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AIAA Science and Technology Forum and Exposition (AIAA SciTech Forum)

作者： Diaz, Patricia Ventura Meurisse, Jeremie B. E. Brandis, Aaron M. Bessire, Brody K. Barnhardt, Michael Yoon, Seokkwan NASA Ames Res Ctr STC Moffett Field CA 94035 USA NASA Ames Res Ctr AMA Inc Moffett Field CA 94035 USA NASA Ames Res Ctr Moffett Field CA 94035 USA

ISBN: (数字)9781624106095

ISBN: (纸本)9781624106095

Arc-jet testing is a fundamental tool in the screening of thermal protection systems under atmospheric entry conditions. In this work, high-fidelity computational fluid dynamics simulations coupled with machine learning methods for the Hypersonic Materials Environmental Test System arc-jet facility have been carried out. This effort improves the MEDLI2 data reconstruction fidelity by understanding the impact of the NuSil coating over the PICA thermocouple plugs. Thermochemical non-equilibrium models are employed to simulate the flows inside the arc-jet nozzle and chamber and machine learning techniques are used to calibrate the arc-jet inflow conditions. The material response is simulated with the recession and in-depth numerical results compared to experimental measurements.

关键词： Hypersonic Flows Thermal Protection System computational fluid dynamics simulation Thermocouples Machine Learning Jet Nozzle Stagnation Pressure Mass Flow Rate Python Pyrometer

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Characterization of Supersonic Wind Tunnel Flow Quality Using Planar Laser CO₂ Rayleigh Scattering

Characterization of Supersonic Wind Tunnel Flow Quality Usin...

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AIAA Propulsion and Energy Forum / IEEE Electric Aircraft Technologies Symposium (EATS)

作者： Aguilera, Camilo Sosa, Jonathan Hyde, Evan W. Goodwin, Gabriel B. Kessler, David A. Hess, Andrew M. Miklosovic, David S. US Naval Res Lab Naval Ctr Space Technol Spacecraft Engn Div Washington DC 20375 USA US Naval Res Lab Labs Computat Phys & Fluid Dynam Washington DC 20375 USA US Naval Acad Aerosp Engn Dept Annapolis MD 21402 USA

ISBN: (数字)9781624106118

ISBN: (纸本)9781624106118

A complementary experimental and computational investigation of the flow characteristics in a supersonic wind tunnel are presented. Stereoscopic planar laser Rayleigh scattering of CO2 particles, typically several nanometers to tens of nanometers in size, were used in this study allowing cross-sectional visualization of the supersonic flow and turbulent boundary layers throughout the test section of an academic scale facility. The optical diagnostic measurements show asymmetric boundary layer growth between the top and bottom walls of the test section as well as a disturbed bottom boundary layer due to the induced pressure and velocity gradient. The computational fluid dynamics simulations were used to provide additional detail and insight into the mechanisms driving these features.

关键词： Rayleigh Scattering Hypersonic Wind Tunnels Lasers Boundary Layer Separation Compressible Flow computational fluid dynamics simulation Flow Characteristics Free Stream Velocity Reynolds Averaged Navier Stokes Static Pressure

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Research on Heat Dissipation Performance and Long-term Reliability of the Flapping Wing Cooling Technology Applied to the 5G Communications Equipment 27

Research on Heat Dissipation Performance and Long-term Relia...

