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Thermal performance of a boiling-driven heat spreader using passive flow control

CASE STUDIES IN THERMAL ENGINEERING 2023年 41卷

作者： Lim, Hyunmuk Doh, Su-Yoon Shin, Dong Hwan You, Seung M. Lee, Jungho Ajou Univ Dept Mech Engn Suwon 16499 South Korea Korea Inst Machinery & Mat Dept Thermal Energy Solut Daejeon 34103 South Korea Univ Texas Dallas Mech Engn Dept Richardson TX 75080 USA

This study investigates a wickless two-phase heat spreader with boiling heat transfer (boiling -driven heat spreaders) for the thermal management of hot spots with a high heat flux of more than 200 W/cm2. Thermal management studies are performed using two different approaches. First, a boiling-driven heat spreader is fabricated to confirm the thermal performance according to the heat flux, orientation, and internal support design. Second, the working mechanism of the heat spreader is established for a visualization test sample (90 x 90 mm2, inner gap of 1 mm), along with the high-speed in-situ visualization of the boiling/condensation phenomena. It is essential to understand the working mechanism of the heat spreader for improving its thermal performance. Consequently, we propose a new advanced boiling-driven heat spreader with improved thermal performance using a passive flow control design. The internal supports provide a bubble escape passage with different pressure drop characteristics. As a result, the thermal performance of the advanced boiling-driven heat spreader is independent of the orientation up to a heat flux of 200 W/cm2, and the thermal resistance is less than 0.17 K/W. Hence, the advanced heat spreader is suitable for dissipating highly concentrated heat in various thermal management applications.

关键词： Boiling-driven heat spreader passive flow control Visualization Thermal resistances

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Simultaneous flow measurement and deformation tracking for passive flow control experiments involving fluid-structure interactions

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JOURNAL OF FLUIDS AND STRUCTURES 2023年第1期121卷

作者： Koesters, Wolf Iring Hoerner, Stefan Otto von Guericke Univ Magdeburg OvGU Inst Fluid Dynam & Thermodynam Lab Fluid Dynam & Tech Flows Univ Pl 2 D-39106 Magdeburg Germany Tallinn Univ Technol Taltech Ctr Biorobot Akad Tee 15A EE-12616 Tallinn Estonia

Fluid-structure interactions (FSI) on highly flexible structures involve large deformations and require specific techniques for a thorough investigation of the flow field and structural deformation. To this purpose, a physics-informed method is introduced that allows for simultaneous determination of the flow fields and the structural deformation by using Particle Image Velocimetry (PIV) raw images. The method combines apriori knowledge of the mechanical characteristics of the flexible structure with classical image processing techniques for segmentation. PIV recordings of an actively pitched, highly deformable hydrodynamic profile experiment in a closed water tunnel serve as an example case. To achieve accurate results, the contour obtained from image segmentation is further defined under the assumption that its flexure can be described with the Euler-Bernoulli beam theory model. This makes it possible to determine the neutral fiber of the structure and the final reconstruction becomes possible from knowledge of the original geometry. The resulting procedure allows for a recognition of the structure itself and is suitable for cross-section deformation measurements and for masking of the structure in the raw images to improve the PIV processing. A test case comprising synthetic data similar to the application with a modeled profile geometry of known shape is used to investigate the accuracy of the method and its validity for deformation measurements. Under conditions of cyclic dynamic stall, a mean absolute error of 0.84 & DEG;could be reached, with a deterioration up to 2 & DEG;mean absolute error under static stall. The method has a major advantage compared to other technically more sophisticated and complex methods, such as the combination of Laser interferometers combined with Laser-Doppler Anemometry: the method allows for the usage of a single data source for both, fluid and solid in a unified measurement method. Therefore a direct comparison of instantaneous

关键词： Fluid-structure interaction Deformation tracking PIV Masking NACA0018 hydrofoil passive flow control

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Design of a passive flow control solution for the mitigation of vortex induced vibrations on wind turbines blade sections as a response to extreme weather events

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SUSTAINABLE ENERGY TECHNOLOGIES AND ASSESSMENTS 2023年 56卷

作者： Martin-Alcantara, Antonio Motta, Valentina Tarantino, Andrea De Giorgi, Maria Grazia Univ Cordoba Elect Engn Escuela Politecn Super Cordoba Campus Rabanales Cordoba 14071 Spain Gen Elect Adv Technol & Sci Franklinstr 14 D-10587 Berlin Germany Univ Salento Dep Engn Innovat Via Monteroni I-73100 Lecce Italy

