جستجوی مقالات مرتبط با کلیدواژه
تکرار جستجوی کلیدواژه aerodynamics در نشریات گروه فنی و مهندسی
aerodynamics
در نشریات گروه مکانیک-
Stratospheric balloons are an essential part of the scientific research community. In previous stratospheric balloon models used for trajectory prediction and station-keeping, the aerodynamic drag has usually been modeled as similar to that of a sphere. However, with recent proposals to use propulsion systems on the payload of stratospheric balloons to achieve trajectory control in the horizontal plane, it is important to refine our understanding of the drag of stratospheric balloons, especially at low horizontal velocities near transition, where spherical assumptions may deviate significantly. This study conducts a Computational Fluid Dynamics (CFD) investigation into the aerodynamic characteristics of both superpressure balloons (SPBs) and zero pressure balloons (ZPBs) using Large Eddy Simulations (LES). The analysis was conducted over a range of Reynolds numbers that correspond to reasonable forward airspeeds for horizontal stratospheric propulsion-based balloon systems. The results show that both balloons have drag characteristics qualitatively similar to a sphere. This includes an initially high drag coefficient, a drag crisis, and a lower eventual drag coefficient. Quantitatively, however, differences emerge between the balloon aerodynamics and that of a sphere. For example, the drag crisis occurs at a lower Reynolds number for both types of balloons when compared to a sphere. This is critical as proposed propulsion-based balloon systems aim to operate near the Reynolds number where this drag crisis occurs. The drag coefficient for the SPB was found to be less than the ZPB at all Reynolds numbers. A sensitivity analysis revealed that increasing the number of gores decreased the drag coefficient, with the flow separation delayed and the wake narrowing as the gore count increased. For example, a reduction of 32% in drag was observed when the number of gores increased from 30 to 50.Keywords: Large Eddy Simulation, Superpressure Balloon, Zero Pressure Balloon, Drag Coefficient, Stratospheric Propulsion, Aerodynamics
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This study proposes a numerical investigation for assessing the primary design parameters influencing the efficiency of a Darrieus type vertical axis wind turbine. The methodology consists in the numerical solution of the continuity and momentum equations utilizing the Unsteady Reynolds Averaged Navier-Stokes (URANS) approach. The turbulence closure model is the SST k-ω, and the Finite Volume Method is applied to solve the three-dimensional geometries. The findings confirm that variations in solidity and aspect ratio of twisted blade turbines, in comparison to straight blade configurations, exert a similar influence on the torque coefficient, surpassing the impact of blade torsion angle variations. Results corroborated previous findings of literature about the fluctuations in the torque coefficient (Cm) being smoothed in 55% when helical blades are used in comparison with straight configuration. However, the increase in blade torsion angle corresponded to a decrease in the torque coefficient, with maximum difference of 37% when solidity (σ) is σ = 0.75 and the ratio between height and radius of the turbine is H/R = 1.5. Results also demonstrated that the increase in the solidity from σ = 0.4 to 0.8 reduced the effect of the ratio H/R on the Cm. The increase of σ allowed a gain in Cm of nearly 60%. For constant σ and tip speed ratio (λ), the increase of H/R from 2.5 to 7.5 led to an increase of 79% in Cm. In general, results supplied a guideline on the influence of λ, twisted angle, σ, and H/R on the performance of helical Darrieus turbines.Keywords: Vertical Axis Wind Turbine, Twisted Blade Darrieus, Design, Aerodynamics, Numerical Simulation, Finite Volume Method
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Given the vast global capacity of wind turbines, even minor enhancements in their overall performance can substantially increase energy production. To achieve this, several techniques have been developed and implemented commercially to create advanced blades with improved efficiency. However, the fixed aerodynamic shape of these blades imposes certain constraints. This study conducts a numerical analysis of a 660 kW wind turbine, revealing that under specific operating conditions, the blades experience off-design conditions, leading to performance degradation. Simulations indicate that because the blades are designed for a single operating point, flow separation occurs on some sections of the blade surface in other situations. Further investigation demonstrates that the fixed geometry of the blades hinders the flow’s ability to adapt to their shape. To address this challenge, the method of boundary layer suction is proposed. Results indicate that by applying an appropriate level of suction intensity, the aerodynamic performance of the rotor can be enhanced by up to 8% under the specified working conditions by facilitating flow reattachment at the inboard section.Keywords: Wind Turbine, Boundary Layer Suction, Flow Separation, Aerodynamics, Performance
