A Study of Active and Inactive Regions in Turbulence by Photon Correlation Spectroscopy
In a turbulent flow, it is the relative velocity V(R) between a pair of particles separated by a distance R, that is important rather than the instantaneous velocity v(t) at a point in the fluid1. If v1 and v2 are the velocities of a pair of particles seeded in the fluid with a separation R, then the velocity difference between them at the same instant of time will be V(R) = v1 − v2. By virtue of the Central limit theorem and Gaussian random nature of v1 and v2, the probability distribution function for the relative velocity fluctuations V(R) will have the form2where ρ defines the correlation between v1 and v, and has a Lorentzian form. In our experiment, we calculated Pρ(V(R)) from the measurements of intensity autocorrela-tion function g(τ) behind a grid of mesh size 3 mm. using the equation2 given below and is displayed in Fig. 1.
KeywordsDecay Time Photon Correlation Spectroscopy Central Limit Theorem Probability Distribution Function Slit Width
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© Springer Science+Business Media New York 1996