Computational fluid dynamics (CFD) is a reliable numerical technique for the evaluation of fluid flow behavior particularly in solar air heaters (SAHs). In modern research, there is a lot of emphasis on saving time and cost in developing the SAH system through analytical and numerical methods. The experimental evaluation is used for validation and testing of the final prototype of the finished products. The numerical tool is preferred over the analytical tool for designing complex geometry and turbulent fluid models. The function of CFD is based upon the mathematical and turbulent models along with the three basic governing equations. CFD is mainly used to predict the fluid flow direction, turbulence, reattachment points, secondary flow generation inside SAH, and mixing of fluid flow to break the laminar sublayer. The present study is a state-of-the-art review of a recent analysis conducted in SAH using external roughness using CFD. The choice of turbulent and mathematical models by various studies are highlighted for future research in the field.