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flow sensitivity to trailing edge design for a two-element airfoil at low Reynolds numbers

PROGRESS IN COMPUTATIONAL FLUID DYNAMICS 2025年第3期25卷 159-175页

作者： Parmar, Dilip Lalchand Singh, Deepak Kumar Sharma, Arjun Indian Inst Technol Delhi Dept Appl Mech New Delhi 110016 India

The sensitivity of flow past a two-element airfoil to changes in the geometry of trailing segment of the main element is studied using Reynolds-averaged-Navier-Stokes simulations at Reynolds numbers, 5 x 10(4) and 1.5 x 10(5) and angles of attack in the range 0 to 7 degrees. Adjoint-based gradient data are used to make systematic changes to the shape in a localised region around the trailing edge of the main element with the objective of maximising the lift-to-drag ratio. The introduced shape changes tend to modify the converging-diverging flow passage that forms in the overlap region between main element and flap such that separation on the flap suction surface is delayed. Improvements in lift-to-drag ratio of 28% and 10% are obtained at angles of attack 0 and 5 degrees respectively at lower Reynolds number of 5 x 10(4) whereas the improvements at higher Reynolds number are comparatively lower.

关键词： high-lift system boundary layer separation boundary layer reattachment passive flow control shape modification adjoint-based gradient

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The Effect of Various Wedge Flap Configurations on the Performance of Wind Turbine Airfoil

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IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY-TRANSACTIONS OF MECHANICAL ENGINEERING 2024年第4期48卷 1879-1899页

作者： Abdalkarem, Asmail A. M. Fazlizan, Ahmad Muzammil, Wan Khairul Lim, Chin Haw Ibrahim, Adnan Wong, Kok Hoe Kazem, Hussein A. Univ Kebangsaan Malaysia Solar Energy Res Inst SERI Bangi 43600 Selangor Malaysia Univ Malaysia Sabah Fac Engn Energy Res Unit Kota Kinabalu 88400 Malaysia Univ Southampton Malaysia Carbon Neutral Res Grp CNRG Iskandar Puteri 79200 Malaysia Sohar Univ Fac Engn POB 44 Sohar PCI 311 Oman

controlling turbulent flow to improve wind turbine airfoils' aerodynamic characteristics is a desirable task. The current study evaluated the potential of adding a wedge flap (WF) at the trailing edge of the NACA0021 airfoil. The effect of different WF heights and lengths on optimum height (L/H) on the aerodynamic performance and flow over the airfoil has been studied numerically using two-dimensional computational fluid dynamics simulation. The simulation solves the Reynolds-Averaged-Navier-Stokes with shear stress transport k-omega turbulent model. The results indicate that adding WF can effectively suppress flow separation and improve aerodynamic efficiency in all studied cases compared to clean airfoil. The aerodynamic performance is influenced significantly by the height of WF compared to the slight influence by the length at L/H < 1. Inclined WF achieves the highest lift and lift-to-drag values with total maximum increments of 71.67% and 45.79%, respectively, at optimum height and length with 6%c and 1%c, respectively, in comparison with the clean airfoil case. The results observed that WFs have advantages over the Gurney flaps discussed in this study. WF appears to be an effective passive flow control device that can be used in wind turbines if its dimensions are properly chosen.

关键词： CFD NACA0021 Wind turbine Wedge flap passive flow control

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Measurements of flow Characterization Revealing Transition to Turbulence Associated with the Partial Flexibility-Based flow control at Low Reynolds Number

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ARABIAN JOURNAL FOR SCIENCE AND ENGINEERING 2024年第12期50卷 9061-9077页

作者： Koca, Kemal Keskin, Sinem Sahin, Rumeysa Veerasamy, Dhamotharan Genc, Mustafa Serdar Erciyes Univ Dept Energy Syst Engn Wind Engn & Aerodynam Res Lab TR-38039 Kayseri Turkiye Abdullah Gul Univ Dept Mech Engn TR-38080 Kayseri Turkiye MSG Teknol Co Erciyes Teknopark Tekno 1Binasi 61-20 TR-38039 Kayseri Turkiye Loughborough Univ Epinal Way Loughborough LE11 3TU Leics England Erciyes Univ Energy Convers Res & Applicat Ctr TR-38039 Kayseri Turkiye

