Drag Reduction in Turbulent Flows, 2nd Edition

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

Deadline for manuscript submissions: 28 February 2025 | Viewed by 2182

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Theoretical and Applied Aerodynamic Research Group, University of Naples Federico II, 80125 Naples, Italy
Interests: aerodynamics; CFD; fluid dynamics; turbulence; drag reduction
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Special Issue Information

Dear Colleagues,

In recent years, concerns over environmental pollution have become one of the main issues for the world’s governments, which are forcing manufacturers to reduce the environmental impact of their products. Aviation, automotive, nautical, and other industries are involved in a significant effort to achieve the objective of reducing pollutant emissions, thus also leading to economic benefits. In the aviation sector, the reduction in pollutant emissions is clearly linked to the aerodynamic efficiency of aircrafts; this has led to an increasing interest in drag reduction, which has become a keyword for next-generation aircrafts and for lifting bodies in general. The scientific community is involved in the research of new technologies or in the improvement of well-known drag reduction techniques. Reductions in aerodynamic and fluid dynamic drag can be attained through basic mechanisms such as the control of separation, the control of transition, and a reduction in skin friction in the turbulent flow region. There are two categories of devices that are able to initiate the drag reduction mechanism: active and passive devices. Active devices usually involve a moving surface, such as oscillating walls or micro-actuators, and require an energy input. Passive devices are more appealing because they do not require energy input or natural laminar flow (NLF) control, and riblets are probably the most interesting passive drag reduction technique in the aeronautical field. Polymers, surfactants, and super hydrophobic surfaces are very appealing in marine engineering. The scope of this Special Issue of Fluids covers all theoretical, analytical, computational, and experimental studies concerning drag reduction in turbulent flows. Applications of drag reduction techniques in different industrial fields, such as aerospace, automotive, marine engineering, and others, are welcome. Research on and applications of recent developments in the manufacturing of drag reduction devices are also encouraged.

Dr. Benedetto Mele
Guest Editor

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Keywords

  • drag reduction
  • boundary layer control
  • turbulence
  • aerodynamics
  • fuel consumption reduction
  • aviation
  • automotive
  • nautical

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Published Papers (2 papers)

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Research

17 pages, 3956 KiB  
Article
Adaptive Free-Form Deformation Parameterization Based on Spring Analogy Method for Aerodynamic Shape Optimization
by Jinxin Zhou, Xiaojun Wu, Hongyin Jia and Jing Yu
Fluids 2024, 9(11), 256; https://doi.org/10.3390/fluids9110256 - 31 Oct 2024
Viewed by 446
Abstract
An adaptive Free-Form Deformation parameterization method based on a spring analogy is presented for aerodynamic shape optimization problems. The proposed method effectively incorporates the gradients of the objective and constraint functions, achieving automatic control point adjustment based on variances in design variable components. [...] Read more.
An adaptive Free-Form Deformation parameterization method based on a spring analogy is presented for aerodynamic shape optimization problems. The proposed method effectively incorporates the gradients of the objective and constraint functions, achieving automatic control point adjustment based on variances in design variable components. To evaluate the performance of the adaptive FFD parameterization method, two 2D airfoil optimization design problems are examined. The optimization of the RAE2822 airfoil with 12, 18 and 24 design variables demonstrates superior results for the adaptive method compared to uniform parameterization. The adaptive method requires fewer iterations and achieves lower objective function values. Additionally, the optimization design from NACA0012 to RAE2822 airfoil with 18 design variables shows that the adaptive parameterization method achieves a lower drag coefficient while satisfying the optimization objective. This validates the method’s capability to finely adjust airfoil shapes and capture more optimal design points by exerting stronger control over local shapes. The proposed adaptive FFD parameterization method proves highly effective for optimizing aerodynamic shapes, offering stability and efficiency in the early stages of optimization, even with a limited number of design variables. Full article
(This article belongs to the Special Issue Drag Reduction in Turbulent Flows, 2nd Edition)
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23 pages, 40945 KiB  
Article
Reducing Aerodynamic Drag on Roof-Mounted Lightbars for Emergency Vehicles
by Michael Gerard Connolly, Malachy J. O’Rourke and Alojz Ivankovic
Fluids 2024, 9(5), 113; https://doi.org/10.3390/fluids9050113 - 11 May 2024
Cited by 1 | Viewed by 1269
Abstract
This paper investigates the impact of contemporary lightbars on vehicle fuel efficiency with a focus on quantifying their effects on fuel consumption and exploring strategies to improve drag performance through modifications. Simulations showed an 8–11% increase in drag for square-back vehicles, with greater [...] Read more.
This paper investigates the impact of contemporary lightbars on vehicle fuel efficiency with a focus on quantifying their effects on fuel consumption and exploring strategies to improve drag performance through modifications. Simulations showed an 8–11% increase in drag for square-back vehicles, with greater penalties outlined for vehicles with rear-slanting roofs. Given the moderate drag increase, the impact on the driving range, especially for electric vehicles, remains minimal, supporting the continued use of external lightbars. Positioning experiments suggest marginal drag reductions when lowering the lightbar to its lowest position due to additional drag effects that can be caused by the mounting mechanism in its condensed form. Angling the lightbar showed negligible drag increases up to an angle of 2.5 degrees, but beyond that, a 4% increase in drag was observed for every additional 2.5 degrees. Additionally, fitting drag-reducing ramps ahead of the lightbar yielded no significant drag savings. Noise analysis identified that the lightbar’s wake and rear surfaces were responsible for the largest production of noise. The optimal lightbar design was found to incorporate overflow rather than underflow and rear tapering in sync with roof curvature. Appendable clip-on devices for the lightbar, particularly rear clip-ons, demonstrated appreciable drag reductions of up to 2.5%. A final optimised lightbar design produced a minimal 2.8% drag increase when fitted onto an unmarked vehicle, representing a threefold improvement compared with the current generation of lightbars. This study advances the field of lightbar aerodynamics by precisely quantifying drag effects by using highly detailed geometry and examines the significance of optimal positioning, angle adjustment, and appendable clip-on devices in greater depth than any existing published work. Full article
(This article belongs to the Special Issue Drag Reduction in Turbulent Flows, 2nd Edition)
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