# Experimental Investigation on Jet Vector Deflection Jumping Phenomenon of Coanda Effect Nozzle
###### Abstract
[PERSON] et al. [13] studied the flow characteristics of a supersonic jet on the inclined wall with a fixed deflection angle and, for the first time, obtained the pressure in the starting area, the range of the recirculation area, the jet trajectory, and pointed out that the jet separation and attachment are determined by the transverse pressure gradient developed between the space environment and the separation area. [PERSON] et al. [14] used a hot wire anemometer to conduct experimental research on inclined wall jets with different incoming velocities at a fixed deflection angle of 30 degrees. They gave the deflection angle and Reynolds number boundary conditions for jet attachment and separation. In 2015, [PERSON] et al. [15] used particle image velocimetry and conventional pressure sensors to obtain the results of the transient velocity field. The Reynolds stress field of the near\(-\)wall flow under the stable control state for the reverse flow vectoring nozzle model demonstrated that the lateral pressure gradient generated by the negative suction pressure and the reverse flow shear layer, under the combined action of the induced negative pressure on the wall, is the cause of the jet vector deflection. [PERSON] et al. [16] experimentally conducted numerical simulation research on the phenomenon of wall\(-\)attached deflected jet due to the Coanda effect. Through practical means, they studied the effects of the inclination angle and Reynolds number on the wall\(-\)attached and separation phenomena, as well as hysteresis and jumping. They used the Galerkin projection of the Navier-Stokes equation on POD basis function to obtain a low\(-\)dimensional dynamic model, which qualitatively represented flow characteristics. [PERSON] et al. [17] studied the phenomenon of the jet deviating from the straight direction due to the presence of the Coanda wall from the experimental point of view. The velocity field results clearly show that the inclination of the jet attached to the wall depends on the side wall distance itself. The self\(-\)similarity analysis along the inclined jet direction shows that the Coanda wall attachment effect will fail for wall distances more significant than five jet widths. [PERSON] et al. [18] studied the physical mechanism of the Coanda jet wall separation process under a high\(-\)pressure ratio and qualitatively described the physical characteristics of wall\(-\)attached expansion and jet separation using an optical schlieren system. For complex dynamic systems, commonly used dimensionality reduction methods include the inertial manifold/approximate inertial manifold method, the Eigen orthogonal decomposition POD method, and the primary manifold method [19], in which the POD method is widely used in the dimensionality reduction modeling of fluid dynamic systems. Because the POD method has a relatively small calculation, the numerical results or experimental data based on high\(-\) resolutions have clear physical significance. [PERSON] [20; 21] first introduced the POD method into the turbulent field, and then [PERSON] [22] introduced the snapshot method to study the dynamics of fluctuating flow and the dynamics of wave flow. [PERSON] [23] et al. and [PERSON] et al. [24] conducted a numerical simulation of the flow around a cylinder through the POD Galerkin method, and found that the evolution characteristics of the flow field could be accurately captured by using a less pod basis. The fluid thrust vectoring nozzle was an unsteady flow process in the process of vector deflection. As far as the usual structure analysis method of unsteady flow is concerned, the dynamic mode decomposition (DMD) method is commonly used. [PERSON] developed the DMD method from Koop in recent years; it is a low\(-\)dimensional system decomposition technology developed based on man analysis [25]. Dynamic mode decomposition (DMD) can solve or approximate the dynamic system according to the coherent growth structure, attenuation, and oscillation in time.