Heat transfer and fluid flow analysis in circular tubes with multi-delta-winglets vortex generators

In this work, the positive projection plane of self-join winglet vortex generator is modified into a non-circular design, aiming to provide novel insights into optimizing vortex interaction in tubes equipped with winglets. The experimental and numerical investigation of heat transfer and fluid flows in circular tubes equipped with multi-delta-winglets vortex generators is conducted. The influence of three structural parameters (included angle (alpha), blockage ratio (BR), winglet pairs number (PN)) on the thermal performance of the enhanced tube are explored across a Reynolds number range of 7577 to 27,276. It is found that the vortex pairs near the tube wall contribute to enhancing the mixing uniformity of fluid flows in tubes. Furthermore, the dissipation intensity of the vortex pairs near the tube wall is increased with increasing alpha. The Nusselt number and friction factor are increased by 1.90-2.32 and 2.23-5.10 times, respectively, compared with the smooth tube. The maximum thermal enhancement factor reaches 1.63 when BR = 0.10, PN = 4, and alpha = 90 degrees. Optimization strategies are performed through similarity analysis, and the similarity equations between structural parameters and flow field characteristics are obtained. These findings offer valuable theoretical insights for the design of winglet structures and the optimization of flow fields.