Turbulence eddy turnover time

Equation (3.82) illustrates the importance of the scalar spectral energy transfer rate in determining the scalar dissipation rate in high-Reynolds-number turbulent flows. Indeed, near spectral equilibrium, 7 (/cd, 0 (like Tu(kDi, 0) will vary on time scales of the order of the eddy turnover time re, while the characteristic time scale of (3.82) is xn <[Pg.99]

To determine the turbulent reaction rate, conceptualize the reaction as a single-step process where the fuel and oxidant are converted to a product. Furthermore, visualize a turbulent flame as a collection of burning eddies. For a reaction to take place, the fuel and oxidant must be simultaneously available, and the reaction product must be removed properly. That is, the reaction can be limited by the availability of fuel, oxidant, or by the removal of product. Once the fuel and oxidant are mixed, combustion takes place, on average, within one eddy turnover time, k/e, so that the reaction rate can be written as... 

Unfortunately, the simplified engineering method doesn t provide much information about the structure of turbulence and the dynamics of the interactions between the turbulent vortexes. The only structural information extracted from the second moments in relation to the structure of turbulence is the length scale. A, and the only information in relation to the dynamics of turbulence is the time constant representing the eddy turnover time, A A A ... 

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