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For each point p of a mean line on a meridional flow surface a 2D coordinate frame is given by the circumferential direction t and the meridional direction m. The blade angle βB equals the tangent angle of the mean line in this frame. For the point p, this direction corresponds to the intersection of the mean surface with the m,t-plane, locally. By completing the frame in 3D with an orthogonal direction n (being perpendicular to t and m), other plane intersections with the mean surface can be analyzed.

While blade angle βB only depends on the mean line itself, blade lean angle λ is measured in n,t-plane and gives an information about the slope between mean lines in circumferential direction.

Using the surface normal direction nMS on mean surface the blade lean angle λ is calculated from the ratio of the portion in n and t:

With an example of a compressor some means for the manipulation of the blade lean angle are given:

•λ1↑: blade angle βB1 ↓

•λ1↑↓: move second Bezier point at leading edge

•λ1↑: wrap angle ↑

•λ1↑ and enlargement of the curvature: reduction of the meridional extension of the meridional contour