Parametric Study of Blade Profile Losses

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Parametric Study of Blade Profile Losses

• P M V Subbarao
• Professor
• Mechanical Engineering Department

Identification of Additional Design Variables.
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Overall profile loss Vs Lift
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Stage Velocity Triangle to Achieve a Lift
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Design of Blade Angles for Minimum Profile Losses
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Class 1 Guided Flow Selection of Profile
Parameters

• Relative profile thickness, tmax/b,
• Position of maximum thickness, xtmax/b
• Relative radius of curvature, Ru/Rd

Depending on the distribution of Design loading,
decisions are made on the position of maximum
thickness, the relative value of curvature
upstream and downstream of the throat, Ru/Rd.
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Preferred Ranges of Key design parameters
0.20ltxtmax/blt0.35, 0.15lttmax/blt0.30 and 4.0 lt
Ru/Rd lt 10
The lower range of Ru/Rd corresponds to a lower
degree of aft loading.
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The Seriousness of Unguided Flow
Attached flow
Flow stall on Suction side
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Class 2 Unguided zone design parameters

• One major aspect of profile design is the
  behaviour of flow in the unguided zone.
• In this zone, flow diffusion takes place.
• The flow behaviour in the unguided zone highly
  influenced by
• curvature variation and turning downstream of the
  throat,
• the wedge angle and
• the trailing edge thickness.

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Unguided Zone
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Losses in Unguided Zone Nozzle Cascades
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Losses in Unguided Zone Bucket Cascades
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Clues to Design Unguided Zone

• These parameters determine the resulting
  dissipation in the dead steam region.
• The deviation angleand must be carefully
  optimized during the profile design process.
• The trailing edge thickness, having the
  predominant influence on trailing edge loss
  generation, has to be reduced to a minimum
  thickness compatible with structural and
  manufacturing constraints

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Class 3 Leading Edge Parameters

• Leading edge radius, LER,
• Wedge angle, eLE

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Clues to Design Leading Edge

• The sizing of the leading edge radius and leading
  edge wedge angle has to be compatible with
  incidence range considerations.
• Higher values of eLE are desirable.
• Quasi 3D and 3D design aspects also important to
  control (reduce) loading in the leading edge
  region.

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Correlations for Profile Losses

• The profile loss correlation is presented in the
  form of a basic loss correlation for
  incompressible flow conditions.
• A basic correlation is derived original low speed
  tests where it is assumed that the Ma effects are
  negligible.
• To this basic value multiplying correction
  factors are presented which are to be applied
  where values of the other parameters differ from
  the standard values assumed in the basic
  condition.

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Effect of Mach Number
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Performance of Supersonic Blades
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Performance of Supersonic Blades