The goal of the present work is to perform exploratory assessments on the suitability of microcylinder devices to mitigate wind turbine blade vortex induced vibration in small cross flow regimes, specially occurring under adverse weather events. For this purpose, the deep stall behavior of the NACA0021 has been evaluated for the first time on a wide range of high angles of attack (50 degrees -130 degrees) by means of CFD assessments, and the effects of microcylinders have been studied in terms of the reduction of aerodynamic coefficient magnitudes and fluctuations. In a first step, the passive flow control solution at 90 degrees has been analyzed for a total number of investigated cases equal to 15, keeping constant the diameter of the microcylinders and varying the relative positions of these devices with respect to the blade. Mitigations of the load standard deviations between 63% and 97% across all the tested angles of attack have been found. Additionally, genetic programming (GP) was used to obtain a more general viewpoint of the effect of the microcylinders on the aerodynamics forces. Assessments of the flow fields confirm that properly located microcylinders disrupt the coherent vortical structures in the wake, responsible for periodic loading on the blade section.

关键词： Load alleviation passive flow control Deep stall Wind turbine Microcylinders

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passive flow-field control using dimples for improved aerodynamic flow over a wing

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SCIENTIFIC REPORTS 2024年第1期14卷 1-14页

作者： Ali, Haris Rasani, Mohammad Rasidi Harun, Zambri Shahid, Muhammad Ashhad Univ Kebangsaan Malaysia Fac Engn & Built Environm Dept Mech & Mfg Engn Bangi 43600 Selangor Malaysia DHA Suffa Univ Dept Basic Sci Karachi 75500 Sindh Pakistan

This study explores the efficacy of dimples in influencing the aerodynamic performance of a straight rectangular wing. Computational Fluid Dynamics based numerical simulations were performed to model turbulent flow and quantify the forces exerted on the wing. The k-omega Shear-Stress Transport turbulence model was chosen to solve the underlying equations. To ascertain reliability, the results of numerical simulations were compared with both experimental and simulation results of the previous studies. The impact of various dimple configurations, placed at 15%, 50% and 85% of the chord length, on the aerodynamic performance of the wing was investigated. The evaluation involved analyzing the drag coefficient (C D ), lift coefficient (C L ), lift-to-drag (L/D) ratio, streamlines and the flow field around wing in both chordwise and spanwise directions. The findings indicated that a wing with a dimpled surface could yield a reduced drag coefficient of up to 6.6% compared to the unmodified wing. This reduction is attributed to the dimples ability to sustain attached airflow and delay flow separation. The results demonstrated negligible deviation in the lift coefficient with the incorporation of dimples. The incorporation of dimples on the wing surface has been demonstrated to enhance the aerodynamic performance of lifting surfaces.

关键词： Aerodynamics CFD RANS Turbulence passive flow control Dimples Boundary layer

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A novel VAWT passive flow control numerical and experimental investigations: Guided Vane Airfoil Wind Turbine

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OCEAN ENGINEERING 2022年 257卷

作者： Aboelezz, Ahmed Ghali, Hani Elbayomi, Gamal Madboli, Mohamed Cairo Univ Fac Engn Aerosp Engn Depertment Giza Egypt Ctr Emerging Learning Technol CELT British Unviresty Egypt BUE Cairo Egypt Fac Engn Elect Engn Depertment British Unviresty Egypt BUE Cairo Egypt

Guided Vane Airfoil was introduced as a novel passive flow control approach to control the dynamic stall of the Darrieus vertical axis wind turbine. ANSYS fluent SW tool has been used to solve the unsteady Reynolds-averaged Navier-Stokes equations with an SST k-omega turbulent model to investigate the effect of the Guide Vane on the aerodynamics performance of NACA 0018 airfoil. Furthermore, a parametric study has been conducted to determine the optimum vane geometry to improve the airfoil aerodynamics efficiency. Based on the 2D airfoil investigation results, the best configuration of the vane and airfoil combination have been used to numerically study the dynamic stall control of one airfoil through actual vertical axis wind turbine rotation. In addition, the vane angle relative to the airfoil has been studied in the turbine CFD investigation. For the sake of validating the new concept, a wind turbine test rig has been constructed to, experimentally, investigate the performance of the Guided Vane Airfoil wind turbine. The performance of the original wind turbine has been firstly measured and then the Guided Vane is added to the turbine blades. Based on the experimental data, about 26% increase in the maximum power output has been measured from the Guided Vane airfoil wind turbine.

