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Numerical investigation of passive cavitation control using a slot on a three-dimensional hydrofoil

INTERNATIONAL JOURNAL OF NUMERICAL METHODS FOR HEAT & FLUID flow 2020年第7期30卷 3585-3605页

作者： Liu, Cheng Yan, Qingdong Wood, Houston G. Beijing Inst Technol Sch Mech Engn Beijing Peoples R China Beijing Inst Technol Sch Mech Engn Dept Vehicle Engn Beijing Peoples R China Univ Virginia Dept Mech & Aerosp Engn Charlottesville VA USA

Purpose The purpose of this paper is to study the mechanism and suppression of instabilities induced by cavitating flow around a three-dimensional hydrofoil with a particular focus on cavitation control with a slot. Design/methodology/approach The transient cavitating flow around a Clark-Y hydrofoil was investigated using a transport-equation-based cavitation model and the stress-blended eddy simulation model was used to capture the flow turbulence. A homogeneous Rayleigh-Plesset cavitation model was used to model the transient cavitation process and the results were validated with test data. A slot was applied to the hydrofoil to suppress cavitation instabilities, and various slot widths and exit locations were applied to the blade and the cavitation behavior, as well as drag/lift forces, were simulated and compared to investigate the effects of slot geometries on cavitation suppression. Findings The large eddy simulation based turbulence model was able to capture the interactions between the cavitation and turbulence. Moreover, the simulation revealed that the re-entrant jet was responsible for the periodic shedding of cavities. The results indicated that a slot was able to mitigate or even suppress cavitation-induced instabilities. A jet flow was generated at the slot exit and disturbed the re-entrant jet. If the slot geometry was properly designed, the jet could block the re-entrant jet and suppress the unsteady cavitation behavior. Originality/value This study provides unique insights into the complicated transient cavitation flows around a three-dimensional hydrofoil and introduces an effective passive cavitation control technique useful to researchers and engineers in the areas of fluid dynamics and turbomachinery.

关键词： Cavitation control passive flow control Unsteady cavitation Performance degradation flow-induced vibration Reynold-averaged Navier stokes

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passive control on wake structure of a wall-mounted cube by using a horizontal hole

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OCEAN ENGINEERING 2020年 213卷 107680-107680页

作者： Li, Jiawei Rinoshika, Hiroka Rinoshika, Akira Beijing Univ Aeronaut & Astronaut Key Lab Fluid Mech Minist Educ 37 Xueyuan Beijing 100191 Peoples R China Yamagata Univ Dept Mech Syst Engn 4-3-16 Jonan Yonezawa Yamagata 9928510 Japan

To control the wake flow around a wall-mounted cube, a passive control method is proposed by drilling a horizontal hole from the front surface to rear surfaces of the cube. The controlled and uncontrolled wakes are measured by using particle image velocimetry (PIV). The cube model has a side length of D = 70 mm, and the diameter of horizontal control hole (HCH) is d = 10 mm. Reynolds number based on side length of cube is Re-D = 11, 550. Furthermore, to study the positional effect of the HCH, three kinds of holes with different heights h are used. The time-averaged statistical characteristics show that the jet generated from the HCH reduces the scale of the arch-type vortex, turbulence intensity, Reynolds shear stress and turbulent kinetic energy in the wake, and enhances the recovery of streamwise velocity. Among three HCHs, the HCH of h = 35 mm has the optimal control effectiveness. The analysis of vortex dynamics indicates that the HCH jet effectively suppresses the periodic flow structures and accelerates the wake vortex shedding. Meanwhile, the HCH jet exhibits different effect on the spanwise vortex at its different heights. The POD analysis implies that under the influence of the HCH, the alternant spanwise vortices are suppressed, but symmetric vortices are relatively enhanced.

关键词： passive flow control Wall-mounted cube Wake Vortex dynamics PIV POD

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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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Effect of incidence angle on the wake of a wall mounted slotted cylinder in an open channel flow

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JOURNAL OF FLUIDS AND STRUCTURES 2025年 136卷

作者： Boamah, John A. Shinneeb, A. -M. Balachandar, R. Univ Windsor Dept Mech Automot & Mat Engn 401 Sunset Ave Windsor ON N9B 3P4 Canada Univ Windsor Dept Civil & Environm Engn 401 Sunset Ave Windsor ON N9B 3P4 Canada

This experimental study investigates the wake flow generated by a vertically, wall-mounted slotted-cylinder in shallow channel flow. The slot, uniformly cut along the central plane of the cylinder, has a thickness equal to 0.1 times the cylinder diameter. The primary parameter examined is the incidence angle theta between the slot axis and the main flow direction, selected by rotating the slotted-cylinder clockwise to four different positions. The study aims to understand the impact of theta on the wake flow characteristics by investigating both the instantaneous and mean velocity fields, as well as the coherent structures. The Reynolds number, based on the water depth, is approximately 25,000. Particle image velocimetry (PIV) measurements were conducted along the vertical mid-plane and on three horizontal planes. The results revealed the formation of three-dimensional (3D) mean recirculation zones in the wake of the cylinder without a slot, resembling a counter-rotating U-shaped vortical structure. For theta >= 60 degrees, this 3D shape persists, while for theta < 60 degrees, it varies by the angle. The jet emanating from the slot suppresses velocity fluctuations when injected into the wake region at incidence angles theta < 60 degrees In contrast, at theta >= 60 degrees, there is a transition to a stimulating effect that enhances turbulent kinetic energy (TKE) production. Proper orthogonal decomposition (POD) results highlight differences in kinetic energy transfer to the turbulent flow across various cases of the slotted-cylinder. Moreover, the slot flow exhibits both blowing and suction effects, with varying intensity and dominance throughout the shallow water layer.

