Fluids

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12 pages, 1842 KiB

Open AccessArticle

Fully Coupled Fluid–Structure Interaction with Heat Transfer Effects in an Adaptive NACA Airfoil

by Paolo Caccavale, Benedetto Mele, Marco Brandizzi and Gianpaolo Ruocco

Fluids 2023, 8(2), 39; https://doi.org/10.3390/fluids8020039 - 20 Jan 2023

Cited by 3 | Viewed by 2375

In the framework of innovative aerodynamics, active airfoils can be developed and exploited based on the integration of shape memory metal alloys (SMAs), allowing for surface adaptation, i.e., shape changes in response to operative thermal inputs, depending on the desired aerodynamic behavior. The [...] Read more.

In the framework of innovative aerodynamics, active airfoils can be developed and exploited based on the integration of shape memory metal alloys (SMAs), allowing for surface adaptation, i.e., shape changes in response to operative thermal inputs, depending on the desired aerodynamic behavior. The purpose of thermally activated shape-changing (TASC) airfoils’ improved capabilities is to offer benefits in terms of aircraft performance and fuel consumption rate. TASC airfoil design hinges upon three intertwined and nonlinear phenomena, namely the solid–fluid–thermal interactions. In this paper, in order to approach the definition of appropriate design parameters, the space of operating variables is explored for the first time by devising a finite element method simulation encompassing the equations of structural motion, energy, and turbulent Reynolds-averaged Navier–Stokes. Such a fully coupled model is then tested by implementing a sensitivity analysis for a preliminary design of a TASC/NACA airfoil. Temperature and velocity distributions are presented and discussed, including new metrics leading to aerodynamic lift calculations. When the efficiency is computed as the lift-to-drag ratio, it is found to vary nonlinearly in the 0–45 range, with the activating power feed in the 0–1000 W range. Full article

(This article belongs to the Special Issue Drag Reduction in Turbulent Flows)

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8 pages, 2101 KiB

Open AccessArticle

Drag Reduction in Polymer-Laden Turbulent Pipe Flow

by Francesco Serafini, Francesco Battista, Paolo Gualtieri and Carlo Massimo Casciola

Fluids 2022, 7(11), 355; https://doi.org/10.3390/fluids7110355 - 18 Nov 2022

Cited by 4 | Viewed by 1755

Abstract

The turbulence of a realistic dilute solution of DNA macromolecules is investigated through a hybrid Eulerian–Lagrangian approach that directly solves the incompressible Navier–Stokes equation alongside the evolution of

10^{8}

polymers, modelled as finitely extensible nonlinear elastic (FENE) dumbbells. At a friction Reynolds [...] Read more.

The turbulence of a realistic dilute solution of DNA macromolecules is investigated through a hybrid Eulerian–Lagrangian approach that directly solves the incompressible Navier–Stokes equation alongside the evolution of

10^{8}

polymers, modelled as finitely extensible nonlinear elastic (FENE) dumbbells. At a friction Reynolds number of 320 and a Weissenberg number of

2 \times 10^{4}

, the drag reduction is equal to 26%, which is similar to the one obtained at the lower Reynolds number of 180. The polymers induce an increase in the flow rate and the turbulent kinetic energy, whose axial contribution is predominantly augmented. The stress balance is analysed to investigate the causes of the drag reduction and eventually the effect of the friction Reynolds number on the probability distribution of the polymer configuration. Near the wall, the majority of the polymers are fully stretched and aligned along the streamwise direction, inducing an increase in the turbulence anisotropy. Full article

(This article belongs to the Special Issue Drag Reduction in Turbulent Flows)

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24 pages, 23122 KiB

Open AccessArticle

Turbulence Modulation by Slender Fibers

by Davide Di Giusto and Cristian Marchioli

Fluids 2022, 7(8), 255; https://doi.org/10.3390/fluids7080255 - 28 Jul 2022

Cited by 5 | Viewed by 1941

Abstract

In this paper, we numerically investigate the turbulence modulation produced by long flexible fibres in channel flow. The simulations are based on an Euler–Lagrangian approach, where fibres are modelled as chains of constrained, sub-Kolmogorov rods. A novel algorithm is deployed to make the [...] Read more.

