A new diagnostic for fluid flow instability and turbulence generation

Picture rights: Miguel Teixeira.

Turbulence controls mixing in both natural and industrial processes. The Richardson number (Ri) is a universal diagnostic for turbulence generation in stratified flows, being a ratio between stabilization due to density stratification and instability due to flow shear. While stratification always acts in the vertical, flow shear can act in any direction. As the traditional Ri omits turbulence generation by horizontal shear, we propose a new Ri that includes horizontal shear, to improve the detection and modelling of mixing. This new turbulence diagnostic is tested against aviation clear-air turbulence observations in the atmosphere, where horizontal shear is important near jets.