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Corner Vortex Structures Within Recirculation Zones of Confined Bluff-Body Flows

AIAA JOURNAL 2024年第8期62卷 2900-2911页

作者： Squeo, Joseph N. Sykes, Joshua P. Comer, Adam L. Gallagher, Timothy P. Rankin, Brent A. Innovat Sci Solut Inc Dayton OH 45459 USA AF Res Lab Edwards AFB CA 93524 USA AF Res Lab Wright Patterson AFB OH 45433 USA

The vortical structures of recirculation zones in turbulent nonreacting and premixed reacting flows around confined equilateral-triangle bluff bodies are investigated using large-eddy simulations. A three-dimensional flow structure is observed within the recirculation zones of reacting and nonreacting cases;the structure includes both the "spanwise" vortices that extend the length of the recirculation zone and "corner vortex structures" that are situated adjacent to the bluff-body trailing edge and spanwise walls. The corner vortex structures enhance the mixing and residence times of fluid inside the recirculation zone. fluid is circulated between the spanwise vortices and corner vortex structures. Corner vortex structures always appear downstream (relative to the local flow) of the boundary-layer separation location on the spanwise walls within the recirculation zone, and they are absent when boundary-layer formation on the spanwise walls is prevented. Laminar boundary-layer theory predicts the boundary-layer separation locations within similar to 12% of the calculated values from the large-eddy simulations in all but one case. These results suggest that 1) boundary-layer separation on the spanwise walls is a necessary condition for the formation of corner vortex structures, and 2) boundary-layer separation on the spanwise walls is caused by an adverse pressure gradient in the recirculation zone.

关键词： Vortex Structure Boundary Layer Separation Non Reacting Flow computational fluid dynamics simulation Adverse Pressure Gradient Combustion Chambers Combustors Lean Premixed Combustor

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The Effect of Inlet Angle Structure of Concave and Convex Plate on Internal Flow Characteristics of Alkaline Electrolyzer

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Frontiers in Heat and Mass Transfer 2024年第3期22卷 855-868页

作者： Bo Hui Shengneng Zhu Sijun Su Wenjuan Li Key Laboratory of Low-Grade Energy Utilization Technologies and Systems Ministry of EducationSchool of Energy and Power EngineeringChongqing UniversityChongqing400044China Lanzhou Lanshi Group Co. Ltd.Lanzhou730300China

The structure of the concave-convex plates has proven to be crucial in optimizing the internal flow characteristics of the electrolyzer for hydrogen *** paper investigates the impact of the gradual expansion angle of the inlet channel on the internal flow field of alkaline *** flow distribution characteristics of concave-convex plates with different inlet angle structures in the electrolytic cell is ***,the system with internal heat source is *** results indicate that a moderate gradual expansion angle is beneficial for enhancing fluid ***,an excessively large gradual expansion angle may lead to adverse reflux phenomena,reducing the overall performance of the electrolytic cell.

关键词： Inlet angle structure vortex motion distribution uniformity computational fluid dynamics simulation

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PRESSURE GRADIENT COMPUTATION FOR FOAMS WITH DIFFERENT GEOMETRIC PROPERTIES: BASED ON ANN AND SVR MACHINE LEARNING MODEL AND TRAINED BY CFD simulationS

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JOURNAL OF POROUS MEDIA 2023年第9期26卷 49-76页

作者： Jafarizadeh, Azadeh Ahmadzadeh, MohammadAli Mahmoudzadeh, Sajad Panjepour, Masoud Isfahan Univ Technol Esfahan Iran Univ Tehran Tehran Iran

In this research work, a combination of computational fluid dynamics (CFD) simulation and artificial intelligence (AI) methods are conducted to study the effects of geometric properties of aluminum foams on airflow and to compute and predict pressure gradients in foams with such varied geometric parameters as porosity (65-90%) and pore diameter (200-2000 mu m). The 3D foam structures are created by the Laguerre-Voronoi tessellations method. Based on the CFD results, pressure gradient for 114 different foams can be calculated in terms of inlet flow velocity (in the range 0.1-8 m/s). Foam pressure gradient is found to increase with increasing inlet flow velocity but with decreasing pore diameter and porosity. Comparisons reveal that the results obtained in the present study for pressure gradient are consistent with the data reported in the literature. It is, therefore, concluded that CFD simulation is a useful tool for pressure gradient estimation in a variety of foam types. Unique simulations are, however, needed each time foam structural properties change, which entails significant increases in the associated computation costs. This drawback may, nonetheless, be at least partially addressed by taking advantage of soft computing methods such as machine learning (ML). Artificial neural network (ANN) and support vector regression (SVR) as subsets of AI are designed (models with input variables inlet velocity and the foam structural parameters: porosity, pore diameter, and strut diameter) and trained using CFD results to predict pressure gradients in a large number of foams. When applied to new foam samples, the ML models exhibit an acceptable performance in predicting pressure gradients. Using such provisions, the method can be effectively used for predicting pressure gradient in various porous media at minimum computation costs.