In order to comprehend the flow characteristics of both controlled and uncontrolled SD7062 wind turbine airfoils with local flexible membrane material throughout a variety of angles of attack at a Reynolds number of 1.05 x 105, an experimental investigation was conducted. The time-dependent force measurement, the hot-wire experiment with a boundary layer and glue-on probes, and the oil-flow visualization technique were all utilized in the present study to measure the flow over the airfoil and examine the laminar-turbulent transition, laminar separation bubble, and the impact of a special flow control method that uses flexibility. A comprehensive intermittency analysis by utilizing hot-wire results was employed to obtain the flow physics effects of the local flexibility the first in the literature. The key results of the experiment demonstrated that the stall was delayed from alpha = 10 degrees to 12 degrees by the local flexibility. The hot-wire results are dedicated to laminar, transitional and turbulent regions and the transition phenomena at different locations over the suction surface of the airfoil in the analysis graphs. As demonstrated by the results of the oil-flow visualization experiment, in the uncontrolled case, the laminar separation bubble formed over the airfoil at alpha = 8 degrees between x/c = 0.16 and x/c = 0.42. The use of flexible membrane material over the airfoil provided that the oscillation of this material triggered the transition to turbulence and a bypass transition, which resulted in the reattached flow.

关键词： Partially flexible membrane passive flow control Intermittency measurement Transition to turbulence Airfoil Lift coefficient

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Ground effect of an inverted double element wing diffuser on a sedan car

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HELIYON 2024年第8期10卷 e29435页

作者： Abood, Mustafa Sabeeh Hussain, Ihsanyahya Univ Baghdad Mech Engn Dept Baghdad Iraq

The diffuser is a critical component in sports cars, enhancing aerodynamics by increasing downforce and reducing drag. Previous studies have focused on its dependence on diffuser incidence, height, and base pressure. The design of the car, particularly the rear end shape and the rear wing's presence, affect base pressure and the diffuser's performance. Previous studies have investigated the effects of diffuser geometry on aerodynamic performance, but the current study is the first to examine the relationship between the diffuser and the rear tires. It also provides specific and quantitative results on the impact of different diffuser design parameters on drag and downforce. The relationship between the rear tires and the double-element inverted wing diffuser using computational fluid dynamics (CFD) was investigated. This is an essential problem because the diffuser is a critical component of sports cars, and its design can significantly impact aerodynamic performance. CFD was used to simulate the flow of air around the car model. The CFD model was based on the Nissan Sunny (Versa) type Almera design, and the diffuser main element and flap wing angles were set at 4 and 15.5 degrees, respectively. The flap gap, overlap distance, and wing ride height above the ground were varied to achieve an optimal aerodynamic design. The study found that the wing's ride height significantly influences the flow through the diffuser. The diffuser significantly impacts base pressure and downforce production. Increasing the ride height decreases base pressure, leading to an increase in downforce until a specific point near the car body, where downforce further increases. The study concluded that the best double-element diffuser design was selected based on lift-to-drag results and the allowable dimensions of the car, wing ride height, element gap, and overlap distances. Ultimately, the best diffuser wing design features a ride height of 154 mm, a gap distance of 10 mm, and an overlap of

关键词： Ground effect Double -element inverted wing Nissan sunny car Car diffuser CFD Drag reduction passive flow control

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Experimental and Numerical Investigation of Roughness Structure in Wind Turbine Airfoil at Low Reynolds Number

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INTERNATIONAL JOURNAL OF THERMODYNAMICS 2024年第3期27卷 26-36页

作者： Tanurun, H. E. Akin, A. G. Acir, A. Sahin, I. Kahramanmaras Istiklal Univ Elbistan Engn Fac Dept Energy Syst Engn Kahramanmaras Turkiye TC Presidency Def Ind Naval Platforms Dept Ankara Turkiye Gazi Univ Fac Technol Dept Energy Syst Engn Ankara Turkiye Purdue Univ Sch Mech Engn W Lafayette IN 47906 USA

