## Abstract

In this work, a variational multiscale finite element formulation is used to approximate numerically the lid-driven cavity flow problem for high Reynolds numbers. For Newtonian fluids, this benchmark case has been extensively studied by many authors for low and moderate Reynolds numbers (up to $Re=10,000$), giving place to steady flows, using stationary and time-dependent approaches. For more convective flows, the solution becomes unstable, describing an oscillatory behavior. The critical Reynolds number which gives place to this time-dependent fluid dynamics has been defined over a wide range $7,300\lesssim Re35,000$, using different numerical approaches. In the non-Newtonian case, the cavity problem has not been studied deeply for high Reynolds number ($Re>10,000$), specifically, in the oscillatory time-dependent case. A VMS formulation is presented to be validated using existing results, to determine flow conditions at which the instability appears, and lastly, to establish new benchmark solutions for high-Reynolds numbers fluid flows using the power-law model. Obtained results show a good agreement with those reported in the references, and new data related with the oscillatory behavior of the flow has been found for the non-Newtonian case. In this regard, time-dependent flows show dependence on both Reynolds number and power-law index, and the unsteady starting point has been determined for all studied cases. It is determined that the critical Reynolds number (Rec) that defines the first Hopf bifurcation for Newtonian fluid flow is ranged between $8,100\lesssim Re_{c}\lesssim 8,250$, whereas for power-law indexes $n=0.5$ and $n=1.5$ it is $7,100\lesssim Re_{c}\lesssim 7,200$ and $18,250\lesssim Re_{c}\lesssim 18,250$, respectively.