설계조건에서 선형 익렬의 익단 간극 크기가 익단 간극 누설유동에 미치는 영향에 관한 수치해석

Abstract

A steady-state Reynolds averaged Navier-Stokes simulations was conducted to investigate the effect of tip clearance size on the distribution of tip leakage flow inside a linear cascade. Two different tip clearance size, t=2 mm and 4 mm, were considered under design condition(i.e. inlet flow angle β = 29.3°). As the tip clearance increased, the gradient of the static pressure trough at the endwall became larger and the tip leakage flow rolled-up more strongly in a helical form. In addition, high total pressure loss region corresponding to the distribution of tip leakage vortex was somewhat enlarged in the downstream positions of the blade trailing edge. The flow rate through the tip clearance increased in proportion to tip clearance size, and as a result, the swirling flow became stronger, so that the center of tip leakage vortex moved more from the blade tip to the hub. Additionally, the region with high turbulent intensity where the leakage flow exited the tip clearance in the form of jet, was extended to the inside of the flow path along the endwall. Finally, it was confirmed that there were several indicators to confirm the existence of tip leakage vortex. The defect of axial velocity in the tip region of blade flow path, the dimensionless helicity with a magnitude close to 1, the endwall pressure trough, the region with high total pressure loss, and strong roll-up of the particle trajectory were the typical examples. By taking these indicators as a comprehensive consideration, the existence of tip leakage vortex can be effectively found.