A numerical investigation is performed into the natural convection heat transfer characteristics within an
enclosed cavity filled with nanofluid. The left and right walls of the cavity have a complex-wavy geometry
and are maintained at a low and high temperature, respectively. Meanwhile, the upper and lower walls of
the cavity are both flat and insulated. The nanofluid is composed of Al2O3 nanoparticles suspended in pure
water. In performing the analysis, the governing equations are formulated using the Smoothed Particle
Hydrodynamics and the complex-wavy-surface is modeled as the superimposition of two sinusoidal functions.
The simulations examine the effects of the volume fraction of nanoparticles, the Rayleigh number and the
complex-wavy-surface geometry parameters on the flowstreamlines, isotherm distribution and Nusselt number
within the cavity. The results show that for all values of the Rayleigh number, the Nusselt number, increases as
the volume fraction of nanoparticles increases. In addition, it is shown that the heat transfer performance can be
optimized by tuning the wavy-surface geometry parameters in accordance with the Rayleigh number. Overall,
the results presented in this study provide a useful insight into potential strategies for enhancing the convection
heat transfer performance within enclosed cavities with complex-wavy-wall surfaces.