Text: Reynolds Numbers: In 1883, Osborne Reynolds experimented with laminar and turbulent flow. His basic experiment was to inject a dye in a small section of fluid flowing in a tube and find where the flow changed from laminar to turbulent flow. He found that the flow could change abruptly and always happened where the following ratio occurred. density x speed x length (see below) ------------------------- viscosity (see below) (The length for Reynolds was tube diameter but can be any characteristic length such as wing chord.) (The viscosity of a fluid is the tendency to resist shear deformation. It is then the friction resistance to distortion of shape.) If the right set of units is chosen, then this ratio is dimensionless, and is called a Reynolds Number. D x S x L R.N. = -------- V This ratio is also proportional to the ratio of inertial forces to viscous forces or: inertial D x S x L ------ = ------- viscous V

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