起动射流出口形状对其推力特性影响研究

Effects of Exit Geometry on the Propulsive Characteristics of the Starting Jet

本文采用数值模拟方法研究起动射流推进器出口形状对其产生的推力与冲量的影响。将圆管和圆孔喷管入口直径与出口直径的比值Dr (定义Dr为直径比)作为变量,通过改变直径比的值来表征起动射流出口形状的差异。研究发现,在射流过程中,由于圆孔喷管出口形状对射流具有收缩作用,其出口一直有持续的过压效应发生,而圆管喷管只有在射流起始加速阶段会有较强的过压产生,因此圆孔喷管能向尾迹中产生更大的冲量Ih,并获得更大的推力FT。而且起动射流的冲量Ih及推进冲量FT随着直径比Dr的增大而增大,直到直径比达到临界值2.5时,Ih和FT几乎不再增长。

The effect of the exit geometry of a vortex ring generator on thepropulsive characteristics of the starting jet was studied numerically.For theorifice and tube nozzle configurations,the ratio of the nozzle entrance toexit diameters,dubbed as the diameter ratio Dr,was found to have significant effect on propulsivecharacteristics of the starting jet.The higher impulse generated by theorifice nozzle(Dr>1)than that of the tube nozzle(Dr=1)is attributed to the consistent over-pressure effect at the nozzle exitplane during the entire fluid ejection history,while the over-pressure effectonly exist during the initial jet startup for the tube nozzle.The results showthat the hydrodynamic impulse and net propulsive impulse of the starting jetincreases against the diameter ratio until a critical value of around Dr=2.5 is approached.