关键词： foam structural parameters fluid flow predicting pressure gradient computational fluid dynamics simulation machine learning models artificial neural network support vector regression

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Design and simulation of a conformal optical window pair by the quasi-quantitative Schlieren measurement in a cylindrical isolator

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OPTICAL ENGINEERING 2023年第3期62卷 35107-35107页

作者： Ou, Yang Dai, Yifan Chen, Shanyong Fan, Xiaoqiang Xiong, Bing Xu, Shangcheng Hu, Hao Xiong, Yupeng Yan, Yuepeng Du, Chunyang Peng, Wenxiang Guan, Chaoliang Natl Univ Def Technol Coll Intelligent Sci Changsha Peoples R China Natl Univ Def Technol Lab Sci & Technol Integrated Logist Support Changsha Peoples R China HuNan Key Lab Ultraprecis Machining Technol Changsha Peoples R China Natl Univ Def Technol Coll Aerosp Sci & Engn Changsha Peoples R China

To realize the quasi-quantitative Schlieren measurement of the shock train structure across the cylindrical isolator in the supersonic flow field, based on the theory of Schlieren measurement and light transmission, we propose the design scheme of conformal windows and discuss the machining feasibility with the window's parameters. The relationship between the Schlieren imaging effect, the deflection of parallel light in the Schlieren apparatus, and the conformal optical window aberrations was researched, putting forward the optical simulation model of the conformal optical windows and the quasi-quantitative Schlieren measurement. Moreover, considering the actual wind tunnel test conditions, under the speed of Mach 2 at the isolator's inlet, the distortion brought by conformal optical windows in the Schlieren observation region was simulated by the computational fluid dynamics method. Finally, the image correction algorithm for the distorted picture caused by the conformal windows was presented, and the quasi-quantitative Schlieren measurement through the conformal optical window pair was conducted for the experimental verification. The results reveal the quasi-quantitative Schlieren measurement effect across the high-precision conformal optical window pair of the cylindrical isolator, providing guidance on maintaining the balance between the manufacturing feasibility and the observation performance of conformal windows. (c) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

关键词： optical imaging conformal window cylindrical isolator Schlieren measurement computational fluid dynamics simulation

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Evaluation of Spray and Combustion Models for Simulating Dilute Combustion in a Direct-Injection Spark-Ignition Engine

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JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME 2023年第8期145卷 081006页

作者： Kim, Joohan Ameen, Muhsin Scarcelli, Riccardo Kim, Namho Singh, Eshan Sjoberg, Magnus Argonne Natl Lab Lemont IL 60439 USA Sandia Natl Labs Livermore CA 94551 USA

Dilute combustion in spark-ignition engines has the potential to improve thermal efficiency by mitigating knock and by reducing throttling and wall heat losses. However, ignition and combustion processes can become unstable for dilute operation due to a lowered laminar flame speed, resulting in excessive cycle-to-cycle variability (CCV) of the combustion process. To compensate for the slower combustion in less reactive mixtures, a modified intake port geometry can be employed to generate a strong tumble flow in the cylinder and elevate turbulence levels around the spark plug, thereby promoting a faster transition to turbulent deflagration. Consequently, optimizing combustion chamber geometry and operating strategy is crucial to maximizing the benefits of using dilute combustion with enhanced in-cylinder turbulence across a wide range of operating conditions. computational fluid dynamics (CFD) simulations can be utilized for virtual engine optimization tasks, but this would require the models to be truly predictive regarding the impact of changes to the engine design and operational *** this study, multicycle large-eddy simulations (LES) are performed for a direct-injection spark-ignition engine to investigate the model performance in predicting engine combustion characteristics with respect to changes in the intake configuration. A tumble plate that blocks the lower part of the intake port inlet is used to vary the tumble. A set of CFD models that have been recently developed are employed, which takes into account the drag of nonspherical droplets, flash-boiling behavior of liquid sprays, spray-wall interaction, surrogate formulation of a research-grade E10 gasoline, and fast chemical kinetic solvers. simulation results are compared to experimental engine data in terms of cylinder pressure, apparent heat release rate, mass fraction burned timing, and flame images. It is found that LES employing the state-of-the-art CFD models are capable of properly predic

关键词： computational fluid dynamics simulation large-eddy simulation direct-injection spark-ignition engine dilute combustion cycle-to-cycle variability tumble plate

