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Andy QUB June 8, 2010 09:12

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,

Max Efficiency July 7, 2010 08:52

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).

Andy QUB July 7, 2010 08:55

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.

Max Efficiency July 8, 2010 03:41

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).

Andy QUB July 8, 2010 05:10

Great, thanks..

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