关键词： Bluff body with a slot Turbulence Wake flow passive flow control PIV

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passive control of a front inclined hole on flow structures around a surface-mounted short cylinder

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OCEAN ENGINEERING 2019年 189卷 106383-106383页

作者： Rinoshika, Hiroka Rinoshika, Akira Yamagata Univ Grad Sch Sci & Engn Dept Mech Syst Engn 4-3-16 Jonan Yonezawa Yamagata 9928510 Japan Beijing Univ Aeronaut & Astronaut Sch Aeronaut Sci & Engn 37 Xueyuan Beijing 100191 Peoples R China

To control the wake flow of a short cylinder, a passive flow control method, a front inclined hole in the cylinder was drilled from the front surface side to the free end surface. A cylinder of an aspect ratio H/D =1 with a height H = 70 mm and a diameter D = 70 mm is used. A circulation water tunnel is used to perform NV measurements at Reynolds number of 8,570 for comparing the flow structures between the no hole and hole wakes. In order to consider the influence of the hole position, the different cylinder models of the hole height at the front from the wall are tested. Comparing with the flow structures around standard cylinder, it is found that the separation zone near the free end surface decreases and the rear separation ron increases because of the blown flow from the inclined hole. The vorticity and Reynolds shear stresses are also suppressed in the rear recirculation zone. The instantaneous large-scale eddies in the rear separation zone are divided into several small-scale eddies as increasing the angle of the inclined hole.

关键词： flow measurement passive flow control PIV Visualization Vortex Wake

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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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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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Prediction of three-dimensional flow characteristics for cylinders with wavy geometric disturbance using deep learning models

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OCEAN ENGINEERING 2024年第Part1期312卷

作者： Seo, Janghoon Yoon, Hyun Sik Hong, Seok Beom Pusan Natl Univ Dept Naval Architecture & Ocean Engn 2Busandaehak Ro 63beon Gil Busan 46241 South Korea

For the first time, this study extracts three-dimensional flow characteristics of geometric disturbances as passive flow control using deep learning models, which will contribute to innovatively advancing research in passive flow control. It addresses the limitations of predicting two-dimensional flow and the lack of methods for predicting flow characteristics under variable geometric disturbances. Specifically, the study establishes a convolutional neural network (CNN) and an encoder-decoder (ED) model to predict 3D flow characteristics for cylinders with wavy geometric disturbances. To generate the dataset for the deep learning models, large eddy simulation is utilized. The accuracy of the CNN model is validated by comparing the predicted and true force coefficients. The study also examines common features of mean 3D flow structures, reconstructed by the established ED model. The ED model constructs longer 3D spanwise vorticity structures, jet-like flows, and weaker turbulence kinetic energy, which are correlated with smaller force coefficients. Finally, parametric studies of the geometric disturbances are conducted using the established deep learning models. The ED model generates reasonable mean 3D flow fields, supporting the physical understanding of changes in force coefficients. Consequently, approaches presented in this study are reliable and efficient for conducting parameter studies on geometric disturbances.

关键词： Geometric disturbance passive flow control Deep learning

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The Influence of the Geometry of Grooves on the Operating Parameters of the Impeller in a Centrifugal Pump with Microgrooves

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ENERGIES 2024年第12期17卷 2807页

作者： Bieganowski, Marcin Skrzypacz, Janusz Chomiuk, Bartlomiej Wroclaw Univ Sci & Technol Fac Mech & Power Engn Dept Energy Convers Engn Wybrzeze Stanislawa Wyspianskiego 27 PL-50370 Wroclaw Poland

Centrifugal pumps are one of the most widely used machines in all branches of industry. For this reason, their efficiency has a significant impact on energy consumption in global industry (about 20%). It is extremely difficult to design low-specific-speed centrifugal pumps at acceptable efficiency levels due to increasing losses in the impeller (hydraulic, volumetric, and mechanical). This article presents the influence of the geometric features of grooves (width, depth), and the number of them, on the operating parameters of the impeller in a centrifugal pump with microgrooves. The principle of operation of this solution involves the passive control of the flow in the boundary layer using rectangular grooves. The grooves are made inside the flow channels of the impeller and are intended to reduce hydraulic losses occurring during flow. This is mainly due to a reduction in losses in the boundary layer. In order to determine the influence of the grooves' parameters on the energy characteristics of the impeller, numerical calculations and experimental measurements were performed on 15 sets of impellers, which were obtained using experimental planning methods. The CFD calculations were conducted in order to understand the flow phenomena that occur in the impeller with the microgeometry and their effect on a reduction in internal flow losses. Based on the research results, useful guidelines for designing impellers with low-speed characteristics were formulated.

关键词： low specific speed centrifugal pump passive flow control experimental planning increasing energy efficiency CFD

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