Amplitude Modulations on Strato-Rotational Instabilities (SRI) with applications to star formation in accretion disks

In geophysical and astrophysical flows, stratified vortices can be found from small to large scales, and they are relevant in the distribution of heat and momentum in stably stratified systems such as the atmosphere or oceans. In the astrophysical context, accretion disks (from which solar systems are formed) can be seen as stratified vortices. In such systems, understanding the mechanisms that can result in an outward transport of angular momentum is a central problem. For a planet or star to be formed in a disk, angular momentum has to be carried away from its center to allow matter aggregation by gravity; otherwise, its rotation speed would be far too large, avoiding this matter aggregation (and the consequent star formation) to happen. In such gas systems, turbulence is the most likely mechanism to achieve such a large angular momentum transport. However, it was shown that the flow profile of accretion disks is stable with respect to purely shear instabilities, and the question arises about how the turbulence can be generated. Among other candidates, the strato-rotational instability (SRI) has attracted attention in recent years. The SRI is a purely hydrodynamic instability that manifests itself as non-axisymmetric spirals and can be modeled by a classical Taylor-Couette (TC) system with stable density stratification. The density stratification causes a change in the marginal instability transition when compared to classical non-stratified TC systems, making the flow unstable in regions where, without stratification, it would be stable. This characteristic makes the SRI a relevant phenomenon in planetary and astrophysical applications, particularly in accretion disk theory In this work, we will present confrontations of experimental data with non-linear High-performance numerical simulations of strato-rotational flows that reveal non-linear interactions of SRI modes leading to periodic changes in the SRI spirals axial direction of propagation. These spiral pattern changes lead to low-frequency velocity amplitude modulations related to two competing spiral wave modes. In this presentation, it will then be presented how two different spirals linearly interacting could lead to these pattern changes, also connected to the non-linear transfer of energy from the base flow to these secondary instabilities. We will also present the impacts of these amplitude modulations on the momentum transfer regime and the net momentum flux driven by the SRI, which might represent strong influences on star formation regimes in accretion disks.