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passive flow control at impeller radial bend for stall delay in centrifugal compressors with fishtail pipe diffusers

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AEROSPACE SCIENCE AND TECHNOLOGY 2024年 145卷

作者： Ashrafi, Farzad Vo, Huu Duc Ecole Polytech Montreal Dept Mech Engn 2900 Blvd Edouard Montpetit2500 Chemin Polytech Montreal PQ H3T 1J4 Canada

This paper proposes a new strategy for extending centrifugal compressor stall margin through shroud passive flow control placed at the impeller radial bend. Relative to the usual leading-edge location, the radial bend presents fewer geometrical constraints for flow control devices and allows them to have potentially more impact on low-momentum flow structures that lead to stall. Two centrifugal compressors with fishtail pipe diffusers are chosen for study: a high-speed transonic design exhibiting diffuser stall and a low-subsonic design with exducer stall. Four passive flow control techniques placed on the impeller shroud at the radial bend are evaluated for each compressor, in terms of stall margin improvement and efficiency penalty at design mass flow, using unsteady RANS CFD simulations. These are circumferential groove, slots, impeller recirculation pipe and diffuser-impeller recirculation pipe. The results indicate that passive flow control at the impeller shroud radial bend can be significantly more effective than at the impeller leading edge. For each compressor, the flow mechanisms associated with stall initiation and its delay by the most effective studied flow control technique as well as the associated efficiency penalty are elucidated. The findings indicate that techniques having flow injection with high spanwise penetration and low relative streamwise momentum are most effective for delaying diffuser stall, while the opposite applies to exducer stall. The design point efficiency penalty is due to mixing/shear losses from the jet-in-cross flow phenomenon in the impeller and shear losses from flow redistribution in the diffuser.

关键词： Centrifugal compressor Fishtail pipe diffuser Stall margin passive flow control RANS CFD Efficiency

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passive flow control for Centrifugal Compressors with Bents Intake Manifold

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MECHANIKA 2023年第5期29卷 369-376页

作者： Maammeur, M. Benarous, A. Bettahar, A. Liazid, A. Univ Hassiba Benbouali Chlef UHBC POB 151 Chlef Algeria Univ Saad Dahleb USDB POB 270 Blida Algeria Univ AbouBakr Belkaid UAB Tlemcen POB 119 Tilimsen Algeria

Centrifugal compressors installations often require bents conduits at the intake due to space constraints. The intake bent manifold creates flow distortion affecting unfavorably the global performance of the compressor. The degradation generated by the inadequate inlet conditions due to turbulence and inlet flow disturbance, which negatively affects the flowing fluid through the curved intake manifold. Hence, significant distortions, within presence of single or twin core vortices whirling off center of the impeller intake alter flow incidence angle and consequently the impeller circumferential energy. Furthermore, inadequate bends configurations generate higher incidence angles, which lead to boundary layer separation and stalling. This paper deals with a {TA \s "a"} 3D {TA \1 "3D: three dimentions" \s "3D" \c 1} numerical investigations of dual bends located upstream of the centrifugal compressor. Several bend setting positions at the compressor intake describing various sequences of intake piping are considered. As first results, specific positions of dual bends are identified for fewer flow disturbance at the impeller eye and stable outflow controlling the incidence angel in a passive mode. it is less cumbersome and cost effective compared to additional devices. For practical industrial prediction, this investigation contributes also toward a mathematical correlation to check the adequacy of intermediate manifold configuration in order to predict the corresponding incidence angle at the impeller intake of the centrifugal compressor for enhanced performance and instantaneous control.

关键词： passive flow control intake manifold double bends inlet distortion

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passive flow control of shock-induced dynamic stall via surface-based trapped vortex generators

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PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART G-JOURNAL OF AEROSPACE ENGINEERING 2022年第2期236卷 308-323页

作者： Al-Jaburi, Khider Feszty, Daniel Carleton Univ Dept Mech & Aerosp Engn Rotorcraft Res Grp 3135 Mackenzie Bldg1125 Colonel By Dr Ottawa ON K1S 5B6 Canada

