Effect of a gap on natural transition to turbulence in a boundary layer

Abstract

The proposal constitutes a research project to be developed at the University of Liverpoolunder the supervision of Prof. Theofilis. The topic is the effect of a cavity in transitionto turbulence in a compressible flat plate boundary layer. Transition is an importanttopic in drag reduction of airplanes and the prediction of the transition point is still achallenge. Surface imperfections affect transition and make prediction even more difficult.Among the many types of imperfections that exist, cavity is apparently the least research.Yet the few studies available in the literature report a very complex process with verydifferent phenomena for different ranges of flow parameters. There are some indicationsthat the process may be associated with instabilities of the cavity itself. Wavepackets areoften observed in natural transition and are considered a good model for the transitionprocess that occurs in practical conditions. The proposer has investigated the evolutionof wavepackets in boundary layers while the host has extensive experience in cavity flowinstability. The work will combine these expertise, involving direct numerical simulationsof Wavepackets in boundary layers with cavities and interpretation of results with the helpof global instability analysis. The proposer and the host have collaborated successfullyin the supervision of one PhD student and one MSc student in two projects, one in thecontext of a FP7 Marie-Curie/EU program and the other in a visiting professor programsupported by CNPq. The numerical tools that are going to be used in the project arealready available in the proposer research group, namely the DNS code and the globalinstability analysis codes, the latter being developed during a MSc. dissertation to be finish this year in collaboration with professor Theofilis. The project aims at further developing the tools and initiating a research programin this topic that can establish a road map that can foster a longer term collaborationin the field involving students exchange and experiments in the new low turbulence andlow acoustic wind tunnel built at USP with support from FINEP. The project will alsobenefit from the supercomputer recently built at the University of Liverpool of which prof.Theofilis is responsible for large part and has access to the full machine.