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Numerical analysis of the mixing process invariable density jets emanating from polygonal nozzles

INTERNATIONAL JOURNAL OF HEAT AND FLUID flow 2024年 110卷

作者： Wawrzak, Karol Stempka, Jakub Tyliszczak, Artur Czestochowa Tech Univ Fac Mech Engn Al Armii Krajowej 21 PL-42201 Czestochowa Poland

This paper focuses on the flow dynamics of jets originating from circular and non-circular nozzles (square, triangular, hexagonal, hexagram) evolving in a co-flowing stream at the Reynolds numbers Re = 5 000 and Re = 20000. The jets are cold, 300 K, while the surrounding co-flow is heated up to 1000 K. This temperature difference results in a density ratio 0.3. We consider low Mach number non-reactive flows, though, the density/temperature levels are typical for configurations in which the auto-ignition and flame- lifting mechanisms are studied. The research aims to highlight the differences in the jet evolutions caused by its initial azimuthal non-uniformity. We apply the Large Eddy Simulation (LES) method and utilize ANSYS Fluent software and an in-house high-order code SAILOR. They are used separately, i.e., the ANSYS Fluent is employed to compute the flows inside the nozzles from which ends the inlet data are extracted for the jet simulations performed by the SAILOR code. The instantaneous solutions show that, depending on the nozzle shape and the Reynolds number, the jet shapes differ significantly. The corners of the nozzles induce azimuthal irregularity of the Kelvin-Helmholtz toroidal vortices (rings) and the appearance of elongated riblike vortices connecting subsequent rings. The mutual interactions between generated small-scale vortices and naturally occurring toroidal vortices result in a fast breakup of the jets close to the nozzles. The axial velocity profiles show substantial variability of the potential core lengths and the downstream velocity decay rates. This manifests by significantly different growths of the mean temperature values (Delta T approximate to 200 K) and its fluctuations. The enhancement of the global mixing process is quantified by the entrainment rate and axial profiles of the temperature, averaged spatially in the radial direction. In the case of triangular and square jets, the near-field entrainment is more than twice that of the

关键词： passive flow control Jet dynamics Polygonal nozzles Mixing enhancement Large eddy simulation

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Aerodynamic performance and wake development of NACA 0018 airfoil with serrated gurney flaps

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FRONTIERS IN ENERGY RESEARCH 2024年 12卷

作者： Zheng, Zhehui Chen, Liu Univ Shanghai Sci & Technol Energy & Power Shanghai Peoples R China Univ Shanghai Sci & Technol Shanghai Peoples R China

Improving the aerodynamic performance of the airfoil is important for optimising the rotor efficiency of the vertical axis wind turbines. As a simple passive control method, the Gurney flap is widely used to improve the aerodynamic performance of airfoils. In this paper, we study the impact of applying a novel serrated gurney flap with different heights on the NACA 0018 airfoil. An improved delayed detached eddy simulation method is adopted to investigate the lift-enhancing mechanism of the serrated gurney flap and the evolution of the downstream vortex system. The results show that the serrated gurney flap can effectively increase the airfoil lift coefficient and the lift-to-drag ratio. The improvement of the serrated gurney flap on the aerodynamic performance of the airfoil is more pronounced at moderate angles of attack. Further analysis of the downstream wake shows that a pair of vortices wraps over both sides of the airfoil and rotates perpendicular to the wake flow, which is produced by the columnar vortex upstream of the flap. These vortices mixed with the wake and accelerated the dissipation of the separated vortex on the suction surface of the airfoil.

