scholarly journals NUMERICAL STUDY ON AERODYNAMIC CHARACTERISTICS OF BUNDLE CONDUCTOR FOR UHV BASED ON ALE METHOD

2014 ◽  
Vol 44 (3) ◽  
pp. 237-245
Author(s):  
J. SI ◽  
K. ZHU
Keyword(s):  
Transmission Lines ◽  
Numerical Study ◽  
Experimental Studies ◽  
Reynolds Numbers ◽  
Aerodynamic Characteristics ◽  
Element Discretization ◽  
Critical Range ◽  
The Common ◽  
The Difference ◽  
Circle Model

The bundle conductor is often threatened by the wind-excited or wake-induced vibration generated by vortex shedding. So as to simulate the common fluid–structure nonlinear interaction problems in Ultra-High Voltage (UHV) transmission lines, the N-S equations of incompressible viscous fluid with the ALE description has been adopted to formulate the fluid-solid governing equations in the analogue computation and the 2-bundle and 6bundle sectional models, as well as the deduced finite element discretization scheme of conductor displacement are introduced in the algorithm. Wind tunnel experimental studies are carried out based on the single stranded model, 6-bundle stranded and 6bundle circle model for the focus of aerodynamic characteristics and the difference between stranded cable and circle cable. Results show that solution of numerical model agrees favorably with experimental results. The aerodynamic coefficients decrease significantly within the expected critical range of wind speed or Reynolds numbers and the cables roughness is not the principle factor to the aerodynamic coefficient when the Reynolds numbers belong to the critical region. However, the interference effect of the bundle conductor widely influenced the wind load applied on the surface of each cable.

Cross-Wind Influence on Low Aspect Ratio Wings at Low Reynolds Numbers

2013 ◽  
Author(s):  
Amir Karimi Noughabi ◽  
Mehran Tadjfar
Keyword(s):  
Aspect Ratio ◽  
Numerical Study ◽  
Three Dimensional ◽  
Micro Air Vehicles ◽  
Reynolds Numbers ◽  
Aerodynamic Characteristics ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Lift And Drag ◽  
Lift And Drag Coefficient

The aerodynamics of the low aspect ratio (LAR) wings is of outmost importance in the performance of the fixed-wing micro air vehicles (MAVs). The flow around these wings is widely influenced by three dimensional (3D) phenomena: including wing-tip vortices, formation of laminar bubble, flow separation and reattachment, laminar to turbulent transition or any combination of these phenomena. All the recent studies consider the aerodynamic characteristics of the LAR wings under the effect of the direct wind. Here we focus on the numerical study of the influence of cross-wind on flow over the inverse Zimmerman wings with the aspect ratios (AR) between 1 and 2 at Reynolds numbers between 6×104 and 105. We have considered cross-wind’s angles from 0° to 40° and angle of attack from 0° to 12°. The results show that lift and drag coefficient generally decrease when the angle of the cross-wind is increased.

scholarly journals Numerical Study on the Aerodynamic Characteristics of the NACA 0018 Airfoil at Low Reynolds Number for Darrieus Wind Turbines Using the Transition SST Model

Processes ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 477
Author(s):  
Krzysztof Rogowski ◽  
Grzegorz Królak ◽  
Galih Bangga
Keyword(s):  
Reynolds Number ◽  
Turbulence Model ◽  
Wind Turbines ◽  
Numerical Study ◽  
Experimental Studies ◽  
Turbulence Models ◽  
Vertical Axis ◽  
Reynolds Numbers ◽  
Time Step ◽  
Sst Turbulence Model

A symmetrical NACA 0018 airfoil is often used in such applications as small-to-medium scale vertical-axis wind turbines and aerial vehicles. A review of the literature indicates a large gap in experimental studies of this airfoil at low and moderate Reynolds numbers in the previous century. This gap has limited the potential development of classical turbulence models, which in this range of Reynolds numbers predict the lift coefficients with insufficiently accurate results in comparison to contemporary experimental studies. Therefore, this paper validates the aerodynamic performance of the NACA 0018 airfoil and the characteristics of the laminar separation bubble formed on its suction side using the standard uncalibrated four-equation Transition SST turbulence model and the unsteady Reynolds-averaged Navier-Stokes (URANS) equations. A numerical study was conducted for the chord Reynolds number of 160,000, angles of attack between 0 and 11 degrees, as well as for the free-stream turbulence intensity of 0.05%. The calculated lift and drag coefficients, aerodynamic derivatives, as well as the location and length of the laminar bubble quite well agree with the results of experimental measurements taken from the literature for validation. A sensitivity study of the numerical model was performed in this paper to examine the effects of the time-step size, geometrical parameters and mesh distribution around the airfoil on the simulation results. The airfoil data sets obtained in this work using the Transition SST and the k-ω SST turbulence models were used in the improved double multiple streamtube (IDMS) to calculate aerodynamic blade loads of a vertical-axis wind turbine. The characteristics of the normal component of the aerodynamic blade load obtained by the Transition SST approach are much better suited to the experimental data compared to the k-ω SST turbulence model.

scholarly journals A 2D numerical study of the effect of particle shape and orientation on resistivity in shallow formations

Geophysics ◽  
2007 ◽  
Vol 72 (1) ◽  
pp. F9-F17 ◽  
Author(s):  
Etienne Rey ◽  
Denis Jongmans
Keyword(s):  
Aspect Ratio ◽  
Particle Shape ◽  
Numerical Study ◽  
Experimental Studies ◽  
Theoretical Models ◽  
Particle Orientation ◽  
Effective Resistivity ◽  
The Matrix ◽  
The Difference ◽  
Geotechnical Tests