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27th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC)

作者： Guo, Yanhua Zhang, Xianming Lan, Daiyan Zhu, Yue ZTE Corp Reliabil Dept Shenzhen Peoples R China

ISBN: (纸本)9781665418966

To further improve the heat dissipation efficiency of the 5G communications equipment, this study innovatively applies the flapping wing cooling technology to outdoor 5G base stations. A series of experimental and numerical studies have been conducted to explore effects of the flapping wing cooling device on heat dissipation performance and long-term reliability of 5G communications devices. Specifically, (1) Taguchi method was used to determine geometric parameters (length, width and spacing) of the flapping wing cooling device's blades, where airflow and noise were objective functions of the optimization method;(2) additionally, computational fluid dynamics simulation and thermal tests were conducted to demonstrate advantages of forced convection compared to natural convection. The results indicate that: (1) when blades of the flapping wing cooling device are 15 mm in width, 70 mm in length, 14 mm in spacing, the airflow reaches the maximum of 10.7 CFM, with the noise level meeting the permissible noise standard of the 5G outdoor devices;(2) the flapping wing cooling device reduces the temperature of electronic components of the 5G AAU by about 10 degrees C on average. The temperature drop of electronic components near the fan outlet is 6 degrees C higher than that of electronic components 0.5 m away from the fan outlet. In terms of reliability, Finite Element Method simulation was conducted to research the failure probability of the flapping wing cooling device under vibration fatigue;besides, based on a series of environmental durability tests, the reliability of the flapping wing cooling device for long-term usage outdoors was explored. The results show that: (1) the maximal Mises stress of blades is lower than fatigue limit of its own materials, and vibration fatigue life meets the requirement of 10 years;(2) the flapping wing cooling device has passed high temperature aging test, temperature cycling test, high temperature and high humidity aging test, salt sp

关键词： the flapping wing cooling device the 5G communications equipment forced convection natural convection long-term reliability computational fluid dynamics simulation Finite Element Method simulation Taguchi method

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Efficiency of urban greening systems with maximized latent heat effect in urban heat island and climate change mitigation

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Environmental Challenges 2024年 15卷

作者： Park, Seunghwan Kim, Eun-Sub Yun, Seok-Hwan Lee, Dong-Kun Department of Building Energy Research Korea Institute of Civil Engineering and Building Technology Goyang 10223 South Korea Low-Carbon and Climate Impact Research Centre School of Energy and Environment City University of Hong Kong Tat Chee Ave Hong Kong Kowloon Tong Hong Kong National Institute for Environmental Studies 16-2 Onogawa Ibaraki Tsukuba 305-8506 Japan Department of Landscape Architecture and Rural System Engineering Seoul National University Seoul 08826 South Korea

Street, wall, and rooftop greening systems are essential for urban heat reduction and carbon neutrality. In this study, we compared the temperature-reducing effect of current and developed technologies that maximize the latent heat of evaporation through such greening systems. A research site with the maximum urban heat island effect was selected by analyzing the vulnerability of Suwon City, Korea. The latent heat of evaporation for each method was determined by conducting actual measurements and verified by performing computational fluid dynamics simulations. Based on the results of statistical techniques, the validated model was highly reliable. When developed technologies were applied, the temperature of the entire city was reduced by approximately 2 °C. Compared with the existing street greening system, the developed technology achieved a temperature reduction effect even at a distance of 5 m. Current wall greening systems only have a temperature reduction effect at 1 m, but that of the developed technology was approximately 1 °C even at a distance of 2 m. The existing rooftop greening system had a temperature reduction effect only at the height of 1.2 m, whereas that of the developed technology was effective even at 6 m, contributing to a reduction in the temperature of the entire city. © 2024

关键词： Canopy layer urban heat island computational fluid dynamics simulation Evapotranspiration model Numerical analysis Temperature reduction

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A Novel Approach in Realistic Wind Data Generation for The Safe Operation of Small Unmanned Aerial Systems in Urban Environment

A Novel Approach in Realistic Wind Data Generation for The S...

