows. The first part provides a review of alternative approaches, highlighting their rationale and major elements. Next, two particular methods are introduced in greater detail: one based on coupling near-wall RANS models to the outer LES domain on a single contiguous mesh, and the other involving the application of the RANS and LES procedures on separate zones, the former confined to a thin near-wall layer. Examples for their performance are included for channel flow and, in the case of the zonal strategy, for three separated flows. Finally, a discussion of prospects is given, as viewed from the writer's perspective.

Hybrid LES Approach for Practical Turbomachinery Flows—Part I: Hierarchy and Example Simulations

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Paul Tucker ◽  
Simon Eastwood ◽  
Christian Klostermeier ◽  
Richard Jefferson-Loveday ◽  
James Tyacke ◽  
...  
Keyword(s):  
Convex Surface ◽  
Computational Cost ◽  
Companion Paper ◽  
Navier Stokes ◽  
Computationally Efficient ◽  
Turbulent Structures ◽  
Hybrid Strategy ◽  
Eddy Simulation ◽  
Related Approach ◽  
Les Model

Unlike Reynolds-averaged Navier–Stokes (RANS) models that need calibration for different flow classes, LES (where larger turbulent structures are resolved by the grid and smaller modeled in a fashion reminiscent of RANS) offers the opportunity to resolve geometry dependent turbulence as found in complex internal flows—albeit at substantially higher computational cost. Based on the results for a broad range of studies involving different numerical schemes, large eddy simulation (LES) models and grid topologies, an LES hierarchy and hybrid LES related approach is proposed. With the latter, away from walls, no LES model is used, giving what can be termed numerical LES (NLES). This is relatively computationally efficient and makes use of the dissipation present in practical industrial computational fluid dynamics (CFD) programs. Near walls, RANS modeling is used to cover over numerous small structures, the LES resolution of which is generally intractable with current computational power. The linking of the RANS and NLES zones through a Hamilton–Jacobi equation is advocated. The RANS-NLES hybridization makes further sense for compressible flow solvers, where, as the Mach number tends to zero at walls, excessive dissipation can occur. The hybrid strategy is used to predict flow over a rib roughened surface and a jet impinging on a convex surface. These cases are important for blade cooling and show encouraging results. Further results are presented in a companion paper.

Numerical Simulation of Flow around a Cylinder under Different Reynolds Number

2014 ◽  
Vol 543-547 ◽  
pp. 434-440
Author(s):  
Qiang Liu ◽  
Wei Xie ◽  
Wen Yang Duan ◽  
Chang Hong Hu
Keyword(s):  
Reynolds Number ◽  
High Reynolds Number ◽  
Three Dimensional ◽  
Three Dimensional Model ◽  
Initial Field ◽  
Fine Grid ◽  
Flow Around A Cylinder ◽  
Wall Functions ◽  
High Reynolds ◽  
Les Model

Based on fully structured grids parallel numerical simulations of flow around a cylinder under different Reynolds number are carried out. Two-dimensional and three-dimensional models are established at the same time under specific Reynolds number, and further analyze of three-dimensional flow characteristics as well as the generated influence to overall physical quantities are presented. In order to explore efficient high Reynolds number turbulence models, a comparative research of the LES model without wall functions and the Spalart-Allmaras turbulence model is carried out. In order to improve the computational efficiency, a domain decomposition parallel computing strategy is used, and a calculation strategy that results of coarse grid was assigned to fine grid as initial field value by 3D linear interpolation is presented. Simulation results show that: Drag coefficient and Strouhal number have very good consistency with the experimental data, which verifies the correctness of the calculation method; Even if at low Reynolds number (200≤Re≤300), using a three-dimensional model is still necessary; While in the high Reynolds number stage, compared to LES model without wall functions, Spalart-Allmaras model is more applicable and more efficient.

Larger-Eddy Simulation of Velocity Fluctuation in a Mixing T-Junction

2012 ◽  
Vol 152-154 ◽  
pp. 1313-1318
Author(s):  
Tao Lu ◽  
Su Mei Liu ◽  
Ping Wang ◽  
Wei Yyu Zhu
Keyword(s):  
Experimental Data ◽  
Velocity Fluctuation ◽  
Flow Model ◽  
Numerical Results ◽  
Mean Square ◽  
Main Duct ◽  
Velocity Fluctuations ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Les Model

Velocity fluctuations in a mixing T-junction were simulated in FLUENT using large-eddy simulation (LES) turbulent flow model with sub-grid scale (SGS) Smagorinsky–Lilly (SL) model. The normalized mean and root mean square velocities are used to describe the time-averaged velocities and the velocities fluctuation intensities. Comparison of the numerical results with experimental data shows that the LES model is valid for predicting the flow of mixing in a T-junction junction. The numerical results reveal the velocity distributions and fluctuations are basically symmetrical and the fluctuation at the upstream of the downstream of the main duct is stronger than that at the downstream of the downstream of the main duct.

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