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Fluids
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External Aerodynamics
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External Aerodynamics

A special issue of Fluids (ISSN 2311-5521). This special issue belongs to the section "Turbulence".

Deadline for manuscript submissions: closed (30 June 2022) | Viewed by 14979

Special Issue Editor

Dr. Ivette Rodríguez

E-Mail Website
Guest Editor
Turbulence and Aerodynamics Research Group, Universitat Politècnica de Catalunya, 08222 Terrassa, Spain
Interests: bluff bodies; wakes; turbulence; aerodynamics; flow control; fluid–structure interaction
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

In the framework of modern engineering and aerodynamics, as the society becomes more aware of the effects that climate change can have in the environment, there is an increasing need to boost efficiency and to reduce environmental impact. Transport industry is concerned with the new challenges to face regarding performance and sustainability.  In this sense, external aerodynamics analysis is crucial for the optimal design of the new generation of ground and air vehicles, especially when it comes to improve their aerodynamic efficiency and reduce fuel consumption. 

This special issue targets the most recent contributions involving external aerodynamics studies applied to ground and air vehicles.   Potential topics include, but are not limited to the following:

  • Numerical and experimental techniques applied to the study of external aerodynamics
  • Drag reduction mechanisms and devices to improve aerodynamic efficiency
  • Boundary layer and wake flow control
  • Aerodynamic shape optimisation of vehicles
  • Turbulence modelling for analysis of unsteady external flows
  • Data-driven methods applied to aerodynamic optimisation
  • Coherent structures and reduced order modelling
  • Aeroacoustics

Dr. Ivette Rodríguez
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Fluids is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • wind tunnel testing and experimental data
  • computational fluid dynamics
  • numerical modeling
  • flow control
  • aeroacoustics
  • reduced order models
  • optimisation
  • fluid-structure interaction

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Published Papers (4 papers)