关键词： serrated gurney flap airfoil aerodynamics airfoil wake passive flow control vertical axis wind turbine

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Method development for estimation of bleed momentum coefficient using surface pressure measurements and in situ hot wire calibration

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flow MEASUREMENT AND INSTRUMENTATION 2024年 97卷

作者： Cetin, Cenk Yavuz, Mehmet Metin Turkish Aerosp Ind Inc TR-06890 Ankara Turkiye Middle East Tech Univ Mech Engn Dept TR-06800 Ankara Turkiye

Recently, as a passive flow control method, bleeding technique allowing flow of upstream towards suction side by interior passages, has been utilized on non-slender delta wing planforms, where effective geometries can enhance the flow field characteristics. In order to quantify the effect of the flow control, estimation of the momentum induced by the technique is of significant importance in addition to quantified aerodynamic favor. In the current work, passive bleeding momentum coefficient estimation method is developed and presented based on surface pressure measurements by utilizing Bernoulli equation and loss coefficient for a 45 degrees swept non-slender delta wing. For the characterization of the presented technique in-situ hot wire measurements were performed allowing to extract across bleed slot pressure loss coefficient. Results represent that proposed approach can be used to compute the bleeding momentum where further advancements might lead to an important control parameter for potential active bleeding systems in different flow regimes.

关键词： Experimental aerodynamics Non -slender delta wing passive flow control Bleeding Momentum coefficient In situ calibration List of Symbols

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Large scale structures modification of a spatially evolving turbulent boundary layer grazing over circular cavities

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INTERNATIONAL JOURNAL OF HEAT AND FLUID flow 2024年 108卷

作者： Scarano, Francesco Jacob, Marc C. Gowree, Erwin R. Univ Toulouse Dept Aerodynam & Prop DAEP ISAE SUPAERO 10 Ave Edouard Belin F-31400 Toulouse France Ecole Cent Lyon Lab Mecan Fluides & Acoust 36 Ave Guy Collongue F-69134 Ecully France Inst Natl Sci Appl Lyon F-69134 Ecully France Univ Claude Bernard Lyon I 36 Ave Guy Collongue F-69134 Ecully France Univ Lyon Ctr Natl Rech Sci 36 Ave Guy Collongue F-69134 Ecully France

Two experimental investigations were conducted to characterise the impact of circular cavities on the streamwise development of a turbulent boundary layer. Hot-wire anemometry was employed to measure the boundary layer at different streamwise locations along a perforated surface. While the modification of the boundary layer thickness was negligible, the shape factor increased and the friction coefficient decreased with respect to the smooth baseline case. The skin friction downstream of the perforations was investigated by oil droplet interferometry, confirming the skin friction reduction reported in previous investigations. The contour of the premultiplied energy spectrogram showed a "two-peaks"behaviour, where the inner peak shifted towards lower wavelengths, lambda(+)(X), and upwards, suggesting that the streaks were shortened and lifted up by the cavities in the perforated region. The outer peak, can be associated with the enhancement of turbulent mixing and inner/outer layer interaction. Particle image velocimetry measurements, conducted in a streamwise plane downstream of the cavities, showed an increased Reynolds shear stress associated with a significant enhancement of the ejections contribution. A negligible variation in the number of Uniform Momentum Zones in the presence of cavities was observed, but a reduction in the modal velocity associated with the logarithmic region would confirm the formation of low momentum pathways. These outer structures play a significant role in the turbulent mixing enhancement that could be exploited for heat transfer purposes.

关键词： Circular cavities Uniform momentum zones Turbulent boundary layer passive flow control

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control of flow Structures on Nonslender Delta Wing Utilizing Nozzle-Type Bleeding Slots

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AIAA JOURNAL 2024年第10期62卷 4017-4027页

作者： Cetin, Cenk Yilmaz, Oguzhan Yavuz, Mehmet Metin Turkish Aerosp Ind Inc TR-06890 Ankara Turkiye Middle East Tech Univ Mech Engn Dept TR-06800 Ankara Turkiye

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Analyzing dynamic stall on tubercle mounted VAWT blades: A simplistic experimental approach using an oscillating rig

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SUSTAINABLE ENERGY TECHNOLOGIES AND ASSESSMENTS 2024年 71卷

作者： Joseph, Jeena Sridhar, Surya Sathyabhama, A. Radhakrishnan, Jayakrishnan Karavali Inst Technol Dept Aeronaut Engn Mangaluru 575029 India Politecn Milan Dept Aerosp Sci & Technol Via La Masa 34 I-20156 Milan Italy Natl Inst Technol Karnataka Dept Mech Engn Surathkal 575025 Karnataka India Manipal Acad Higher Educ Manipal Inst Technol Dept Aeronaut & Automobile Engn Manipal 576104 Karnataka India

