3.2. Grooves effect on sealing performance
In order to study the effect of a textured shaft on “EHD”
behavior of the lip, several shaft surfacefinishes have been considered and are designated inTable 2.
To perform this parametric study, we consider the lip roughness defined previously with profile 2 (Nx2¼1 andNy2¼3) and the
amplitudeA2equals to 1μm.Fig. 7shows simulation results concerning three cases: a roughlip versus smooth shaft, a smooth lip versus a textured shaftSAT#1
and a rough lip versus a textured shaftSAT#1. It also shows the
film thickness, the pressure distribution and the radial lip
displacement.
Simulations show that the maximumfilm pressure is greater
when the lip is rough. This proves, once again, that the lip
roughness is the main reason for the pressure generation. Indeed,
the surface micro-undulation increases the hydrodynamic effect
and consequently, the radial lip displacement and the film
thickness.
To analyze the effect of the groove density on sealing performance, reverse pumping variation is plotted versus time for shaft
surfacefinishes:SAT#1,SAT#2, andSAT#3(Fig. 8). This plot confirms Jia et al. [7,8]results and shows that the reverse pumping
increases with the groove density. It shows that the groove density
improves significantly the pumping referring to a smooth shaft
case. Also, it is clearly proved that considering the lip surface as a
smooth surface underestimates this rate.
Fig. 9shows the variation of reverse pumping versus the groove
angle of shaft surfacefinishes:SAT#2,SAT#4 andSAT#5.
Fig. 9 shows that the reverse pumping decreases with the
increase of the groove angle. Thus, in order to raise the pumping
rate, it is mandatory to have a low angle groove.
The variation of reverse pumping versus groove depth is illustrated inFig. 10. It is shown that the averaged flow is proportional
to the pattern depth. It is also important to notice that, increasing
the groove depth leads to significantfluctuations of theflow.
Fig. 11shows the friction torque variation versus time, for different shaft forms. It can be noted that assuming the lip as a
smooth surface leads to an overestimation of the friction torque. It
is interesting to observe that the groove angle and depth only
slightly influence the friction torque.