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Understanding how protrusions, such as fins attached to flat or streamlined bodies, affect aerodynamics, especially in high-speed contexts, is vital for aerospace applications. These protrusions significantly influence overall aerodynamics and require a comprehensive understanding for accurate analysis and prediction of aerodynamic performance. This understanding is particularly critical in supersonic flight, where even minor aerodynamic disturbances can impact vehicle stability and efficiency. Therefore, a thorough understanding of protrusion-induced flow phenomena is essential for advancing aerospace engineering and improving supersonic vehicle performance and safety. The present paper focuses on the complex supersonic flow over a vertical fin, using a combination of experimental and computational methods. The study aims to understand how variations in fin height influence the behavior of the Lambda shock and any resulting changes in shock length. Specifically, the paper investigates different fin height-to-diameter (H/D) ratios ranging from 0.5 to 1.5 in steps of 0.25. To achieve this, both experimental testing in a supersonic wind tunnel and numerical simulations using the commercial CFD tool ANSYS-FLUENT are employed. Through this dual approach, the paper seeks insights into the characteristics of the Lambda shock and its effects on key aerodynamic parameters, such as shock strength and drag coefficient. By thoroughly investigating these aspects, the paper contributes to a deeper understanding of the complex flow phenomena associated with supersonic flow over vertical fins, potentially guiding the design and optimization of aerospace vehicles. The outcomes indicate that a fin height of 12 mm (H/D=1.0) provides the best balance in terms of pressure distribution, Lambda shock length, and drag coefficient, making it the optimal choice for enhancing aerodynamic stability and performance in supersonic conditions.Keywords: Protrusions, Vertical Fin, Aerodynamics, Experimental Testing, Supersonic Flow, Aerospace Applications, Flow-Phenomena
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Investigation of similarity or dissimilarity in aerodynamic performance and noise pollution of H-Darrieus wind turbinesJournal of Theoretical and Applied Vibration and Acoustics, Volume:9 Issue: 1, Winter & Spring 2023, PP 0 -0This article investigates the impact of wind speed on the non-dimensional curve of power coefficient-tip speed ratio and noise pollution of an H-Darrieus wind turbine. Here, the URANS and the SST-kω turbulence model are applied to simulate flow around the turbine in four wind speeds and four tip speed ratios. The results showed no similarity in the aerodynamic performance when wind speed changes. Next, noise pollution is investigated using the FW-H equations at the tip speed ratio of 2.64 for all wind speeds. The directivity is calculated at distances of 4 m and 16 m and angle positions of 0o to 360o. It is observed that although the noise behavior is more similar to the monopole form, the angle position has a considerable effect on the noise received by observers. Increasing the wind speed significantly amplifies the wind turbine noise, but there is no similarity in the directivity profiles obtained for all wind speeds. Finally, the frequency distribution is investigated, and the results show that the highest frequency is at blade passing frequency in all cases. However, the results based on rotor frequencies show no similarity in the shape of frequency distribution.Keywords: VAWT, Noise Pollution, Aeroacoustics, CFD, Aerodynamics
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This study explored the aerodynamic aspects of the Hyundai Universe Express Noble bus, a common passenger bus model in Bangladesh, and proposed modifications to improve its performance. The airflow around the bus was analyzed using Computational Fluid Dynamics (CFD) simulations. Consequently, areas of high drag and turbulence were identified. These results led to the redesign and testing of several shape modifications for the bus, including adjustments to the roof spoiler, side mirrors, and front grille. After finding the bus model with the lowest drag coefficient, that model is further analyzed to find the aerodynamic effects of side windows on a bus and their impact on fuel efficiency. The aim is to determine how much side windows significantly affect fuel efficiency. The aerodynamic effect with windows open and closed is also evaluated after identifying an appropriate model. Model 1.2 uses 7.72% less fuel than base Model 1.0. Model 1.2 with windows uses 2.5% more fuel than Model 1.2. The study also evaluates the fuel cost per 500 km for all models suggesting that non-ac buses with side windows consume slightly more fuel than AC buses. Changing the bus shape to Model 1.2 will reduce the drag coefficient by 8.67% and fuel consumption by 7.72%. The study offers insights into reducing drag force, minimizing air resistance, enhancing exterior styling, and improving vehicle stability. Furthermore, these findings have practical implications for the transportation industry as they demonstrate the potential for improving the efficiency and sustainability of large vehicles through aerodynamic design.Keywords: Aerodynamics, Bus, Computational Fluid Dynamics, Reynolds-Averaged-Navier-Stokes, Side Windows
