Experimental study of the flow in a helical circular tube

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 β 0 , 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 β 0 increases, and it decreases toward that of the straight tube as β 0 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 β 0 and has a minimum at β 0 ≃ 1.3. The minimum critical Reynolds number at δ = 0.1 is about 800.