The sudden closure of the refueling valve during the refueling process will cause the water hammer phenomenon in the pipeline of the large aircraft fuel system and produce pressure waves propagating along the pipeline. In serious cases, it will cause severe damage to the pipeline. The pressure surge in the pipeline can be affected by many design factors. In this study, the numerical modeling method of the large aircraft fuel system is studied using the Flowmaster program, and the accuracy of steady and transient state analysis of the simulation method is verified by experimental data. Based on this numerical method, a complete system-level simulation model of the large aircraft fuel system was established. Using this model, the effects of valve closure speed, diameter of the refueling main pipe, and refueling volume flow rate on pipeline pressure surge during the refueling process are investigated. The results indicate that all three factors have a significant impact on the pipeline pressure surge of the fuel system. The effect of the valve closing speed and the pipe diameter on the pressure surge of the pipeline is nonlinear and gradually weakened with the decrease of valve speed and the increase of pipe diameter, while the effect of refueling volume flow rate on the pipeline pressure surge is approximately linear.
The air distribution system is one of the key systems for ensuring the safety and comfort of the passenger aircraft. The large number of components poses a severe challenge to the efficiency, accuracy, and convergence of system simulation. For the 3D CFD method, the complex and large number of meshes leads to low computational efficiency. The 1D simulation has high efficiency, but the local accuracy is inadequate. To solve this problem, the 1D Fluid System Simulation Software Flomaster with the linearization algorithm is used to establish the system-level model. The flow characteristic curve is obtained by the CFD (computational fluid dynamics) method for the local irregular ducts and introduced into the 1D system model for iteration. The effects of local flow resistance and thermal insulation on the flow distribution and thermal performance of the system are studied using this simulation model. The results show that the local flow resistance affects the total flow and uniformity of the cabin distribution, the improvement of insulation performance is weakened with increasing insulation layer thickness, and the application of thicker insulation layers on the downstream pipeline is more advantageous to limit the maximum temperature change of the conditioned air.
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