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Accurate predictions of aerodynamic performance and near wake expansion around Horizontal Axis Wind Turbine (HAWT) rotors is pivotal for studying wind turbine wake interactions and optimizing wind farm layouts. This study introduces a novel engineering model centered on stall delay correction to enhance the precision of the Actuator Disk Method (ADM) predictions in both aerodynamic performance and near wake expansion around HAWT rotors. The model is developed based on a comprehensive study of the 3D lift coefficient evolution over the rotor blade, incorporating a shift parameter that considers both stall angle detection and radial decrement. The proposed approach demonstrates remarkable agreements, showcasing discrepancies as low as 7% for both loads and axial wake predictions. These quantifiable results underscore the effectiveness of the model in capturing intricate aerodynamic phenomena. Looking forward, the success of this approach opens avenues for broader applications, guiding future research in wind energy towards improved simulation accuracy and optimized wind farm designs.Keywords: Aerodynamics, Wind energy, Effect of rotation, Near wake, Full Navier-Stokes, Actuator disk
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A computational fluid dynamic (CFD) and machine learning approach is used to investigate heat transfer on NASA airfoils of type NACA 0012. Several different models have been developed to examine the effect of laminar flow, Spalart flow, and Allmaras flow on the NACA 0012 airfoil under varying aerodynamic conditions. Temperature conditions at high and low temperatures are discussed in this article for different airfoil modes, which are porous mode and non-porous mode. Specific parameters included permeability of 11.36 x 10-10 m2, porosity of 0.64, an inertia coefficient of 0.37, and a temperature range between 200 K and 400 K. The study revealed that a temperature increase can significantly increase lift-to-drag. Additionally, employing both a porous state and temperature differentials further contributes to enhancing the lift-to-drag coefficient. The neural network also successfully predicted outcomes when adjusting the temperature, particularly in scenarios with a greater number of cases. Nevertheless, this study assessed the accuracy of the system using a SMOTER model. It has been shown that the MSE, MAE, and R for the best performance validation of the testing case were 0.000314, 0.0008, and 0.998960, respectively, at K = 3. However, the study shows that epoch values greater than 2000 increase computational time and cost without improving accuracy. This indicates that the SMOTER model can be used to classify the testing case accurately; however, higher epoch values are not necessary for optimal performance.Keywords: Computational modeling, Aerodynamics, Subsonic flow around airfoils, Heat transfer, Machine learning, CFD
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The innovative bus designs, inspired by the whales, have been developed. The designs are confined to the frontal area of the buses. The new designs are named as the Beluga buses. Several variants of the models all mimicking Beluga whales are proposed. Both numerical analysis and experimental have been conducted to determine the drag coefficients of various models. The ANSYS CFD program was used for numerical simulations. WT tests were conducted to experimentally determine the drag coefficients. Both methods indicate that the beluga-inspired buses offer significant reductions in drag, which can lead to lower fuel consumption. The new beluga design is expected to reduce fuel consumption by 12.64%. Comparing the experimental and numerical results, a 6.4% discrepancy in the drag coefficients is observed at low Reynolds numbers, which became negligible at higher Reynolds numbers. The new geometry is expected to offer an economical solution for reducing fuel consumption.Keywords: Aerodynamics, Biomimetics, Drag Coefficients, CFD, WT Tests, Buses
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Noise pollution is a significant challenge in developing the use of wind turbines, especially in residential areas. H-Darrieus turbine is a wind turbine widely used in residential areas, usually exposed to variable wind speeds, and works in a wide range of tip speed ratios. In this article, the importance of tip speed ratio on the output power and noise pollution of an H-Darrieus turbine is numerically investigated using the SST-kω model (for flow simulation at tip speed ratios of 2.04 to 3.3) and the Ffowcs Williams-Hawkings equations (for noise calculation in far-field). The directivity results show that the angle position of maximum noise differs for different tip speed ratios. Therefore, noise calculation only at the angle position of 0o, widely used for wind turbines, is insufficient. The results show that in terms of noise pollution, tip speed ratios of 2.04 and 3.3 have the best and worst performances, with maximum noises of 67.91 dB and 71.85 dB, respectively. On the other hand, the tip speed ratio of 2.64 has the highest power (2.92 times the power of 2.04) with a maximum noise of 68.26 dB, which is negligibly higher than that for the tip speed ratio of 2.04. Overall, it is concluded that in terms of compromise between noise pollution and power generation, the tip speed ratio of 2.64 is the best point for this turbine.
