Abstract
A new geometry parametric method of winglet-cavity tip has been introduced in the optimization procedure based on three-dimensional steady CFD numerical calculation and analysis. Firstly, the reliability of numerical method and grid independency are studied. Then an aerodynamic optimization is performed in an unshrouded axial high pressure turbine with winglet-cavity tip. The optimum winglet-cavity tip has higher turbine stage efficiency and smaller tip leakage mass flow rate than the cavity tip and flat tip. Compared with the results of cavity tip, the effects of the optimum winglet-cavity tip indicate that the stage efficiency is improved effectively by 0.41% with less reduction of tip leakage mass flow rate. The variation of turbine stage efficiency with tip gap states that the optimum winglet-cavity tip obtains the smallest efficiency change rate ∆η/(∆τ/H). For the optimum winglet-cavity tip, the endwall flow and blade tip leakage flow pattern are used to analysis the physical mechanical of losses. In addition, the effects of pressure-side winglet and suction-side winglet are analyzed respectively by the deformation of the optimum winglet-cavity tip. The numerical results show that the pressure-side winglet reduces the tip leakage flow effectively, and the suction-side winglet shows a great improvement on the turbine stage efficiency.
Nomenclature
- Notation
- c
Axial chord
- cp
Specific heat capacity at constant pressure
- Cp
Static pressure coefficient
- Cpt
Total pressure loss coefficient
Mass averaged total pressure loss
- d
Winglet extension width
- h
Normalized blade span
- H
Blade height
- mleak,r
Relative tip leakage mass flow rate
- mleak
Tip leakage mass flow rate
- mmain
Main mass flow rate
- M
Torque
- Ma
Mach number
- p
Pressure
- P
Pitch
- R
Relative arc length
- T
Temperature
- y+
Dimensionless distance from the wall
- α
Angle between tip leakage flow and main flow
- α2
Flow angle of blade outlet
- β
Winglet blending angle
- γ
Specific heat ratio
- τ
Tip clearance
- η
Turbine stage efficiency
- ν
Velocity
- ω
Rotating velocity
- ∆mleak,r/(∆τ/H)
The change rate of relative tip leakage flow to tip clearance
- Δs
Entropy production
- ∆η⁄(∆τ/H)
The change rate of turbine efficiency to tip clearance
- Subscripts
- end
Winglet ending point
- leak
Leakage flow
- main
Main flow
- mix
Mixing
- P
Pressure side
- r
Relative value
- start
Winglet starting point
- S
Suction side
- t
Stagnation value
- 0
Vane inlet
- 1
Blade inlet
- 2
Blade outlet
Funding
The work was supported by theNational Natural Science Foundation of China (grant numbers 51776048 and 51436002).
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