This paper experimentally and numerically investigates the effects of suction side surface roughness on the aerodynamic performances of the NACA 0015 turbine blade profile. Three different NACA 0015 turbine blade configurations, which are smooth (K0), 0 ), single roughness (K1), 1 ), and double roughness (K2), 2 ), are considered. The experimental studies were conducted using the HM-170 GUNT open wind tunnel model. The aerodynamic characteristics of these three blade configurations are evaluated in terms of their lift coefficient (C-L), drag coefficient (CD), and aerodynamic efficiency (C-L/C-D). The maximum C-L (C-L,C-max ) for K0 0 was obtained at 25 degrees, whereas the C-L,C-max angles for the K-1 and K-2 roughness blade profiles were reduced to 22.5 degrees, utilizing the rough surfaces on the suction side. The experimental analysis revealed that the K-2 profile demonstrated a 21% and 19% enhancement in maximal CL over the K-0 and K-1 profiles, respectively. The highest C-L/C-D was observed with K-1, except at low attack of angle (alpha o alpha), alpha o alpha ), where the smooth blade profile resulted in slightly better performance. Experimental analysis showed peak C-L/C-D at alpha o alpha of 7.5 degrees for K0, 0 , and 12.5 degrees for both K 1 and K2, with K1's optimal C-L/C-D being 2.85% and 8.5% higher than K-0 and K-2, respectively. Numerical analysis indicated that the C (L) /C-D,C-avg for K1 1 was observed to be 11% and 8% higher than that of K0 0 across all alpha o alpha. .

关键词： Airfoil roughness aerodynamic performance passive flow control experimental

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Effects of wavelength on vortex structure and turbulence kinetic energy transfer of flow over undulated cylinders

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THEORETICAL AND COMPUTATIONAL FLUID DYNAMICS 2023年第4期37卷 485-504页

作者： Lyons, Kathleen Cal, Raul Bayoan Franck, Jennifer A. Univ Wisconsin Madison Dept Engn Phys Madison WI 53706 USA Portland State Univ Dept Mech & Mat Engn Portland OR USA

passive flow control is commonly used on bluff bodies for drag and oscillating lift reduction across a range of engineering applications. This research explores a spanwise undulated cylinder inspired by seal whiskers that is shown to reduce hydrodynamic forces when compared to smooth cylinders. Although the fluid flow over this complex geometry has been documented experimentally and computationally, investigations surrounding geometric modifications to the undulation topography have been limited, and fluid mechanisms by which force reduction is induced have not been fully examined. Five variations of undulation wavelength are simulated at Reynolds number Re = 250 and compared with results from a smooth elliptical cylinder. Vortex structures and turbulence kinetic energy (TKE) transfer in the wake are analyzed to explain how undulation wavelength affects force reduction. Modifications to the undulation wavelength generate a variety of flow patterns including alternating vortex rollers and hairpin vortices. Maximum force reduction is observed at wavelengths that are large enough to allow hairpin vortices to develop without intersecting each other and small enough to prevent the generation of additional alternating flow structures. The differences in flow structures modify the magnitude and location of TKE production and dissipation due to changes in mean and fluctuating strain. Decreased TKE production and increased dissipation in the near wake result in overall lower TKE and force reduction. Understanding the flow physics linking geometry to force reduction will guide appropriate parameter selection in bio-inspired design applications.

