Unsteady impulsive oblique stagnation-point flow impinging axisymmetrically on a vertical circular cylinder with mixed convection heat transfer

For the rst time, the problem of impulsive oblique stagnation-point ow on a vertical cylinder along with mixed convection heat transfer due to buoyancy forces has been solved in this study. The uid at rest with uniform temperature, T1, around the cylinder starts owing towards it at strength rate of k, and the cylinder temperature rises to Tw at t = 0, simultaneously. The governing equations induced by the impinging ow on the constant-temperature vertical cylinder at any obliqueness angle, , have been reduced to ODEs by using similarity transformations, and then they have been solved numerically. Considering a sample case of incompressible ow with Re = 1 and Pr = 0:7, the results of Nusselt number and similarity functions of velocity and temperature distributions have been obtained for dierent values of time and angle, . At the initial instants of time, the Nusselt number, regardless of ʹs magnitude, has large values; for example Nu = 5:1 at  = 0:01. As time passes, the value of the Nusselt number reduces intensely within a short period of time (until   0:4), and then it changes with a moderate reduction rate, such that in the steady-state situation, its value reaches 0.67, 0.61, and 0.51 for obliqueness angles  = 10, 30, 60.