Keywords: Aerodynamics, CFD, Darrieus turbine, noise pollution, Vertical-axis wind turbine -
Due to the distinctive structure of the test section, the open jet wind tunnel generates low-frequency pressure fluctuations (LFFs) within the range of typical wind speeds. These fluctuations significantly compromise the quality of the flow field in the test section. The evolution of the flow structure and vortex is analysed through the improved delayed detached eddy simulations (IDDES). The LFFs and the control mechanism in the open jet wind tunnel of Jilin University are then studied. The interaction between the large-scale vortex shedding at the nozzle exit and the collector forms the edge feedback, which is the main reason for the pressure fluctuation. According to the feedback mechanism, the LFFs are suppressed using the throat gap and by improving the collector shapes. The results show that the increase of the throat gap length at the collector can significantly alleviate the pressure accumulation inside the collector. The change of the collector shapes can control the impact area and time of the incoming flow, or produce permanent vortex structure to affect the impact shape of the vortex and the flow field at the collector, which allows to control the LFFs. This study lays a solid foundation for further comprehension of the aerodynamic characteristics of the open jet wind tunnels.Keywords: Pressure fluctuation, Wind tunnel, Convective instability, Detached eddy simulation, Jet shear layer, Aerodynamics
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الگوگیری از بال پرندگان و نحوه ی پرواز آن ها از دیرباز موضوعی جذاب برای بشر بوده است. در سالیان اخیر به دلیل پیدایش برخی مواد و عملی کردن الگوگیری از پرواز پرندگان، بال های شکل پذیر تغییر شگرفی در موضوعات علمی پیرامون وسایل نقلیه ی هوایی ایجاد کرده اند. مطالعه ی عددی آیرودینامیکی و هواصوتی یکی از حالات شکل پذیری (پیچش حول محور طولی) این نوع بال ها هدف این مطالعه، بررسی پارامترهای آیرودینامیکی و هواصوتی یک بال شکل پذیر در حالت پیچش برای یک هندسه ی شبیه به پهپاد شاهد- 129 می باشد. از دیگر اهداف، معرفی یک روش نوین با استفاده از محرک ها برای تغییرشکل بال مورد نظر است. برای این منظور، علاوه بر حل معادلات متوسط گیری رینولوز شده ی حاکم بر جریان مغشوش، برای محاسبه تنش های رنیولوز ظاهر شده در این معادلات، با فرض لزجت گرایی بوزینسک(Boussinesg) ، از مدل اغتشاشی k- ω- SST برای تعیین لزجت مغشوش بهره گرفته شده است. این معادلات با استفاده از نرم افزار تجاری فلوینت ویرایش... حل گردیده اند. نتایج شبیه سازی بیان گر آن است که با افزایش زاویه ی پیچش و زاویه ی حمله تا 15 درجه، ضریب برآ و پسا افزایش می یابند. همچنین، در زاویه حمله های یکسان، با افزایش زاویه ی پیچش، رشد گردابه ها زیادشده و منجر به افزایش کم ضریب برآ در زوایای پیچش بالا می شود.کلید واژگان: آیرودینامیک، هواصوتیات، بال، شکل پذیری، پهپاد، اکچویتورInspiring from bird’s wings and flights has long been a fascinating subject. In recent years, due to advent of materials and implementation of bird’s flights, use of morphing wings have created considerable changes in scientific issues related to air vehicles. In this article, for the first time, aerodynamic and aeroacoustic studies of a type of (twist) morphing wing are performed. The main pupose of this article is to numerically investigate aerodynamics and aeroacoustics of a twisted morphing wing for a geometry similar to Shahed- 129 UAV. In the manufaturing part of this article, a new method is introduced, which uses actuators to change the wing’s shape. In this article, k- ω- SST modeling for turbulent flow and Fluent software were used. Our results show that with increase of twist angle and attack angle of up to 15 degrees, both lift and drag increase. In addition, at the same angle of attack, for high twist angles, increasing twist angle increases the growth of vortices, causesing a small increase in lift coefficient.Keywords: Aerodynamics, Aeroacoustics, Morphing, Wings, Drone, Actuators
