A delayed detached eddy simulation of a sub-scale cold-gas dual-bell nozzle flow at high Reynolds number in transition operation mode will be carried out at nozzle pressure ratio NPR=49.2. In this regime, the over-expanded flow exhibits an asymmetric flow separation in the inflection region that could lead to the generation of content of aerodynamic side loads comparable to conventional bell nozzles used for space launchers. The nozzle wall-pressure signature will be analyzed in the frequency domain and compared with the experimental data available in the literature for the same geometry and flow conditions. The Fourier spectra in time and space (azimuthal wavenumber) will be studied in order to assess the role of the asymmetric shock movement and its connection with the possible development of a helical mode inside the nozzle. This could confirm the damping of the inflection point on the aero-acoustic interaction between the separation shock and the detached shear layer.
The aim of the present project is to advance the knowledge of the unsteady flow behavior inside dual-bell nozzles. A careful analysis of the available literature had shown that previous numerical studies have been performed mainly relying on RANS and URANS simulations. Few studies have been performed with hybrid RANS/LES approaches but not focusing on the physical mechanism that leads to the generation of side loads and the effect of the inflection point in the passive control of the flow. The main objective of this project is to carry out comprehensive studies to understand the complex physical phenomena occurring during the nozzle transition phase. This will lead to the clarification of the role of the helical mode that could develop due to a resonance aero-acoustic feedback loop mechanism. The outcomes are expected to have a strong impact from the viewpoint of both fundamental science and engineering, bringing advances to a critical research area in the space field and constituting a resource for researchers involved in the study of nozzle flows.