水下欠膨胀高速气体射流的实验研究

EXPERIMENTAL STUDY OF UNDEREXPANDED SONIC AIR JETS IN WATER

采用实验途径研究了水下高速气体射流的动力学特性，研制了水下高速气体射流实验系统并发展了相应的测试手段．实验中，用插入式静压探针测量了射流轴线静压分布；用γ射线衰减法测量了径向空隙率分布，从而揭示了水下高速气体射流均压和掺混两个过程的基本规律．测量结果表明：水下高速气体射流在欠膨胀工况下运行时，近场将出现含有复杂波系结构的膨胀压缩区域，由于气水的掺混作用，水下欠膨胀气体射流均压化过程比空气中衰减得快．测量结果还表明，水下射流在近场区的混合层由气水两相占据：其流态从靠近气体侧的液滴流型过渡到靠近液体侧的气泡流型．

The structure and mixing properties of underexpanded turbulent air jets in still water were experimentally investigated in this paper. The experimental system, which consists of compressor, gas tank, injector, water tank as well as pipe, regulator and mount, was built to simulate horizontal sonic jets submerged in water and to measure flow properties of the jets. In order to determine static pressure distribution in the nearfield of the underexpanded jet, two types of horizontally movable, static probes were developed and tested. Static pressures along the axis of jets were obtained for the ratios of static pressures at nozzle passage exit to ambient water being 1.0, 1.2, 1.4, 1.6, 1.8 and 2.0, were illustrated. Using gamma-ray absorption method, where the Gamma-Ray probe is vertically movable, mean void fraction distributions, for the ratios being 1.0 and l.4, were measured at 3 different profiles. Among them, as a reference, the ratio of 1.0 represents the full expansion case. The flow structure and mixing properties were analyzed through the distributions of static pressure and mean void fraction. The results are useful for the analysis of the flow in the external-expansion region near the passage exit. Static pressure measurements show that a shock-wave-containing external-expansion region exists for Underexpanded sonic air jets in water, which is similar to that of underexpanded air jets in air. Underexpanded air jets in water damp faster than underexpanded air jets in air due to different mixing condition. Mixing entrainment layer surrounding the external-expansion region for air jets in water involved a bubble region near the liquid side and a drop-containing region near the gas side.