NOLOT-LNS: Boundary-layer instability analysis for surfaces with perturbations using harmonic-LNS

Kurzfassung

Local (LST) and nonlocal (PSE) stability theories, have been successfully used to study the growth of convective boundary-layer instabilities in many different scenarios. However, there are surfaces with perturbations where the streamwise variations of the mean flow occur locally over a length scale comparable to the characteristic wavelength of the instability modes. In such cases, the LST and PSE methodologies are not formally applicable and other approaches, like direct numerical simulations (DNS) or local scattering approach (LSA), need to be considered. Examples of these types of surfaces with perturbations are: lsolated or distributed roughness, steps, gaps, humps, suction, actuators. The harmonic-LNS (linearized Navier-Stokes) methodology presented here can be seen as the natural extension of the nonlocal concept for such types of surfaces. The assumption of 'slowly varying flows in streamwise direction is no longer considered, and this leads to a fully-elliptic system of equations (as in DNS) but where the harmonic representation of the disturbance is kept (as in PSE). This approach reduces the grid requirements significatively compared with traditional approaches as standard LNS or DNS