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A study on an axial-type 2-D turbine blade shape for reducing the blade profile loss

Abstract

Losses on the turbine consist of the mechanical loss, tip clearance loss, secondary flow loss and blade profile loss etc.,. More than 60 % of total losses on the turbine is generated by the two latter loss mechanisms. These losses are directly related with the reduction of turbine efficiency. In order to provide a new design methodology for reducing losses and increasing turbine efficiency, a two-dimensional axial-type turbine blade shape is modified by the optimization process with two-dimensional compressible flow analysis codes, which are validated by the experimental results on the VKI turbine blade. A turbine blade profile is selected at the mean radius of turbine rotor using on a heavy duty gas turbine, and optimized at the operating condition. Shape parameters, which are employed to change the blade shape, are applied as design variables in the optimization process. Aerodynamic, mechanical and geometric constraints are imposed to ensure that the optimized profile meets all engineering restrict conditions. The objective function is the pitchwise area averaged total pressure at the 30 % axial chord downstream from the trailing edge. 13 design variables are chosen for blade shape modification. A 10.8 % reduction of total pressure loss on the turbine rotor is achieved by this process, which is same as a more than 1 % total-to-total efficiency increase. The computed results are compared with those using 11 design variables, and show that optimized results depend heavily on the accuracy of blade design.

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Abbreviations

A :

Blade sectional area

Cl :

Blade loading coefficient (lift/dynamic pressure)

C p :

Pressure coefficient

Cx:

Axial chord length

Ct:

Tangential chord length

ds :

Length between the inflection points

h :

Enthalpy

k :

Turbulence kinetic energy

P :

Pressure

Pt*:

Total pressure normalized by double of dynamic pressure

Re :

Reynolds number

T :

Temperature

v :

Absolute velocity

w :

Relative velocity

x :

Axial length from the leading edge on a blade

xl :

Violating length by the inflection point

X :

Design variables

Y :

Total pressure loss coefficient

β:

Flow angle

ɛ:

Turbulence dissipation rate

θ:

Angle on the blade surface

ρ:

Density

σ:

Standard deviation

ξ:

Enthalpy loss coefficient

0:

Initial value

in:

Inlet flow condition

out:

Outlet flow condition

N:

Nozzle

R:

Rotor

t:

Stagnation

t-t:

Total-to-total

∞:

Value at reference location

1,2,3:

Nozzle inlet, nozzle exit, rotor exit

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Correspondence to Soo-Yong Cho or Eui-Soo Yoon or Bum-Seog Choi.

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Cho, S., Yoon, E. & Choi, B. A study on an axial-type 2-D turbine blade shape for reducing the blade profile loss. KSME International Journal 16, 1154–1164 (2002). https://doi.org/10.1007/BF02984026

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Key Words

  • Turbine Blade Design
  • Turbine Blade Optimization
  • Axial-Type Turbine
  • Shape Parameters
  • 2-D Turbine Blade
  • Compressible Flow Analysis
  • Heavy Duty Gas Turbine