关键词： passive flow control VAWT Wind turbine CFD Wind tunnel testing Dynamic stall control

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Numerical simulation of the effects of passive flow control techniques on hydrodynamic performance improvement of the hydrofoil

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OCEAN ENGINEERING 2020年 202卷

作者： Kundu, Parikshit Indian Inst Technol Kharagpur Dept Ocean Engn & Naval Architecture Kharagpur 721302 W Bengal India

Efficient hydrofoil design is a massive challenge for the current turbine blade designers. flow separation on the suction side of the hydrofoil reduces the hydrodynamic performance of the current turbine. In this paper, the combined effects of dimple with vortex generators and dimple with tubes on S1210 hydrofoil is numerically studied and compared with baseline hydrofoil. The lift coefficient values increased at a higher angle of attack, and the stall angle is delayed from 10 degrees to 12 degrees. Maximum glide ratio increments are 132% and 144% at an angle of attack of 12 degrees for outward dimple with tubes and outward dimple with vortex generators respectively. The findings will be helpful to design a stronger blade profile for the current turbine.

关键词： passive flow control Hydrofoil Hydrodynamic performance Lift and drag coefficient

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passive flow control technique for enhancing power efficiency of vertical-axis wind turbines: Leading-edge slot structure

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Journal of Ocean Engineering and Science 2025年

作者： Zhang, Rui Zhan, Lingyu Kuang, Limin Yushan, Redili Tu, Yu Zhu, Hongbo Su, Jie Han, Zhaolong Zhou, Dai State Key Laboratory of Ocean Engineering Shanghai Jiao Tong University Shanghai 200240 China School of Ocean and Civil Engineering Shanghai Jiao Tong University Shanghai 200240 China Institute of Polar and Ocean Technology Institute of Marine Equipment Shanghai Jiao Tong University Shanghai 200240 China Shenzhen Research Institute of Shanghai Jiao Tong University Shenzhen 518063 China Department of Housing and Urban-Rural Development of Jiangxi Province Nanchang 330046 China

Vertical-axis wind turbines (VAWTs) are receiving growing interest in offshore wind energy exploitation. However, they often exhibit suboptimal energy conversion efficiency, particularly at low tip speed ratios (TSRs). One critical challenge is suppressing flow separation and dynamic stall on the blades. passive flow control techniques have shown potential in improving blade aerodynamics, yet a simple and effective approach is still desired. This study proposes a novel leading-edge slot structure aimed at enhancing the power efficiency of VAWTs without additional energy input. The structure facilitates natural suction and blowing flows on the suction side of the blades. High-fidelity computational fluid dynamics simulations incorporating a transition shear stress transport model are employed to examine turbine aerodynamics. The power performance and aerodynamic loads of VAWTs with various slotted blade designs (different start locations, 0.02c ≤ x_I ≤ 0.31c, and end locations, 0.1c ≤ x_II ≤ 0.35c, where c denotes the blade chord length) are compared to identify the relatively optimal slot configuration. The analysis of blade boundary layer phenomena and flow state in the slot further elucidates the flow control mechanism. Results indicate that the leading-edge slot structure significantly enhances the power efficiency of the VAWT at low TSRs. The relatively optimal slot configuration (x_I = 0.16c, x_II = 0.2c) yields an average power increase of 38.33 % under studied operating conditions. Laminar separation bubble bursting is delayed or even eliminated for slotted blades at low and moderate TSRs. The leading-edge slot structure also delays trailing-edge separation, suppresses dynamic stall vortex formation, and reduces shedding vortex strength, thereby increasing the blade lift-to-drag ratio. This study would facilitate the blade design of VAWTs. © 2025

关键词： Aerodynamic performance Dynamic stall Leading-edge slot structure Offshore wind energy passive flow control Vertical-axis wind turbine

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Optimization of the anti-snow performance of a high-speed train based on passive flow control

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WIND AND STRUCTURES 2020年第4期30卷 325-338页

作者： Gao, Guangjun Tian, Zhen Wang, Jiabin Zhang, Yan Su, Xinchao Zhang, Jie Cent South Univ Sch Traff & Transportat Engn Key Lab Traff Safety Track Minist Educ Changsha 410075 Peoples R China Cent South Univ Z2Joint Int Res Lab Key Technol Rail Traff Safety Changsha 410075 Peoples R China Natl & Local Joint Engn Res Ctr Safety Technol Ra Changsha 410075 Peoples R China

