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12 pages, 4573 KiB

Open AccessArticle

The Effect of Bifurcated Geometry on the Diodicity of Tesla Valves

by Sean Wiley and Huei-Ping Huang

Fluids 2024, 9(12), 294; https://doi.org/10.3390/fluids9120294 - 11 Dec 2024

Viewed by 226

Abstract

The Tesla valve is a fluidic diode that enables unidirectional flow while impeding the reverse flow without the assistance of any moving parts. Conventional Tesla valves share a distinctive feature of a bifurcated section that connects the inlet and outlet. This study uses [...] Read more.

The Tesla valve is a fluidic diode that enables unidirectional flow while impeding the reverse flow without the assistance of any moving parts. Conventional Tesla valves share a distinctive feature of a bifurcated section that connects the inlet and outlet. This study uses computational fluid dynamic (CFD) simulations to analyze the importance of the bifurcated design to the efficiency of the Tesla valve, quantified by diodicity. Simulations over the range of the Reynolds number, Re = 50–2000, are performed for three designs: the T45-R, D-valve, and GMF valve, each with two versions with and without the bifurcated section. For the T45-R valve, removing the bifurcated section leads to a consistent increase in diodicity, particularly at high Re. In contrast, the diodicity of the GMF valve drops significantly when the bifurcated section is removed. The D-valve exhibits a mixed behavior. Without the bifurcated section, its diodicity is suppressed at low Re but begins to increase for Re > 1100, eventually matching the diodicity of the bifurcated version at Re = 2000. The results highlight the intricate relationship between valve geometry and efficiency of Tesla-type valves and the dependence of this relationship on the Reynolds number. Full article

(This article belongs to the Special Issue Flow Control Techniques: Advances in Flow System Analysis, Modeling and Applications)

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19 pages, 10536 KiB

Open AccessFeature PaperArticle

Numerical Study of Laminar Unsteady Circular and Square Jets in Crossflow in the Low Velocity Ratio Regime

by Francisco C. Martins and José C. F. Pereira

Fluids 2024, 9(12), 292; https://doi.org/10.3390/fluids9120292 - 10 Dec 2024

Viewed by 303

Abstract

The unsteady three-dimensional flow interactions in the near field of square and circular jets issued normally to a crossflow were predicted by direct numerical simulations, aiming to investigate the effect of the nozzle cross-section on the vortical structures formed in this region. The [...] Read more.

The unsteady three-dimensional flow interactions in the near field of square and circular jets issued normally to a crossflow were predicted by direct numerical simulations, aiming to investigate the effect of the nozzle cross-section on the vortical structures formed in this region. The analysis focuses on jets in crossflow with moderate Reynolds numbers (

R e_{j} = 200

and

R e_{j} = 300

) based on the jet velocity the characteristic length of the nozzle and low jet-to-cross-flow velocity ratios,

0.25 \leq R \leq 1.4

, where the jets are absolutely unstable. In this regime, the flow becomes periodic and laminar, and three distinct wake flow configurations were identified: (1) symmetric shedding of hairpin vortices at

R e_{j} = 200

; (2) the formation of toroidal vortices as the legs of hairpin vortices merge and the vortices roll up at

R e_{j} = 300

and

R \leq 0.67

; (3) asymmetric shedding of hairpin vortices in the square jet at

R e_{j} = 300

and

R \geq 0.9

, where higher-frequency hairpin vortex shedding combines with a low-frequency spanwise oscillation in the counter-rotating vortex pair. The dynamics of each of these flow states were analyzed. Power spectral density plots show a measurable increase in the shedding frequencies in

R e_{j} = 300

jets with R, and that these frequencies are consistently larger in circular jets. Full article

(This article belongs to the Special Issue Flow Control Techniques: Advances in Flow System Analysis, Modeling and Applications)

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22 pages, 14340 KiB

Open AccessArticle

Passive Control of the Flow Around a Rectangular Cylinder with a Custom Rough Surface

by Mario A. Aguirre-López, Filiberto Hueyotl-Zahuantitla, Pedro Martínez-Vázquez and José Ulises Márquez-Urbina

Fluids 2024, 9(11), 253; https://doi.org/10.3390/fluids9110253 - 29 Oct 2024

Viewed by 684

Abstract

Motivated by existing techniques for implementing roughness on cylinders to control flow disturbances, we performed delayed detached eddy simulations (DDES) at Re =

6 \times 10^{6}

that generated unsteady turbulent flow around a rectangular cylinder with a controlled wrinkled surface and a [...] Read more.

