What is it about?

The Reynolds number is an important parameter to determine whether the flow is laminar or turbulent. The flow transition is, therefore, best characterized by the critical Reynolds number. The critical Reynolds number is of practical importance in many engineering applications, particularly in determining the aerodynamic characteristics of airplanes. However, the number of studies that investigated the critical Reynolds number over airfoil-shaped bodies is limited mainly due to the variety of affecting parameters and the complexity of the transition. In this study, we investigated the laminar-turbulent transition location over NACA 0012, NACA 0015, and NACA 0018 airfoil profiles determine the critical Reynolds number at an angle of attack of zero degrees.

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Why is it important?

The aerodynamic performance of airfoils and streamlined bodies, in general, is a strong function of the laminar-turbulent transition, and consequently, the critical Reynolds number. However, the number of studies in the literature that investigated the critical Reynolds number over airfoil-shaped bodies is limited mainly due to the variety of affecting parameters and the complexity of the transition. In this study, we have shown that the critical Reynolds number for flow over NACA 0012, NACA 0015, and NACA 0018 airfoils is 100,000, 50,000, and 35,000, respectively.

Perspectives

I hope this article provides a benchmark for the critical Reynolds number over the NACA 0012, NACA 0015, and NACA 0018 airfoils, although the paper is relatively limited at the current format. It should be noticed here that we estimated the lower critical Reynolds number which is not an indicator of a Reynolds number that ensures the flow can be considered fully turbulent. We suggest considering a value 4-5 times bigger than the lower critical Reynolds number reported in this study to ensure a fully developed turbulent flow over the NACA 0012, NACA 0015, and NACA 0018 airfoils.

Kianoosh Yousefi
University of Delaware

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This page is a summary of: Determination of the Critical Reynolds Number for Flow over Symmetric NACA Airfoils, January 2018, American Institute of Aeronautics and Astronautics (AIAA),
DOI: 10.2514/6.2018-0818.
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