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AIAA Aviation Forum and Exposition

作者： Vuppala, Rohit K. S. S. Kara, Kursat Oklahoma State Univ Sch Mech & Aerosp Engn Mech & Aerosp Engn Stillwater OK 74075 USA

ISBN: (数字)9781624106101

ISBN: (纸本)9781624106101

In this study we present a preliminary work for a method to efficiently generate realistic wind data for urban environments using existing Large Eddy simulation (LES) data for safe operation of small unmanned aerial vehicles. A single building setup in neutral atmospheric conditions is considered as a test case for demonstration of the method. The method relies on using Large Eddy simulation data from a computational fluid dynamics simulation and a non-intrusive Reduced Order Modeling approach (ROM) coupled with Recurrent Neural Networks like Long Short Term Memory (LSTM). Proper Orthogonal Decomposition (POD) transform is used to extract modal coefficients from the high-resolution data snapshots and LSTM network is trained on a specific number of modal coefficients defined by their relative information content. Modal predictions for future time-steps are then obtained using this trained LSTM network, without the need of computationally expensive CFD simulations. The corresponding velocity fields for future time-steps are obtained by a inverse POD transform on these modal coefficients. Since no prior information about the underlying governing equations are utilized for the predictions, the method is a completely non-intrusive approach.

关键词： Small Unmanned Aircraft System computational fluid dynamics simulation Convolutional Neural Network Unmanned Aerial Vehicle Atmospheric Conditions Absolute Temperature Machine Learning Gas Constant Ground Control Station Singular Value Decomposition

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CFD simulations of the Truncated IHF Semi-Elliptical Nozzle Flow: Convective Calibration Plate

CFD Simulations of the Truncated IHF Semi-Elliptical Nozzle ...

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AIAA Aviation Forum and Exposition

作者： Gokcen, Tahir AMA Inc NASA Ames Res Ctr MS 230-2 Moffett Field CA 94035 USA

ISBN: (数字)9781624106101

ISBN: (纸本)9781624106101

This paper reports computational simulations of a high-enthalpy panel test facility at NASA Ames Research Center. The recently developed facility configuration uses a truncated version of an existing semi-elliptical nozzle in the 60-MW Interaction Heating Facility, and it provides testing capability for panel test articles as large as 43.2 cm x 43.2 cm (17 in x 17 in). A water-cooled calibration plate, which is attached to the semi-elliptical nozzle bottom surface and instrumented with twenty Gardon-gage heat flux calorimeters and twelve pressure gages, is used to characterize the convective heating environment over the panel test articles. The present analysis comprises computational fluid dynamics simulations of the nonequilibrium flowfield in the facility nozzle and test box, and the flowfields over panel test articles. Both laminar and turbulent simulations are performed, and the computational results are compared with the calibration plate measurements. Comparisons of computed and measured heat fluxes indicate that the boundary layer in the semi-elliptical nozzle is transitional at certain conditions (relatively higher arc-heater pressures or mass flow rates).

关键词： computational fluid dynamics simulation Transitional Flow Heat Flux Enthalpy Boundary Layer Transition Total Mass Flow Rate Gardon Gages NASA Ames Research Center Turbulence Models Mach Number

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Fusing distributed aerodynamic data using Bayesian Gappy Proper Orthogonal Decomposition

Fusing distributed aerodynamic data using Bayesian Gappy Pro...

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AIAA Aviation Forum and Exposition

作者： Bertram, Anna Bekemeyer, Philipp Held, Matthias German Aerosp Ctr DLR Inst Aerodynam & Flow Technol D-38108 Braunschweig Germany Airbus Operat GmbH Aircraft Aerodynam D-28199 Bremen Germany

ISBN: (数字)9781624106101

ISBN: (纸本)9781624106101

During the development of an aircraft, a multitude of aerodynamic data is required for different flight conditions throughout the flight envelope. Nowadays, a large portion of this data is routinely acquired by computational fluid dynamics simulations. However, due to modeling and convergence issues especially for extreme flight conditions, numerical data cannot be reliably generated throughout the entire flight envelope yet. Hence, numerical data is complemented by data from wind tunnel experiments and flight testing. However, the data from these different sources will always show some discrepancies to deal with. Data fusion methods aim at combining the individual strengths and weaknesses of data from different sources in order to provide a consistent data set for the entire parameter domain. In this work we propose an extension to the well established gappy proper orthogonal decomposition technique by interpreting the occurring least-squares problem as a regression task. A Bayesian perspective is imposed to account for uncertainties during the data fusion process. This involves a kernelized regression formulation which also leverages the problem of linearity imposed by the dimensionality reduction method. We demonstrate the performance and robustness of the approach investigating an industrial-relevant, large-scale aircraft test case fusing high quality experimental and numerical data.

