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Proof of concept study on a self-driven pulsed jet on a compressor stator blade by numerical simulation

PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART G-JOURNAL OF AEROSPACE ENGINEERING 2024年第1期238卷 89-102页

作者： Lu, Weiyu Deng, Qiulin Jiao, Yanmei Nanjing Tech Univ Sch Phys & Math Sci Nanjing Peoples R China Nanjing Tech Univ Sch Phys & Math Sci 30 Puzhunan Rd Nanjing 211800 Jiangsu Peoples R China

This study presents a new concept of self-driven pulsed jet flow control on a compressor stator blade. This passive unsteady flow control method has the advantage that neither external flow nor electrical source is needed. This study's preliminary proof-of-concept study on a low-speed compressor stator blade is performed using numerical simulation. When the pulsed jet frequency is 100 Hz, the optimum control performance and control efficiency are reached, and the total pressure loss coefficient is reduced by 8.9%. As the valve's rotational speed increases, the pulsed jet's momentum coefficient decreases gradually. The analysis of the unsteady characteristics of the self-driven pulsed jet shows that the jet velocity is close to a periodic square wave signal, and the typical reduced jet velocity ranges from approximately 0.15 to 0.8. Moreover, the time-averaged driving torque on the valve depends on the rotational speed and is relevant to the self-starting and self-driven characteristics of this passive flow control method. Under different bearing resistance torque, the self-driven valve behaves differently in three cases that can self-start and be self-driven, cannot self-start but can be self-driven, and cannot self-start nor be self-driven.

关键词： passive flow control unsteady flow control flow separation self-driven pulsed jet

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Numerical Analysis of a Novel Casing Treatment in an Axial flow Fan

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JOURNAL OF PROPULSION AND POWER 2024年第6期40卷 818-832页

作者： Amin, Gautham Salunkhe, Pramod Kini, Chandrakanth Manipal Acad Higher Educ Manipal Inst Technol Dept Aeronaut & Automobile Engn Manipal 576104 India

The present paper reports the use of a slotted casing treatment of trapezoidal shape to enhance the stall margin of an axial flow fan. The Taguchi method was used to optimize the rectangular slotted casing treatment based on that which the trapezoidal slots were designed. The unsteady numerical simulations were carried out using the shear-stress-transport turbulence model. The rotor with trapezoidal slots led to the stall margin improvement of 23.4% and mild pressure rise of 0.54%. Without the casing treatment, the tip leakage trajectory was directed from the suction surface of the blade toward the pressure surface of the adjacent blade. After incorporating the trapezoidal slots, the tip leakage trajectory was significantly shifted toward the suction surface of the same blade. This alteration in flow characteristics near the blade-tip region may be attributed to the exchange of momentum due to the simultaneous suction and blowing through the trapezoidal slots. It was also found that the trapezoidal slots improved the axial flow velocity and reduced the diffusion factor in the blade-tip region as compared to the baseline case.

关键词： Casing Treatment Fan Performance Stall Margin Improvement Axial Slots Axial flow Fan passive flow control Compressor Map

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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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Vibration control of the straight bladed vertical axis wind turbine structure using the leading-edge protuberanced blades

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ENGINEERING STRUCTURES 2024年 319卷

作者： Vel, E. Karthik Pillai, S. Nadaraja SASTRA Deemed Univ Turbulence & Flow Control Lab Thanjavur 613401 Tamil Nadu India

This study investigates the impact of structural responses resulting from alterations in aerodynamic characteristics caused by incorporating leading-edge protuberance (LEP) blades in vertical-axis wind turbines (VAWTs) under various wind speeds. The current experimental investigation was conducted on a scaled-down straightblade VAWT with multiple wind speeds at a fixed pitch angle and uniform blade configuration. The unsteady structural excitation caused by the decay of vortices due to the different aerodynamic loads and its effect on the VAWT structure is examined in great detail. The presence of counter-rotating vortices from the LEP profile, however, enhances the aerodynamics of the blades at higher angles of attack. It is crucial to understand the structural characteristics resulting from changes in aerodynamics. The paper presents the effects of the LEP on the structural excitation of the VAWT by analyzing the acceleration and displacement data obtained from the static structure of VAWT for various operational wind speeds. The results showed decreased acceleration and displacement amplitudes for the VAWT with LEP at medium and higher wind speeds. Significant aerodynamic and structural damping was observed in the VAWT with LEP blades. The results obtained were in close agreement with the time and frequency domains of the measured displacement and acceleration from the structure. The bidirectional vibration control was observed for the VAWT with LEP, which was found to have a reduction ratio of 70 %.

