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Pre-arranged sequences of micropillars for passive mixing control of water and ethanol

CHEMICAL ENGINEERING JOURNAL 2023年第1期461卷

作者： Antognoli, Matteo Donato, Laura Galletti, Chiara Stoecklein, Daniel Di Carlo, Dino Brunazzi, Elisabetta Univ Pisa Dipartimento Ingn Civile & Ind Largo Lucio Lazzarino 2 I-56122 Pisa Italy Rose Hulman Inst Technol Dept Mech Engn 5500 Wabash Ave Terre Haute IN 47803 USA Univ Calif Los Angeles Dept Bioengn 410 Westwood Plaza Los Angeles CA 90055 USA

Microfluidic reactors have enabled the continuous conduction of chemical reactions with exceptional control of fluids and operating conditions. To enhance reagent mixing in laminar flow conditions, the effective strategy of adding cylindrical obstacles (i.e., pillars) in the mixing channel is appealing. Indeed, they can passively extend the contact surface of the incoming fluid streams, where diffusion and reaction occur. From our previous work, optimized sequences of pillars in a T-microchannel - that differ in diameter and position - can significantly improve the mixing for single-phase flow (i.e., mixing of miscible fluids of similar density and viscosity). However, real-world mixing applications often require the merging of fluids with significantly different fluid properties before, during, and after mixing. Hence, further investigations are required to unveil efficiency and robustness in these more complex practical mixing conditions. We jointly carried out experiments and numerical simulations on miscible fluids in an optimized sequence of pillars called IAF. Our analysis shows how the fluid velocity (i.e., the Reynolds number, Re) and the pillar configuration affect the formation of horseshoe vortices, which we consider crucial for water mixing when 1 < Re < 100. Then, we analyzed water- water and water-ethanol mixtures at Re=40 to observe how fluid properties alter the flow passively controlled by the pillar sequence. Eventually, the analysis extends within Re=10-100, showing efficiency and pressure drops of optimized designs that depend on the evolution of physical properties. These findings provide insights into the predictions of confined fluid flow around obstacles and its optimization for engineering processes, e.g., nanoparticle precipitation.

关键词： Cylindrical obstacle passive flow control Horseshoe vortex Micromixer Design optimization Microreactor

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Numerical Investigations of passive flow control Elements for Vertical Axis Wind Turbine 10

Numerical Investigations of Passive Flow Control Elements fo...

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10th International Conference on Mathematical Problems in Engineering, Aerospace and Sciences (ICNPAA)

作者： Frunzulica, Florin Dumitrache, Alexandru Suatean, Bogdan Univ Politehn Bucuresti Fac Aerosp Engn Polizu 1-6 RO-011061 Bucharest Romania Romanian Acad Gheorghe Michoc Caius Iacob Inst Math Stat & Appl Bucharest 050711 Romania

ISBN: (纸本)9780735412767

In this paper we numerically investigate the possibilities to control the dynamic stall phenomenon, with application to vertical axis wind turbines. The dynamic stall appears at low tip speed ratio (TSR<4) and it has a great impact on structural integrity of the wind turbine and power performances. For this reason we performed a CFD 2D analysis of the dynamic stall phenomenon around NACA 0012 airfoil equipped with a passive flow control device, in pitching motion at relative low Reynolds number (similar to 10(5)). Three passive flow control devices are numerically investigated: a turbulence promoter mounted on the leading edge, a thin channel and a step on the upper surface of the airfoil. For the present studies, the unsteady Reynolds averaged Navier-Stokes (RANS) model is the suitable approach to perform the dynamic stall simulations with an acceptable computational cost and reasonable accuracy. The results are compared to those of an existing experimental case test for unmodified NACA 0012 airfoil. The capability of this device was investigated numerically on a vertical axis wind turbine (2D model), where blades are generated with NACA 0018 airfoil.

关键词： vertical axis wind turbine dynamic stall passive flow control RANS

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Sensitivity analysis of hybrid methods for the flow around the ahmed body with application to passive control with rounded edges

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COMPUTERS & FLUIDS 2021年 214卷

作者： Delassaux, Francois Mortazavi, Iraj Itam, Emmanuelle Herbert, Vincent Ribes, Charles CNAM Paris Equipe M2N 2 Rue Conte F-75003 Paris France Grp PSA Route Gisy F-78943 Velizy Villacoublay France