Leading-edge tubercles, inspired by the flippers of humpback whales, are widely adopted passive flow control devices to enhance the aerodynamic performance of various lifting surfaces. This experimental study investigates the implementation of sinusoidal and triangular tubercles on H-type Vertical Axis Wind Turbine blades to analyze their effects on dynamic stall characteristics. Experimental tests were conducted using a specially designed oscillating rig to replicate blade motion at different reduced frequencies. The results reveal that tubercle blades exhibit a lower stall angle and maximum normal force compared to the baseline configuration. Moreover, the dynamic stall characteristics of tubercle blades are notably smoother, leading to reduced hysteresis losses. A variation in the tubercle amplitude-wavelength ratio further decreases hysteresis, albeit at the cost of reduced normal force generation. At the highest tested reduced frequency of 0.065, tubercles reduce hysteresis by up to 38%. Despite the reduction in normal force, tubercles effectively mitigate the effects of dynamic stall vortices, resulting in smoother stall behavior. The observed reduction in hysteresis can contribute to enhancing the turbine's lifespan and increasing power production efficiency. This experimental approach provides a cost-effective alternative to more expensive methods for studying dynamic stall characteristics.

关键词： VAWT Leading-edge tubercles Dynamic stall Hysteresis passive flow control

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Effect of Pitch Angle on Structural and Aerodynamic Characteristics of Vertical-Axis Wind Turbines (VAWTs) Using Leading-Edge Protuberance Blades

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ENERGIES 2025年第2期18卷 286-286页

作者： Elangovan, Karthikvel Pillai, S. Nadaraja SASTRA Deemed Univ Sch Mech Engn Turbulence & Flow Control Lab Thanjavur 613401 Tamil Nadu India

An experimental investigation was carried out to understand the effects of LEP (leading-edge protuberance) blades on the structural characteristics of VAWTs. A series of experiments were performed on VAWTs with straight and LEP blades for a wide range of wind velocity (6 m/s to 20 m/s) and pitch angles (-20 degrees to 20 degrees), and the structural excitations on the VAWT structure were measured using a triaxial accelerometer in each case. The raw acceleration data were extensively processed in the time and frequency domains to identify the variation in structural excitation caused by the unsteady wind and aerodynamic loads on the VAWT structure. Understanding the aerodynamic changes and their impact on structural characteristics is essential. The current study examines how LEP influences the structural excitation of VAWTs. However, a great deal of aerodynamic variation was observed for the LEP blades, so the straight blades of the VAWT were replaced with various modified LEP blades, for which a similar set of experiments was carried out. The study presents a better performance (self-starting, stall-mitigating) for VAWTs with LEP 3 and 2 blades, with a significant reduction in the excitation of loads due to wind load and the changes in aerodynamics observed in the along- and across-wind directions.

关键词： dynamic stall VAWT (vertical-axis wind turbine) leading-edge protuberance energy reduction index vibration passive flow control condition monitoring dynamic testing

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A Novel 1D Approach for Modelling Gas Bladder Suppressors on the Delivery Line of Positive Displacement Pumps

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ENERGIES 2024年第7期17卷 1610页

作者： Casoli, Paolo Vescovini, Carlo Maria Masoud, Hatami Garousi Rundo, Massimo Univ Parma Dept Engn & Architecture I-43124 Parma Italy Politecn Torino Dept Energy Cso Duca Abruzzi 24 I-10129 Turin Italy

This paper concerns the utilisation of a gas bladder hydraulic suppressor to mitigate oscillations in the delivery flow rate of positive displacement machines. The research focuses on two primary objectives: first, the experimental validation of the potential of this solution and second, the formulation of a one-dimensional fluid dynamic model for the suppressor. The foundational framework of the fluid dynamic model is based on the equations governing fluid motion with a one-dimensional approach. To accurately depict the fluid dynamics within the suppressor, a unique approach for determining the speed of sound was incorporated, and it implemented the instantaneous cross-sectional area and the inertial effect of the bladder. This paper is a development of a previous work to also investigate the positioning along the delivery pipe of the suppressor with respect to the pump. The study presents the performance of the suppressor and points out the effects of its relative position with respect to the pump that becomes particularly relevant at high speeds.