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This article studies the aerodynamic performance of a novel bypass shock-induced thrust vector nozzle. An arc-shaped bypass is innovatively designed to optimize nozzle performance and equips a variable shrinkage part. The nozzle performance is investigated numerically under diverse shrinkage area ratios. Computational results indicate that both geometry and friction choking have important effects on the nozzle performance. Normally, in the case of without any bypass shrinkage, the flow choking occurs at the bypass outlet. Very small bypass shrinkage is unable to change the flow choking location. The bypass geometry choking comes up at its throat as the shrinkage area ratio of the bypass reaches 0.06. According to computational results, the vectoring angle diminishes with the increasing shrinkage area ratio of the bypass, thrust force ratio, thrust efficiency, specific impulse ratio, and coefficient of discharge increase. As the NPR enlarges, the deflection angle and thrust efficiency decrease, and the thrust force ratio increases.Keywords: Aerodynamics, Aeronautics, Supersonic nozzle, Shock-induced thrust vector control, Flow control
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Accurate predictions of the near wake of horizontal-axis wind turbines are critical in estimating and optimizing the energy production of wind farms. Consequently, accurate aerodynamic models of an isolated wind turbine are required. In this paper, the steady-state flow around an experimental horizontal-axis wind turbine (known as the MEXICO model) is investigated using full-geometry computational fluid dynamics (CFD) simulations. The simulations are performed using Reynolds-Averaged Navier-Stokes (RANS) equations in combination with the transitional k-kl-w turbulence model. The multiple reference frame (MRF) approach is used to allow the rotation of the blades. The impacts of the nacelle and blade rotation on the induction region and near wake are highlighted. Simulation cases under attached and detached flow conditions with and without the nacelle were compared to the detailed particle image velocimetry (PIV) measurements. The axial and radial flow behaviors at the induction region have been analyzed in detail. This study attempts to highlight the nacelle effects on the near wake flow and on numerical prediction accuracy under various conditions, as well as the possible reasons for these effects. According to simulation results, the rotation of blades dominates the near wake region, and including the nacelle geometry can improve both axial and radial flow prediction accuracy by up to 15% at high wind speeds. At low wind speeds, the nacelle effects can be ignored. The presence of the nacelle has also been shown to increase flow separation at the trailing edges of the blade airfoils, increasing both root and tip vorticities. Finally, small nacelle diameters are recommended to reduce flow separation on the blades and increase the average velocity downstream of the rotor, thereby optimizing wind farm output power.Keywords: Wind turbine, Aerodynamics, Near wake, Nacelle-blade interaction, CFD, Mexico
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The stall of an aircraft is one of the most dangerous phenomena in the aviation world, resulting in a sudden loss of lift because of boundary layer separation. This work aims to delay separation and to improve wing aerodynamic performances by introducing bumps and cavities on the upper surfaces of the wing. A numerical study on the effects of both cavities and bumps on flow structures and wing aerodynamics of NACA 0012 profile is conducted. The CFX code has been used to perform calculations of steady and uncompressible Reynolds Averaged Naviers-Stokes equations. The airfoil has been exposed to a free stream velocity of 5.616 m/s and chord based Reynolds number of 3.6 x 105 (chord length). A series of test on unmodified airfoil has been carried out for various turbulence models at angles of attack ranging from 0° to 15°. Then, the two-equation k-ω SST (Shear Stress Transport) has been retained for the further cases. Different configurations obtained through a modification of cavities and bumps shape, dimension, and position on the