| Summary: | 碩士 === 中原大學 === 機械工程研究所 === 82 === The transient mixed convection of the second grade viscoelastic
fluid on the backward facing step are analyzed in the present
study. The effects to the flow of the fluid on the backward
facing step flow are examined under different Reynolds numbers
、Richardson numbers and viscoelastic coefficients. The flow
fields are studied by numerical computational. The finite
difference method is used on the vorticity function、stream
function and energy equations.The Gauss-Seidel method with
successive over relaxation is implemented to the finite
difference method to obtain the solutions. The results indicate
the flow field formes a primary recirculation at the downstream
of the step plate. The range of the primary recirculation zone
increases with Richardson number increases and decreases with
viscoelastic coefficients increases. The vorticity inside the
primary recirculation zone is positive and the vorticity on the
primary flow layer is negative.The phenomenon indicates both of
their rotational direction are oppositive. The thickness of
thermal boundary layer is increasing from bottom to inside the
flow field with time.In the primary recirculation zone , the
thermal gradient of Y-direction increases along the direction
of the primary flow , and the max-thermal gradient happen
around the reattachment point. From Y=0.1 to Y=0.5 , the
temperature has retrflexion phenomenon. Finally ,we discover
that the reattachment lengths has overshoot phenomenon when
Reynolds number is 50、Richardson number is 1 and viscoelastic
coefficient is 0.001; Reynolds number is 75, Richardson number
is 1 and coelastic coefficient is 0.001 .This phenomenon has
never been found in the newtonian fluid.In addition,the
secondary recirculation zone can exist at steady state when
Reynolds number is 75,Richardson number is 1 and viscoelastic
coefficient is 0.001. The similar results can only be found in
newtonian fluid when Reynolds numbers excess 400
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