| The longitudinal jet ventilation technology has become the mainstream ventilation way of long and large road tunnel because of its simple system, convenient control and less cost. However, the efficiency of this ventilation mode is low because of the influence of jet characteristics and fan arrangement, so how to improve the efficiency of ventilation is a focus in the study of tunnel jet ventilation technology at present. This paper based on the Lianhua tunnel in Xiamen, by the mean of combining the model experiment and numerical simulation to study the velocity field and the design parameters of fan under the influence of relevant parameters such as temperature.According to the tunnel jet ventilation test model to analyze the features of velocity field about the ventilation system under 4 series modes: normal condition(20?)and jet flow temperature is 26??31??and 40? respectively. The results showed that with increasing of jet temperature, the jet characteristics have no change and no difference with normal temperature condition, but the distance that needed to stabilize the air velocity is increased.By the FLUENT14.5 software to set up 3D simulation model of the tunnel, simulated the velocity field of the highway tunnel of jet ventilation system under the normal working condition(20?), the correctness of numerical simulation method was proved by comparing the calculated value with the experimental value. And according to the simulated results, determined the longitudinal control distance is 120 m, the initial length is 5.6m. It is found that the values accord with the empirical formula computed results, so the correctness of simulation method was proved. And with the comprehensive effect coefficient K as the evaluation index to analyze the longitudinal distance influence on ventilation effect. it shows that: the ventilation effect is best if two groups of jet fan was opened and the longitudinal distance between jet fan is 100~110 m.The focus of simulation is the different temperature influence on the velocity field of jet ventilation system. It turns out that: the change of temperature have no effect on characteristics of air flow field, it only change the velocity and affect design parameters of the system. The main conclusions show as follows:(1)The rise of jet temperature will lead to the longitudinal impact scope increased and the efficiency of ventilation reduced. So in practical engineering, the longitudinal control distance of jet groups that located in exit section of tunnel should be set about 15 m more than normal temperature condition.(2)The outside tunnel temperature will influence on the distance between jet fan and tunnel entrance. So considering the change of outside tunnel temperature, when the distance between jet fan and tunnel entrance is set to 130 m the ventilation effect is better.(3) In high rock wall temperature tunnel or under the condition of fire, as the tunnel temperature increased, the induction period and longitudinal spacing decreased, the velocity of uniform section will reduce. Aim at the influence of temperature, in practical engineering we should increase the longitudinal control distance of jet groups that located in central tunnel according to the change of temperature. |
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