Turbine Blade Static Strength assessment
Nonlinear static strength analysis of the cooled turbine blade was performed.
Finite element model (FEM) was built based on finalized 3D CAD design (Figure 1). Mesh model consisted of 3D hexahedral and tetrahedral elements. FEM was refined in regions with stress concentration (blade root section and fillets).
Material’s stress-strain nonlinearity and changes in yield and ultimate stress area were taken into account.
Turbine blade alloy have yield stress at 490 MPa and ultimate stress at 605 MPa for maximum operatiing temperature 1100 deg C. Variation of material Young's modulus due to temperature was also taken into account.
In temperature range 750-900 deg C abnormally mechanical properties observed. Yield and tensile strength a bit increase when temperature reaches 900 deg C and only then decrease (Figure 2).
Turbine blade was investigated according to the three main types of load:
All these loads were taken into account in analysis preparation.
Aerodynamic load was distributed on the blade.
Pressure drop on the blade profile is about 0.5 MPa.
Working speed of the turbine is 3000 rpm.
Blade temperature is in range 500 - 1100 deg C.
In the results stress and deformation levels were determined and investigated. Figures with stress (Figure 3) and displacement (Figure 4) diagram are shown in the left.
Maximum radial displacement is approx. 4.2 mm.
Small areas of plastic strain occur near contact reagions.
Maximum stresses in the root section of the blade (Figure 5) are not exceed limitation.
Figure 5. Equivalent Von Mises stress in the root section of the turbine blade
Figure 4. Radial displacements in the turbine blade
Figure 3. Equivalent Von Mises stress in the turbine blade
Figure 1. 3D CAD model of the turbine blade
Figure 2. Changes of yield and ultimate stress vs temperature