关键词： computational fluid dynamics simulation Data Analysis Wind Tunnel Tests Flight Testing Flight Envelope Probability Distribution Lift Coefficient Pressure Coefficient Numerical Analysis Aerodynamic Flows

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3D printed scaffold design for bone defects with improved mechanical and biological properties

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JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS 2022年 134卷 105418页

作者： Fallah, Ali Altunbek, Mine Bartolo, Paulo Cooper, Glen Weightman, Andrew Blunn, Gordon Koc, Bahattin Sabanci Univ Integrated Mfg Technol Res & Applicat Ctr TR-34906 Istanbul Turkey Sabanci Univ Nanotechnol Res & Applicat Ctr TR-34956 Istanbul Turkey Sabanci Univ Fac Engn & Nat Sci TR-34956 Istanbul Turkey Univ Manchester Manchester Inst Biotechnol Sch Mech Aerosp & Civil Engn Manchester M13 9PL England Univ Portsmouth Sch Pharm & Biomed Sci Portsmouth PO1 England Nanyang Technol Univ Singapore Ctr Printing 3D Sch Mech & Aerosp Engn Singapore 639798 Singapore Sabanci Univ Fac Engn & Nat Sci TR-34956 Istanbul Turkey

Bone defect treatment is still a challenge in clinics, and synthetic bone scaffolds with adequate mechanical and biological properties are highly needed. Adequate waste and nutrient exchange of the implanted scaffold with the surrounded tissue is a major concern. Moreover, the risk of mechanical instability in the defect area during regular activity increases as the defect size increases. Thus, scaffolds with better mass transportation and mechanical properties are desired. This study introduces 3D printed polymeric scaffolds with a continuous pattern, ZigZag-Spiral pattern, for bone defects treatments. This pattern has a uniform distribution of pore size, which leads to uniform distribution of wall shear stress which is crucial for uniform differentiation of cells attached to the scaffolds. The mechanical, mass transportation, and biological properties of the 3D printed scaffolds are evaluated. The results show that the presented scaffolds have permeability similar to natural bone and, with the same porosity level, have higher mechanical properties than scaffolds with conventional lay-down patterns 0-90 degrees and 0-45 degrees. Finally, human mesenchymal stem cells are seeded on the scaffolds to determine the effects of geometrical microstructure on cell attachment and morphology. The results show that cells in scaffold with ZigZag-Spiral pattern infilled pores gradually, while the other patterns need more time to fill the pores. Considering mechanical, transportation, and biological properties of the considered patterns, scaffolds with ZigZag-Spiral patterns can mimic the properties of cancellous bones and be a better choice for treatments of bone defects.

关键词： 3D bioprinting Bone defects Nonlinear finite element analysis computational fluid dynamics simulation Permeability analysis

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Investigation of O3-NOx-VOCs chemistry and pollutant dispersion in street canyons with various aspect ratios by CFD simulations

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BUILDING AND ENVIRONMENT 2022年 226卷

作者： Hang, Jian Liang, Jie Wang, Xuemei Zhang, Xuelin Wu, Luolin Shao, Min Sun Yat Sen Univ Sch Atmospher Sci Southern Marine Sci & Engn Guangdong Lab Zhuhai Zhuhai Peoples R China Sun Yat Sen Univ Guangdong Prov Key Lab Climate Change & Nat Disas Zhuhai Peoples R China Sun Yat Sen Univ Key Lab Trop Atmosphere Ocean Syst Minist Educ Zhuhai 519000 Peoples R China Jinan Univ Inst Environm & Climate Res Guangzhou 510632 Peoples R China