airfoil chord are investigated. Both the shapes considered are semi-spherical and semi-cylindrical, placed at two positions on the airfoil chord. The first location is in suction pick at X/C= 0.3 and the second one is at 0.7. Results show that the application of bumps delays the boundary layer separation and increase drag coefficient. A slight enhancement in lift and drag is observed at angle of attack of 15° for the cases where the cavities are placed at 0.7 m from the leading edge. In addition, calculations show that the stability of the vortex formed inside the cavities depends strongly on their shape and the cylindrical one has better performances.Keywords: Aerodynamics, CFD analysis, Dimple, Drag, Lift, NACA 0012, Turbulence models
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The current research illustrates the optimization of Vertical Axis Wind Turbine (VAWT) blades with implementation of added winglets displaying improved self-starting capabilities. The application of improved design is to be utilized in a university campus located in United Arab Emirates (UAE) in order to reduce its margin of consumed electrical energy by 15%. The study is conducted over a mean wind speed value of 5 m/s achieved in a one-year period at a specific altitude of 50 m in the UAE. Two aerodynamic simulation software were adopted, namely ANSYS FLUENT CFD and QBlade, with designs being modelled using AutoCAD. The analytical analysis included some aerodynamic characteristic such as power, lift, and drag coefficients. Through 2D-computational fluid dynamics (CFD), simulation study tested 20 different symmetrical as well as asymmetrical airfoils including the cambered S-0146 with 26.83% higher power output and lower noise amongst the test subjects. Turbine torque for added winglet design results in 4.1% higher compared to the benchmark. The modified design aims to produce at least 2% more power and have an improvement in self-starting of at least 20%. VAWTs tend to have higher potential and sensitivity towards wind direction (no yawing mechanism required) illustrating them as more cost-effective. Future scope includes utilizing wind lens technology to increase the free-stream velocity.Keywords: VAWT, Aerodynamics, Winglet, Self-starting
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تا به امروز تلاش های بسیاری برای استخراج انرژی از باد و افزایش ظرفیت توربین های بادی انجام شده است. از جمله این سیستم ها می توان به اینولاکس، روتورهای دارای شرود و داکت اشاره کرد. در بررسی های صورت گرفته در خصوص سیستم توربین بادی اینولاکس، اغلب اثرات کارکرد روتور توربین باد تعبیه شده در بخش ونتوری، در مشخصه های جریان، دخالت داده نشده است. مضافا طراحی و مدلسازی یک توربین باد بهینه متناسب با هندسه و شرایط ایرودینامیکی بخش ونتوری صورت نگرفته است. لذا در این مقاله با استفاده از نظریه BEM و با در نظر گرفتن ضرایب اصلاح نوک پره و توپی پرانتل و نیز تصحیح دنباله آشفته، یک کد نیمه تحلیلی توسعه داده شده و ابتدا یک توربین باد بهینه و اختصاصی بر مبنای داده های هندسی و عملکردی اینولاکس فرض شده، طراحی گردیده است. در ادامه مدلسازی و مطالعه عملکرد بصورت پارامتری حول مشخصه های هندسی توربین، نیز انجام شده است. نتایج اعتبارسنجی نشان می دهد کد توسعه یافته توافق بسیار خوبی با نتایج تجربی، عددی و تحلیلی پیشین داشته و از این رو هندسه طراحی شده برای پره ها قابل اتکا خواهد بود. بعلاوه بکارگیری تصحیحات گلوارت و برتون در همین بستر ارزیابی شده است. بر اساس دستاوردهای این پژوهش، در صورتی که توربین باد طراحی شده در بخش ونتوری سیستم اینولاکس استفاده شود، توان استحصال شده از آن 4425/2 برابر می شود. همچنین در شرایط یکسان، تصحیح برتون مقادیر کمتری را نسبت به تصحیح گلوآرت پیش بینی می کند. با فرض روتور 3 پره و سرعت باد 6/10 متر بر ثانیه و با در نظر گرفتن ضریب اصلاح نوک پره و توپی پرانتل، حداکثر ضریب توان و سرعت نوک پره متناظر با احتساب تصحیح برتون به ترتیب برابر 335/0 و 095/7 و با احتساب تصحیح گلوارت به ترتیب برابر 385/0 و 825/7 بوده است. از بستر فراهم شده به منظور بهینه سازی شکل پره و ساختار توربین باد اینولاکس می توان بهره گیری نمود.