A comparative study of SST RANS and three hybrid approaches (SAS, DDES and SEES methods) is performed to analyse the flow around the 25 degrees Ahmed body. The DDES approach is then selected as the reference model, based on comparison of numerical results. The main study is based on grid and time step influence over the simulation results. All results are compared to in-house experiments. The three grids 151, 201 and 301 (related to the number of prism layers in the boundary layer) show a fair prediction for both drag C-d and lift C-l coefficients. The best prediction is obtained with the 301 grid with an accurate prediction of C-d and C-l values as well as the main flow characteristics, compared to experiments. Another part of this paper focuses on the time step effect on the computational accuracy. Then, the flow around various rounded edge Ahmed body configurations is compared to experiments in order to validate the robustness of the numerical methodology. The rounded edge flow topologies are therefore deeply investigated. It is shown that they act as passive flow control and significantly influence the flow topology and aerodynamical coefficients. In fact, the rounded strategy modifies the flow detachment and weakens the onset of C-pillar vortices, which directly reduce drag and lift coefficients. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： Turbulence modeling Hybrid methods Ahmed body Rounded and sharp edges passive flow control

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control of a boundary layer over a wind turbine blade using distributed passive roughness

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RENEWABLE ENERGY 2022年第0期184卷 421-429页

作者： Ozkan, Musa Erkan, Onur Bilecik Seyh Edebali Univ Dept Mech Engn TR-11230 Bilecik Turkey

Wind turbines are mostly prone to reduced aerodynamic performance due to the inevitable occurrence of the roughness on blades. However, it may be possible to control the boundary layer by means of the right sort of roughness. In this study, distributed passive roughness is applied to the surface of NACA 63-415 airfoil. The influence of the roughness on the aerodynamic performance is numerically investigated by means of the TSST turbulence model for 10(3) <= Re <= 3 x 10(6) and for the angle of attack alpha = 6 & DEG;. Results show that the effect of roughness on the airfoil performance is negligible for Re <= 10(4). However, for 5 x 10(4) <= Re <= 1.5 x 10(5), the surface roughness can significantly improve the aerodynamic performance. Furthermore, for Re = 2.5 x 10(5), the roughness still has a favourable effect until the roughness height of h = 0.1 mm. Moreover, it is observed that for 2.5 x 10(5) <= Re <= 3 x 10(6), the lift to drag ratio is decreased by the application of roughness. Consequently, this study reveals that the implementation of the right sort of roughness can enhance the aerodynamic performance of the investigated wind turbine blade profile for some particular flow conditions.& nbsp;(c) 2021 Elsevier Ltd. All rights reserved.

关键词： Drag reduction passive flow control Surface roughness Wind turbines

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Wake flow characteristics of diamond-shaped cylinder with splitter plate

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OCEAN ENGINEERING 2025年 326卷

作者： Onel, Huseyin C. Durhasan, Tahir Aksoy, Muhammed Murat Karasu, Ilyas Adana Alparslan Turkes Sci & Technol Univ Dept Aerosp Engn TR-01250 Adana Turkiye Osmaniye Korkut Ata Univ Dept Energy Syst Engn TR-80000 Osmaniye Turkiye Samsun Univ Dept Aerosp Engn TR-55060 Samsun Turkiye

A numerical study is performed to emphasize the influence of splitter plates on the wake of a diamond-shaped cylinder at Reynolds (Re) numbers of 80, 100, and 150. Dimensionless plate lengths (L) vary from L = 0.25D to L = 6D in order to explore the sensitivity of the flow structure to the inclusion of the splitter plate. Key insights are provided through flow streamlines, vorticity contours, drag coefficients, and wake thicknesses;offering a comprehensive understanding of the flow behavior. Three distinct flow regimes are identified depending on the plate lengths and Re number. Vortex shedding is attenuated gradually up to L/D = 1 for all Re. The rolling up vortices from the trailing edge of the plate generate different flow regimes at L/D = 1.5. Furthermore, a steady wake regime is observed for L/D = 2 and 4 at Re = 80 and 100, respectively. A decreasing trend of Strouhal (St) number with the increasing splitter plate length is observed even though non-monotonic behavior is discerned at longer lengths. This reduction in the fluctuations brings out the efficacy of the splitter plates in suppressing vortex shedding. The results demonstrate how passive flow control can be achieved with reduced base pressure of the diamond cylinder by adding splitter plates.

