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16 pages, 5108 KiB

Open AccessArticle

Experimental Evaluation of Gas-Dynamic Conditions of Heat Exchange of Stationary Air Flows in Vertical Conical Diffuser

by Leonid Plotnikov, Mikhail Ershov, Alexander Nikitin, Vladimir Tuponogov and Alexander Ryzhkov

Appl. Sci. 2024, 14(21), 10080; https://doi.org/10.3390/app142110080 - 4 Nov 2024

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Conical diffusers are widely used in technical devices (gasifiers, turbines, combustion chambers) and technological processes (ejectors, mixers, renewable energy). The perfection of flow gas dynamics in a conical diffuser affects the intensity of heat and mass transfer processes, the quality of mixing/separation of [...] Read more.

Conical diffusers are widely used in technical devices (gasifiers, turbines, combustion chambers) and technological processes (ejectors, mixers, renewable energy). The perfection of flow gas dynamics in a conical diffuser affects the intensity of heat and mass transfer processes, the quality of mixing/separation of working media and the flow characteristics of technical devices. These parameters largely determine the efficiency and productivity of the final product. This article presents an analysis of experimental data on the gas-dynamic characteristics of stationary air flows in a vertical, conical, flat diffuser under different initial boundary conditions. An experimental setup was created, measuring instruments were selected, and an automated data collection system was developed. Basic data on the gas dynamics of air flows were obtained using the thermal anemometry method. Experimental data on instantaneous values of air flow velocity in a diffuser for initial velocities from 0.4 m/s to 2.22 m/s are presented. These data were the basis for calculating and obtaining velocity fields and turbulence intensity fields of the air flow in a vertical diffuser. It is shown that the value of the initial flow velocity at the diffuser inlet has a significant effect on the gas-dynamic characteristics. In addition, a spectral analysis of the change in air flow velocity both by height and along the diffuser axis was performed. The obtained data may be useful for refining engineering calculations, verifying mathematical models, searching for technical solutions and deepening knowledge about the features of gas dynamics of air flows in vertical diffusers. Full article

(This article belongs to the Special Issue Advances in Active and Passive Techniques for Fluid Flow Manipulation)

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26 pages, 7675 KiB

Open AccessArticle

Parametric Optimization Study of Novel Winglets for Transonic Aircraft Wings

by Panneerselvam Padmanathan, Seenu Aswin, Anbalagan Satheesh, Parthasarathy Rajesh Kanna, Kuppusamy Palani, Neelamegam Rajan Devi, Tomasz Sobota, Dawid Taler, Jan Taler and Bohdan Węglowski

Appl. Sci. 2024, 14(17), 7483; https://doi.org/10.3390/app14177483 - 23 Aug 2024

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Abstract

This paper deals with the topic of reducing drag force acting on aircraft wings by incorporating novel winglet designs, such as multi-tip, bird-type, and twisted. The high-speed NASA common research model (CRM) was selected as the baseline model, and winglet designs were retrofitted [...] Read more.

This paper deals with the topic of reducing drag force acting on aircraft wings by incorporating novel winglet designs, such as multi-tip, bird-type, and twisted. The high-speed NASA common research model (CRM) was selected as the baseline model, and winglet designs were retrofitted while keeping the projected wingspan constant. Computational analysis was performed using RANS coupled with the Spalart–Allmaras turbulence model to determine aerodynamic coefficients, such as C_L and C_D. It was observed that the multi-tip and bird-type designs performed exceptionally well at a low angle of attack (0°). A parametric study was conducted on multi-tip winglets by tweaking the parameters such as sweep angle (Λ), tip twist (Є), taper ratio (λ), and cant angle (Φ). The best combination of parameters for optimal aerodynamic performance while maintaining the wing root bending moment was determined using both the Taguchi method and Taguchi-based grey relational analysis (T-GRA) coupled with principal component analysis (PCA). Also, the percentage contribution of each parameter was determined by using the analysis of variance (ANOVA) method. At the design point, the optimized winglet design outperformed the baseline design by 18.29% in the Taguchi method and by 20.77% in the T-GRA coupled with the PCA method based on aerodynamic efficiency and wing root bending moment. Full article

(This article belongs to the Special Issue Advances in Active and Passive Techniques for Fluid Flow Manipulation)

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17 pages, 10093 KiB

Open AccessArticle

Vortex Characterization and Parametric Study of Miniature Vortex Generators and Their Near-Field Boundary Layer Effects

by Gilles De Baets, András Szabó, Péter Tamás Nagy, György Paál and Maarten Vanierschot

Appl. Sci. 2024, 14(16), 6966; https://doi.org/10.3390/app14166966 - 8 Aug 2024

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Abstract

Delaying the onset of laminar-turbulent transition is an attractive method in reducing skin friction drag, especially on streamlined bodies where Tollmien–Schlichting instabilities are the dominating mechanism for transition. Miniature Vortex Generators (MVGs) offer an effective approach to attenuate these instabilities by generating counter-rotating [...] Read more.

