This article presents the detailed study of rotor tip leakage related phenomena in a low speed axial compressor rotor passages for three sweep configurations [Unswept (UNS), Tip Chordline Swept (TCS) and Axially Swept (AXS)]. Fifteen domains are numerically studied with 5 sweep configurations (0°(), 20° () TCS, 30° () TCS, 20° () AXS, and 30° () AXS) and for 3 tip clearances (0.0%, 0.7% and 2.7% of the blade chord). Results were well validated with experimental data. Observations near the tip reveal that UNS rotor shows high sensitivity than the swept rotors in the blade pressure distribution with change in tip clearance. AXS rotor has high loading capability and less tip clearance effect on blade loading at the near stall mass flow. Downstream shift of the vortex rollup along the chord is observed with increased flow coefficient and increment in the tip gap height. In particular, the effect of flow coefficient is more predominant on this effect. Tip vortex-related flow blockage is less with the swept rotors. Among the rotors, the AXS rotor is found to incur low total pressure losses attributable to tip leakage. Effect of incidence is observed on the flow leakage direction. Copyright © 2010 P. V. Ramakrishna and M. Govardhan.

Mukka S. Govardhan

AXIAL-FLOW COMPRESSOR

BLADE CHORD

blade loading

BLADE PRESSURE

Experimental data

FLOW BLOCKAGE

Flow coefficients

GAP HEIGHT

HIGH LOADINGS

High sensitivity

Low speed axial compressor

Mass flow

ROTOR TIP

SWEPT ROTORS

Tip clearance

TIP LEAKAGE

Tip vortex

Total-pressure loss

Axial flow

Axial flow turbomachinery

ROTORS

Compressors

Fulltext

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Study of Sweep and Induced Dihedral Effects in Subsonic Axial Flow Compressor Passages—Part II: Detailed Study of the Effects on Tip Leakage Phenomena

International Journal of Rotating Machinery

This article presents the study of Tip Chordline Sweeping (TCS) and Axial Sweeping (AXS) of low-speed axial compressor rotor blades against the performance of baseline unswept rotor (UNS) for different tip clearance levels. The first part of the paper discusses the changes in design parameters when the blades are swept, while the second part throws light on the effect of sweep on tip leakage flow-related phenomena. 15 domains are studied with 5 sweep configurations (0 °, 20 °TCS, 30 °TCS, 20 °AXS, and 30 °AXS) and for 3 tip clearances (0.0%, 0.7%, and 2.7% of the blade chord). A commercial CFD package is employed for the flow simulations and analysis. Results are well validated with experimental data. Forward sweep reduced the flow incidences. This is true all over the span with axial sweeping while little higher incidences below the mid span are observed with tip chordline sweeping. Sweeping is observed to lessen the flow turning. AXS rotors demonstrated more efficient energy transfer among the rotors. Tip chordline sweep deflected the flow towards the hub while effective positive dihedral induced with axial sweeping resulted in outward deflection of flow streamlines. These deflections are more at lower mass flow rates. Copyright © 2009 P. V. Ramakrishna and M. Govardhan.

Study of sweep and induced dihedral effects in subsonic axial flow compressor passages - Part I: Design considerations - Changes in incidence, deflection, and streamline curvature

Experimental investigations were carried out on a two-dimensional cascade fitted with a 120° deflection rotor blades to study the effect of incidence angle on the endwall flow in the presence of tip clearance. A total of five incidence angles, namely: -10°, -5°, 0°, 5°, 10° were chosen and for each incidence angle, the experiments were conducted for five tip clearance values at a constant space -chord ratio of 0.79. The results are presented in the form of contours of static pressure coefficient on the endwall and the blade tip surface. In addition, the variation of static pressure coefficient ahead of the blade leading edge and from the pressure surface to the suction surface at various axial stations, and discharge coefficient at different axial stations are presented. The results indicate that the adverse pressure gradient upstream of the leading edge is reduced as tip clearance is increased. The contours of static pressure coefficient on the endwall indicate a deep low-pressure trough near the suction surface in comparison to the normal trough for zero clearance. Loading also increases as incidence changes from the negative to positive values. Due to area contraction caused by the tip separation vortex, the fluid moving towards the tip gap from the pressure side is accelerated. Downstream of the tip separation vortex, the endwall pressure increases due to flow mixing. The maximum value of discharge coefficient increases and the point at which maximum value occurs shifts towards leading edge when incidence is changed from-10° to 10°.

Journal of Thermal Science

Experimental study of endwall and tip clearance flows in a two - Dimensional turbine rotor blade cascade - Effect of incidence angle

Results obtained from an experimental study of the three-dimensional flow survey within and exit of a large deflection linear turbine cascade are presented for a tip clearance levels of 0.08, 1.5, 3.0 percent of chord and compared with the help of boundary layer probes and that within and exit of a blade passage was done with a miniaturised five hole probe. End wall and blade tip surface static pressures were also obtained, in addition to flow visualisation studies. A strong horse-shoe vortex forms in front of the leading edge for zero clearance whereas this vortex does not appear for 3 percent clearance indicating that for large clearance the pressure forces have dominating influence than the viscous forces. In addition to normally known clearance vortex, a small tip separation vortex was noticed on the blade tip surface inside the tip gap. Due to the area contraction caused by the tip separation vortex, the fluid moving towards the tip gap from the pressure side is accelerated. Downstream of the vortex, the endwall pressure increases due to flow mixing. Both vortices increase in size and strength along the chord. The mixing is incomplete in the aft portion of the blade. The tip gap velocity profiles exhibit wake like characteristics especially at axial positions where the mixing is incomplete. The passage vortex in the present investigations did not diminish with increase in clearance. The discharge coefficient and the total pressure loss coefficient within the tip gap show similar tendency with lower values near the leading and trailing edge regions.

Experimental investigations of the three-dimensional flow in a large deflection turbine cascade with tip clearance

Volume 7: Turbomachinery, Parts A and B

Combined Effects of Forward Sweep and Tip Clearance on the Performance of Axial Flow Compressor Stage

Journal of Turbomachinery

A Criterion for Axial Compressor Hub-Corner Stall

Study of sweep and induced dihedral effects in subsonic axial flow compressor passagespart II: Detailed study of the effects on tip leakage phenomena

Journal	International Journal of Rotating Machinery
ISSN	1023621X
Open Access	Yes