Flow and Reynolds number dependencies of one-dimensional vorticity fluctuations

Abstract

Although significant attention has been given to the evolution of various characteristics of turbulent velocity and scalar fields with R λ, the Taylor microscale Reynolds number, there is a scarcity of data relating to the dependence of vorticity statistics on R λ. In this paper, we examine the dependence on R λ (= 27–1067) of the statistics of the spanwise (or lateral) vorticity component ω z , obtained in different types of flows. Measurements in grid turbulence, circular cylinder wakes and plane and square jets issued from different geometry nozzles were made using a 4-hot-wire vorticity probe. The vorticity variance, normalized by Kolmogorov scales, satisfies local isotropy closely and does not depend on R λ or the type of flow. Vorticity spectra in grid and wake flows agree with isotropic calculations and evolve with R λ at low wavenumbers. In wakes, the spectra do not change significantly even at low wavenumbers when R λ is greater than about 160. By contrast, the vorticity spectra in jets show a significant departure from local isotropy at low wavenumbers, irrespectively of R λ. The pdf of the vorticity fluctuation exhibits good symmetry with single exponential tails for R λ < 160, independently of the flow. The tails stretch out to larger amplitudes and have a double exponential structure at largerR λ. Although the pdf depends on R λ, its dependence on the flow is small.