Why These "Three Coordinates" (3D) Are Critical:

• Centrifugal impellers are complex 3D shapes with compound curves. 2D measurements (like using calipers or micrometers) are insufficient.

• Performance depends on precise 3D geometry. Small errors in blade twist or lean can cause imbalance, vibration, or reduced efficiency.

• Modern manufacturing (5-axis milling, casting) requires 3D verification to ensure the digital design is accurately realized.

Here’s a breakdown:

1. Geometric Profile Accuracy

• Blade Surfaces (Pressure & Suction Sides): The most critical measurement. A CMM probes numerous points along each blade's 3D surface contour to ensure it matches the designed airfoil profile within tight tolerances.

• Why it matters: Even minor deviations can drastically affect aerodynamic performance, efficiency, pressure ratio, and surge margins.

2. Dimensional & Positional Accuracy

• Key Dimensions:

  • Hub & Shroud Contours: The meridional flow path geometry.

  • Leading Edge (Inlet) & Trailing Edge (Outlet) Positions: Axial and radial locations must be precise to ensure proper flow entry/exit and alignment with diffuser.

  • Throat Area: Critical for determining flow capacity and Mach number.

  • Blade Heights and Tip Clearances: Affects efficiency and vibration.

• Why it matters: Ensures the impeller fits correctly in the assembly and maintains design flow/performance characteristics.

3. Orientation & Angular Relationships

• Blade Angles:

  • Inlet Blade Angle (β1bβ1b​): Influences incidence angle and shock losses.

  • Outlet Blade Angle (β2bβ2b​): Directly impacts work input, pressure rise, and slip factor.

• Blade Stacking Line: The alignment of blade sections from hub to shroud.

• Blade Perpendicularity/Twist: Ensures blades are correctly oriented relative to the axis of rotation.

• Why it matters: Correct angles are essential for optimal energy transfer and avoiding flow separation.