A novel passive approach for controlling the flow in a 2D dynamic stall at variabl freestream is investigated. 2D computational fluid dynamics simulations of an SC1095 airfoil with surface-based trapped vortex generator (STVG) type passive flow control were conducted. The airfoil was exposed to a fluctuating freestream of Mach 0.537 +/- 0.205 and Re = 6.1 x 10(6) (based on the mean Mach number) and experienced a 10 degrees +/- 10 degrees pitch oscillation with a frequency of 4.25 Hz. These conditions were selected as an approximation to the flow experienced by a UH-60A helicopter rotor airfoil section in an actual fast forward flight test case. The baseline simulations were cautiously validated with experimental data for both transonic flow and dynamic stall under the variable freestream. Then, 20 different local STVGs type geometry modifications were investigated as a means of passive flow control. Modifications were examined on both the airfoil's upper and lower surfaces. Results showed that the STVGs were able to mitigate the negative effects of shock-induced dynamic stall. The best geometries could reduce the peak negative pitching moment by as much as 9-23% during the transonic phase of a cycle and by as much as 19-71% during the dynamic stall phase. Also, they were able to reduce peak drag by 8-20% in the transonic phase and by 15-44% in the dynamic stall phase. On the other hand, the lift-to-drag ratio was significantly increased by 3-28% per one rotor cycle. All the above advantages came at virtually no penalty in the lift.

关键词： Transonic flow unsteady freestream velocity shock-induced dynamic stall Mach fluctuation pitching airfoil passive flow control surface-based trapped vortex generator

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Mitigation of flow separation in a highly bent intake duct with active and passive flow control

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AERONAUTICAL JOURNAL 2025年第1335期129卷 1381-1398页

作者： Max, P. Stoessel, M. Kozulovic, D. Krummenauer, M. Univ Bundeswehr Munich Inst Jet Prop Dept Aerosp Engn Munich Germany Bundeswehr Tech Ctr Aircraft & Aeronaut Equipment Manching Germany

Typically, the fuselage of a modern military aircraft is designed in such a way that the propulsion system is integrated into it. The main reasons are reduction of installation space and minimisation of radar signature. Those requirements can be achieved by using highly bent engine intakes, which are occluding a direct line of sight to the compressor system. Depending on their design, secondary flows and flow separation can be expected due to the strong curvature of the intake system. In this study, a serpentine intake in front of the Larzac 04 test engine is investigated experimentally and its performance compared with and without flow stabilising measures. In detail, a configuration with vortex generators was compared experimentally with a configuration of active flow control by injected air. In order to analyse and compare the efficiency of both systems, the dimensionless total pressure coefficient, the distortion coefficient (DC60) and detailed surface pressure distributions as well as the aerodynamic interface plane are evaluated. In addition, different throttle lines were recorded for surge line evaluation of the low pressure compressor of the Larzac engine and compared for each flow-stabilising measure investigated. It was found that the application of injecting air showed a larger improvement in surge margin and reduction in distortion coefficients compared to the passive flow control.

关键词： highly bent engine intakes active flow control passive flow control

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Experimental analysis of a passive flow control structure within a turbulent boundary layer using particle image velocimetry

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EXPERIMENTAL THERMAL AND FLUID SCIENCE 2025年 166卷

作者： Moore, Tyler Wu, Wen Yeom, Taiho Univ Mississippi Dept Mech Engn 1764 Univ Circle University MS 38677 USA

In this study, turbulent statistics over a novel additive surface structure are explored within turbulent channel flow at friction Reynolds number Re tau approximate to 380. Experimental data is gathered in a purpose-built 3D-printed wind channel which allows for 2D Particle Image Velocimetry. The Multi Jet Fusion 3D-printed additive structure, consisting of two side walls and a top wall, is analyzed for its flow control capabilities. Potential desirable flow control outputs include localized flow acceleration, deceleration, and vortex generation. The proposed structure is configurable by manipulating the structure's height and the angle of attack of the side and top walls. Heights of 3, 4, 6, and 7 mm of the structure are investigated, ranging from 12 %-25 % of the boundary layer thickness. All observed structure heights fall within the log-law region of the flow. Discussed structures include default, diffuser, and nozzle-type geometries, defined by different angles of attack of the three control walls. Instantaneous and time-averaged ensemble data are collected. Manipulations to velocity, Reynolds stresses, and turbulence kinetic energy are discussed. Results show that for 6 mm and 7 mm height surface structures, a default structure geometry produces localized near-wall flow acceleration without significantly perturbing free-stream flow. Further, nozzle geometries produce slight free-stream flow deceleration while diffuser geometries produce slight free-stream flow acceleration. Diffuser geometries produce three downstream regions of noteworthy turbulence energy production. Nozzle geometries produce a large region of intense turbulence energy production over the structure's top wall. Additionally, certain 6 mm height structure geometries impact turbulence statistics more than 7 mm height structures. Recommendations are made for future study.