Delaying the onset of laminar-turbulent transition is an attractive method in reducing skin friction drag, especially on streamlined bodies where Tollmien–Schlichting instabilities are the dominating mechanism for transition. Miniature Vortex Generators (MVGs) offer an effective approach to attenuate these instabilities by generating counter-rotating vortex pairs. They are placed in pairs within an array and resemble small-winglet-type elements. The conventional methodology involves adjusting the MVG parameters and conducting computationally expensive DNS and/or downstream stability analyses to assess their effectiveness. However, analyzing the vortex parameters of MVG-generated vortices can potentially guide a more targeted approach to modifying the MVG parameters and identifying the critical factors for transition delay. Therefore, this study investigates the changes in three primary MVG parameters, namely inner distance, periodicity, and height, and utilizes computational fluid dynamics (CFDs) analysis to create a dataset that examines the characteristics of the generated counter-rotating vortex pairs and their potential in drag reduction. The objective is to establish correlations among these parameters and their influence on delaying transition. The results show that there is an optimal ratio between the MVG height and boundary layer thickness. Higher MVGs cause a decrease in the vortex radius and an increase in the amount of circulation, raising the likeliness of bypass transition. The derived correlations between the different MVG parameters show that the vortex radius is the most critical one and is hence an important parameter in the drag reduction potential. Full article

(This article belongs to the Special Issue Advances in Active and Passive Techniques for Fluid Flow Manipulation)

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17 pages, 6251 KiB

Open AccessArticle

Effects of Materials and Riblets on Erosion Mitigation Induced by Multiple Collapses of Cavitation Bubbles

by Ebrahim Kadivar, Sasan Rezaee, Udo Löschner and Ould el Moctar

Appl. Sci. 2024, 14(15), 6452; https://doi.org/10.3390/app14156452 - 24 Jul 2024

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Abstract

The current research investigates the effects of materials and riblets on cavitation-induced erosion morphology, depth, and cross-sectional area through experimental approaches. To achieve these aims, the erosion of pure aluminum (1xxxAl or Al) and alpha brass (CuZn37 or CZ108), in the presence and [...] Read more.

The current research investigates the effects of materials and riblets on cavitation-induced erosion morphology, depth, and cross-sectional area through experimental approaches. To achieve these aims, the erosion of pure aluminum (1xxxAl or Al) and alpha brass (CuZn37 or CZ108), in the presence and absence of bio-inspired sawtooth riblets, was examined after exposure to multiple collapses of single cavitation bubbles with a wall distance of 1.8 (dimensionless). The results indicate that the erosion morphology resembles a rounded cone with a circular cross-section. Brass provides 21.6% more erosion resistance compared to that of Al in terms of material properties. Furthermore, the erosion for both Al (depth by 3.8% and width by 18.3%) and brass (depth by 7.9% and width by 27.4%) decreases in the presence of riblets compared to the results for flat surfaces. The greater erosion resistance of brass compared to Al is attributed to the superior mechanical stability of brass, making it a potentially suitable alloy for use in propellers and hulls in the shipping industry. In summary, the results reveal that riblet-equipped materials with high mechanical durability are promising erosion-resistant materials for the shipping industry. However, the potential for chemical reactions in a cathodic environment should be addressed to provide a comprehensive perspective in regards to reducing corrosion intensity. Full article

(This article belongs to the Special Issue Advances in Active and Passive Techniques for Fluid Flow Manipulation)

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17 pages, 6847 KiB

Open AccessArticle

Numerical Modeling of Venous Outflow from the Cranial Cavity in the Supine Body Position

by Marian Simka, Joanna Czaja, Agata Kawalec, Paweł Latacz and Uliana Kovalko

Appl. Sci. 2024, 14(9), 3878; https://doi.org/10.3390/app14093878 - 30 Apr 2024

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Abstract

The hemodynamic relevance of differently located stenoses of the internal jugular veins remains undetermined. It particularly concerns nozzle-like strictures in the upper parts of these veins and stenotic jugular valves located at the end of these veins. This study was aimed at understanding [...] Read more.

The hemodynamic relevance of differently located stenoses of the internal jugular veins remains undetermined. It particularly concerns nozzle-like strictures in the upper parts of these veins and stenotic jugular valves located at the end of these veins. This study was aimed at understanding flow disturbances caused by such stenoses. The computational fluid dynamics software Flowsquare+ was used. We constructed 3-dimensional models of the venous outflow, comprising two alternative routes: the tube representing the internal jugular vein and an irregular network representing the vertebral veins. At the beginning of the tube representing the internal jugular vein, differently shaped and sized short strictures representing nozzle-like strictures were built in. At the end of this tube, differently shaped membranes representing the jugular valve were built in. With the use of computational fluid dynamics modeling, we studied how these two obstacles influenced the outflow. We found that the most relevant outflow disturbances were evoked by the nozzle-like strictures in the upper part of the internal jugular vein that were small, long, or asymmetrically positioned. Very tight stenotic valves and septum-like malformed valve were equally hemodynamically relevant. These findings suggest that both upper and lower strictures of the internal jugular vein can be of clinical significance. Full article

(This article belongs to the Special Issue Advances in Active and Passive Techniques for Fluid Flow Manipulation)

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27 pages, 6049 KiB

Open AccessArticle

Beacon, a Lightweight Deep Reinforcement Learning Benchmark Library for Flow Control

by Jonathan Viquerat, Philippe Meliga, Pablo Jeken-Rico and Elie Hachem

Appl. Sci. 2024, 14(9), 3561; https://doi.org/10.3390/app14093561 - 23 Apr 2024

Viewed by 1092

Abstract

Recently, the increasing use of deep reinforcement learning for flow control problems has led to a new area of research focused on the coupling and adaptation of the existing algorithms to the control of numerical fluid dynamics environments. Although still in its infancy, [...] Read more.

