Research Papers

Design of Compressor Endwall Velocity Triangles

[+] Author and Article Information
Kiran Auchoybur

Whittle Laboratory,
University of Cambridge,
Cambridge CB2 1TN, UK
e-mail: ka268@cam.ac.uk

Robert J. Miller

Whittle Laboratory,
University of Cambridge,
Cambridge CB2 1TN, UK
e-mail: rjm76@cam.ac.uk

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received September 22, 2016; final manuscript received October 20, 2016; published online February 1, 2017. Editor: Kenneth Hall.

J. Turbomach 139(6), 061005 (Feb 01, 2017) (11 pages) Paper No: TURBO-16-1254; doi: 10.1115/1.4035233 History: Received September 22, 2016; Revised October 20, 2016

The operating range of a compressor is usually limited by the rapid growth of three-dimensional (3D) separations in the endwall flow region. In contrast, the freestream region is not usually close to its diffusion limit and has little effect on overall range. In light of these two distinct flow regions, this paper considers how velocity triangles in the endwall region should be designed to give a more balanced spanwise failure across the span of a blade row. In the first part of this paper, the sensitivity of 3D separations in a single blade row to variations in realistic multistage inlet conditions and endwall geometry is investigated. It is shown that a blade's 3D separation size is largely controlled by the dynamic pressure within the incoming endwall “repeating stage” boundary layer and not the detailed local geometry within the blade row. In the second part of this paper, the traditional design process is “flipped.” Instead of redesigning a blade's endwall geometry to cope with a particular inlet profile into the blade row, the endwall region is redesigned in the multistage environment to “tailor” the inlet profile into downstream blade rows, giving the designer a new extra degree-of-freedom. This extra degree-of-freedom is exploited to balance freestream and endwall operating range, resulting in a compressor having an increased operating range of ∼20%. If this increased operating range is traded with reduced blade count, it is shown that a design efficiency improvement of ∼0.5% can be unlocked.

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Fig. 1

Stator 3D flow field in the repeating stage. LHS: conventional design and RHS: design used to tailor inlet endwall region (each at same off-design flow coefficient).

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Fig. 2

SMURF multistage low-speed compressor

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Fig. 3

Endwall geometry configurations considered

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Fig. 4

SMURF stator 2 experiment versus CFD model loss contours (CFD uses LHS measured profile), ϕ/ϕref = 0.85

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Fig. 5

Effect of blade row inlet conditions and local endwall geometry on endwall 3D separation size (ϕmid/ϕref = 0.92)

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Fig. 6

Parallel compressor model of freestream and endwall regions

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Fig. 7

Total pressure rise coefficient (LHS) and loading (RHS) characteristics for endwall and freestream regions

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Fig. 8

Ideal characteristics for changing exit flow angle

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Fig. 9

Movement of endwall loading characteristic with changing exit angle (±2 deg), extracted from CFD

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Fig. 10

The effect of blade exit flow angle on the spanwise distribution of φ, ω, and local cp (ϕ/ϕref = 0.85)

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Fig. 11

Endwall loss against pressure rise coefficient: LHS— nondimensionalized by freestream dynamic pressure and RHS—nondimensionalized by local endwall dynamic pressure

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Fig. 12

Schematic showing design procedure for blade rows with low and high endwall loss

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Fig. 13

Loss characteristics of freestream and endwall regions for the three case studies

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Fig. 14

Spanwise distribution of flow coefficient at stator inlet and stator exit wake loss (ϕ/ϕref = 0.77, ideal shroud)

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Fig. 15

Spanwise distribution of stator exit flow angle, rotor inlet flow coefficient, and rotor cp (ϕ/ϕref = 1.0, ideal shroud)

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Fig. 16

LHS: Loading characterisitics and RHS: loss characteristics of baseline design and redesign (ideal shroud)

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Fig. 17

Spanwise distribution of flow coefficient at stator inlet and stator exit wake loss (ϕ/ϕref = 0.79, real shroud)

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Fig. 18

LHS: Loading characterisitics and RHS: loss characteristics of baseline design and redesign (real shroud)

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Fig. 19

Spanwise distribution of flow coefficient at stator inlet and stator exit wake loss (ϕ/ϕref = 0.81, cantilever)

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Fig. 20

LHS: Loading characterisitics and RHS: loss characteristics of baseline design and redesign (cantilever)

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Fig. 21

Comparison of operating range for all the case studies: LHS—baseline designs and RHS—redesigns

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Fig. 22

Effect of new design method on overall operating range and design point efficiency (cantilever)

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Fig. 23

LHS: Loading characteristics and RHS: stator exit loss contours at ϕ/ϕref = 0.79, for SMURF baseline and redesigns

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Fig. 24

Influence of local endwall velocity triangle design on the “effective dynamic pressure factor,” F. LHS: Radial profiles, center: baseline velocity triangle (adapted from Koch [15] and Smith [18]), and RHS: endwall redesign velocity triangle.

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Fig. 25

Conventional and new method for increasing the “effective dynamic pressure factor”

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Fig. 26

Demonstration of endwall re-energization by endwall redsign. LHS: rotor exit traverse profile and RHS: stator exit loss contours, ϕ/ϕref = 0.85.




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