Based on the OpenFOAM environment, a new CFD code named as APFoam coupling turbulence with the complex photochemical mechanism of NOx-O3-VOCs reactions has been developed. The standard k-epsilon model is selected for turbulent airflow simulation and the SAPRC07 is for complex NOx-O3-VOCs photochemical reactions. Two-dimensional(2-D) full-scale street canyons with two aspect ratios(AR = H/W = 1 and 5, W = 24 m) are stud-ied. By considering both physical effects and chemical reactions, the influences of three key factors on the photochemical pollutant dispersion and human health risk analysis are investigated, including the background wind speeds(Uref = 1.5 m/s, 3 m/s), pollutant concentrations from ambient air(O3-NOx-VOCs) and the emission (NOx-VOCs) source settings at the pedestrian-level. Besides, the effective measures to control O3 concentration is *** study mainly concludes below. 1) The variations of NOx concentration increases about 20 times and O3 concentration decreases about 30% with the increase of AR. The chemical effect on photochemical pollutants is more important for the deep canyon(AR = 5) than that for the typical canyon(AR = 1). 2) The indoor and pedestrian-level exposure risk of NO2 is much larger than that of O3. The deep street canyon(AR = H/W = 5) has a higher exposure risk of NO2 than the typical canyon(AR = H/W = 1). 3) The NOx concentration increases about twice and O3 concentration decreases 6.5-13.5% with the decrease of Uref. 4) O3 concentration decreases after removing the background NOx and VOCs;it increases if there are no traffic emissions. 5) Simple traffic control measures can effectively reduce NOx but the reduction of O3 still requires additional VOCs control measures in a street canyons.

关键词： computational fluid dynamics simulation (CFD) NOx-O3-VOCs chemistry Urban air pollution Two-dimensional (2-D) street canyon OpenFOAM APFoam

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Development and verification of a reduced dimethoxymethane/n-heptane/toluene kinetic mechanism and modelling for CI engines

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APPLIED THERMAL ENGINEERING 2022年 214卷

作者： Shi, Xiuyong Qian, Weiwei Wang, Haoyu Pan, Mingzhang Wang, Qiwei Ni, Jimin Tongji Univ Sch Automot Studies Shanghai 201804 Peoples R China Guangxi Univ Coll Mech Engn Nanning 530004 Peoples R China

Dimethoxymethane (CH3OCH2OCH3, DMM) has been regarded as a potential alternative fuel for CI engines due to its advantage of high oxygen contents and renewability. However, little investigation has been conducted for computational fluid dynamics (CFD) simulation because of the lack of appropriate reduced mechanisms of DMM. In this study, a reduced DMM/n-heptane/toluene kinetic mechanism is developed, which contains 173 species and 698 reactions based on the decoupling methodology. In addition, the new reduced mechanism has been validated via comparison to experiments of ignition delay times, laminar flame speeds, and species concentrations. It is found that the prediction of reduced kinetic mechanism proposed by this study can well capture the combustion characteristics of dimethoxymethane, n-heptane, and toluene. Meanwhile, it is worth noting that the maximum flame speeds of DMM appears at a slightly richer mixture (higher equivalence ratio) in comparison with n-heptane. The DMM maximum laminar flame speeds of 45 cm/s, 55 cm/s, and 64 cm/s are observed at temperatures of 298 K, 328 K, and 358 K, respectively. Eventually, the proposed model has been coupled with CFD software to simulate the combustion process of CI engines, the results indicate that both the simulated pressure and heat release rate have a good agreement with the experiments. Moreover, the addition of DMM leads to an increase in NO product, while a reduction in soot distribution.

关键词： Dimethoxymethane Reduced kinetic modeling Ignition delay times Laminar flame speed computational fluid dynamics simulation

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