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RANS-Based CFD simulation of Jet-Induced Mixing and Jet Impingement on Large Bubble in Microgravity

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NUCLEAR TECHNOLOGY 2023年第12期209卷 2016-2029页

作者： Armer, Chase Letronne, Florent DeBenedictis, Erika Univ Washington Seattle WA USA Carnegie Mellon Univ Pittsburgh PA USA Francis Crick Inst London England

For National Aeronautics and Space Administration's space mission planning, tons of cryogenic propellants need to be stored under microgravity conditions. Because of heat leaks into cryogenic propellant tanks, thermal stratification develops from lack of natural convection leading to boil-off of precious propellants. A thermodynamic vent system operates with a jet mixer to reduce thermal gradients within the fluid and control pressure inside the tank. In this work, a Reynolds-averaged Navier-Stokes-based computational fluid dynamics model was developed to study the fluid dynamics of jet-induced mixing and jet impingement on the large ullage bubble in the Tank Pressure Control Experiment (TPCE) under microgravity conditions. First, the computational model was benchmarked against existing experimental flow visualization data on the jet impingement. The jet mixing was then compared quantitatively with correlations for the jet radius to analyze the volumetric flow rate of the jet due to entrainment in the near field of the nozzle. The findings show that the confinement of the jet due to the ullage and the walls contributes positively to the jet entrainment rate, thus increasing the jet volumetric flow rate. In addition, the turbulence parameters are plotted to study the flow development for the TPCE case where the jet does not penetrate the ullage. Last, the model was used to determine the jet Weber number for penetration on the ullage bubble by varying jet inlet velocities. Numerical results show that the jet can penetrate the ullage when the jet Weber number is greater than 1.3.

关键词： Jet mixing bubble impingement microgravity Tank Pressure Control Experiment computational fluid dynamics simulation

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computational fluid dynamics simulation of 13CO Distillation in Structured Packing

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CHEMICAL ENGINEERING & TECHNOLOGY 2012年第2期35卷 334-340页

作者： Li, Hu-Lin Ju, Yong-Lin Li, Liang-Jun Xu, Da-Gang Shanghai Jiao Tong Univ Inst Refrigerat & Cryogen Shanghai 200240 Peoples R China Shanghai Res Inst Chem Ind Shanghai Peoples R China

Physical 3D models were established for corrugated packing used in the enrichment of the isotope 13C. computational fluid dynamics (CFD) simulation results indicated that common corrugated packing was not well wetted when used for isotope distillation. It is concluded that liquid misdistribution in the packed tower results from the structure of the packing rather than from the height of the packing beds. The existence of entrainment was also demonstrated by CFD simulation. It is proved that mass transfer equations based on the Nusselt theory are not suitable for distillation calculation in such a corrugated packing system. By comparison, the recently developed structured packing model with a corrugation geometry based on the right-angled triangle, known as Zigzag-pak, describes vapor-liquid distribution properties well and has significant advantages over common corrugated packing due to its better liquid distribution character.

关键词： computational fluid dynamics simulation Corrugated packing Cryogenic distillation Isotope 13C Zigzag-pak

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Internal flow field analysis of heterogeneous porous scaffold for bone tissue engineering

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COMPUTER METHODS IN BIOMECHANICS AND BIOMEDICAL ENGINEERING 2023年第7期26卷 807-819页

作者： Wang, Xiaokang Chen, Jigang Guan, Yabin Sun, Li Kang, Yongxing Yanshan Univ Sch Mech Engn Qinhuangdao Hebei Peoples R China Yanshan Univ Aviat Key Lab Sci & Technol Gener Technol Aviat S Qinhuangdao Hebei Peoples R China Yanshan Univ Sch Arts & Design Qinhuangdao Hebei Peoples R China

The internal pore structure of the porous scaffold for bone tissue engineering and the pressure and velocity distributions of its flow field affect the attachment, proliferation and differentiation of osteoblasts. The permeability of the porous scaffold determines its ability to transport cellular nutrients and metabolites. Therefore, studying the fluid flow characteristics of the porous scaffold plays a vital role in its biological applications. Heterogeneous porous scaffolds (HPS) with irregular internal pore structure have more bionic characteristics of natural structure than uniform porous scaffolds with regular internal pore structure. In order to comprehensively grasp the biological properties of HPS, this article designed HPS with different porosities based on the Voronoi generation method and random theory, and then used computational fluid dynamics (CFD)software to conduct fluid flow simulations. The velocity and pressure distribution rules of the internal flow field of HPS with different porosities were obtained by CFD simulation analysis, and the relationship between the porosity and the distribution rules was studied. Furthermore, the permeabilities of HPS with different porosities were calculated based on Darcy's law, and the influence rule of porosity on the permeability was obtained.

