Pitch and frame change
 

Hi all,

Just a quick question. I'm simulating a rotor and the CFX literature often refers to pitch change and frame change at the interface between rotor and stator. I roughly undestand the principle but I don't really see a difference in the two. Could someone explain them for me as I can't find a definition anywhere?

Many thanks,
Andy

Also you have made this post nearly one month ago I will give you an answer:

A Frame Change occurs when you change the speed of rotation (for example from 310 rad/s to 0 rad/s -> Rotor - Stator). A change of speed from 310 to 155 rad/s is another example. In CFX you can do such a frame change with a Stage or with a Frozen Rotor Interface.

Pitch change is necessary if the number of blade is different. Example: 4 blades in rotor, 5 blades in diffusor. The pitch change describes the ratio between those different numbers (in this example 0.8).

Thanks for that. That makes much more sense now..

Just to clarify, is Frame Change for the two domains at a point in time (ie stator is stationary @ 0rad/s while the rotor is rotating at 310rad/s) or for when the relative rotational speed changes in time (ie, relative rotation between rotor and stator is 310rad/s and then changes to 0rad/s)? I think its the first option but I just want to be clear.

Frame Change is for one point in time. Your first assumption is correct.

Your second example (reduction of rotational speed from 310 rad/s to 0 rad/s) requires a transient simulation. Therefore you can nevertheless use a frozen rotor interface (as far as i know).

In this way both of your assumptions should be correct (the first one is to 100% correct, for the second assumption I'm not 100% sure).

Great, thanks..