Experimental study of the flow in a helical circular tube

Abstract

The effect of torsion on the flow in a helical tube of circular cross-section is experimentally investigated over a range of Reynolds numbers from about 500 to 20000. Three cases of dimensionless curvature δ were studied, i.e. δ = 0.01, 0.05 and 0.1. The torsional parameter β0, which is defined as with dimensionless torsion τ, was considered for seven cases between 0.45 and 1.72. The results reveal rather large effect of torsion on the flow: the friction factor of the flow at a fixed δ deviates from that of the toroidally curved tube without torsion as β0 increases, and it decreases toward that of the straight tube as β0 further increases. It is also found that the torsion has a destabilizing effect on the flow. The critical Reynolds number at the onset of turbulence varies with β0 and has a minimum at β0 ≃ 1.3. The minimum critical Reynolds number at δ = 0.1 is about 800.