关键词： Vibration control VAWT Leading edge protuberance Dynamic stall passive flow control Experimental study Aerodynamic damping

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Improvement of vertical axis wind turbine performance by using the optimized adaptive flap by the Taguchi method

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ENERGY SOURCES PART A-RECOVERY UTILIZATION AND ENVIRONMENTAL EFFECTS 2024年第1期46卷 71-90页

作者： Tanurun, Himmet Erdi Kahramanmaras Istiklal Univ Elbistan Engn Fac Energy Syst Engn Dept Kahramanmaras Turkiye

In light of the growing use of Vertical Axis Wind Turbines (VAWTs) in urban settings, research is increasingly focusing on passive control methods to enhance VAWT efficiency. This study aims to refine VAWT performance by optimizing an advanced turbine design equipped with an adaptive flap on the blade, focus on the power coefficient (C-P). Using the Taguchi method, the optimization incorporated five control factors: flap position (l(d)), flap length (l(f)), flap angle (theta), flap tip length (l(t)), and angle of the flap tip length (alpha(tip)). The study employed an L-16 (5(4)) orthogonal array design. At a 2.62 tip speed ratio (TSR), all models underwent computational fluid dynamics (CFD) simulation. The influence of each factor was assessed using the ANOVA (Analysis of variance), and C-P predictions were made based on these factors through Regression Analysis (RA). The results revealed optimal configurations of l(d) = 0.65c, l(f) = 0.15c, theta = 70 degrees, l(t) = 0.06c, and alpha(tip) = 8, leading to a C-P 74.01% greater than a conventional VAWT. ANOVA ranked factor contributions as: l(d) > l(t) > theta > l(f) > alpha(tip), with l(d) contributing 39.58% and alpha(tip) only 1.34%. Predictions from the RA aligned well with the numerical findings. In conclusion, the adaptive flap design enhances performance by expanding the wake and amplifying the vortices behind the turbine blade.

关键词： Vertical-axis wind turbine (VAWT) adaptive flap analysis of variance (ANOVA) passive flow control Taguchi method computational fluid dynamics (CFD) Optimization

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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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Turbulent separation control with a tilted wavy wall: A promising approach for energy savings in aerodynamic systems

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ENERGY 2025年 324卷

作者： Kaminski, Piotr Tyliszczak, Artur Elsner, Witold Niegodajew, Pawel Czestochowa Tech Univ Dept Thermal Machinery Al Armii Krajowej 21 PL-42200 Czestochowa Poland

Recently, Kami & nacute;ski et al. (2024) demonstrated that a two-dimensional streamwise waviness with carefully selected amplitude and period can be effectively used in postponement of a flow separation at high Reynolds number which is out of reach for other commonly known passive flow control strategies. This paper demonstrates that this approach can be substantially improved by introducing a novel type of surface waviness characterized by tilting the subsequent waves. The research is performed by applying the Large Eddy Simulation (LES) method allowing for a detailed analysis of both instantaneous and time-averaged flow characteristics. It is shown that the tilting eliminates the occurrence of separation zones in waviness troughs, which minimizes the shape drag and maximizes the wall shear stress. In particular, compared to an optimal classical sinusoidal waviness shape the drag coefficient drops 14%. Simultaneously, 70% better performance in separation control is achieved. Moreover, it is also shown that when this issue is a priority, even further improvement can be achieved, though at the expense of greater drag.