关键词： Seal whisker Wavy cylinder passive flow control Vortex dominated flows Wake dynamics

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Numerical investigation of parietal pressure distribution on NACA0012 wing controlled by micro-cylindrical rod arranged in tandem

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PROGRESS IN COMPUTATIONAL FLUID DYNAMICS 2023年第4期23卷 231-248页

作者： Larabi, Abderrahim Pereira, Michael Ravelet, Florent Azzam, Tarik Oualli, Hamid Menfoukh, Laiche Bakir, Farid Ecole Mil Polytech Lab Mecan Fluides BP 17 Bordj El Bahri Algiers 16214 Algeria HESAM Univ Arts & Metiers Inst Technol CNAM LIFSE F-75013 Paris France

A parametric investigation of the influence of a small cylinder on the laminar separated boundary layer over NACA0012 wing is performed using numerical simulations. The (gamma - Re-theta,Re-t) steady RANS transitional model is first validated in capturing the separation on the baseline wing suction surface. The effects of three rod diameter ratios (d/c = 0.67%, 1.33% and 2%) on the laminar separation bubble and aerodynamic performances were examined. The qualitative analysis of the flow structures revealed the mechanisms of the control device for the aerofoil performance improvements. The formation of vortices in the rod wake exerted considerable effects on LSB size, pressure coefficient and flow streamlines. Particularly, it contributes to eliminate the boundary layer separation with pronounced decrease of 75% by energising the shear layer over a significant extent, resulting in a mean drag dropping of 73% at 12 degrees incidence, and a lift enhancement of about 23% at 15 degrees.

关键词： laminar separated flow SST transition model passive flow control bodies' wake interaction laminar separation bubble LSB drag reduction lift enhancement

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Drag reduction of a commercial bus with add-on aerodynamic devices

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PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART D-JOURNAL OF AUTOMOBILE ENGINEERING 2023年第7期237卷 1623-1636页

作者： Garcia-Ribeiro, Daniel Bravo-Mosquera, Pedro D. Ayala-Zuluaga, Jimmy A. Martinez-Castaneda, Diego F. Valbuena-Aguilera, Jeisson S. Ceron-Munoz, Hernan D. Vaca-Rios, John J. Inst Tecnol Aeronaut ITA Sao Jose Dos Campos Brazil Univ Sao Paulo Sao Carlos Engn Sch Dept Aeronaut Engn Sao Carlos Brazil Fdn Univ Libertadores Programa Ingn Aeronaut Bogota Colombia

In the automotive industry, the implementation of drag reduction systems has provided considerable decreases in fuel consumption. These outcomes are in line with the increasing demands of the environmental regulations and consumers' requirements. Although some studies explain how aerodynamic devices reduce the aerodynamic drag on light and heavy vehicles such as Ahmed bodies and trucks, buses have received almost no attention. For this reason, the flow over the Marcopolo Paradiso 1200 G7 commercial bus and the influence of several aerodynamic devices on the drag force and fuel consumption of the bus are discussed in this article. Three distinct devices (vortex generators, lateral devices, and rails) were proposed after flow visualization tests on the baseline bus. Thus, the entire evaluation consisted of 11 arrangements by combining the three aerodynamic devices. The changes in drag due to all arrangements are estimated using wind tunnel tests, which are validated using Computational Fluid Dynamics simulations. The fuel consumption is evaluated in a simplified long-haul driving cycle between two cities. The devices were able to alter the flow behavior on the bus, resulting in a maximum decrease of 8.63% in the drag coefficient and 3.92% in fuel consumption. Given that the devices used are just first prototypes, we estimate that greater reductions can be achieved with optimized systems. Likewise, this paper probably leads to real applications in other commercial buses due to the evident drag reductions.

关键词： Road vehicle aerodynamics passive flow control experimental analysis drag coefficient fuel consumption

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Turbulence model study for aerodynamic analysis of the leading edge tubercle wing for low Reynolds number flows

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HELIYON 2024年第11期10卷 e32148页

作者： Ali, Intizar Hussain, Tanweer Unar, Imran Nazir Kumar, Laveet Ul Ahad, Inam Mehran Univ Engn & Technol Dept Mech Engn Jamshoro 76080 Sindh Pakistan Dublin City Univ Form Adv Mfg Res Ctr 1 Sch Mech & Mfg Engn Dublin D09 V209 Ireland Mehran UET Natl Ctr Robot &Automat Condit Monitoring Syst Jamshoro Pakistan Mehran Univ Engn & Technol Dept Chem Engn Jamshoro 76080 Sindh Pakistan Qatar Univ Coll Engn Dept Mech & Ind Engn Doha Qatar

