Decay of Swirling Flow in Circular Pipe

Abstract

The decay of the intensity of swirl downstream is described with circulation in swirling pipe flow.
From theoretical considerations it was found that the dimensionless circulation Γ^* should be a function of the product of two dimensionless factors, (Z/R) and (ν/R²ω_i).
From the results of experiments under several conditions, the relation between Γ^* and (Z/R) (ν/R²ω_i) can be expressed as the following equation :
Γ^*=γexp {-κ (Z/R) (ν/R²ω_i)}
where κ is a function of streamwise Reynolds number, Re=DU_av/ν, and γ is a characteristic constant of the apparatus. In the range of Re> 5, 000 and Re<2, 000, κ shows constant values 7.1×10³ and 2.7×10³, respectively. And in the range of 2, 000<Re<5, 000, κ changes with Re, and, with respect to the decay of swirl, this range is presumed to be the transitional range from Re<2, 000 to Re>5, 000.