Wind Turbine Aerodynamics - 5a - Steady Momentum Model

17 August 2026, Galih Bangga

• Usually assumed to be 1-dimensional
• Wake rotation can be included or excluded
• Introducing the definition of induced velocity and induction factors

Blade Element Momentum Method

When wake rotation is considered, the rotational speed of the flow in the wake increases from $\omega$ to $\omega + \omega_w$ - The wake rotational velocity varies throughout the span (higher towards the tip)

Turbulent Wake State Correction

• induction factor larger 0.5 causes momentum theory to break down
• this condition is called turbulent wake state
• therefore, different empirical relations for $C_T$ and $a$ are needed (Glauert, Spera, Buhl)

Tip Loss Correction

defined in the form of axial induction, circulation or aerodynamic coefficient

Combination of Momentum Theory and Blade element Theory: Blade Element Momentum Theory: BEM

BEM procedure can be found on slide 20

Double Multiple Stream Tube Model DMS

• Similar to BEM, but for VAWT
• Differentiates the induction factor between the first upwind half and the second downwind half
• VAWT can be represented by a pair of actuator discs at each level of rotor
• Can be improved with correction models such as DMS CAM, DMS WE, DMS DS
• See slide 23