Recently, the increasing use of deep reinforcement learning for flow control problems has led to a new area of research focused on the coupling and adaptation of the existing algorithms to the control of numerical fluid dynamics environments. Although still in its infancy, the field has seen multiple successes in a short time span, and its fast development pace is certainly partly imparted by the open-source effort that drives the expansion of the community. Yet this emerging domain is still missing a common ground to (i) ensure the reproducibility of the results and (ii) offer a proper ad hoc benchmarking basis. To this end, we propose beacon, an open-source benchmark library composed of seven lightweight one-dimensional and two-dimensional flow control problems with various characteristics, action and observation space characteristics, and CPU requirements. In this contribution, the seven considered problems are described, and reference control solutions are provided. The sources for the following work are publicly available. Full article

(This article belongs to the Special Issue Advances in Active and Passive Techniques for Fluid Flow Manipulation)

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26 pages, 45915 KiB

Open AccessArticle

Analysis of a Novel Fluidic Oscillator under Several Dimensional Modifications

by Kavoos Karimzadegan, Masoud Mirzaei and Josep M. Bergada

Appl. Sci. 2024, 14(5), 1690; https://doi.org/10.3390/app14051690 - 20 Feb 2024

Viewed by 1080

Abstract

To activate the boundary layer in Active Flow Control (AFC) applications, the use of pulsating flow has notable energy advantages over constant blowing/suction jet injections. For a given AFC application, five parameters, jet location and width, inclination angle, frequency of injection, and the [...] Read more.

To activate the boundary layer in Active Flow Control (AFC) applications, the use of pulsating flow has notable energy advantages over constant blowing/suction jet injections. For a given AFC application, five parameters, jet location and width, inclination angle, frequency of injection, and the momentum coefficient, need to be tuned. Presently, two main devices are capable of injecting pulsating flow with a momentum coefficient sufficient to delay the boundary layer separation: these are zero-net-mass-flow Actuators (ZNMFAs) and fluidic oscillators (FOs). In the present study, a novel FO configuration is analyzed for the first time at relatively high Reynolds numbers, and fluid is considered to be incompressible. After obtaining the typical linear correlation between the incoming Reynolds number and the outlet flow oscillating frequency, the effects of dimensional modifications on outlet width and mixing chamber wedge inclination angle are addressed. Modifications of the outlet width were observed to create large variations in FO performance. The origin of self-sustained oscillations is also analyzed in the present manuscript and greatly helps in clarifying the forces acting on the jet inside the mixing chamber. In fact, we can conclude by saying that the current FO configuration is pressure-driven, although the mass flow forces appear to be much more relevant than in previously studied FO configurations. Full article

(This article belongs to the Special Issue Advances in Active and Passive Techniques for Fluid Flow Manipulation)

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26 pages, 53961 KiB

Open AccessArticle

Numerical and Experimental Characterization of a Coanda-Type Industrial Air Amplifier

by Miguel Chávez-Módena, Alejandro Martinez-Cava, Sergio Marín-Coca and Leo González

Appl. Sci. 2024, 14(4), 1524; https://doi.org/10.3390/app14041524 - 14 Feb 2024

Viewed by 1109

Abstract

The performance of an industrial air amplifier is assessed through experimental and numerical characterization, with a focus on examining the influence of various operating conditions (isolated, “blowing,” and “suction” modes) and direct geometric scaling of the device within the specified range of the [...] Read more.

The performance of an industrial air amplifier is assessed through experimental and numerical characterization, with a focus on examining the influence of various operating conditions (isolated, “blowing,” and “suction” modes) and direct geometric scaling of the device within the specified range of the injection gap (

δ

) and the inlet pressure characteristic values. The findings underscore the presence of a linear trend of the entrained mass flow and a nonlinear decay of the amplification factor, both with notable sensitivity to the gap width. Numerical RANS simulations validate the experimental data, characterize the asymmetric flow downstream from the device, and facilitate the exploration of more complex scenarios. In this regard, scaling the device’s dimensions reveals an optimal aspect ratio between the minimum diameter (

D_{m}

) and

δ

to maximize the entrained mass flow. This research provides valuable insights into the behavior of air amplifiers, offering guidance for their design and application across various industrial contexts. Full article

(This article belongs to the Special Issue Advances in Active and Passive Techniques for Fluid Flow Manipulation)

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