A turbulence model study was performed to analyze the flow around the Tubercle Leading Edge (TLE) wing. Five turbulence models were selected to evaluate aerodynamic force coefficients and flow mechanism by comparing with existing literature results. The selected models are realizable k-epsilon, k-omega Shear Stress Transport (SST), (gamma - Re theta) SST model, Transition k-kl-omega model and Stress- omega Reynolds Stress Model (RSM). For that purpose, the TLE wing model was developed by using the NACA0021 airfoil profile. The wing model is designed with tubercle wavelength of 0.11c and amplitude of 0.03c. Numerical simulation was performed at chord-based Reynolds number of Rec = 120,000. The Computational Fluid Dynamic (CFD) simulation reveals that among the selected turbulence models, Stress- omega RSM estimated aerodynamic forces (i.e. lift and drag) coefficients closest to that of the experimental values followed by realizable k-epsilon, (gamma - Re theta) SST model, k-omega SST model and k-kl-omega model. However, at a higher angle of attacks i.e. at 16 degrees & 20 degrees k-omega SST model predicted closest drag and lift coefficient to that of the experimental values. Additionally, the critical observation of pressure contour confirmed that at the lower angle of attack Stress- omega RSM predicted strong Leading Edge (LE) suction followed by realizable k-epsilon, (gamma - Re theta)SST model, k-omega SST model and k-kl-omega model. Thus, the superiority of Stress- omega RSM in predicting the aerodynamic force coefficients is shown by the flow behavior. In addition to this pressure contours also confirmed that k-kl-omega model failed to predict tubercled wing aerodynamic performance. At higher angles of attacks k-omega SST model estimated aerodynamic force coefficients closest to that of the experimental values, thus k-omega SST model is used at 16 degrees & 20 degrees AoAs. The observed streamline behavior for different turbulence models showed that the Stress-

关键词： passive flow control Leading edge tubercle CFD simulation Turbulence model Low Reynolds number flows

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control of flow structure over a non-slender delta wing using passive bleeding

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AEROSPACE SCIENCE AND TECHNOLOGY 2020年 106卷

作者： Kestel, Kayacan Ramazanl, Burcu Yavuz, Mehmet Metin Middle East Tech Univ Mech Engn Dept TR-06800 Ankara Turkey

Recently, it has been demonstrated that the bleeding, which utilizes passages inside the wing to allow the fluid flowing from the pressure side to the suction side by using inherent pressure difference, could be used as an effective flow control method for non-slender delta wings. In the present study, this technique is applied to a non-slender delta wing with sweep angle of Lambda = 45 deg with particular interests in delaying stall and eradication of three-dimensional surface separation. The experiments are conducted in a low speed wind tunnel using surface pressure measurements, Particle Image Velocimetry (PIV) measurements on near surface and cross flow planes, and aerodynamic force measurements. The bleeding passage orientation defined as back angle theta and bleeding passage size defined as bleed opening ratio bor are varied and the corresponding wings along with the Base planform are tested for the Reynolds numbers 35000 <= Re <= 100000 and the angles of attack 0 <= alpha <= 36 deg. The results indicate that at sufficiently high angle of attack where the pronounced surface separation appears on the Base planform, which is indicated by focus point along with large-scale swirl in the near surface streamline pattern, the elimination of surface separation is achieved with passive bleeding. This is incorporated with significant increases in the magnitudes of surface normal vorticity and suction pressure coefficient-C-p, which indicate recovery of leading-edge vortex. Considering the back angle and bleed opening ratio, the results indicate that increases in both parameters provide better performances in terms of elimination of surface separation. In addition, aerodynamic coefficient measurements show that proper bleeding configuration provides significant improvement in stall angle and lift coefficients. (C) 2020 Elsevier Masson SAS. All rights reserved.

关键词： Non-slender delta wing passive flow control Leading edge vortex Bleeding Three-dimensional surface

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