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Vikram October 20, 2005 09:52

Stage Interface Without Frame Change

My doubt is about the interface options offered by CFX 5 in the Turbo Mode.

CFX documentation says the following about the stage interface "…Two or more blade passages are solved simultaneously with circumferential "averaging" between rotating and stationary regions. The stage averaging at the frame change interface incurs a one-time mixing loss. This loss is equivalent to assuming that the physical mixing supplied by the relative motion between components is sufficiently large to cause any upstream velocity profile to mix out prior to entering the downstream machine component."

What does CFX do when we use a stage interface without frame change. Is there a mixing plane assumed again? Because if there is no frame change then there is no relative motion and therefore no mixing. So if we use a mixing plane in this situation we would be non-physical as far as the mixing is concerned.

This is a worrisome issue if there are some CFX experts or CFX support guys who could answer this it would be great.

Regards, Vikram

PS: Robin, any comments?

Neale October 20, 2005 22:14

Re: Stage Interface Without Frame Change
Why are you worried? If there is no frame change then don't use the Stage model???

Perhaps you are talking about the "Same Frame with Stage" frame change option? This model still circumferentially averages the flow from upstream to downstream. It is a model after all and may or may not be appropriate to your particular situation.

Vikram October 21, 2005 04:55

Re: Stage Interface Without Frame Change
Hi Neale,

I am worried because there is a pitch change. With a stage interface I can reduce the mesh size by a factor of two. If I use a None interface I have to employ multiples of a grid on both sides(7 on 1 and 2 on the other instead of 1 on each side). The mesh size is huge even if I use a stage interface. So I don't have time to experiment with both the interfaces.

Regards, Vikram

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