Computational Analysis of Unsteady Swirling Flow Around a Decelerating Rotating Porous Disk in Nanofluid

Here, we analyze the unsteady nanofluid flow triggered around a decelerating (permeable) rotating disk immersed in an otherwise calm environment. The present model assumes that disk angular velocity follows inversely linear time dependency. By following a similarity approach, the distributions of velocity and thermal fields above the disk are estimated numerically for six nanoparticle materials, namely Ag, Cu, CuO, Fe3O4, TiO2 and Al2O3. The solutions involve a dimensionless parameter S measuring the decay rate of the disk angular velocity. We primarily focus on how solid volume fraction affects the key physical attributes, namely resisting torque, volumetric flow rate and cooling rate when unsteady action of the disk is present. Similar to pure fluid flow, there exists a critical unsteady parameter S = S* which corresponds to the free disk requiring no torque. For some range of S, flow field surrounding the disk revolves faster than the disk itself. Similar to the steady-state case, suction seems to contribute vitally toward heat transfer enhancement of nanoparticle working fluid. Radial and circular motions around the disk diminish, and axial velocity becomes uniform when disk is subjected to sufficient amount of suction.