کلید واژگان: انرژی باد، آیرودینامیک، سیستم توربین باد اینولاکس، نظریه BEM، مطالعه پارامتریIn previous studies on the INVELOX system, the effect of turbine blades embedded in the venturi section has not accounted. In addition, the design and modeling of an optimal wind turbine in accordance with the geometry and aerodynamic conditions of the venturi section has not been done. Therefore, in this paper, using the BEM (blade element momentum) theory and considering Prandtl's tip and hub loss factors, and also turbulent wake correction, a semi-analytical code has been developed. First of all, an optimal wind turbine according to geometrical and operational assumed INVELOX system is designed. In the continuation, modeling and performance study of geometric parameters of the designed wind turbine has been done. The validation results show that the developed code agrees accurately with the previous experimental, numerical, and analytical results, and therefore the geometry designed for the blades will be reliable. In addition, the application of Glauert and Burton's corrections has been evaluated in this manuscript. Based on the research findings, it is concluded that under the same conditions, Burton's correction yields more conservative results than Glauert's correction. So that assuming 3 blades and a wind speed of 11 meters per second m/s and taking into account Prandtl's tip and hub loss factor, the maximum power coefficient and blade tip speed corresponding to Burton's correction are 0.335 and 7.178, respectively, and corresponding to Glauert's correction, are 0.385 and 7.825, respectively. The provided substrate can be used to optimize the blade shape and structure of the INVELOX wind turbine system.Keywords: Wind energy, Aerodynamics, INVELOX system, Horizontal axis wind turbine, BEM theory, Parametric study
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With the advent of various advanced materials, the idea of flying like birds has attracted considerable attention in recent years. In addition, aeroacoustics has become an important issue and is being widely studied. In this work, based on the shape of Owls’ wings, an attempt was made to improve the aeroacoustic and aerodynamic performances of conventional aircraft wings. For this purpose, wings with different elements, namely, square, triangular, and semicircular, on their top surface were examined. In addition, three different spatial distributions of the elements according to the Owl’s wings shape were considered. For incompressible airflow, aerodynamic and aeroacoustic parameters of wing with structured surfaces were investigated. Also, a wing with serrations was examined. The results indicate that wings with elements distributed starting from maximum section thickness and continuing up to the trailing edge are the most suitable case for both aerodynamic and aeroacoustic improvements. On the other hand, a two-sided serrated wing and a serrated wing in the trailing edge reduce the sound level significantly. In addition, the use of both elements and serrations delays wing stall and thus markedly increases the maximum lift coefficient.Keywords: Aeroacoustics, Aerodynamics, UAVs, Owl, Wing with structured surfaces
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بهبود عملکرد آیرودینامیکی وسایل نقلیه به علت تاثیر بر مصرف سوخت، پایداری و کنترل پذیری خودروها همواره مورد توجه مهندسان بوده است. در این پژوهش جهت دستیابی به دیدگاه اجمالی از تاثیرگذاری روش های بهبود عملکرد آیرودینامیکی خودروها، مروری بر تحقیقات انجام شده در زمینه کاهش نیروهای آیرودینامیکی با استفاده از روش کنترل جریان انفعالی صورت گرفته است که می تواند در بررسی، پیاده سازی و انتخاب روش مناسب تاثیرگذار باشد. نتایج حاصل نشان دهنده اهمیت بالای طراحی بدنه خودرو در کاهش نیروی پسا و نیروی برآاست به طوری که ایجاد کانال و انحنا در طرفین خودرو جهت انتقال جریان هوا از نواحی فشار بالا در جلوی بدنه به نواحی فشار پایین در پشت بدنه بیشترین میزان کاهش نیروی پسا را در پی دارد. همچنین استفاده از اسپویلر در انتهای بدنه به جهت تاخیر در جدایش و هدایت جریان هوا به سمت بالا، موجب کاهش نیروی برآ می گردد. تاثیر این روش ها بر کاهش نیروهای آیرودینامیکی بیش از سایر مکانیزم ها است، اما میزان دقیق تاثیرگذاری هر روش به نوع خودرو و نحوه پیاده سازی آن بر روی بدنه بستگی دارد.
