Flow Instability: Transition and Non Linearity

The boundary layer transition over a rotor blade is studied by means of Reynolds-Averaged Navier-Stokes simulations performed with NASA OVERFLOW solver using transitional turbulent model, as well as Large-Eddy Simulations done on a finer grid. The obtained steady-state rotational flow is compared to the Falkner-Skan-Cooke flow model commonly used as its surrogate, and the possible ways to better approximate the steady state-flow are discussed. A number of linear stability techniques of increasing level of complexity are used to analyze the flow and predict the location of the transition, including the Local Stability Theory, the newly proposed streamwise-marching SCALES (Stability Calculation using Local Elliptic Subscales) method, as well as spanwise BiGlobal analysis capable of accounting for spanwise variability of the steady-state flow. It is found that periodic boundary conditions in the spanwise BiGlobal analysis work sufficiently well for a small fraction of the length of the blade (a few percent), while increasing the spanwise domain would require an alternative approach to the boundary conditions. The obtained results are compared against the available experimental data for the blade of the same geometry.

Funding acknowledgement

This work is funded in part by Office of Naval Research (ONR) Grant N000142312297.