关键词： Heterogeneous porous scaffold computational fluid dynamics simulation flow field analysis permeability

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computational fluid dynamics modelling approaches of gas explosion in the chemical process industry: A review

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PROCESS SAFETY AND ENVIRONMENTAL PROTECTION 2023年 170卷 112-138页

作者： Shamsuddin, Dyg Siti Nurzailyn Abg Fekeri, Ahmad Faris Mohd Muchtar, Andanastuti Khan, Faisal Khor, Bee Chin Lim, Bee Huah Rosli, Masli Irwan Takriff, Mohd Sobri Univ Kebangsaan Malaysia Dept Chem & Proc Engn Fac Engn & Built Environm Bangi 43600 Malaysia Univ Kebangsaan Malaysia Fuel Cell Inst Bangi 43600 Malaysia Univ Kebangsaan Malaysia Fac Engn & Built Environm Dept Mech Mfg Engn Bangi Malaysia Texas A&M Univ Artie McFerrin Dept Chem Engn 400 Bizzell St College Stn TX 77843 USA Technol Innovat Sect Indah Water Konsortium Sdn Bhd Kuala Lumpur Malaysia Univ Sharjah Chem & Water Desalinat Program Sharjah 27272 U Arab Emirates

Previous studies have revealed that major accidents in Chemical Process Industry (CPI) are most commonly due to explosions. Thus, analytical studies of explosion-related risk assessments are performed to predict the consequences of potential explosions. As physical experiments on explosions are very expensive, modelling and simulation techniques using theoretical models are becoming increasingly popular, allowing researchers to replicate the potential explosion scenarios. In this regard, computational fluid dynamics (CFD) models are more than appropriate. Although CFD simulations are widely applied, they have several weaknesses such as high computational costs as well as potential simulation inaccuracies due to inaccurate modelling steps. The weaknesses can be overcome with appropriate techniques such as model simplification, defining the appropriate method, grid design and boundary conditions. Many studies have reported different aspects and perspectives of explosion modelling and simulation techniques, but few evaluate the techniques across every different type of explosion. This subject is critical, as modelling steps and techniques directly affect the accuracy of simulation results. Hence, a review of the assumptions and simulation techniques that are used to reduce the computational costs associated with gas explosion modelling for each of the different explosion types is presented.

关键词： Chemical process industry Explosion computational fluid dynamics simulation Risk assessment FLACS Fluent

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Surrogate Models for Hypersonic Aerothermodynamics and Aerodynamics using Gaussian Process Regression

Surrogate Models for Hypersonic Aerothermodynamics and Aerod...

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AIAA SciTech Forum

作者： Rataczak, Jens A. Boyd, Iain D. McMahon, Jay W. Univ Colorado Boulder Dept Aerosp Engn Sci Boulder CO 80302 USA

ISBN: (数字)9781624107115

ISBN: (纸本)9781624107115

This work presents a method for generating efficient surrogate models for hypersonic aerothermodynamics and aerodynamics using Gaussian process regression (GPR). Three surrogate models are developed. The first is trained to simultaneously predict the stagnation-point heat flux and axial-force coefficient. It is shown that the trained model is able to predict the two quantities of interest with a high level, and the chemical kinetic uncertainty in the underlying CFD data is naturally incorporated into the Gaussian process's (GP) predictions of the stagnation-point convective heat flux. A second model is trained to predict entire distributions of convective heat flux on the vehicle surface. Excellent predictive capabilities at inputs that are both included and excluded in the training data is demonstrated, emphasizing ability of GPR to generalize well to new data. Finally, a model is designed to predict the vehicle lift and drag coefficient considering variations in angle of attack. It is shown that, as the training data set grows in size, the trained GP is able to produce excellent out-of-distribution predictions - a characteristic that is not typically observed when using GPR. This single-fidelity model GP is compared to a multi-fidelity GP that uses computationally efficient axisymmetric CFD simulations as low-fidelity data and computationally expensive 3D-CFD simulations as high-fidelity data. The multi-fidelity model produces more accurate predictions when compared to the single-fidelity model, such that the multi-fidelity model requires only half of the high-fidelity data that the single-fidelity model does. Finally, the developed models are implemented within a trajectory simulation framework to demonstrate the advantage of using probabilistic aerodatabases compared to heritage lookup table aerodatabases.

关键词： Hypersonic Aerothermodynamics Numerical Stability Aerodynamic Characteristics Gaussian Process Regression Stagnation Region Lift Coefficient Heat Flux Distribution computational fluid dynamics simulation Gaussian Process Thermal Protection System

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