Behavior of supersonic overexpanded jets impinging on plates

Kurzfassung

Behaviors of supersonic jets impinging on plates have wide applications, for example, in rocket launching systems, lunar landing modules, V/STOL aircraft and others. At the Institute of Aerodynamics and Flow Technology of DLR this problem is of interest in connection with the development of the method of cold gas-dynamic spray deposition. In this a deposition of coatings on substrates is achieved by high-velocity impacts of solid particles. Powder particles are accelerated by means of a supersonic free jet. In order to obtain adherence of particles their impact velocity needs to exceed a threshold. Therefore, the quality of coatings depends on many process parameters, in particular, on particle trajectories and velocities prior to the impact on the plate (substrate) [1]. In the shock layer ahead of the substrate incoming particles can strongly be decelerated thus changing the conditions of covering. At certain operation conditions a separation bubble can be present in the shock layer. In this case the flow ahead of the plate as well as shape and position of the bow shock typically oscillate strongly in time [2]. Then, a prediction of particle behavior ahead of the substrate is difficult. In addition to numerical computations the complexity of a mathematical description of the flow field in impingement zone requires experimental measurements covering a wide range of parameters. In particular, studying of the behavior of shock wave structures produced by jets impinging on obstacles is important for an interpretation of relevant processes.