Boundary layer transition
- Boundary layer transition (text version)
Flow along a compressor blade from left to right with contours showing the average ensemble average velocity. Initially the boundary layer near the wall is laminar, however as the flow moves along the blade, a separation bubble forms before the flow reattaches to the wall and turbulent flow is established.
The transition mechanism from laminar to turbulent flow remains poorly understood. Transition has an important effect on the performance of fluid machines such as turbines and compressors. Understanding and controlling it will help to reduce aerodynamic losses and make the machines environmentally friendly.” Dr Vasudevan Kanjirakkad
Senior Lecturer in Experimental Thermofluid Mechanics
Gas turbine blade surfaces are known to have large regions of laminar and transitional flow. The significance of transition is particularly important under low Reynolds number operation. Due to the low frictional losses associated with laminar flow, delaying transition is advantageous. However, under adverse pressure gradient conditions, the laminar flow can separate and increase profile losses if open separation persists.
The current research looks at the phenomenon of separated boundary layer transition on the surface of an axial compressor blade under steady and unsteady (wake) inlet conditions. Detailed wind tunnel experiments are being undertaken to understand the prevailing transition mechanisms with and without the presence of incoming wakes. The ultimate aim is to use the knowledge gained from this work to aid efficient blade designs.