Motivated by existing techniques for implementing roughness on cylinders to control flow disturbances, we performed delayed detached eddy simulations (DDES) at Re =

6 \times 10^{6}

that generated unsteady turbulent flow around a rectangular cylinder with a controlled wrinkled surface and a 1:4 aspect ratio. A systematic study of the roughness effect was carried out by implementing different configurations of equally spaced grooves and bumps on the top-surface of the cylinder. Our results suggest that groove geometries reduce energy dissipation at higher rates than the smooth reference case, whereas bumped cylinders produce relative pressures characterized by a sawtooth pattern along the middle-upper part of the cylinder. Moreover, cylinders with triangular bumps increase mean drag and lift forces by up to 8% and 0.08 units, respectively, while circular bumps increase vorticity and pressure disturbances on the wrinkled surface. All of these effects impact energy dissipation, vorticity, pressure coefficients, and flow velocity along the wrinkled surface. Both the surface-manufactured cylinders and the proposed visualization techniques could be replicated in a variety of engineering developments involving flow characterization in the presence of roughness. Full article

(This article belongs to the Special Issue Flow Control Techniques: Advances in Flow System Analysis, Modeling and Applications)

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14 pages, 7748 KiB

Open AccessArticle

Characterization of the Three-Dimensional Flowfield over a Truncated Linear Aerospike

by Roberto Marsilio, Gaetano Maria Di Cicca, Emanuele Resta and Michele Ferlauto

Fluids 2024, 9(8), 179; https://doi.org/10.3390/fluids9080179 - 10 Aug 2024

Viewed by 825

Abstract

The work focuses on the characterization of the flowfield over a truncated linear aerospike by combining theoretical grounds, numerical simulations and experimental tests. The experimental investigations are carried out on a test rig designed at Politecnico di Torino for advanced nozzle testing. Fully [...] Read more.

The work focuses on the characterization of the flowfield over a truncated linear aerospike by combining theoretical grounds, numerical simulations and experimental tests. The experimental investigations are carried out on a test rig designed at Politecnico di Torino for advanced nozzle testing. Fully three-dimensional CFD analyses are performed on the actual geometry of the experimental nozzle model. At low nozzle pressure ratios (nprs) the analysis combines numerical simulations and experimental testing, which are also used for validating the CFD results. At higher nprs, the flowfield characterization is performed only by three-dimensional CFD analyses. In addition to the validation of the numerical method, the edge effects at different nprs have been observed. Full article

(This article belongs to the Special Issue Flow Control Techniques: Advances in Flow System Analysis, Modeling and Applications)

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21 pages, 3500 KiB

Open AccessArticle

AI-Based Detection of Surge and Rotating Stall in Axial Compressors via Dynamic Model Parameter Estimation

by Sara Zanotti, Davide Ceschini and Michele Ferlauto

Fluids 2024, 9(6), 134; https://doi.org/10.3390/fluids9060134 - 1 Jun 2024

Viewed by 927

Abstract

Compressors are an essential component of aircraft engines. Their design and operation must be extremely reliable as engine safety and performance depend greatly on these elements. Axial compressors exhibit instabilities, such as surge or rotating stall, in a region close to the peak [...] Read more.

Compressors are an essential component of aircraft engines. Their design and operation must be extremely reliable as engine safety and performance depend greatly on these elements. Axial compressors exhibit instabilities, such as surge or rotating stall, in a region close to the peak of their performance curves. These fluid dynamic instabilities can cause drops in efficiency, stress on the blades, fatigue, and even failures. Compressors are handled therefore by operating with a safety margin far from the surge line. Moreover, models able to predict onset instabilities and to reproduce them are of great interest. A dynamic system able to describe successfully both surge and rotating stall is the model presented by Moore and Greitzer That model has also been used for developing control laws of the compressor dynamics. The present work aims at developing an artificial neural network (ANN) approach able to predict either the permanence of the system in stable working condition or the onset instabilities from a time sequence of the compressor dynamics. Different solutions were tried to find the most suitable model for identifying the system, as well as the effects of the duration of the time sequence on the accuracy of the predicted compressor working conditions. The network was further tried for sequences with different initial values in order to perform a system analysis that included multiple variations from the initial database. The results show how it is possible to identify with high accuracy both rotating stall and surge with the ANN approach. Moreover, the presence of an underlying fluid dynamic model shares some similarities with physically informed AI procedures. Full article

(This article belongs to the Special Issue Flow Control Techniques: Advances in Flow System Analysis, Modeling and Applications)

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20 pages, 2113 KiB

Open AccessArticle

Performance of DBD Actuator Models under Various Operating Parameters and Modifications to Improve Them

by Raul Alberto Bernal-Orozco, Ignacio Carvajal-Mariscal and Oliver Marcel Huerta-Chavez

Fluids 2023, 8(4), 112; https://doi.org/10.3390/fluids8040112 - 28 Mar 2023

Cited by 1 | Viewed by 2488

Abstract

Simulation is a valuable tool for the study of DBD actuators, therefore accurate, computationally efficient, and robust numerical models are required. The performance of three DBD actuator models was studied: the phenomenological Shyy and Suzen models, and the empirical Dörr and Kloker model. [...] Read more.

