Numerical analysis of the effect of non-Newtonian properties of fluids on fluid-hammer phenomenon in the pipes

In this paper, the behavior of a non-Newtonian polymer through fluid hammer phenomenon in the pipe investigates. Special properties of this fluid such as nonlinear relation between stress and strain, having relaxation time make the pressure wave resulting from this phenomenon to behave differently from a Newtonian fluid. The system under investigation is reservoir-pipe-valve system and the equations representing the conservation of mass and momentum govern the transitional flow in the pipes. In the modeling of the equations finite difference numerical method is used. After defining non-dimensional numbers of governing equations, the effect of Deborah and Reynolds numbers on pressure historic at critical points such as at valve and midpoint investigate. The modeling results show that about investigating sensitivity to the Reynolds number, the pressure wave produced by non-Newtonian polymer shows a sensitivity similar to that of Newtonian fluids. It was also found that an increase in the Deborah number, indicating the elasticity of the polymer, affects the reduction of tensions and increases the oscillation height and consequently attenuation time of the created transient flow to be longer. It has been observed that in similar conditions, the phenomenon of line packing in viscoelastic fluid is slightly higher than in Newtonian fluid. The reason for this is definitely related to the constant characteristic of the relaxation time, which is strongly inclined to maintain the incoming potential energy and resists the damping of the transfer flow, which causes a long damping time compared to the Newtonian fluid have more.