09. Heat and Mass Transfer

Impinging jets can be used with simple equipment and have a high heat transfer performance. In industrial applications, they are used for cooling electronic equipment and gas turbine blades and for cooling steel materials in the steel industry. Improving the performance and efficiency of these applications is important because this leads to energy conservation. A single impinging jet shows high heat transfer performance in the stagnant region but significantly lower and non-uniform heat transfer performance away from the stagnation region. In addition, the heat transfer decreased at the center of the stagnation point. Therefore, a new high-performance heat transfer method for impinging jets is required to improve the heat transfer at the stagnation point and achieve a uniform heat transfer performance on the impinging surface. Therefore, we focused on periodically changing the direction of the jet and expected to improve the heat transfer characteristics of the impinging jet by significantly controlling the flow characteristics on the impinging surface. In this study, we propose an oscillation control scheme in which the nozzle angle of a single impinging jet varies in sine cycles. Direct Numerical Simulation (DNS) was used to investigate the effects of vibration control on the flow structure and heat transfer characteristics of a single impinging jet with varying vibration frequencies and amplitudes. As a result, it was confirmed that when the vibration frequency is high, the decrease in heat transfer at the center of the stagnation point observed in uncontrolled impinging jets disappears. It was also confirmed that as the vibration amplitude increased, the heat transfer area expanded, and non-uniformity was reduced.