关键词： hydraulic bladder suppressor positive displacement pump passive flow control flow ripple pressure ripple

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The effect of shortfin mako shark skin at the reattachment of a separated turbulent boundary layer

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BIOINSPIRATION & BIOMIMETICS 2024年第5期19卷 056012-056012页

作者： Santos, Leonardo M. Lang, Amy Wahidi, Redha Bonacci, Andrew Gautam, Sashank Parsons, Jacob Univ Alabama Dept Aerosp Engn Tuscaloosa AL 35487 USA

This smooth flat experimental study investigates the capability of mako shark scales to control flow separation when placed downstream of the onset of turbulent boundary layer separation and within the reattachment region. The objective of the study is to validate the hypothesis that the shark scales' bristling and recoiling would prevent the flow separation on the flank region (the fastest flow region) of the shark. A rotating cylinder was used to induce an adverse pressure gradient over a flat plate to produce a region of separated flow where the shark skin specimen was mounted. Two types of mako shark scales (flank (B2) and between flank and dorsal fin (B1)) were positioned in the preferred flow direction on a flat plate. The B2 scales are slender, 200 mu m tall, and can bristle up to 50 degrees. In contrast, B1 scales are wider, shorter, and can bristle at 30 degrees. The bristling angle and shape are the main mechanisms by which the scales act to inhibit flow from moving upstream near the wall. Thus, the difference in the bristling angles and structures of the scales is attributed to the fact that the B2 scales function in a thicker boundary layer (behind the shark's gills) where they must bristle sufficiently high into the boundary layer to control the flow separation, and because the adverse pressure gradient in this region is higher where flow separation is more likely. The scales are placed in the reattachment region to elucidate their ability to control and reattach an already separated turbulent flow. The results show that B2 scales placed in the reattachment region reduce the size of the turbulent separation bubble and decrease the turbulent kinetic energy, while B1 scales have the opposite effect.

关键词： shark skin passive flow control separation control boundary layer reattachment region turbulence

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Aerodynamic Analysis and Geometric Optimization of Diversion Grooves in Blunt-Nose Corrected Projectiles

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ARABIAN JOURNAL FOR SCIENCE AND ENGINEERING 2025年 1-24页

作者： Luo, Angang Xiao, Qinkun Liu, Xing Si, Xinlu Sun, Wei Zhang, Lijun Xian Technol Univ Sch Mechatron Engn Xian 710021 Shaanxi Peoples R China Xian Technol Univ Sch Elect Informat Engn Xian 710021 Shaanxi Peoples R China Sci & Technol Elecctromechan Dynam Control Lab Beijing 100081 Peoples R China

Active and passive flow control methods are utilized to achieve two-dimensional trajectory correction for projectiles, facilitating the intelligent enhancement of conventional munitions. This study implements passive flow control by optimizing diversion groove geometry to leverage the aerodynamic properties of asymmetric flow fields for subsonic trajectory correction. Wind tunnel tests are conducted on both traditional and modified models featuring straight-wall grooves on the blunt nose. The investigation explores the effects of asymmetric flow fields induced by the diversion groove under varying conditions on aerodynamic performance. Numerical simulation results are analyzed to visualize complex flow phenomena. A divergent groove is introduced at the blunt nose, and its geometric parameters, including divergence angle and groove length, are varied in iterative numerical calculations. Key flow characteristics are identified, and the findings demonstrate that the divergent groove significantly enhances the aerodynamic performance of asymmetric flow fields. The optimal configuration, with a divergence angle of gamma = 10 degrees and a groove length of 45 mm, results in an increase in the lift coefficient by 82% and the yaw force coefficient by 78%, compared to the straight-wall groove.

关键词： Blunt corrected projectiles Diversion groove passive flow control Asymmetric flow field Trajectory correction

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