go to top scroll for more


Projects: Projects for Investigator
Reference Number EP/F045093/1
Title Streak Instability and Bypass Transition
Status Completed
Energy Categories Energy Efficiency(Transport) 2%;
Not Energy Related 90%;
Other Power and Storage Technologies(Electric power conversion) 5%;
Energy Efficiency(Industry) 3%;
Research Types Basic and strategic applied research 100%
Science and Technology Fields PHYSICAL SCIENCES AND MATHEMATICS (Applied Mathematics) 35%;
ENGINEERING AND TECHNOLOGY (Mechanical, Aeronautical and Manufacturing Engineering) 65%;
UKERC Cross Cutting Characterisation Not Cross-cutting 100%
Principal Investigator Dr X Wu
No email address given
Imperial College London
Award Type Standard
Funding Source EPSRC
Start Date 15 December 2008
End Date 14 June 2012
Duration 42 months
Total Grant Value £353,257
Industrial Sectors Aerospace; Defence and Marine
Region London
Programme NC : Engineering
Investigators Principal Investigator Dr X Wu , Mathematics, Imperial College London (99.998%)
  Other Investigator Dr T Zaki , Department of Mechanical Engineering, Imperial College London (0.001%)
Professor SJ Sherwin , Aeronautics, Imperial College London (0.001%)
Web Site
Abstract Laminar-turbulent transition is a fundamental problem in fluid mechanics that has great implications for the prediction of drag, aerodynamic heating, and flow separation. For example, transition to turbulence can bypass flow separation in compressors, and in the low-pressure-turbine stage, 50% of the flow can be transitional. While the end-state may always be an equilibrium turbulent boundary layer, transition itself can be mediated by different mechanisms and each results in distinctly different transition locations and lengths.The literature generally divides transition scenarios into the natural, or orderly, route and the bypass mechanism. The former is characterized by viscous Tollmien-Schlichting (T-S) instability waves which can be observed experimentally under quiet testing conditions. In the presence of free-stream disturbances, which are loosely referred to as free-stream turbulence (FST), transition takes place more swiftly, thus bypassing the natural route, and hence the term "bypass transition".In the bypass mechanism, elongated high-amplitude disturbances, known as boundary layer streaks, are observed in the pre-transitional region of the flow. Breakdown has been attributed to a secondary instability of these streaks, but the exact dependence has only been speculated and never satisfactorily quantified. The proposed research is first to accurately and efficiently compute the non-linear streaks by using a combined theoretical and numerical approach. We will also analyze the stability of these streaks, and our study will provide an estimate for the required threshold of free-stream disturbances for streak instability. It will also give a quantitative relation between the location where the streaks first become unstable and the intensity of the free-stream disturbances. Such information will be useful for the design of airfoils which operate in transitional flow regimes
Publications (none)
Final Report (none)
Added to Database 17/03/08