An accurate data base on laminar-to-turbulent transition in variable pressure gradient flows

An experimental data base on attached and separated-flow transitional boundary layers, under various levels of free-stream turbulence, Reynolds number and pressure gradient has been composed, with the aim of providing high-accuracy data and boundary conditions for development and testing of laminar-to-turbulent transition models. Experiments were carried out on the boundary layer developing on a flat plate installed within a channel with a variable opening angle. The test section imposes acceleration to the boundary layer followed by deceleration, which can be varied. Time Resolved Particle Image Velocimetry (TR-PIV) and Laser Doppler Velocimetry (LDV) data have been acquired on the boundary layer evolution, as well as the free-stream properties in terms of mean velocity and fluctuating velocity components. The overall test matrix spans 3 Reynolds numbers (70,000;150,000;220,000), 4 free-stream turbulence intensity levels (Tu=1.5;2.5;3.5;5%) and 4 pressure gradients (opening angle α=0;5;9;12deg). This large variation of flow parameters allows a gradual shift of the mode of transition from a bypass process in attached flow, occurring with zero (Blasius like) and mild adverse pressure gradients at high free-stream turbulence, to separated-flow transition, occurring with low Reynolds number, low free-stream turbulence intensity and elevated adverse pressure gradient.