【摘要】 采用实验与数值模拟相结合的方法研究了基于流体柯恩达效应而形成的自激励旋进射流的流动特性。采用热线风速仪测量旋进喷嘴出口射流的速度,并对该射流进行功率谱分析以研究其旋进特性,结果表明,实验所用的膨胀比E=10、长径比L/D=2的喷嘴同样能产生明显的旋进射流,旋进频率主要取决于喷嘴的尺寸和射流的流速,并随流速的增大和喷嘴直径的减小而增大。采用大涡模拟(LES)方法数值研究了喷嘴内部自激励旋进射流的流动,得到了流场的速度分布和压力分布,比较了喷嘴膨胀比、长径比和雷诺数的影响。数值模拟结果显示,即使射流进入对称的圆筒中,突然膨胀后的流动也是不稳定的,在膨胀比E=5时射流的自维持旋进特征较为明显。更多还原

【Abstract】 Experimental study and numerical simulation were used to investigate the flow characteristics of a self-excited precessing jet,which was generated based on the principle of Coanda effect.A hotwire anemometer was used to measure the jet velocity at the exit of the precessing jet nozzle and the power spectrum density was obtained afterwards in order to analyze the precessing feature of the jet.It is shown that an obvious precession motion is generated in a nozzle even with a large expansion ratio E=10 and a small length-to-diameter ratio L/D=2.The precessing frequency is mainly dependent on the nozzle diameter and the intake flow rate,increasing with the enhancement of the flow rate and with the reduction of nozzle diameter.The flow fields inside precessing jet nozzles were simulated numerically using large-eddy simulation(LES) approach.The velocity and pressure distributions of the precessing flows were obtained and compared at different expansion ratios,length-to-diameter ratios and Reynolds numbers.The simulations show that the flows in axisymmetric sudden expansions are inherently unstable.The self-sustained precessing phenomenon is more obviously at the expansion ratio E=5 compared with another case(E=10) herein.更多还原