کلید واژگان: آیرودینامیک، خودرو، نیروی پسا، نیروی برآ، کنترل جریان انفعالیImproving the aerodynamic performance of vehicles due to the impact on fuel consumption, stability and controllability of vehicles has always been on the attention of engineers. In this study, in order to obtain a brief view of the effectiveness of methods to improve the aerodynamic performance of vehicles, a review of research conducted to reduce aerodynamic forces using the passive flow control method, which can be effective in consideration, implementation and selection of the proper method. The results show the high importance of car body design in reducing drag and lift such that implementing the channel and curvature on the sides of the car to transfer air flow from high pressure areas in front of the body to low pressure areas behind the body has the highest value of reduction in drag force. Also, using a spoiler at the end of the body to delay separation and to direct airflow upwards reduces the lifting force. The effect of these methods on reducing aerodynamic forces is more than other mechanisms, but the exact extent of the effectiveness of each method depends on the type of vehicle and the way of its implementation on the body.
Keywords: Aerodynamics, vehicle, drag force, lift force, passive flow control -
با انجام آزمایش در آزمایشگاه های ایروبالستیک می توان ضرایب آیرودینامیکی یک جسم پرنده را با دقت بالا استخراج نمود. اما برای برنامه ریزی انجام آزمایش ها، تعیین تعداد و نوع متغیرهای اندازه گیری شده، چینش ایستگاه های اندازه گیری در هر آزمایش ضروری می باشد. بدین منظور می توان حساسیت مقادیر اندازه گیری شده نسبت به ضرایب آیرودینامیکی مورد نظر را محاسبه و بررسی نمود. در این مقاله با توجه به غیرخطی بودن معادلات حرکت شش درجه آزادی یک وسیله پرنده، با استفاده از روش حداقل مربعات و ماتریس اطلاعات فیشر از داده های شبیه ساز آزمایش ایروبالستیک، ضرایب آیرودینامیک استخراج شده و حساسیت هر یک از خروجی ها نسبت به تغییرات ضرایب آیرودینامیکی بررسی و ارایه شده است. به بیان دیگر این نتایج بیان می کند که در یک آزمایش ایروبالستیک، اگر داده های آزمایش نظیر سرعت و زاویه پیچ اندازه گیری شود دقت و حساسیت آن ها نسبت به هر کدام از ضرایب آیرودینامیکی و خطای ضرایب چه مقدار خواهد بود.
کلید واژگان: ایروبالستیک، آیرودینامیک، شناسایی ضرایب، روش حداقل مربعات، ضرائب آیرودینامیکی، حساسیت سنجیThe aerodynamic coefficients of any flying object can be estimated with high accuracy, by aero-ballistic tests, monitored in aerodynamic laboratories. For test-running management, it is necessary to determine the number and type of estimated variables and the station placement of each test. For this purpose, the sensitivity of variables under measurement, in relation to the associated aerodynamic coefficients must be calculated and surveyed. As the trajectory path is a nonlinear equation with six degrees of freedom, in this article we estimate the aerodynamic coefficients and sensitivity of each output to the changes of aerodynamic coefficients using the least square method and fisher data matrix. In other word, if the test data such as the speed and pitch angle are to be measured in an aero-ballistic test, the results of this research can specify their accuracy and sensitivity to each aerodynamic coefficient and the relevant coefficient errors.
Keywords: Aero-ballistic, Aerodynamics, coefficients identification, least square method, Aerodynamic Coefficients, Sensitivity
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