Simulation is a valuable tool for the study of DBD actuators, therefore accurate, computationally efficient, and robust numerical models are required. The performance of three DBD actuator models was studied: the phenomenological Shyy and Suzen models, and the empirical Dörr and Kloker model. The first objective of this work is to determine the ability of these models to reproduce the force and induced flow by comparing the numerical results with experimental reference data reported in the literature. As a second objective, modifications have been proposed to improve these models. Several simulations were performed in OpenFOAM with different geometrical parameters, voltages, and frequencies. Discrepancies and limitations of the models were identified. The modified Dörr and Kloker model allows more consistent use of this model by considering a factor that relates it to voltage and frequency. Shyy’s modified model reduces the overestimation of force and velocity. Suzen’s modified model is the one that fits the reference data better, so its use is suggested over the other models. The proposed modifications are easy to implement and allow significant improvements in the capacity of the models to reproduce the effects of a DBD actuator. Full article

(This article belongs to the Special Issue Flow Control Techniques: Advances in Flow System Analysis, Modeling and Applications)

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23 pages, 12564 KiB

Open AccessArticle

Evaluation of Synthetic Jet Flow Control Technique for Modulating Turbulent Jet Noise

by Jairo Murillo-Rincón and Carlos Duque-Daza

Fluids 2023, 8(4), 110; https://doi.org/10.3390/fluids8040110 - 27 Mar 2023

Cited by 2 | Viewed by 2146

Abstract

The use of a synthetic jet as the flow control technique to modulate a turbulent incompressible round jet was explored and assessed by numerical simulations. The flow response was characterised in terms of turbulent statistics and acoustic response in the far-field. A quasi-Direct [...] Read more.

The use of a synthetic jet as the flow control technique to modulate a turbulent incompressible round jet was explored and assessed by numerical simulations. The flow response was characterised in terms of turbulent statistics and acoustic response in the far-field. A quasi-Direct Numerical Simulation (qDNS) strategy was used to predict the turbulent effects. The Ffowcs-Williams and Hawkings (FWH) acoustic analogy was employed to compute the far-field acoustic response. An amplification effect of the instabilities induced by the control jet was observed for some of the parameters explored. It was observed that the control technique allows controlling the axial distribution of the production and dissipation of turbulent kinetic energy, but with respect to the acoustic aspects, the appearance of a greater number of noise sources was observed, which in the far-field, resulted in an increase from 1 to 20 dB of the equivalent noise for the different operating parameters of the control technique studied. Full article

(This article belongs to the Special Issue Flow Control Techniques: Advances in Flow System Analysis, Modeling and Applications)

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Review

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35 pages, 2694 KiB

Open AccessReview

Synthetic Jet Actuators for Active Flow Control: A Review

by Howard H. Ho, Ali Shirinzad, Ebenezer E. Essel and Pierre E. Sullivan

Fluids 2024, 9(12), 290; https://doi.org/10.3390/fluids9120290 - 6 Dec 2024

Viewed by 573

Abstract

A synthetic jet actuator (SJA) is a fluidic device often consisting of a vibrating diaphragm that alters the volume of a cavity to produce a synthesized jet through an orifice. The cyclic ingestion and expulsion of the working fluid leads to a zero-net [...] Read more.

A synthetic jet actuator (SJA) is a fluidic device often consisting of a vibrating diaphragm that alters the volume of a cavity to produce a synthesized jet through an orifice. The cyclic ingestion and expulsion of the working fluid leads to a zero-net mass-flux and the transfer of linear momentum to the working fluid over an actuation cycle, leaving a train of vortex structures propagating away from the orifice. SJAs are a promising technology for flow control applications due to their unique features, such as no external fluid supply or ducting requirements, short response time, low weight, and compactness. Hence, they have been the focus of many research studies over the past few decades. Despite these advantages, implementing an effective control scheme using SJAs is quite challenging due to the large parameter space involving several geometrical and operational variables. This article aims to explain the working mechanism of SJAs and provide a comprehensive review of the effects of SJA design parameters in quiescent conditions and cross-flow. Full article

(This article belongs to the Special Issue Flow Control Techniques: Advances in Flow System Analysis, Modeling and Applications)

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