Multi-objective optimization analysis on cooling characteristics of swirling flow for exhaust pipe

Due to the high energy conversion efficiency and portability, diesel engines are chosen as the main power source for the basic power generation of mobile military units. However, the exhaust gas emitted will heat up the pipe and generate a large amount of thermal radiation signals, which can be captured by enemy and thereby expose the location information of the military base. To reduce the thermal radiation signals generated by the heating of the pipelines by the exhaust, this study proposes to introduce swirling cold air between the high-temperature exhaust of the diesel engine and the pipeline wall to prevent the heating of the pipeline wall by the high-temperature exhaust gas. Using the validated numerical model, studies were conducted on the local maximum temperature of the pipe wall and corresponding pressure loss under different temperatures, swirl angles, and cold flows. The analysis of the influencing mechanism was carried out through single-factor analysis and response surface analysis. The results show that the lower the temperature of the cold fluid, the stronger its cooling capacity, but the temperature that needs to be controlled for cooling is also smaller, which makes winter the key protection stage. In addition, the results also reveal the non-monotonic influence of the increase in cold flows and angles on the local maximum temperature rise of the pipe wall. For the two target values with opposite trend changes, the optimal operating conditions determined by multi-objective optimization and ideal point method are respectively optimized with average ratio of 59.67 % and 20.66 % compared to the baseline operating conditions.