Numerical study of the effects of lid oscillation on the periodic flow pattern and convection heat transfer in a triangular cavity

This study is concerned with a periodic flow pattern with mixed convection in a triangular cavity caused by the effects of lid oscillation and buoyancy. The dimensionless stream function–vorticity formulation is adopted, and a curvilinear grid method for solving the stream function–vorticity equations in irregular geometries is used. Attention is in particular focused on the flow behaviour under the interaction between the frequency of the oscillation of the lid velocity and the frequency of the natural periodic flow. Meanwhile, numerical predictions of the thermal characteristics represented by local and average Nusselt numbers on the walls as well as the transient flow patterns are also provided. Results show that the frequency of oscillation of lid velocity and the natural periodic flow frequency both appear to be major frequencies in the frequency spectrum of the cavity flow, for cases with a dimensionless lid oscillation frequency less than 0.5. When the dimensionless frequency of the oscillation of the lid velocity is equal to or higher than 0.5, the flow and thermal fields are completely locked-on to the lid oscillation, and the natural periodic flow frequency is no longer visible in the spectrum.