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Research Papers

Effects of Rotor Tip Blade Loading Variation on Compressor Stage Performance

[+] Author and Article Information
Aniwat Tiralap

Department of Mechanical Engineering,
MIT Gas Turbine Laboratory,
Cambridge, MA 02139
e-mail: aniwat@mit.edu

Choon S. Tan

Department of Aeronautics and Astronautics,
MIT Gas Turbine Laboratory,
Cambridge, MA 02139

Eric Donahoo, Matthew Montgomery

Siemens Energy, Inc.,
Orlando, FL 32828

Christian Cornelius

Siemens AG,
Mulheim an der Ruhr 45473, Germany

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received September 6, 2016; final manuscript received October 28, 2016; published online January 24, 2017. Editor: Kenneth Hall.

J. Turbomach 139(5), 051006 (Jan 24, 2017) (11 pages) Paper No: TURBO-16-1227; doi: 10.1115/1.4035252 History: Received September 06, 2016; Revised October 28, 2016

Changes in loss generation associated with altering rotor tip blade loading of an embedded rotor–stator compressor stage are assessed with unsteady three-dimensional computations, complemented by control volume analyses. Tip-fore-loaded and tip-aft-loaded rotor blades are designed to provide variation in rotor tip blade loading distributions for determining a compressor design hypothesis that aft-loading a rotor blade tip yields a reduction in loss generation in a stage environment. Aft-loading a rotor blade tip delays the formation of tip leakage flow, resulting in a relatively less mixed-out tip leakage flow at the rotor outlet and a reduction in overall tip leakage mass flow, hence a lower loss generation. However, the attendant changes in tip flow angle distribution are such that there is an overall increase in the flow angle mismatch between tip flow and main flow, leading to higher loss generation. The latter outweighs the former; therefore, rotor passage loss from aft-loading a rotor tip is higher unless a constraint is imposed on tip flow angle distribution so that the associated induced loss is negligible. Tip leakage flow, which is not mixed-out at the rotor outlet, is recovered in the downstream stator. The tip leakage flow recovery process yields a higher benefit for a relatively less mixed-out tip leakage flow in the tip-aft-loaded rotor blades on a time-averaged basis. These characterizing parameters together determine the attendant overall loss associated with rotor tip leakage flow in a compressor stage environment. The revised design hypothesis is thus as follows: A rotor should be tip-aft-loaded and hub-fore-loaded while a stator should be hub-aft-loaded and tip-fore-loaded with tip/hub leakage flow angle distribution such that it results in no additional loss. For the compressor stage being assessed here, an estimated 0.15 points enhancement in stage efficiency is possible from aft-loading rotor tip only.

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References

Figures

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Fig. 1

The locus of the peak blade loading on a rotor and a stator blade designed according to the proposed design guideline

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Fig. 2

Reduced frequency of tip leakage flow from various published results as well as current computations. Adapted from Ref. [28].

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Fig. 3

Periodic behavior of corrected mass flow suggesting overall periodicity and convergence of unsteady computations. (a) Temporal variation in corrected mass flow over 11 blade passing periods (ten cycles). (b) Similar distribution in frequency of corrected mass flow temporal variation collected over two different one-revolution time periods.

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Fig. 4

Time-averaged blade loading distribution of the tip-aft-loaded, tip-fore-loaded, and original rotor blades at two locations: (a) near blade tip (1% span below the tip) and (b) 75% span

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Fig. 5

Minimal changes in the flow fields outside the tip region at the rotor outlet in the tip-aft-loaded and tip-fore-loaded blade designs: (a) radial distribution of total pressure and (b) radial distribution of flow angle

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Fig. 6

Changes in time-averaged loss generation in the rotor–stator compressor stage of the tip-aft/fore-loaded rotor blade designs

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Fig. 7

Time-averaged tip leakage mass flow distribution in various blade designs

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Fig. 8

Changes in time-averaged loss from tip leakage flow formation delay

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Fig. 9

Effect of tip leakage flow formation delay on the time-averaged local entropy generation rate in the tip region (75% span to 100% span)

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Fig. 10

Flow angle mismatch between the main flow (at 80% span) and the tip flow (at the midtip clearance)

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Fig. 11

Effect of tip blade loading variation on total tip leakage mass flow in the four blade designs

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Fig. 12

Tip leakage flow mixed-out loss from the control volume method and computed results

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Fig. 13

Attenuation of axial velocity disturbance of tip leakage flow (in the dashed circle) in the downstream stator passage: (a) stator inlet and (b) stator outlet

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Fig. 14

Attenuation of two layers of streamwise vorticity disturbance (positive and negative disturbance in the dashed circle) in the downstream stator passage: (a) stator inlet and (b) stator outlet

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Fig. 15

Time-averaged overall computed loss in a stage environment from the key flow effects: (a) stage total, (b) tip leakage formation delay, (c) tip leakage flow angle mismatch and mass flow, and (d) stator

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Fig. 16

The progression of structure and velocity disturbance of rotor wake in a stator [11]

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Fig. 17

The distribution of velocity disturbance and two layers of streamwise vorticity in tip leakage flow

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Fig. 18

The stretching of tip leakage flow and the attenuation of streamwise vorticity in a diffuser

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Fig. 19

The ineffective attenuation of axial velocity disturbance when tip leakage flow (in the dashed circle) enters the stator in the proximity of the stator blade SS: (a) stator inlet and (b) stator outlet

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Fig. 20

The ineffectiveness of the tip leakage recovery process due to lack of alignment in the direction of velocity disturbance and stretching of the fluid contour

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