关键词： Particle image velocimetry Fluid mechanics passive flow control

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flow characteristics and passive flow control of circular cylinders with triangular vortex generators: An experimental investigation

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APPLIED OCEAN RESEARCH 2024年 142卷

作者： Aksoy, Muharrem Hilmi Konya Tech Univ Fac Engn & Nat Sci Dept Mech Engn TR-4200 Konya Turkiye

Optimizing flow patterns around cylinders is crucial for diverse engineering applications, aiming to mitigate vibrations induced by vortex shedding and minimize drag. Strategies, such as the implementation of vortex generators and modifications in the cylinder's surface geometry, are explored to optimize flow patterns and enhance the performance of structures exposed to fluid dynamics. This study investigated the flow characteristics of a smooth circular cylinder and cylinders equipped with triangular vortex generators placed at different position angles (alpha=15 degrees, 30 degrees, 60 degrees, and 75 degrees) and yaw angles (beta=30 degrees, 45 degrees, 60 degrees, and 75 degrees) at the surface. The particle image velocimetry technique is used to measure the instantaneous and time-averaged velocities of the fluid flow over cylinders at Reynolds Number 8000. It is found that flow characteristics are highly dependent on the position angle of the triangular vortex generators. Specifically, at alpha=30 degrees and beta=60 degrees, a substantial reduction of 17.3, 10.3, and 19.5 % occurred in normalized streamwise and root mean square of cross-stream velocity fluctuations and turbulent kinetic energy values, respectively, in comparison to that of the smooth circular cylinder. Furthermore, a noteworthy drag reduction of 33.3 % was achieved in the case of alpha=30 degrees and beta=60 degrees through the elongation of the recirculation length and the establishment of a low-pressure zone away from the base of the circular cylinder. On the other hand, the lowest Strouhal number is obtained as 0.180 in the case of alpha=75 degrees and beta=30 degrees where it was 0.211 at the smooth CC case. As a result, triangular vortex generators with an area of 1.1% of the total side projection area of the cylinder were found to be very effective in flow control.

关键词： Circular cylinder Drag coefficient flow characteristics passive flow control Particle Image velocimetry Vortex generators

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passive flow control on Ahmed body by rear linking tunnels

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JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS 2020年 205卷

作者： Mohammadikalakoo, B. Schito, P. Mani, M. Politecn Milan Mech Engn Dept Via La Masa 1 Milan Italy Amirkabir Univ Technol Aerosp Dept Hafez Ave Tehran Iran

This paper concentrates on the interaction of a car body with the surrounding airflow, in order to provide small changes for reducing vehicle fuel consumption by reducing drag. There are many passive and active methods for this purpose, the main goal of this project is the development of passive drag reduction devices for the simplified reference model (Ahmed body with 25 degrees, 30 degrees, and 35 degrees slant angle) used to represent bluff body vehicles. passive flow control is performed by adding linking tunnels at the rear of the bluff body, blowing the flow from the sidewalls (high-pressure zone) to the wake region (low-pressure zone). The movement of a high-pressure flow to the wake zone reduces the wake size, which reduces the pressure drag. A numerical and experimental analysis of this passive method is carried out. The optimal configuration was reached by numerical analysis (showing a drag reduction of up to 5%) and after that, experimental tests were performed in a wind tunnel to check the effect of this passive flow control on an Ahmed body 25 degrees.

关键词： passive flow control Bluff body Ahmed body Linking tunnels Wind tunnel CFD

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Aerodynamic performance improvement of Savonius wind turbine through a passive flow control method using grooved surfaces on a deflector

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OCEAN ENGINEERING 2023年 284卷

作者： Fatahian, Esmaeel Ismail, Farzad Ishak, Mohammad Hafifi Hafiz Chang, Wei Shyang Univ Sains Malaysia Sch Aerosp Engn Nibong Tebal 14300 Penang Malaysia

