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Activity title

Reynolds Number Scaling Effects on Swept Wing Flows

Activity Reference

AVT-298

Panel

Applied Vehicle Technology

Security Classification

NATO UNCLASSIFIED

Status

Active

Activity type

RTG

Start date

2018

End date

2020

Keywords

Aerodynamics, Leading edge, Reynolds, Scale, Separation, Trailing edge, Transition, Wing

Background

Future combat air vehicle requirements are likely to result in wing shapes which will have challenging stability and control characteristics. Examples include demonstrator programmes such as X-45C and X-47B in the US and nEUROn and Taranis in Europe. Experience in these programmes, and in previous in research activities (including AVT-161, 201, 183), has shown that the aerodynamics of wings in this class is challenging to predict using numerical tools and that low Reynolds number wind tunnel testing does not produce results that are adequately representative of full scale vehicles. Without further research to understand these problems, the result will be that conservative estimates must be used for aircraft sizing, resulting in larger and more costly vehicle designs. There are similar issues for future civil and military blended or hybrid wing-body (BWB/HWB) configurations, which widens the appeal of this activity and hence improves access to resources and expertise. A complimentary topic for this activity is Reynolds number effects on intake and propulsion integration aerodynamics for unconventional future configurations. Main motivations: • To improve understanding of the full scale aerodynamics of this class of wing and how this differs from what is measured at low Reynolds numbers or predicted with CFD • Understand implications for propulsion integration • To minimise the safety margin that has to be allowed in combat aircraft design to account for uncertainty in maximum usable lift determined from sub-scale wind tunnel test and/or CFD prediction • To identify improved ways of applying CFD methods to the prediction of these flows and, where appropriate, to recommend improvements to the methods themselves. • To identify ways in which traditional approaches to transition fixing could be improved for sub-scale wind tunnel testing of this class of wing • To propose ways of improving the effectiveness of wing design methods Addressing this should improve our ability to design cost effective future air vehicles in the future and reduce risk in their development.

Objectives

• Draw together existing expertise and knowledge in this field, including AVT-183 and AVT-201 participants • Define and agree one or more representative test cases • Perform high and low Reynolds number wind tunnel testing on a suitable wing configuration • Share variable Reynolds number intake dataset • CFD investigations including studies into turbulence models and transition prediction • Understand and interpret the results

Topics

• Understanding flow physics • Boundary layer development and its influence • Leading-edge and trailing-edge flow breakdown mechanisms • Separated and vortex dominated flows • Intake boundary layer ingestion • CFD modelling • Boundary layer and transition modelling • Turbulence modelling • Design of relevant experimental test cases and identification of appropriate test facilities • Wind tunnel test technique • Cryogenic testing • Transition fixing approaches

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