The establishment of the flow field in the test section of a short duration test rig is a complex process. In order to gain understanding during the transient phase, the time-accurate 1D Euler equations have been solved. The code is validated with two test cases: a steady nozzle flow and an unsteady flow in a shock tube. It is also applied to the short duration facility with an instantaneous opening of the shutter valve. Then, the code is modified to model the progressive opening of the shutter valve using moving boundaries. Finally, pressure and heat losses are also implemented using appropriate additional terms in the momentum and energy equations. The results obtained for the three different cases (instantaneous shutter opening, progressive opening, pressure and heat losses) are compared and discussed. In spite of the simplified approach that is used, the present simulation is able to provide the basic structure and behaviour of the flow field at different locations in the facility. The results show strong transient shock waves that propagate first forward and then backward in the settling chamber and put into evidence oscillations for both pressure and temperature at the test section inlet. In the case of a progressive opening, the process is delayed and the oscillations are smoother. The pressure losses damp significantly the oscillations.

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