CFD-based optimization of aperture geometry for reducing forced convection losses in a cylindrical cavity receiver of a dish/stirling system

Convective heat losses due to airflow recirculation at the cavity aperture are among the main efficiency limitations of Dish/Stirling solar receivers. While previous studies have primarily focused on internal modifications or advanced working fluids to mitigate thermal losses, the aerodynamic role of the cavity opening region has received comparatively limited attention. In this study, a numerical investigation using Computational Fluid Dynamics (CFD) is conducted to analyze the influence of receiver inclination on airflow behavior and to evaluate geometric modifications to the aperture of a cylindrical cavity receiver used in a commercial Parabolic Dish Concentrator (PDC–Trinum®) system. Simulations were performed under the climatic conditions of Itajubá–MG (Brazil) for receiver inclinations ranging from 0° to 90°, considering four different aperture geometry configurations. The results show that airflow recirculation intensity is strongly dependent on receiver inclination and can be significantly reduced through appropriate aperture design. Among the proposed configurations, a torus-like geometry applied at the cavity opening achieved the best aerodynamic performance, reducing internal air recirculation by up to 95.6%, depending on the inclination angle. When the velocities obtained through the CFD analysis were used as inputs to the mathematical heat-transfer model, the results indicate a potential reduction of approximately 96% in forced convection losses compared to the original receiver. The findings demonstrate that aerodynamic optimization of the cavity aperture is an effective and low-complexity strategy for enhancing the thermal performance of Dish/Stirling receivers.