Structure analysis of a new type of flow straightener used in fire fighting water cannon

摘要

A new type of flow straightener designed with two coaxial circular pipes structure has been proposed. Flow straightener is used to improve the range of fire fighting water cannon. To know the influence of structure sizes on the performance of water cannon, four factors and three levels orthogonal test was designed. Simulation are carried out using commercial software ANSVS FLUENT. Standard k-ε turbulence model was selected for modelling turbulence in water cannon. By extreme difference analysis and variance analysis, the orthogonal test results show that the length of flow straightener has greatest influence on outlet turbulence kinetic energy of the water cannon, also, the blade thickness of straightener plays an important role on the total hydraulic loss. As far as the material structure strength is permitted, it is recommended to select flow straightener with thinner thickness. Different length was studied to find that there is a suitable length for the flow straightener, as the length extends to a certain value, the outlet turbulence kinetic energy decreased slowly. The hydraulic loss produced by straightener contributes to about 41% to 70% of the total hydraulic loss. The pressure drop varies with the variation of different straightener factor significantly. Detail flow field analysis is performed to understand the flow pattern in the water cannon. The streamlines pattern show that the swirl has overcame and the turbulence intensity was reduced largely which is benefit for the range of fire fighting water cannon.