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Research

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23 pages, 44891 KiB  
Article
On the Wake Dynamics of an Oscillating Cylinder via Proper Orthogonal Decomposition
by Benet Eiximeno, Arnau Miró, Juan Carlos Cajas, Oriol Lehmkuhl and Ivette Rodriguez
Fluids 2022, 7(9), 292; https://doi.org/10.3390/fluids7090292 - 2 Sep 2022
Cited by 4 | Viewed by 2634
Abstract
The coherent structures and wake dynamics of a two-degree-of-freedom vibrating cylinder with a low mass ratio at Re=5300 are investigated by means of proper orthogonal decomposition (POD) of a numerical database generated using large-eddy simulations. Two different reduced velocities of [...] Read more.
The coherent structures and wake dynamics of a two-degree-of-freedom vibrating cylinder with a low mass ratio at Re=5300 are investigated by means of proper orthogonal decomposition (POD) of a numerical database generated using large-eddy simulations. Two different reduced velocities of U*=3.0 and U*=5.5, which correspond with the initial and super-upper branches, are considered. This is the first time that this kind of analysis is performed in this kind of system in order to understand the role of large coherent motions on the amplification of the forces. In both branches of response, almost 1000 non-correlated in-time velocity fields have been decomposed using the snapshot method. It is seen that a large number of modes is required to represent 95% of the turbulent kinetic energy of the flow, but the first two modes contain a large percentage of the energy as they represent the wake large-scale vortex tubes. The energy dispersion of the high-order modes is attributed to the cylinder movement in the inline and cross-stream directions. Substantially different POD modes have been found in the two branches. While the first six modes resemble those observed in the static cylinder or in the initial branch of a one-degree of freedom cylinder in the initial branch, the modes not only contain information about the wake vortexes in the super-upper branch but also about the formation of the 2T vortex pattern and the Taylor–Görtler structures. It is shown that the 2T vortex pattern is formed by the interplay between the Taylor–Görtler stream-wise vortical structures and the cylinder movement and is responsible for the increase in the lift force and larger elongation in the super-upper branch. Full article
(This article belongs to the Special Issue External Aerodynamics)
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23 pages, 27008 KiB  
Article
Dynamic Stall Characteristics of Pitching Swept Finite-Aspect-Ratio Wings
by Al Habib Ullah, Kristopher L. Tomek, Charles Fabijanic and Jordi Estevadeordal
Fluids 2021, 6(12), 457; https://doi.org/10.3390/fluids6120457 - 16 Dec 2021
Cited by 7 | Viewed by 2871
Abstract
An experimental investigation regarding the dynamic stall of various swept wing models with pitching motion was performed to analyze the effect of sweep on the dynamic stall. The experiments were performed on a wing with a NACA0012 airfoil section with an aspect ratio [...] Read more.
An experimental investigation regarding the dynamic stall of various swept wing models with pitching motion was performed to analyze the effect of sweep on the dynamic stall. The experiments were performed on a wing with a NACA0012 airfoil section with an aspect ratio of AR = 4. The experimental study was conducted for chord-based Reynolds number Rec =2×105 and freestream Mach number Ma=0.1. First, a ‘particle image velocimetry’ (PIV) experiment was performed on the wing with three sweep angles, Λ=0o, 15o, and 30o, to obtain the flow structure at several wing spans. The results obtained at a reduced frequency showed that a laminar separation bubble forms at the leading edge of the wing during upward motion. As the upward pitching motion continues, a separation burst occurs and shifts towards the wing trailing edge. As the wing starts to pitch downward, the growing dynamic stall vortex (DSV) vortex sheds from the wing’s trailing edge. With the increasing sweep angle of the wing, the stall angle is delayed during the dynamic motion of the wing, and the presence of DSV shifts toward the wingtip. During the second stage, a ‘turbo pressure-sensitive paint’ (PSP) technique was deployed to obtain the phase average of the surface pressure patterns of the DSV at a reduced frequency, k=0.1. The phase average of pressure shows a distinct pressure map for two sweep angles, Λ=0o, 30o, and demonstrates a similar trend to that presented in the published computational studies and the experimental data obtained from the current PIV campaign. Full article
(This article belongs to the Special Issue External Aerodynamics)
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21 pages, 5751 KiB  
Article
On the Characteristics of the Super-Critical Wake behind a Circular Cylinder
by Ivette Rodriguez and Oriol Lehmkuhl
Fluids 2021, 6(11), 396; https://doi.org/10.3390/fluids6110396 - 3 Nov 2021
Cited by 3 | Viewed by 2556
Abstract
The flow topology of the wake behind a circular cylinder at the super-critical Reynolds number of Re=7.2×105 is investigated by means of large eddy simulations. In spite of the many research works on circular cylinders, there are [...] Read more.
The flow topology of the wake behind a circular cylinder at the super-critical Reynolds number of Re=7.2×105 is investigated by means of large eddy simulations. In spite of the many research works on circular cylinders, there are no studies concerning the main characteristics and topology of the near wake in the super-critical regime. Thus, the present work attempts to fill the gap in the literature and contribute to the analysis of both the unsteady wake and the turbulent statistics of the flow. It is found that although the wake is symmetric and preserves similar traits to those observed in the sub-critical regime, such as the typical two-lobed configuration in the vortex formation zone, important differences are also observed. Owing to the delayed separation of the flow and the transition to turbulence in the attached boundary layer, Reynolds stresses peak in the detached shear layers close to the separation point. The unsteady mean flow is also investigated, and topological critical points are identified in the vortex formation zone and the near wake. Finally, time-frequency analysis is performed by means of wavelets. The study shows that in addition to the vortex shedding frequency, the inception of instabilities that trigger transition to turbulence occurs intermittently in the attached boundary layer and is registered as a phenomenon of variable intensity in time. Full article
(This article belongs to the Special Issue External Aerodynamics)
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Review

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15 pages, 6126 KiB  
Review
Flow Control in Wings and Discovery of Novel Approaches via Deep Reinforcement Learning
by Ricardo Vinuesa, Oriol Lehmkuhl, Adrian Lozano-Durán and Jean Rabault
Fluids 2022, 7(2), 62; https://doi.org/10.3390/fluids7020062 - 1 Feb 2022
Cited by 40 | Viewed by 5812
Abstract
In this review, we summarize existing trends of flow control used to improve the aerodynamic efficiency of wings. We first discuss active methods to control turbulence, starting with flat-plate geometries and building towards the more complicated flow around wings. Then, we discuss active [...] Read more.
In this review, we summarize existing trends of flow control used to improve the aerodynamic efficiency of wings. We first discuss active methods to control turbulence, starting with flat-plate geometries and building towards the more complicated flow around wings. Then, we discuss active approaches to control separation, a crucial aspect towards achieving a high aerodynamic efficiency. Furthermore, we highlight methods relying on turbulence simulation, and discuss various levels of modeling. Finally, we thoroughly revise data-driven methods and their application to flow control, and focus on deep reinforcement learning (DRL). We conclude that this methodology has the potential to discover novel control strategies in complex turbulent flows of aerodynamic relevance. Full article
(This article belongs to the Special Issue External Aerodynamics)
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