Slop distance

S = ntul/f V can also be interpreted as a dimensionless relaxation time r, where tn/f is a characteristic time for particle motion and v/u] h a characteristic time for the turbulent fluctuations. Hence S" " = r". The viscous sublayer is the region near a smooth wall where momentum transport is dominated by the viscous forces, which are large compared with eddy diffusion of momentum. Fol lowing the usual practice and taking the sublayer thickness to extend to y = 5, particles with a slop distance < 5 would not reach the wall if the sublayer were truly stagnant. 

However, the experiments of Friedlander and Johnstone (1957) (Fig, 4.12a) and later measurements by Liu and Agarwai (1974) Fig. 4.12b) and others clearly demonstrated that particle deposition took place at values of S " < 5. The data show that particles penetrate the viscous sublayer and deposit even though their slop distance based on the r.m.s. fluctuating velocity in the core is insufficient to propel the particles through a completely stagnant... 

Numerical experiments provided the critical EPR density Acr 2.5. No stagnation is formed if A < Acr the profiles U(z) in the EPR bottom tend to a constant slop, and r0 = r(0) = const + 0. Stagnation begins at a certain distance Xs (Fig. 3.8) if A > Acr and then ranges to infinity. At this distance, the shear on the wall reaches the value r(Xs, 0) 0, and the computing program loses its stability. 

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