In this paper, the improvement of the anti-snow performance of a high-speed train (HST) is studied using the unsteady Reynolds-Averaged Navier-Stokes simulations (URANS) coupled with the Discrete Phase Model (DPM). The influences of the proposed flow control scheme on the velocity distribution of the airflow and snow particles, snow concentration level and accumulated mass in the bogie cavities are analyzed. The results show that the front anti-snow structures can effectively deflect downward the airflow and snow particles at the entrance of the cavities and alleviate the strong impact on the bogie bottom, thereby decrease the local accumulated snow. The rotational rear plates with the deflecting angle of 45 degrees are found to present well deflecting effect on the particles' trajectories and force more snow to flow out of the cavities, and thus significantly reduce the accretion distribution on the bogie top. Furthermore, running speeds of HST are shown to have a great effect on the snow-resistance capability of the flow control scheme. The proposed flow control scheme achieves more snow reduction for HST at higher train's running speed in the cold regions.

关键词： bogie cavity High-Speed Train (HST) numerical simulation passive flow control

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passive flow control of the corner separation in an annular compressor cascade with a micro-blade

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PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART A-JOURNAL OF POWER AND ENERGY 2019年第3期233卷 293-308页

作者： Wang, Bo Wu, Yanhui Northwestern Polytech Univ Sch Power & Energy 1 Dongxiang Rd Xian Shaanxi Peoples R China

Corner separation contributes greatly to the loss and the passage blockage in a compressor stage. In order to mitigate the corner separation and improve the aerodynamic performance of compressors, a novel passive flow control method, an off-surface micro-blade installed upstream of the separation onset location, was proposed. A numerical investigation has was performed in an annular compressor cascade to assess the control effectiveness of the micro-blade. The results show that the location of the micro-blade affects the control effect significantly. The application of the well-designed micro-blade enhances the diffusion capacity considerably under the inflow incidence from -2 degrees to +10 degrees, accompanied by a slight loss reduction at some particular incidences. Detailed analysis of the predicted flow field was carried out to understand the underlying mechanism. It indicates that a "jet" forms upstream of the separation onset location with the application of the micro-blade. The formation of the jet reduces the thickness of boundary layer on the suction surface and builds a "jet barrier" near the endwall to hinder the accumulation of the low momentum fluid. The influence of the incidence was also investigated. It is concluded that the incidence increase has both positive and negative influences on the control effect of the micro-blade. As a result, the performance of the micro-blade is sensitive to the variation of inlet incidence.

关键词： Annular compressor cascade corner separation micro-blade passive flow control

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On the influence of porous coating thickness and permeability on passive flow and noise control of cylinders

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JOURNAL OF SOUND AND VIBRATION 2023年 549卷

作者： Sharma, Sparsh Geyer, Thomas F. Arcondoulis, Elias J. G. Brandenburg Univ Technol Cottbus Senftenberg Tech Acoust D-03046 Cottbus Germany Southern Univ Sci & Technol Dept Mech & Aerosp Engn Shenzhen 518055 Peoples R China German Aerosp Ctr DLR Inst Electrified Aero Engines D-03046 Cottbus Germany

Aeroacoustic studies of porous cylinder coatings, which reduce the vortex shedding noise of cylinders in uniform flow, have received increased attention. To further understand how porous coatings suppress the vortex shedding tone, a numerical and experimental investigation of porous coated cylinders at a Reynolds number of 1.27 x 105 is presented herein. Two parameters were varied: (1) the ratio of the porous thickness to the bare cylinder diameter, and (2) the airflow resistivity of the porous media. Numerical simulations were performed using the large-eddy simulation approach with the Smagorinsky sub-grid length-scale model, and the Ffowcs-Williams and Hawkings acoustic analogy was used to predict the acoustic far-field pressure field. A numerical investigation of the internal flow field within the porous layer is presented, which provides a better understanding of the influence of the aforementioned parameters on the development of boundary layers within the porous media and the passive flow and noise control capability. Experiments were performed in an aeroacoustic open-jet wind tunnel to validate the acoustic and external flow field results, which typically showed very good agreement with the numerical results. For porous coatings with low airflow resistivity, the thickness of the porous coating, relative to the inner diameter, has a strong influence on passive flow and noise control. Vortex shedding originates from the inner diameter. Conversely, porous coatings with a higher airflow resistivity are less influenced by their thickness, and vortex shedding originates from the outer diameter (porous surface). The complex coupling of these parameters leads to the conclusion that the optimal selection of the thickness and airflow resistivity is typically dependent on the Reynolds number.

关键词： Aeroacoustics Vortex shedding Porous media passive flow control

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