A Numerical Analysis of the Flow Passing through a Cascade with Tip Clearance : Subsonic Flow through a Linear Cascade Composed of Flat Plates

The three-dimensional flow field through a linear cascade with tip clearance was numerically studied by solving Navier-Stokes equations. A fundamental cascade model composed of flat plates, for which corresponding experimental data were available, was adopted to develop the appropriate solution method for the flow through the tip clearance. The computed normal force distributions on blades and velocity vectors in the downstream flow field showed good agreement with the experimental data. The detailed flow phenomena around the blade tip, such as the formation of separation bubbles on the tip surface, were clearly described. The spanwise distributions of the normal force on the blade were investigated for various tip clearances, and it was found that the normal force on the extremity of the blade did not diminish in the case of small clearances of less than 0.6% of the blade span because of the blockage of leakage flow due to the effect of viscosity.