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도로터널 환기설계시 적정 차량항력계수 결정에 관한 연구
이창우(Changwoo Lee),조홍률(Hongryul Cho),박홍채(Hongchae Park) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-
Quantifying the drag forces exerted by vehicles is critical for road tunnel ventilation safety design due to the high ratios they account for. Vehicle-induced forces occupy as much as 32~100% of the total ventilation forces acting inside tunnel, while in safety design, drag forces is in the range of 28 to 65% of the mechanical pressure required for the emergency fan. The method adopted in local design guidelines for determining the drag coefficient does not take into account the effects of slip streaming despite of the recommendation by PIARC. This paper aims at analyzing the effects of slip streaming on drag coefficient by varying vehicle type, blockage ratio, inter-vehicle distance and relative air velocity. A total of 192 cases in 4 different target tunnels with 4 levels of service, 2 types of vehicle, 6 different relative air velocities were numerically studied with SOLVENT. Some of the significant results can be summarized as follows: (1) If the inter-vehicle distance is kept constant, drag coefficient remains almost constant with relative air velocity of 5.0~28.3㎧. (2) Effects of slip streaming become more prominent, as traffic density increases and inter-vehicle distance gets shorter. Reduction of drag coefficient reaches 23~39%. However, differences in reduction ratios are not significant among the different vehicle types . (3) In the case of heavy vehicles, reduction in drag coefficient due to decreasing inter-vehicle distance shows linear relationship, while the relationship is not statistically significant for small vehicles. (4) Drag coefficient of small vehicles noticeably increases with higher blockage ratio under the relative air velocity of 5.0~28.3㎧ and the blockage ratio of 1.8~3.6%. However, the trend in heavy vehicles is not consistent, as drag coefficient increases up to the blockage ratio of 7.% and unexpectedly decreases thereafter. (5) The drag coefficient suggested by current local guidelines must be interpreted as its upper limit, and the suggested method for coefficient derivation should be reappraised.
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