Speaker: Leonardo Santos de Brito Alves
Affiliation: Universidade Federal Fluminense – UFF
Abstract: The accuracy of base flows in linear stability analyses is paramount, leading to more reliable results. Steady-states usually make the best base flows. Unfortunately, standard marching schemes utilized for accurate unsteady simulations almost never reach steady-states of unstable flows. Steady governing equations could be solved instead, by employing Newton-type methods often coupled with continuation techniques. However, such iterative approaches do require large computational resources and very good initial guesses to converge. These difficulties motivated the development of a technique known as selective frequency damping (SFD). On the other hand, this marching approach is unable to damp stationary disturbances and becomes very inefficient for flows with a broad unstable frequency spectrum. Both scenarios appear in convectively, absolutely or globally unstable flows. An alternative approach called Minimal Gain Marching (MGM) is presented here. It modifies the coefficients of a marching scheme in such a way that makes the absolute value of its linear gain smaller than one within the required unstable frequency spectra, allowing the respective disturbance amplitudes to decay given enough time. These ideas are shown here for implicit multi-step schemes. A few chosen test cases shows that they enable convergence toward solutions that are unstable to stationary and oscillatory disturbances, with either a single or multiple frequency content. Finally, current applications are focused on multi-stage MGM schemes applied to laminar hypersonic boundary layers over the circular and elliptic cones found in HIFiRE 1 and 5.
Biosketch: Leo Alves is a Professor of the Mechanical Engineering Department of the Fluminense Federal University (UFF) in Brazil. He has a BS (1998) and a M.Sc. (2000) in Mechanical Engineering from the Federal University of Rio de Janeiro (UFRJ) in Brazil and a M.Sc. (2002) and a Ph.D. (2006) in Mechanical and Aerospace Engineering from the University of California at Los Angeles (UCLA). He is also the recipient of the Outstanding Ph.D. Student award from MAE-UCLA in 2006, Productivity Fellowship award from the Brazilian Government in 2010 and 2013, Young Scientist Award from the state of Rio de Janeiro in 2011 and 2014, Treasury Director of Brazilian Association of Engineering and Mechanical Sciences (ABCM) between 2013 and 2017.
Date(s) - Oct 26, 2017
12:00 pm - 1:00 pm