Long wavelength analysis amendment on the cilia beating assisted peristalsis in a tube

This work delves into the peristaltic rheology of two-wave sinusoidal cilia beating within a tubular pipe. Cilia movement drives the dynamic phenomenon of peristaltic fluid flow. Employing the traditional long-wavelength lubrication assumption, the flow equations are transformed into similarity form. The main objective is to take into account the true peristaltic-ciliary motion effects. We then derive analytical solutions for the radial and axial velocities of fluid particles within the tube. Notably, at this leading approximation level, the impacts of cilia beating are negligible, suggesting the motion is solely driven by peristaltic surface waves. However, analyzing the correction to the long-wavelength limit reveals the emergence of ciliated boundary effects through their largely eccentric elliptic paths. This correction enables us to extract expressions for the pressure gradient, stream function, axial and radial velocities, resultant pressure rise, and drag force, all based on the time-averaged mean flow rate across the pipe. Finally, we present a general discussion of fluid rheology due to cilia-assisted peristaltic motion, illustrated with informative graphical displays. It is shown that the drag force on the tube walls owing to the cilia beating waves in biology or biomedical applications necessitates addition of correction terms to the traditional long-wavelength adoption.