[assassin not ass ass in]

Is anyone familiar with star ccm tutorial "Blade element method: helicopter rotor-fuselage interaction"?


In this tutorial,

Trim Thrust is used to reach target thrust and leading to the increase of collective pitch angle. i want to keep the collective pitch angle constant, but If i don't use trim thrust option, why can't i reach the target thrust?

[kepler123]

You should look into the documentation once more.

You have defined a pitch and ask starccm to change this for you using the trim thrust option. But if you say, hey do not change my pitch, how do you expect the thrust to change? For the same angle of attack (different on each part of the rotor) you are going to get certain force coefficients which sum up to give you the overall thrust.

If you do not want to change pitch in order to alter thrust the other option is to allow a chance in the rpm which will change the localised angle of attack thus giving you a different thrust. If you can achieve your desired thrust this way depends on the rotor and what you setup. But this is also true when you allow a change in pitch.

I have not had to change rpm so you would have to look into how you can do this yourself.

[assassin not ass ass in]

Friend, I'm really glad you replied to me.


I have looked through the document many times. This simulation is a reproduction of a NASA article:Mineck, R.E. and Gorton, S.A. 2000 "Steady and Periodic Pressure Measurements on a Generic Helicopter Fuselage Model in the Presence of a Rotor" , NASA/TM-2000-210286.


The NASA experiment was conducted under fixed collective pitch angle conditions, so I was sure my simulation was also under fixed conditions.
However, the thrust obtained under fixed conditions(which means no trim thrust) was less than that of the NASA experiment(about 350lb),
and I wanted to know why, what went wrong, and my every step was the same as the documentation apart from trim thrust option.


In addition, the document defines the collective pitch angle in one sentence:the pitch angle consists of a collective part theta, which is the same for each blade, so I do not know how them define the specific mathematical method of collective pitch angle.

[kepler123]

Look at the tutorial. It includes a file with the twist of the blade. Make sure you have your blades defined correctly with the pitch from the right location (hub as reference), etc.

If you say your model is supposed to reach a certain thrust with certain settings then that has nothing to do with the pitch algorithm. Also make sure that your units are mentioned in the header of any table you use for lift and drag characteristics, twist, etc. if you are not using SI