Numerical Study on Flow Field for a Solar Collector at Various Inflow Incidence Angles

Previous studies on solar water heaters (SWHs) have primarily focused on the thermal efficiency of a solar collector and structural safety. This study applied a numerical simulation method to examine the characteristics of flowfield. In addition, a solar collector of a SWH was employed to investigate the distribution of average surface pressure and vortex structure for various inflow incidence angles as well as the influence of two types of spoiler. This study adopted a computational fluid dynamics fluid mechanics method, an incompressible flow algorithm (i.e., semi-implicit method for pressure-linked equation [SIMPLE]), to simulate the flow field of the solar collector. A turbulence model (realizable k-epsilon model) was adopted. The obtained numerical values were compared with the experimental results. Because the simulation data were approximated to the experimental results, the turbulence strength and length were set as 11.7% and 0.12, respectively. The parameter for this study was inflow angle (theta = 15 degrees, 22.5 degrees, 30 degrees, 37.5 degrees, and V = 35 m/s). The characteristics of the flow field for various spoilers at inflow angle (theta) = 22.5 degrees were examined. According to the numerical simulation results, the low-pressure area on the upper surface of the solar collector first enlarged and then diminished as the inflow angle increased. The largest low-pressure area occurred at the wind incidence angle (theta) = 30 degrees. Because the cross-sectional aspect ratio in the frontal view changed, the overall lift force increased as the angle. increased. Because the vertical inflow cross-sectional area changed, air resistance gradually reduced. After spoilers of various sizes were installed, inflow airflow directly hit the solar collector, thereby reducing the pressure difference between the upper and lower surfaces of the solar collector. When the length of the spoiler increased, the shielding effect was enhanced; therefore, the increased size of the spoiler gradually reduced the lift force.