Special Issue "Recent Advances on Modeling, Analysis and Applications of Unsteady Aerodynamics"

A special issue of Fluids (ISSN 2311-5521).

Deadline for manuscript submissions: closed (10 April 2021).

Special Issue Editor

Prof. Dr. Haithem Taha
E-Mail Website
Guest Editor
Mechanical and Aerospace Engineering Department, University of California, Irvine, CA 92697, USA
Interests: unsteady aerodynamics; reduced-order modeling; bio-inspired flight; flight mechanics and control; geometric nonlinear control; variational principles

Special Issue Information

Dear Colleagues,

Since its early development in the first half of the last century, the classical theory of unsteady aerodynamics has served the community quite well in studying the flow dynamics over oscillating airfoils and rotary wings, the flutter problem of airplane wings and wind turbine blades, and bio-inspired flight. However, this linear theory has a limited region of applicability confined to inviscid, incompressible, and small angle-of-attack applications. Over the past two decades, the community’s interest in unsteady aerodynamics has been rejuvenated. This research flurry is partly to extend the classical theory to account for viscous, compressible, or high alpha effects, and partly to deepen our understanding of the unconventional flow dynamics in interesting applications such as bio-inspired flight.

This Special Issue aims to present some of the recent advances in the modeling and analysis of unsteady fluid flows. Topics include theoretical modeling of unsteady aerodynamics, high-alpha unsteady aerodynamics, bio-inspired flight, unsteady flow control, data-driven (e.g., machine learning) modeling of unsteady fluid dynamics, reduced-order modeling, and the recent techniques of principal component analysis (PCA); e.g., the dynamic mode decomposition (DMD).

Prof. Dr. Haithem Taha
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 papers will be 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 1600 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

  • unsteady aerodynamics
  • high-alpha aerodynamics
  • flow control
  • oscillating airfoils
  • bio-inspired flight
  • reduced-order modeling

Published Papers (3 papers)

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Research

Article
Turbulence Characteristics of the Flexible Circular Cylinder Agitator
Fluids 2021, 6(7), 238; https://doi.org/10.3390/fluids6070238 - 30 Jun 2021
Viewed by 501
Abstract
A flexible protruding surface was employed as the flow disturbance to promote turbulence at the area of interest. An ultrasonic velocity profiler, UVP technique, was used to study the mean and fluctuating flow properties in the near wake of the rigid and flexible [...] Read more.
A flexible protruding surface was employed as the flow disturbance to promote turbulence at the area of interest. An ultrasonic velocity profiler, UVP technique, was used to study the mean and fluctuating flow properties in the near wake of the rigid and flexible protruding surface in a water tunnel. The polymer based, ethylene-vinyl acetate (EVA) with an aspect ratio of AR = 10, 12, 14, 16 was used as the flexible circular cylinder, and submerged in a flow at Re = 4000, 6000 and 8000. The motion of the cylinder altered the fluid flow significantly. As a means to quantify turbulence, the wakes regions and production terms were analyzed. In general, the flexible cylinders show better capability in augmenting the turbulence than the rigid cylinder. The results show that the turbulence production term generated by the flexible cylinder is higher than that of rigid cylinder. The localized maximum shear production values have increased significantly from 131%, 203% and 94% against their rigid counterparts of AR = 16 at the Re = 4000, 6000 and 8000, respectively. The performance of turbulence enhancement depends heavily on the motion of the cylinder. The findings suggest that the turbulence enhancement was due to the oscillation of the flexible cylinder. The results have concluded that the flexible cylinder is a better turbulence generator than the rigid cylinder, thus improving the mixing of fluid through augmented turbulent flow. Full article
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Article
Some Observations of the Behaviour of an Adverse Pressure Gradient Laminar Boundary Layer under Wake Impingement
Fluids 2021, 6(6), 199; https://doi.org/10.3390/fluids6060199 - 26 May 2021
Viewed by 1886
Abstract
The problem of laminar to turbulent transition in a boundary layer flow subjected to an adverse pressure gradient is relevant to many engineering applications. Under such conditions, the initially laminar flow within the boundary layer can undergo separation and then become turbulent upon [...] Read more.
The problem of laminar to turbulent transition in a boundary layer flow subjected to an adverse pressure gradient is relevant to many engineering applications. Under such conditions, the initially laminar flow within the boundary layer can undergo separation and then become turbulent upon reattachment, as transition is triggered by instabilities within the separated shear layer. In turbomachinery blades with high loading, the transition mechanism is further complicated by the presence of periodic wake disturbances shed by blades that move relatively in the upstream flow. The paper reports an experimental study of the effect of wake disturbances generated upstream on the development of a laminar boundary layer over a flat plate imposed with an adverse pressure gradient that is typical of a highly loaded front-stage compressor blade. Detailed velocity measurements using a hotwire are performed along the plate and the results are analysed both in the time domain and the frequency domain. Description of the major features identified is provided and the leading mechanisms that trigger the transition process are identified to be a possible combination of amplified Tollmien–Schlichting waves and the roll-up of vortices due to the Kelvin–Helmholtz instability of the separated shear layer. Full article
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Article
Vortex Dynamics Study and Flow Visualization on Aircraft Model with Different Canard Configurations
Fluids 2021, 6(4), 144; https://doi.org/10.3390/fluids6040144 - 07 Apr 2021
Viewed by 701
Abstract
Canard configuration on fighter planes is essential for regulating flow and the occurrence of vortex interactions on the main wing, one of which is to delay stall. Stall delays are useful when the aircraft is making maneuvering or short-landing. This study observed the [...] Read more.
Canard configuration on fighter planes is essential for regulating flow and the occurrence of vortex interactions on the main wing, one of which is to delay stall. Stall delays are useful when the aircraft is making maneuvering or short-landing. This study observed the effect of canard configuration on various fighter aircraft models. Fighter models represented the different canard configurations, such as Sukhoi SU-30 MKI, Chengdu J-10, and Eurofighter Typhoon. Water tunnels and computational fluid dynamics (CFD) have made it easier to visualize the flow and aerodynamic forces. The results showed that at a low angle of attack (AoA) < 30°, the Chengdu J-10 and Eurofighter models had the highest lift force coefficient (Cl). When at high AoA, Cl’s highest value occurred on the Sukhoi SU-30 model with a value of 1.45 at AoA 50°. Meanwhile, the highest AoA that still had a high Cl value occurred on the Sukhoi SU-30 and Chengdu J-10 aircraft models, namely at AoA 55° with Cl values more than 1.1. The canard position in the upper of the wing would increase the Cl at low AoA, while the parallel canard position could delay the stall. Full article
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