EFFECT OF A TIP CLEARANCE ON THE PERFORMANCE OF A LOW SPEED CENTRIFUGAL COMPRESSOR

Tip clearance effects on flow field of a low speed centrifugal compressor without and with partial shroud (PS) attached to the rotor blade tip at three values of tip clearance, viz. φ =2.2%, 5.1% and 7.9% of rotor blade height at the exit at three flow coefficients, namely, φ=0.12,0.18 (below design flow coefficient), φ=0.28 (design flow coefficient) and φ=0.34 (above design flow coefficient), is analysed computationally using structured multi block grid with fine grid in the tip clearance region. The paper aims to study several flow characteristics between blade channels using commercial flow solver ANSYS CFX 15.0 based on finite volume techniques. The centrifugal compressor in aerodynamic requirement is that edge velocities along the impeller channel passage surfaces like hub, shroud, pressure and suction surfaces vary smoothly without sudden decelerations, which cause flow separation leading to losses. Using the periodic boundaries and defined flow conditions at inflow / exit flow and blade rotations, the turbulent viscous flow between blade channels are computed. The efficiency related parameters using average quantities, besides flow pattern in terms of velocities, streamlines and pressure distribution on blade surfaces are graphically interpreted. An attempt is also made to study the influence of pressure loads on structural deformations in the chosen blade profile. This paper highlights aero-mechanical features of centrifugal impeller obtained from several numerical simulations, which are expected to provide a sound basis for further investigations.