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CFD Analysis of Transition Models for Low-Reynolds Number Aerodynamics
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0009-0006-4360-587X
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0001-5294-1855
2025 (English)In: Applied Sciences, E-ISSN 2076-3417, Vol. 15, no 18, article id 10299Article in journal (Refereed) Published
Abstract [en]

Low Reynolds number flows are central to the performance of airfoils used in small unmanned aerial vehicles (UAVs), micro air vehicles (MAVs), and aerodynamic platforms operating in rarefied atmospheres. Consequently, a deep understanding of airfoil behavior and accurate prediction of aerodynamic performance are essential for the optimal design of such systems. The present study employs Computational Fluid Dynamics (CFD) simulations to analyze the aerodynamic performance of a cambered plate at a Reynolds number of 10,000. Two Reynolds-Averaged Navier–Stokes (RANS) turbulence models, 𝛾–𝑅𝑒𝜃 and 𝑘-𝑘𝐿-𝜔, are utilized, along with the Unsteady Navier–Stokes (UNS) equations. The simulation results are compared against experimental data, with a focus on lift, drag, and pressure coefficients. The models studied perform moderately well at small angles of attack. The 𝛾–𝑅𝑒𝜃 model yields the lowest lift and drag errors (below 0.17 and 0.04, respectively), while the other models show significantly higher discrepancies, particularly in lift prediction. The 𝛾–𝑅𝑒𝜃 model demonstrates good overall accuracy, with notable deviation only in the prediction of the stall angle. In contrast, the 𝑘-𝑘𝐿-𝜔 model and the UNS equations capture the general flow trend up to stall but fail to provide reliable predictions beyond that point. These findings indicate that the 𝛾–𝑅𝑒𝜃 model is the most suitable among those tested for low Reynolds number transitional flow simulations.

Place, publisher, year, edition, pages
MDPI, 2025. Vol. 15, no 18, article id 10299
Keywords [en]
low Reynolds number, airfoil performance, CFD
National Category
Fluid Mechanics
Research subject
Fluid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-114866DOI: 10.3390/app151810299ISI: 001579507500001Scopus ID: 2-s2.0-105017128136OAI: oai:DiVA.org:ltu-114866DiVA, id: diva2:2000135
Note

Validerad;2025;Nivå 2;2025-09-23 (u2);

Full text: CC BY license;

Available from: 2025-09-23 Created: 2025-09-23 Last updated: 2025-11-28Bibliographically approved
In thesis
1. Modeling and Analysis of Rotorcraft Airfoil Aerodynamics Under Martian Atmospheric Conditions
Open this publication in new window or tab >>Modeling and Analysis of Rotorcraft Airfoil Aerodynamics Under Martian Atmospheric Conditions
2025 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Throughout history, human curiosity and the desire to explore have driven advancements in engineering capabilities and technologies. These efforts have extended our reach beyond Earth, with Mars emerging as one of the most important targets for planetary exploration. While rovers and landers have traditionally been used to study planetary surfaces, rotorcraft and other aerial vehicles have recently shown great promise for exploring the Red Planet. Such vehicles can access diverse terrains that are difficult or impossible for conventional landers and rovers to reach. However, the unique characteristics of the Martian atmosphere present significant aerodynamic challenges that must be overcome to enable sustained and efficient flight. Successful operation under these conditions requires a deep understanding of low Reynolds number aerodynamics, due to the rarefied atmosphere, and the influence of environmental factors such as pervasive Martian dust.

The combination of low Reynolds number flows and suspended dust particles creates unique challenges for rotorcraft aerodynamics on Mars. This thesis investigates these challenges through Computational Fluid Dynamics (CFD) simulations, focusing on the performance of a cambered plate airfoil with 6% camber and 1% thickness, which is well suited to the Martian environment. The research addresses both fundamental aerodynamic phenomena and environmental effects, providing insights into model selection for accurate flow prediction, sensitivity of performance to Reynolds number variations, and the long-term impact of dust accumulation on airfoil behavior.

This work presents a comprehensive overview of the evolution of drone designs for planetary exploration, emphasizing the main aerodynamic and control challenges involved. Operating in planetary atmospheres introduces unique difficulties, particularly due to the low chord-based Reynolds numbers and the presence of floating dust particles that can affect both aerodynamics and system reliability. The aerodynamic behavior at Reynolds numbers on the order of 104 is investigated, focusing on the effect of increasing the rotor or chord dimension. Results show that increasing the Reynolds number from 20,000 to 50,000 does not significantly improve performance, as the formation of Laminar Separation Bubbles (LSBs) on the surface still occurs. The transition model used, γ–Reθ, is able to accurately capture bubble formation. However, its limitations are also identified through comparison with other models, among which  γ–Reθ is found to be the most reliable transition RANS model for these flows, since k-kL-ω fails to reproduce the correct post-stall behavior. Unsteady Navier–Stokes (UNS) simulations exhibit the same inability due to the absence of turbulence modeling; however, their lower computational cost makes them suitable for preliminary studies and acceptable for low angles of attack.

The accumulation of dust particles on the airfoil surface is also examined, showing that particle deposition alters the airfoil geometry and leads to measurable changes in aerodynamic performance. While the effect is modest in the short term, it could become significant over long exposure times. The results are obtained under simplifying assumptions, such as a smooth surface and no detachment of particles. Further refinement is achieved by simulating particle deposition on an airfoil exposed solely to wind, where the wind velocity is modeled using a simple stochastic approach. The simulations account for both particle accumulation and instantaneous detachment during the run, and additional detachment is evaluated in a post-processing step. The resulting surface modification is then used to study its effect on the aerodynamic performance, providing a more complete understanding of how dust environments influence drone operation in planetary exploration.

Overall, the findings contribute to a deeper understanding of low Reynolds number aerodynamics and environmental degradation mechanisms relevant to Martian rotorcraft. The results offer guidance for aerodynamic model selection, design optimization, and long-term operational strategies for future aerial exploration missions on Mars.

Place, publisher, year, edition, pages
Luleå University of Technology, 2025
Series
Doctoral thesis / Luleå University of Technology, ISSN 1402-1544
Keywords
aerodynamics, Martian rotorcraft, CFD, Laminar Separation Bubbles, dust accumulation
National Category
Vehicle and Aerospace Engineering Fluid Mechanics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-115156 (URN)978-91-8048-927-0 (ISBN)978-91-8048-928-7 (ISBN)
Public defence
2025-12-12, E632, Luleå University of Technology, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2025-10-17 Created: 2025-10-17 Last updated: 2025-11-26Bibliographically approved

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Giacomini, EnricoWesterberg, Lars-Göran

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