This article is concerned with the periodic flow induced by non-torsional oscillations of two porous disks rotating about distinct axes. While the porous disks are initially rotating with the same angular velocity about non-coincident axes, they start to execute non-torsional oscillations in their own planes and in the opposite directions. An analytical solution corresponding to the velocity field in the periodic state is obtained. The variations in the components of the horizontal force per unit area exerted by the fluid on the top and bottom disks with the time are investigated for the suction/injection velocity parameter, the Reynolds number, the ratio of the frequency of oscillation to the angular velocity of the disks, and the dimensionless velocity amplitudes of oscillation. It is shown that the horizontal force on the upper disk is not equal to that on the lower disk.

This paper is concerned with the steady flow of a Maxwell fluid between two porous disks rotating with the same angular velocity about noncoincident axes normal to the disks. An exact solution to the problem depending on the Deborah number, the suction/injection velocity parameter, and the Reynolds number is obtained. It is shown that the core of fluid tends to rotate about the -axis that characterizes the line in equal distance to the two axes of rotation when the Deborah and Reynolds numbers increase and a thinner boundary layer occurs in the region adjacent to the top disk when the axial velocity of fluid that is based on the suction/injection velocity parameter is upward. In addition, an approximate solution is presented for small Deborah numbers. The comparison between the exact and approximate solutions is given and found to be in excellent agreement.

While the disks are initially rotating eccentrically, the unsteady flow caused by their oscillations in their own planes and in the opposite directions is studied. The analytical solutions to the problem are obtained for both small and large times, and thus the velocity field is determined for every value of time. The variations of all the parameters on the flow are scrutinized by means of the graphical representations. In particular, the effect of the ratio of the frequency of oscillation to the angular velocity of the disks is analyzed. The dependence of the oscillations in both x-and y-directions on the flow is examined. The influence of the Reynolds number is also investigated.

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The magnetohydrodynamic (MHD) flow of an electrically conducting second order/grade fluid past a porous disk is studied when the disk and the fluid at infinity rotate with the same angular velocity about non-coincident axes. It is found that the existence of solutions is in connection with the sign of the material modulus 1 α for both suction and blowing cases. The effects of all the parameters on the flow are carefully examined.