The authors focus on the study of pulsating fluid flows using the Herschel-Bulkley rheological model, which accounts for the presence of yield strength and nonlinear dependence of stress on strain rate. The Herschel-Bulkley model has been previously used to describe pulsating blood flow in blood vessels, particularly in the presence of abnormal narrowing called stenosis. The authors numerically investigate the effects of pressure drop fluctuations on velocity profiles, flow rates, friction, and the formation of quasi-solid zones in the flow, with specific attention given to pulsating flows of dilatant fluids and fluids with non-monotonic viscosity coefficients.
The paper novelty lies in investigating pulsating flows of non-Newtonian fluids possessing a yield strength. It provides an approximate analytical solution for these flows and explores the impact of pressure drop pulsations on the flow rate. The results indicate that the increase in flow rate is roughly proportional to the relative amplitude of pressure drop oscillations. The paper also delves into the discussion of energy requirements in pulsating flows compared to steady flows, emphasizing the importance of studying pulsating flows of non-Newtonian fluids in diverse applications.
The rheological properties of these fluids are characterized by the Herschel-Bulkley model, encompassing parameters such as yield strength \( (\tau_y )\), consistency \( (K) \), and power index \( (n) \). The study investigates the effects of pressure drop pulsations on velocity profiles, flow rates, friction, and the region where the fluid moves without deformation. It concludes that for fluids with a power index less than or equal to 1, the mean flow rate in pulsating flow surpasses that in the absence of pulsations. Conversely, for fluids with a power index greater than 1, the superimposition of pressure drop pulsations can either increase or decrease the mean flow rate, depending on the frequency and amplitude of oscillations.