关键词： Diamond-shaped cylinder Splitter plate Low Reynolds number CFD passive flow control

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Effects of solidity on the vibrational characteristics of the LEP VAWT

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WIND AND STRUCTURES 2025年第1期40卷 13-28页

作者： Elangovan, Karthik Vel Pillai, S. Nadaraja SASTRA Deemed Be Univ Turbulence & Flow Control Lab Thanjavur 613041 Tamil Nadu India

The primary goal of this research is to explore the influence of structural responses brought about by alterations in aerodynamic characteristics resulting from the incorporation of leading-edge protuberance (LEP) blades in vertical-axis wind turbines (VAWTs). A scaled-down straight-blade VAWT was utilized and subjected to operational wind speeds at a fixed pitch angle and various blade configurations to carry out this investigation. The study specifically aimed to investigate the unsteady structural excitation caused by the decay of vortices due to different aerodynamic loads and their effects on the VAWT structure. The results demonstrated that counter-rotating vortices in the LEP profile enhanced the aerodynamics of the blades at higher angles of attack. Understanding the structural characteristics resulting from aerodynamic changes is essential for developing VAWTs. The current research analyzes the effects of LEP on the structural excitation of a VAWT by examining the acceleration and displacement data obtained from a static-structure VAWT for various solidity ratios and LEP profiles. The results indicated that the VAWT with LEP blades resulted in decreased acceleration and displacement amplitudes for a low solidity ratio, which increased with an increase in the solidity ratio. Significant aerodynamic and structural damping were observed in the VAWT with LEP blades. These results were in close agreement with the time and frequency domains of the measured displacement and acceleration of the structure. The average bi-directional vibration damping of approximately 35% was observed by substituting the straight blade with the LEP blades for the operation of VAWT.

关键词： aerodynamic damping dynamic stall experimental study leading edge protuberance passive flow control solidity ratio VAWT

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Turbulence and vorticity decay of propulsion jets produced by ducted fans coated with a sharkskin-inspired surface

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AEROSPACE SCIENCE AND TECHNOLOGY 2025年 157卷

作者： Maldonado, Victor Fernandes, Guilherme D. Mallory, Aaron Texas Tech Univ Dept Mech Engn Flow Control & Aerodynam Lab Lubbock TX 79409 USA

Turbulent jets are produced by many propulsion systems containing a ducted fan or rotor operating at high speed. In this experimental study, the blades of a 12 cm diameter ducted rotor system were coated with a sharkskin- inspired surface with diverging tip micropillars. Surfaces containing 40 mu m and 70 mu m tall micropillars were applied on the rotor blades in order to study their role on fan aerodynamics and downstream jet flow. The ducted rotor was operated at up to 30,000 revolutions per minute (rpm), creating a turbulent jet with a Reynolds number of 5.97x105 and Mach number of 0.222 based on mean streamwise velocity. The inflow at the inlet of the rotor and the flow-field downstream was measured using high-speed laser Doppler velocimetry (LDV) techniques. The effect of the micropillar coatings on the rotor blades marginally increases the mean streamwise velocity and rotor figure of merit due to mitigating boundary layer separation at higher rotor speeds. Moreover, this occurs due to the micropillar's ability to increase wall-normal turbulence intensity in the boundary layer when the pillar height is scaled appropriately to the boundary layer thickness. The rotor hub and blade tip vortex structures become diffused and undergo breakup into smaller structures accompanied with an acceleration in the decay of absolute mean cross-stream vorticity. This quantity physically represents vortical structures with a lower magnitude of rotation. In a streamwise distance of 1.5 rotor diameters, the decay of mean cross-stream vorticity in the jet flow- field is 42.4% and 44.1% for the jets produced by the rotor blades coated with micropillars with & planckh;= 40 mu m and 70 mu m respectively. This is in comparison to the 38.1% cross-stream vorticity decay for the baseline jet generated by the ducted rotor coated with smooth kapton tape. However, it was found that the decay in turbulence intensity as well as turbulent kinetic energy is more localized near the inlet of the je

关键词： Ducted rotor Turbulent jet passive flow control Drag and vorticity reduction

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Bio-inspired pressure side stepped NACA 23012 C as wind turbine airfoils in low Reynolds number

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ENERGY REPORTS 2025年 13卷 3728-3744页

作者： Elsayed, Ahmed M. Gaheen, Osama A. Elshimy, Haitham Benini, Ernesto Aziz, Mohamed A. Fayoum Univ Fac Engn Mech Engn Dept Fayyum 63514 Egypt Inst Aviat Engn & Technol Mech Engn Dept Giza Egypt United Arab Emirates Univ Dept Mech & Aerosp Engn Al Ain U Arab Emirates Univ Padua Dipartimento Ingn Ind Via Venezia 1 I-35131 Padua Italy Suez Univ Fac Engn Mech Engn Dept POB 43221 Suez Egypt

