Direct Numerical Simulations of High-Speed Turbulent Boundary Layers Over Riblets

Abstract

Direct numerical simulations (DNS) of spatially developing turbulent boundary layers over riblets with a broad range of riblet spacings are conducted to investigate the effects of riblets on skin friction at high speeds. Zero-pressure gradient boundary layers under two flow conditions (Mach 2:5 with Tω/Tr= 1 and Mach 7:2 with Tω/Tr = 0.5) are considered. The DNS results show that the drag-reduction curve (ΔCf/Cf vs ℓ+g) at both supersonic speeds follows the trend of low-speed data and consists of a 'viscous' regime for small riblet size, a 'breakdown' regime with optimal drag reduction, and a 'drag-increasing' regime for larger riblet sizes. Atℓ+g ≈ 10 (corresponding to s+ ≈ 20 for the current triangular riblets), drag reduction of approximately 7% is achieved at both Mach numbers, and confirms the observations of the few existing experiments under supersonic conditions. The Mach- number dependence of the drag-reduction curve occurs for riblet sizes that are larger than the optimal size, with smaller slopes of ΔCf/Cf for larger freestream Mach numbers. The Reynolds analogy holds with 2Ch/Cf approximately equal to that of at plates for both drag-reducing and drag-increasing configurations.

Meeting Name

52nd AIAA Aerospace Sciences Meeting - AIAA Science and Technology Forum and Exposition, SciTech 2014 (2014: Jan. 13-17, National Harbor, MD)

Department(s)

Mechanical and Aerospace Engineering

Research Center/Lab(s)

Center for High Performance Computing Research

Keywords and Phrases

Aerodynamics; Aerospace Engineering; Direct Numerical Simulation; Turbulence; Freestream Mach Number; Optimal Size; Reynolds Analogy; Riblets; Spatially Developing Turbulent Boundary Layers; Supersonic Speed; Turbulent Boundary Layers; Drag Reduction

International Standard Book Number (ISBN)

978-1624102561

Document Type

Article - Conference proceedings

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2014 American Institute of Aeronautics and Astronautics (AIAA), All rights reserved.

Publication Date

01 Jan 2014

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