# Propeller

Dear all,

I am modeling a propeller in Adams using AeroDyn as the aerodynamic model.
Knowing that Aerodyn is created for wind-turbines, I had to be creative in determining the orientation of the blade markers and wind direction.

This all seems to word very well, however I am encountering one problem.

My area of interest is especially the zero-wind condition (at the beginning of take-off), however there seems to be no induced velocity in this case. I am taking into account the wake, as I am using the SWIRL option and at non-zero inflow velocity the induction factor is not zero.
Does aerodyn not model a wake when the wind velocity is 0, or am I doing something wrong?

Dear Lysander,

If there is no flow passing through the rotor, than there can be no induction. When you set the wind speed to zero in AeroDyn, you are implying that there is no flow passing through the rotor.

In your example–where the propeller spins in the abscence of wind or forward speed (e.g., at the beginning of take off)–flow still passes through the rotor when the thrust is nonzero, so, the flow speed upstream of the rotor will be nonzero. To model this case in a wind turbine code, this flow speed upstream of the rotor is what you must specify as the “apparent” wind speed. Of course, a propeller is different from a wind turbine in that the wake contracts in the former and expands in the later. So, the flow in the wake of propeller will be faster than the updstream flow, which means that the induction factor should be negative for the propeller state in a wind turbine code.

I haven’t modeled this state in AeroDyn before, but I assume that the code will work in this case to at least moderately negative induction factors (-0.4 < a < 0). AeroDyn uses the Glauert correction to model the turbulent wake state for a > 0.4, so, I wouldn’t trust AeroDyn for a propoller with high (a < -0.4) induction. But perhaps someone with more knowledge of the workings of AeroDyn can answer this question better.

Best regards,

Hello Jason,

One thing about the induction factor.
In order to correctly model the orientation of the element airfoils, I had to implement a negative angle of attack in combination with a negative wind direction (it would be easier to show this with a picture… but I hope you see what I mean).
This results in a positive induction factor after all.

So logically, the dynamic stall modeling (at a > 4 ) should function correctly am I right?

Dear Lysander,

I don’t think forcing the axial induction to be positive by using a negative wind speed will give you the desired result.

In a wind turbine code, like AeroDyn, the propeller state is modeled with a < 0. The wind turbine state is modeled with 0 < a < 0.5, the turbulent brake state is modeled with 0.5 < a < 1.0, and the vortex ring state is modeled with 1.0 < a. In each of these wake states, a simple plot of thrust coefficient, CT, versus axial induction, a, takes on a different form. See, for example, Figure 3.6 of this paper: wind.nrel.gov/designcodes/papers … h_1974.pdf. CT is not symmetric about zero. So, I don’t think a propeller should be modeled in a wind turbine state with negative wind speed.

But perhaps someone with more knowledge of the workings of AeroDyn can answer this question better.

Best regards,