The current study focuses on obtaining a new form of stepped airfoil inspired by the shape of a bird's wing in nature, which consists of three steps of feathers. A stepped wing can be used for passive flow control to improve the aerodynamic characteristics and delay stall in wind turbine blades. This study focused on a one-stepped NACA 23012 C section and later a three-stepped airfoil section, which was numerically analyzed at various step lengths, depths, and angles of attack. The numerical results were experimentally verified using physical models, and the findings demonstrated a maximum lift coefficient (CL,max) of 11.3 % increment for the threestepped airfoil. Furthermore, the three-stepped airfoil retained more CL values for the angle of attack (AOA) less than 14 degrees and increased lift-to-drag ratio CL/CD for AOA less than 6 degrees. For the one-stepped airfoil, CL,max was increased by 12.5 %, and stall AOA was delayed by 2 degrees while maintaining higher CL values after AOA 14 degrees.

关键词： Stepped airfoil Wind turbine blades passive flow control NACA 23012 C Numerical analysis Experimental investigation

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Review of flow control for atomization and sprays: Application section

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2025年 236卷

作者： He, Wei Luo, Zhen-bing Deng, Xiong Feng, Song-jiang Gao, Tian-xiang Dong, Zhao-feng Space Engn Univ Beijing 101400 Peoples R China Natl Univ Def Technol Coll Aerosp Sci & Engn Changsha 410073 Peoples R China

The enhancement and inhibition of atomization and sprays cover various fields such as industry, agriculture, and biomedical, among others. However, due to the complex mechanisms involved, no reference has provided a comprehensive introduction and systematic classification of these relatively isolated contents. An initial classification of flow control depends on the controlled objectives: indirect for sprays and direct for sprays. However, this formulation is not comprehensive, and this review paper further extends and expands on this basis: the former is the regulation of the internal flow of the nozzle, called as the flow control of atomization. The latter focuses more on the interaction of the external flow of the nozzle, called as the flow control of the sprays. This review provides the academic definition and categorizing criterion of flow control for atomization and sprays for the first time, clearly presenting multifarious techniques for readers. With a focus on practical requirements, we introduce the conceptual descriptions, key principles, successful applications, significant conclusions, and major drawbacks of the typical control methods. Finally, future directions and perspectives are included.

关键词： Active flow control passive flow control Atomization Sprays

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An Experimental Study on the Effectiveness of the Backward-Facing Step Technique on Small-Scale Horizontal-Axis Wind Turbine Rotor Blades

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ENERGIES 2024年第5期17卷 1170-1170页

作者： Morina, Riad Akansu, Yahya Erkan Univ Prishtina Hasan Prishtina Fac Mech Engn Prishtina 10000 Kosovo Nigde Omer Halisdemir Univ Fac Mech Engn TR-51240 Nigde Turkiye

The aim of this research work was to explore how modifying the design of small-scale HAWT rotor blades through the backward-facing step technique affects their efficiency under varying wind speeds. The study involved altering step parameters such as location, length, and depth to create four distinct stepped blade shapes and enhance the aerodynamic performance of a rotor with a diameter of 280 mm. A specific blade profile, NREL S822, was selected to meet both aerodynamic and structural criteria. The rotor models were examined at a Reynolds number of 4.7 x 104 for wind speeds between 8.5 and 15.5 m/s and tip-speed ratios between 2 and 5. The experimental results indicated that for certain geometric step parameter values, the efficiency of the rotor model (B3) increased by approximately 47% compared to the base model (B1), particularly for tip-speed ratios lower than around 3.2. However, beyond this point, the rotor efficiency dropped significantly, reaching approximately 60% in one case. Additionally, a hybrid rotor model (B6) was generated by combining the shape of the rotor model (B4) with the most efficient rotor model from the literature, generated using the leading-edge wavy shape technique. This hybrid rotor model enhanced rotor efficiency for specific values of tip-speed ratio and also ensured its smoother operation. Overall, the rotor model (B2), distinguished by smaller step parameter values and a shift as well as broadening of the power coefficient curve towards lower tip-speed ratio values, exhibited a higher peak power coefficient, approximately 1.4% greater than the base rotor (B1). This increase occurred at a lower tip-speed ratio, allowing the rotor to operate with higher efficiency across a broader range of tip-speed ratios.

关键词： small HAWT rotor blade design power coefficient passive flow control backward-facing step trapped vortex low Reynolds number fixed-pitch rotor wind tunnel

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