Insulation performance of a new annular heated air curtain in cold-region tunnels: numerical modeling, effects analysis, and prediction.

In order to cope with the frost damage problems that occur in cold-region tunnels, the engineers have proposed the measure of setting up a heated air curtain at the tunnel entrance. In this paper, a three-dimensional transient heat transfer numerical model was first established to calculate the temperature distribution of the tunnel under the natural wind, which has a good agreement with field test data. The insulation effects of the heated air curtain were demonstrated, and effects of five factors, namely, temperature (Tn) and speed (Sn) of the natural wind, speed (S), temperature (T), and angle (A) of the jet airflow of the air curtain, were discussed. Then, an orthogonal test sensitivity analysis was conducted on the operating parameters (T, S, and A). Finally, effects of the air curtain were predicted by neural networks. The results show that the use of air curtains can effectively shorten the length of the negative temperature section of the tunnel structure. Low temperatures and large speed of the natural wind will weaken the effects of the air curtain. In the two cases, the operating parameters of the air curtain require adjustment according to demand. Increasing S and T can effectively enhance insulation effects. And the optimal A is between − 15° (toward inside the tunnel) and 0°. The sensitivities of the influences of the three operating parameters on the insulation effects are ranked as T (2.142), S (1.832), and A (0.77). The prediction results of the neural network indicate that using Tn, Sn, T, S, and A to predict the length of the negative temperature section (Lv) and temperature of the tunnel vault surface (Tv) is feasible and efficient. This research can provide a reference for the application of air curtains as anti-freeze measures in cold-region tunnels. [ABSTRACT FROM AUTHOR]