关键词： Turbulent boundary layer Adverse pressure gradient passive flow control flow separation Wall-shear stress

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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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Multi-slotted airfoil design for enhanced aerodynamic performance and economic efficiency

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SCIENTIFIC REPORTS 2025年第1期15卷 1-18页

作者： Aziz, Mohamed A. Khalifa, Mohamed A. Abdelrahman, M. A. Elshimy, Haitham Elsayed, Ahmed M. Suez Univ Fac Engn Mech Engn Dept POB 43221 Suez Egypt Inst Aviat Engn & Technol Mech Engn Dept Giza Egypt Benha Univ Fac Engn Shoubra Fac Engn Mech Engn Dept Banha 11629 Egypt Beni Suef Univ Fac Nav Sci & Space Technol Space Nav Dept Bani Suwayf Egypt Fayoum Univ Fac Engn Mech Engn Dept Al Fayyum 63514 Egypt

Recently, slotted airfoils have been introduced as a passive flow control approach. The slotted airfoil method resulted in stall delay and enhanced the lift coefficient. The single-slot airfoil is unable to delay stall if the flow is injected downstream of the separation point at the stall angle of attack. A multi-slot airfoil ensures air is injected along the airfoil suction side, delaying stalls over a large range of AOA. The current study focuses on enhancing wind turbine blades' efficiency by utilizing a novel multi-slot NACA23012C airfoil design as a passive control approach. A numerical study of the optimal grid number was carried out, followed by validating the numerical model with previous experimental results in the literature. The numerical study is followed by a study of the effect of the number of airfoil slots: one, two, three, four, five, and six. The characteristics of the flow field were analyzed to explain the benefit of applying multi-slotted on the aerodynamic performance of an airfoil with a high AOA at Reynolds number 2.74 x 105. The findings showed a significant improvement in the lift coefficient values and the delayed stall AOA for multi-slot airfoils compared to the clean and single-slot airfoils. Increasing the slots number is effective up to four slots. The four-slot airfoil improved lift by 15.8%, and the two slots achieved a 22.31% CL/CD increase. Future work could optimize slot geometry, validate findings experimentally, and study dynamic and 3D effects.

关键词： passive flow control Multi slotted airfoil Wind turbine NACA 23012C Numerical study

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Wavelength-induced shedding frequency modulation of seal whisker inspired cylinders

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BIOINSPIRATION & BIOMIMETICS 2024年第3期19卷 036004-036004页

作者： Dunt, Trevor K. Heck, Kirby S. Lyons, Kathleen Murphy, Christin T. Cal, Raul Bayoan Franck, Jennifer A. Univ Wisconsin Madison WI USA Naval Undersea Warfare Ctr Newport RI USA Portland State Univ Dept Mech & Mat Engn Portland OR USA Univ Wisconsin Dept Mech Engn Madison WI 53706 USA

The spanwise undulated cylinder geometry inspired by seal whiskers has been shown to alter shedding frequency and reduce fluid forces significantly compared to smooth cylindrical geometry. Prior research has parameterized the whisker-inspired geometry and demonstrated the relevance of geometric variations on force reduction properties. Among the geometric parameters, undulation wavelength was identified as a significant contributor to forcing changes. To analyze the effect of undulation wavelength, a thorough investigation isolating changes in wavelength is performed to expand upon previous research that parameterized whisker-inspired geometry and the relevance of geometric variations on the force reduction properties. A set of five whisker-inspired models of varying wavelength are computationally simulated at a Reynolds number of 250 and compared with an equivalent aspect ratio smooth elliptical cylinder. Above a critical non-dimensional value, the undulation wavelength reduces the amplitude and frequency of vortex shedding accompanied by a reduction in oscillating lift force. Frequency shedding is tied to the creation of wavelength-dependent vortex structures which vary across the whisker span. These vortices produce distinct shedding modes in which the frequency and phase of downstream structures interact to decrease the oscillating lift forces on the whisker model with particular effectiveness around the wavelength values typically found in nature. The culmination of these location-based modes produces a complex and spanwise-dependent lift frequency spectra at those wavelengths exhibiting maximum force reduction. Understanding the mechanisms of unsteady force reduction and the relationship between undulation wavelength and frequency spectra is critical for the application of this geometry to vibration tuning and passive flow control for vortex-induced vibration (VIV) reduction.

关键词： frequency modulation seal whisker undulated cylinders wavy cylinders passive flow control bluff body wakes computational fluid dynamics

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