During the sea-level start-up of liquid rocket engines, the nozzle is highly overexpanded and an internal flow separation takes place, characterized by a shock wave boundary layer interaction (SWBLI) which causes the shedding of vortical structures and the unsteadiness in the shock wave position. This produces dynamic side-loads, which reduce the safe life of the engine and could lead to a failure of the nozzle structure.
The main aim of this research project is to investigate the flow separation unsteadiness in an over-expanded transonic nozzle flow through large-scale numerical simulations. The spectral features of the separation shock when the recirculation bubble is open to the external ambient will be explored through an advanced analysis based on wavelet transform. This characterization will contribute to the basic understanding of the shock induced separation in internal flows of typical rocket engines at start-up, potentially allowing to predict and control the level of side loads. In such a way it will be possible to design larger area ratio nozzle, increasing the nozzle performance and reducing the costs of the access to space.
The second objective of the project is to provide a comparison between a large eddy simulation (LES) and a Detached Eddy Simulation (DES) of the same flow, in order to assess the validity of the DES approach for this kind of flow. This task will be carried out by means of simulations performed with a fully validated in house flow solver based on Finite Volume (FV) approach, which takes advantage of a kinetic energy preserving formulation.
If the ambitious objectives here proposed are fulfilled, the project will bring significant advances in a crucial aerospace research area and will have a strong impact from the technological point of view.