In this paper, we numerically investigate the turbulence modulation produced by long flexible fibres in channel flow. The simulations are based on an Euler–Lagrangian approach, where fibres are modelled as chains of constrained, sub-Kolmogorov rods. A novel algorithm is deployed to make the resolution of dispersed systems of constraint equations, which represent the fibres, compatible with a state-of-the-art, Graphics Processing Units-accelerated flow-solver for direct numerical simulations in the two-way coupling regime on High Performance Computing architectures. Two-way coupling is accounted for using the Exact Regularized Point Particle method, which allows to calculate the disturbance generated by the fibers on the flow considering progressively refined grids, down to a quasi-viscous length-scale. The bending stiffness of the fibers is also modelled, while collisions are neglected. Results of fluid velocity statistics for friction Reynolds number of the flow

R e_{τ} = 150

and fibers with Stokes number

S t

= 0.01 (nearly tracers) and 10 (inertial) are presented, with special regard to turbulence modulation and its dependence on fiber inertia and volume fraction (equal to

ϕ = 2.12

·

10^{- 5}

and

2.12

·

10^{- 4}

). The non-Newtonian stresses determined by the carried phase are also displayed, determined by long and slender fibers with fixed aspect ratio

λ_{t o t} = 200

, which extend up to the inertial range of the turbulent flow. Full article

(This article belongs to the Special Issue Drag Reduction in Turbulent Flows)

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15 pages, 1462 KiB

Open AccessArticle

Riblet Drag Reduction Modeling and Simulation

by Benedetto Mele

Fluids 2022, 7(7), 249; https://doi.org/10.3390/fluids7070249 - 19 Jul 2022

Cited by 7 | Viewed by 3195

Abstract

One of the most interesting passive drag reduction techniques is based on the use of riblets or streamwise grooved surfaces. Detailed flow features inside the grooves can be numerically detected only by Direct Numerical Simulations (DNS), still unfeasible for high Reynolds numbers and [...] Read more.

One of the most interesting passive drag reduction techniques is based on the use of riblets or streamwise grooved surfaces. Detailed flow features inside the grooves can be numerically detected only by Direct Numerical Simulations (DNS), still unfeasible for high Reynolds numbers and complex flows. Many papers report the DNS of flows on microgrooved surfaces providing fundamental details on the drag reduction devices, but all are limited to plate or channel flows far from engineering Reynolds numbers. The numerical simulation of riblets and other drag reduction devices at very high Reynolds numbers is difficult to perform due to the riblet dimensions (microns in aeronautical applications). To overcome these difficulties, some models for riblet simulation have been developed in recent years, due to the data provided by DNS, experiments, and theoretical analyses. In all these models, the drag reduction is modeled rather than effectively captured; however, the analysis of some nonlocal effects on practical aeronautical configurations with riblets, requires their adoption. In this paper, the capabilities of these models in predicting riblets’ performance and some interesting features of the riblets’ effect on form drag and shock waves are shown. Two models are discussed and compared showing their respective advantages and limitations and providing possible enhancements. A comparison between the two models in terms of accuracy and convergence is discussed, and two new formulae are proposed to improve one of these models. Finally, a review of the results obtained by the two models is provided showing their capabilities in the analysis of the riblet effect on complex configurations. Full article

(This article belongs to the Special Issue Drag Reduction in Turbulent Flows)

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21 pages, 1280 KiB

Open AccessEditor’s ChoiceArticle

Dimples for Skin-Friction Drag Reduction: Status and Perspectives

by Federica Gattere, Alessandro Chiarini and Maurizio Quadrio

Fluids 2022, 7(7), 240; https://doi.org/10.3390/fluids7070240 - 13 Jul 2022

Cited by 11 | Viewed by 3529

Abstract

Dimples are small concavities imprinted on a flat surface, known to affect heat transfer and also flow separation and aerodynamic drag on bluff bodies when acting as a standard roughness. Recently, dimples have been proposed as a roughness pattern that is capable of [...] Read more.

Dimples are small concavities imprinted on a flat surface, known to affect heat transfer and also flow separation and aerodynamic drag on bluff bodies when acting as a standard roughness. Recently, dimples have been proposed as a roughness pattern that is capable of reducing the turbulent drag of a flat plate by providing a reduction of skin friction that compensates the dimple-induced pressure drag and leads to a global benefit. The question whether dimples do actually work to reduce friction drag is still unsettled. In this paper, we provide a comprehensive review of the available information, touching upon the many parameters that characterize the problem. A number of reasons that contribute to explaining the contrasting literature information are discussed. We also provide guidelines for future studies by highlighting key methodological steps required for a meaningful comparison between a flat and dimpled surface in view of drag reduction. Full article

(This article belongs to the Special Issue Drag Reduction in Turbulent Flows)

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26 pages, 13354 KiB

Open AccessArticle

Drag Reduction by Wingtip-Mounted Propellers in Distributed Propulsion Configurations

by Mauro Minervino, Giovanni Andreutti, Lorenzo Russo and Renato Tognaccini

Fluids 2022, 7(7), 212; https://doi.org/10.3390/fluids7070212 - 21 Jun 2022

Cited by 8 | Viewed by 3348

Abstract

Tip-mounted propellers can increase wing aerodynamic efficiency, and the concept is gaining appeal in the context of hybrid electrical propulsion for greener aviation, as smaller and lighter electrical motors can help with mitigating structural drawbacks of a tip engine installation. A numerical study [...] Read more.

