Bladed Knowledge Base

Inflow angle vs angle of attack
Category: Aerodynamics

Problem

What's the relationship between inflow angle (phi) and angle of attack (alpha)?

Related question - what coordinates are they expressed in? 

Solution

See Table 7-3 in the Bladed 4.9 manual, also referring to Figure 7-18.

 

Inflow angle = Angle between effective flow speed velocity vector and tangential direction of rotor plane (φ in the figure) 

Angle of attack = Angle between effective flow speed vector and local chord line (α in the figure) expressed at the quarter chord point



The inflow angle is in a coordinate frame based on the un-coned rotor plane, whereas the angle of attack is in the deflected blade station frame.

Thus the cone angle will have an effect on the alpha value, but not the phi value. The only circumstances in which they will be the same is for a blade with no cone, twist or pre-bend / pre-sweep, and with a pitch angle of zero.






Keywords Angle of attack, inflow