A Savonius rotor is a Vertical-Axis Wind Turbine (VAWT) that converts wind force into torque on a rotating shaft. The poor efficiency of this rotor is caused by the unfavorable negative torques generated as the returning blade rotates against the incoming flow. The current study aims to improve the aerodynamic performance of a Savonius wind rotor by installing a cylinder deflector with different grooved surfaces as a unique deflector system to offset the negative impact at the wake zone downstream of the deflector. The grooved surface is essentially one way to alter the surface roughness of a cylinder, which has shown to be quite successful to control vortex shedding and wake formation behind the cylinder. In contrast to previous research, a grooved surface of a cylinder deflector was used instead of traditional deflectors to increase the aerodynamic performance by disrupting the wake zone downstream of the deflector. With this motivation, a systematic parametric study via Computational Fluid Dy-namics (CFD) method was implemented for different combinations of the flow and geometric characteristics including Tip Speed Ratio (TSR) value, groove shapes (rectangular, U, and V), groove number, and size. Besides, the flow over a smooth cylinder was analyzed and compared with that of grooved cases to determine the ideal groove configurations for enhancing the total output power. The results demonstrated that the optimal deflector with the U-grooved surface augmented the aerodynamic performance the most for all TSRs. The optimal deflector has 12 U-grooved surfaces with a diameter size of 0.025 of rotor diameter. The average power coef-ficient enhanced dramatically up to 24.2% and 15.8% through the deflector with a U-grooved surface at TSR = 0.9 in comparison to without deflector case and smooth cylinder deflector case, respectively.

关键词： Savonius rotor Grooved surface Wake zone passive flow control CFD

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Active Versus passive flow control in UVC FILTERs for COVID-19 Containment

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ANNALS OF BIOMEDICAL ENGINEERING 2021年第9期49卷 2554-2565页

作者： Moreno, E. Klochok, G. Garcia, S. Univ Lyon CNRS UJM St Etienne Lab Hubert CurienGrad SchUMR5516Inst Opt F-42023 St Etienne France Moscow State Univ Civil Engn Natl Res Univ Moscow Russia Neurotraumatol & Rehabil Hosp EULEN Grp Granada Spain

Ultraviolet radiation as a germicide is widely used in the health field and even in domestic hygiene. Here, we propose an improvement in low-cost portable units of filtration for indoor air, which is based on ultraviolet radiation. In the current technology, to carry out an air filtration with a suspension of aerosols in which there is a likely concentration of pathogens, whether viral, bacterial or molds, the air is forced to pass as close as possible to the ionizing radiation source (near field). Since the optical mass is very small, the desired effect can be achieved in a considerably short time, deactivating the infective potential of these biological agents. The proposal of this work is the regulation of the flow or speed control of passage through these filters by passive elements instead of by electronic control systems. For this, two devices have been designed, simulated, and built, obtaining similar net pathogen inactivation rates under different flow rates. The passive flow control device has demonstrated higher performance in terms of flow rate and lower cost of production since they do not require electronics and are produced with fewer diodes. This passive device has also shown a lower projection of maintenance cost, lower energy consumption rate (higher efficiency), and longer projection of useful life.

关键词： Indoor air purification passive flow control Pathogen inactivation COMSOL flow Algebraic yPlus interface COVID-19 SARS-CoV-2 UVC Photo diodes

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Experimental study on passive flow control of circular cylinder via perforated splitter plate

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WIND AND STRUCTURES 2021年第6期32卷 613-621页

作者： Sahin, Serdar Durhasan, Tahir Pinar, Engin Akilli, Huseyin Univ Cukurova Dept Mech Engn TR-01330 Adana Turkey Univ Adana Alparslan Turkes Sci & Technol Dept Aerosp Engn TR-01250 Adana Turkey Univ Cukurova Dept Ceyhan Mech Engn TR-01950 Adana Turkey

Present experimental investigation aims to reduce the shedding of vortex in the near wake region of a circular cylinder using a perforated splitter plate. Perforated plates were placed in the wake region of the cylinder and aligned with the streamwise direction. The length of the plates was equal to the diameter of the cylinder. Different plate porosities and locations were examined and obtained results were compared to the baseline cylinder. flow measurements downstream of the cylinder were performed in a water channel by employing a particle image velocimetry technique (PIV) at a Reynolds number of Re=5x103. It is observed that the effect of the porosity on the flow characteristics of the cylinder depends on the location of the plate. The strength of shear layers and flow fluctuations in the near wake region of the cylinder are considerably diminished by the perforated splitter plate. It is found that the porosity of epsilon=0.3 is the most effective control element for gap ratio of G/D=0.5. On the other hand, proper gap ratio is determined as G/D=2 for porosity of epsilon=0.7. It is concluded in the present study that the perforated splitter plate could be used as alternative passive flow control technique in order to reduce vortex shedding of the cylinder.

关键词： circular cylinder passive flow control perforated splitter plate vortex shedding reduction

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