Estimating the integral length scale on turbulent flows from the zero crossings of the longitudinal velocity fluctuation

• Published in: Experiments in fluids 2020-09, Vol.61 (9), Article 199
• Main Authors: Mora, D. O., Obligado, M.
• Format: Article
• Language: English
• Subjects: Autocorrelation functions; Computational fluid dynamics; Computer simulation; Engineering; Engineering Fluid Dynamics; Engineering Sciences; Engineering Thermodynamics; Estimation; Fluid- and Aerodynamics; Fluids mechanics; Heat and Mass Transfer; Integrals; Mechanics; Research Article; Turbulence; Turbulent flow; Velocity measurement; Wind tunnels
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-020-03033-2

The integral length scale ( L ) is considered to be characteristic of the largest motions of a turbulent flow, and as such, it is an input parameter in modern and classical approaches of turbulence theory and numerical simulations. Its experimental estimation, however, could be difficult in certain conditions, for instance, when the experimental calibration required to measure L is hard to achieve (hot-wire anemometry on large scale wind-tunnels, and field measurements), or in ‘standard’ facilities using active grids due to the behaviour of their velocity autocorrelation function ρ ( r ) , which does not in general cross zero. In this work, we provide two alternative methods to estimate L using the variance of the distance between successive zero crossings of the streamwise velocity fluctuations, thereby reducing the uncertainty of estimating L under similar experimental conditions. These methods are applicable to a variety of situations such as active grids flows, field measurements, and large-scale wind tunnels. Graphic abstract