| Summary: | 碩士 === 國立中央大學 === 機械工程研究所 === 93 === The transient flow and thermal characterisitcs of a hot supersonic impinging jet with radiation effects are studied. Two dimensional, cylindrical, unsteady supersonic impinging jet is simulated using the STAR-CD. Turbulent flow is simulated using the κ-ε model. The equation of radiative transfer is solved by the discrete-ordinate method. Results are obtained for two cases. Case one is for fixed nozzle position while case two is for moving nozzle. The effects of various parameters, such as nozzle exit temperature, pressure, velocity and the distance between the nozzle and the impingement surface are studied.
For fixed nozzle case, the results show that as the jet leaves the nozzle, it expands down quickly. Before the circulation bubble come to existence, the Mach disk moves towards the impingement surface gradually. At the time of 0.001 second, the jet has a strong recirculation near the end of the oblique shock, creating a large-scale second high temperature field. Increasing the nozzle exit temperature causes the bubble to form earlier. The flow reaches steady state at 0.01 second approximately.
For the moving nozzle case, the results show that after the circulation bubble come to existence, the Mach disk moves upwards with the moving nozzle, and hence the circulation bubble is also pulled upward. As the nozzle reaches the position where the distance between the nozzle and the impingement surface is 4 times the nozzle diameter (Z/D=4), the circulation bubble vanishes. The bubble will form again at Z/D=6, but become smaller in size. Increasing the nozzle exit pressure or velocity causes the phenomenon of the circulation bubble be pulled upward more obviously. The circulation bubble does not vanish at Z/D=4 for higher relative pressure (PR=3.4) case. After 0.01 second, the nozzle is far from the impingement surface, the flow is not affected by the pressure of the impingement plate.
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