Experimental Study of the Front Velocity in an Interfacial flow across a U-shaped tube

The pressure-driven displacement flow of two immiscible fluids (water and diesel) is experimentally studied in a U-shaped tube. The diesel is injected to the U-tube which is filled with water, discharging it from another end. The flow patterns and the local front velocity (Vf) as a function of Reynolds number and the flow curvature (θ) are examined. At low Reynolds numbers, buoyancy force of water exerted to the diesel front is dominant. The Kelvin-Helmholtz instabilities disturb the interface. By increasing the Reynolds number, the inertia force of diesel gradually overcomes the buoyancy. Depending on the Reynolds number the bamboo waves can be observed. It was found that Vf is highly dependent on the Reynolds number along the flow. Using a normalized front velocity, an empirical relationship is developed to express the front velocity in terms of θ.