Surficial heterogeneous soils such as till, alluvial fans, or slope deposits are difficult to characterize by geotechnical tests because of the presence of decimeter- to meter-sized pebbles or rocks. The effective resistivity of such two-component media composed of a percentage of resistive particles embedded in a conductive matrix is given by the Bussian’s equation. The application of this equation allows the concentration of resistive particles to be determined if the resistivity values of each component and of the mixture, as well as the cementation exponent [Formula: see text], are known. However, previous theoretical and experimental studies have shown that the effective resistivity is affected by the shape of the particles. The objective of this study is to numerically determine the 2D effects of particle shape and orientation on the resistivity. Two configurations have been considered in the finite element (FE) modeling: laboratory-like measurements and field layout. For circular particles, the numerical results fit the Bussian’s equation with an exponent [Formula: see text] of 2. Aligned elongated particles induce an anisotropy which can raise or diminish the exponent [Formula: see text], depending on the particle orientation and the tortuosity of the current paths. Field experiment simulations showed that [Formula: see text] varies between 2.5 and 3.1 for an aspect ratio of 5 and that anisotropy resulting from the particle shape has little effect ([Formula: see text] close to 2) when this ratio is lower than 2.5. This increase of [Formula: see text] with the aspect ratio is in agreement with both theoretical models and experimental studies. For laboratory measurement simulations, [Formula: see text] values vary between 1.3 and 4 for a particle aspect ratio of 5, whatever the resistivity contrast between the particles and the matrix. The difference in results between the two configurations is explained by the paradox of anisotropy.

Numerical Study of the Acoustic Efficiency of Sound-Absorbing Structures with Resonators of Various Forms

2018 ◽  
Vol 931 ◽  
pp. 158-163 ◽  
Author(s):  
Pavel V. Pisarev ◽  
Aleksandr N. Anoshkin ◽  
Karina A. Maksimova
Keyword(s):  
Mathematical Model ◽  
Mathematical Models ◽  
Numerical Solution ◽  
Numerical Experiments ◽  
Numerical Study ◽  
Experimental Studies ◽  
Acoustic Properties ◽  
Acoustic Characteristics ◽  
The Difference ◽  
Comparison Of The Results

The present work is devoted to a numerical study of the acoustic characteristics of cubic and folded resonators of sound-absorbing structures (SAS). In the process of work, a physical statement of the problem and a mathematical model for predicting the effective acoustic properties of the SAS cells are formulated. The validation of the developed mathematical models was carried out. During the comparison of the results of a numerical solution with experimental studies, the difference did not exceed 3%. Based on the results of the numerical experiments, the most effective resonators were identified, and recommendations on the design of the SAS on their basis were formulated.

scholarly journals Aerodynamic Characteristics of Different Airfoils under Varied Turbulence Intensities at Low Reynolds Numbers

2020 ◽  
Vol 10 (5) ◽  
pp. 1706 ◽  
Author(s):  
Yang Zhang ◽  
Zhou Zhou ◽  
Kelei Wang ◽  
Xu Li
Keyword(s):  
Reynolds Number ◽  
Turbulence Intensity ◽  
Flow Separation ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Jet Flow ◽  
Aerodynamic Characteristics ◽  
Aerodynamic Performance ◽  
Low Reynolds Numbers ◽  
Low Reynolds

A numerical study was conducted on the influence of turbulence intensity and Reynolds number on the mean topology and transition characteristics of flow separation to provide better understanding of the unsteady jet flow of turboelectric distributed propulsion (TeDP) aircraft. By solving unsteady Reynolds averaged Navier-Stokes (URANS) equation based on C-type structural mesh and γ - Re ˜ θ t transition model, the aerodynamic characteristics of the NACA0012 airfoil at different turbulence intensities was calculated and compared with the experimental results, which verifies the reliability of the numerical method. Then, the effects of varied low Reynolds numbers and turbulence intensities on the aerodynamic performance of NACA0012 and SD7037 were investigated. The results show that higher turbulence intensity or Reynolds number leads to more stable airfoil aerodynamic performance, larger stalling angle, and earlier transition with a different mechanism. The generation and evolution of the laminar separation bubble (LSB) are closely related to Reynolds number, and it would change the effective shape of the airfoil, having a big influence on the airfoil’s aerodynamic characteristics. Compared with the symmetrical airfoil, the low-Reynolds-number airfoil can delay the occurrence of flow separation and produce more lift in the same conditions, which provides guidance for further airfoil design under TeDP jet flow.

Ḥadith ‘Āishah fī Man’i al-Nisā’ Min al-Masājid; Niqāsh ‘Ulamā’ Bangladesh Ḥaulahu

2020 ◽  
Vol 9 (1) ◽  
pp. 97-115
Author(s):  
Syed Mahmudul Hasan
Keyword(s):  
Analytical Method ◽  
Inductive Method ◽  
The Common ◽  
The Difference ◽  
Common Situation

The Narration of Aisyah (May Allah be pleased with her), is the main focus of the controversy among Bangladeshi scholars on the issue of women's prayer in the mosque. The reason for the dispute is that a group of them issued the ruling based on the phenomenon of the text, and the others explained the ruling of Hadith according to the common situation in the society. If the circumstances change, the ruling will change along with it, because the originality of the issue is permissible, that is proven from other texts. This research adopts an inductive method to survey the Prophetic hadiths that talk about the prayer of women in the Mosque in terms of permissibility and prohibition and analytical method to analyze the difference in opinion of Bangladeshi scholars related to this issue. The research finds that the ruling of Shari’ah is a process that is continuous and permanent. But in necessity and emergency, it has the notion of flexibility and explanation. In the issue of women’s presence in the mosque, they should be allowed if they abide by the suggestions of Prophet (s) and should not if they don’t. So, Prohibition is not from the prophet (s), but it is from their obedience to the ruling.

Sign in / Sign up

Export Citation Format

Share Document