Tip-mounted propellers can increase wing aerodynamic efficiency, and the concept is gaining appeal in the context of hybrid electrical propulsion for greener aviation, as smaller and lighter electrical motors can help with mitigating structural drawbacks of a tip engine installation. A numerical study of tip propeller effects on wing aerodynamics is herein illustrated, considering different power configurations of a Regional Aircraft wing. A drag breakdown analysis using far-field methods is presented for one of the most promising configurations, and a comparison between drag reductions obtained with a tip propeller or a standard winglet installation is also provided. Numerical flow simulations using Finite Volume Methods with actuator disk models are compared with results of a Vortex-Lattice Method, and far-field aerodynamic force calculation is performed for different mesh sizes. A wing drag reduction up to 6% (10%) is predicted under typical cruise (climb) flight conditions when wingtip-mounted propellers take over half of the total thrust usually provided by turbo-prop engines installed at inboard wing position. Drag breakdown analysis confirmed that the observed benefits mainly come from a reduction in the reversible drag component, increasing the effective wing span efficiency. Full article

(This article belongs to the Special Issue Drag Reduction in Turbulent Flows)

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16 pages, 5713 KiB

Open AccessArticle

Experimental Study on Performance of Transonic Compressor Cascade with Microgroove Polyurethane Coatings

by Liyue Wang, Cong Wang, Sheng Qin, Xinyue Lan, Gang Sun, Bo You, Meng Wang, Yongjian Zhong, Yan Hu and Huawei Lu

Fluids 2022, 7(6), 190; https://doi.org/10.3390/fluids7060190 - 2 Jun 2022

Cited by 3 | Viewed by 2048

Abstract

Due to the harsh operating environment of aero-engines, a surface structure that provides excellent aerodynamic performance is urgently required to save energy and reduce emissions. In this study, microgroove polyurethane coatings fabricated by chemical synthesis are investigated in terms of their effect on [...] Read more.

Due to the harsh operating environment of aero-engines, a surface structure that provides excellent aerodynamic performance is urgently required to save energy and reduce emissions. In this study, microgroove polyurethane coatings fabricated by chemical synthesis are investigated in terms of their effect on aerodynamic performance, which is a new attempt to investigate the impact on aerodynamic performance of compressor cascade at transonic speeds. This method reduces manufacturing and maintenance cost significantly compared with traditional laser machining. Wake measurements are conducted in the high-speed linear compressor cascade wind tunnel to evaluate the performance of cascade attached with different microgroove polyurethane coatings. Compared with the Blank case, the microgroove polyurethane coatings have the characteristic of reducing flow loss, with a maximum reducing rate of 5.87% in the area-averaged total pressure loss coefficient. The mechanism of flow loss control is discussed through analyzing the correlation between the total pressure distribution and turbulence intensity distribution. The results indicate that a large quantity of energy loss in the flow field due to turbulence dissipation and the reduction in viscous drag by microgroove polyurethane coatings relates to its effect on turbulence control. This paper demonstrates a great perspective on designing micro-nano surface structure for aero-engine applications. Full article

(This article belongs to the Special Issue Drag Reduction in Turbulent Flows)

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28 pages, 18372 KiB

Open AccessArticle

A Homogenization Approach for Turbulent Channel Flows over Porous Substrates: Formulation and Implementation of Effective Boundary Conditions

by Essam N. Ahmed, Sahrish B. Naqvi, Lorenzo Buda and Alessandro Bottaro

Fluids 2022, 7(5), 178; https://doi.org/10.3390/fluids7050178 - 20 May 2022

Cited by 3 | Viewed by 2400

Abstract

The turbulent flow through a plane channel bounded by a single permeable wall is considered; this is a problem of interest since a carefully chosen distribution of grains and voids in the porous medium can result in skin friction reduction for the flow [...] Read more.

The turbulent flow through a plane channel bounded by a single permeable wall is considered; this is a problem of interest since a carefully chosen distribution of grains and voids in the porous medium can result in skin friction reduction for the flow in the channel. In the homogenization approach followed here, the flow is not resolved in the porous layer, but an effective velocity boundary condition is developed (and later enforced) at a virtual interface between the porous bed and the channel flow. The condition is valid up to order two in terms of a small gauge factor, the ratio of microscopic to macroscopic length scales; it contains slip coefficients, plus surface and bulk permeability coefficients, which arise from the solution of microscale problems solved in a representative elementary volume. Using the effective boundary conditions, free of empirical parameters, direct numerical simulations are then performed in the channel, considering a few different porous substrates. The results, examined in terms of mean values and turbulence statistics, demonstrate the drag-reducing effects of porous substrates with streamwise-preferential alignment of the solid grains. Full article

(This article belongs to the Special Issue Drag Reduction in Turbulent Flows)

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