| Abstract: | This study examines how the complex flow structure within a gas turbine rotor affects aerodynamic loss.An unshrouded linear turbine cascade was built,and velocity and pressure fields were measured using a 5-hole probe.In order to elucidate the effect of tip clearance,the overall aerodynamic loss was evaluated by varying the tip clearance and examining the total pressure field for each case.The tip clearance was varied from 0％ to 4.2％ of blade span and the chord length based Reynolds number was fixed at 2×105.For the case without tip clearance,a wake downstream of the blade trailing edge is observed,along with hub and tip passage vortices.These flow structures result in profile loss at the canter of the blade span,and passage vortex related losses towards the hub and tip.As the tip clearance increases,a tip leakage vortex is formed,and it becomes stronger and eventually alters the tip passage vortex.Because of the interference of the secondary tip leakage flow with the main flow,the streamwise velocity decreases while the total pressure loss increases significantly by tenfold in the last 30％ blade span region towards the tip for the 4.2％ tip clearance case.It was additionally observed that the overall aerodynamic loss increases linearly with tip clearance. |
