What Is Jet Engine Inlet Distortion?

[PhysMaster]

(This is a homework/lab assignment but thought it better suits in this category)

Hi,

This is a scaled model and I am given the pressure tap locations on each rakes. Also given is the pressure data.

Inlet distortion formula is given by: Pdist = (Pmax - Pmin)/Pavg

Question is to find the "total distortion across fan face", "radial distortion" and each "circumferential distortion".

I would appreciate it if some one gives me an insight about the problem and tell me what those terms mean? Which directions are those? I am having a hard time because the topic is not covered in my text.

Thank you,

Neo

(Undergrad Aero class)

 

[Cyrus]

I don't know what it is, but I figured it out from reading your post. I think you should do a little more thinking. The answer is right there, trust me.

 

[FredGarvin]

First things first, do you understand the concept of inlet distortion?

 

[PhysMaster]

Exactly! You know my problem.
I have no idea what they are talking about!
What's distortion and what's it got to do with pressure? (Google search results in very unrelated concepts)

Neo

 

[FredGarvin]

Here's a very basic exerpt from Heiser & Pratt's Aircraft Engine Design

 

[PhysMaster]

I see.
So I can just use the formula.
Radial distortion: use data for same rake, different taps (from center to outwards)
Circumferential: same pressure tap, different rakes
Across fan face: ?

What are some typical values for inlet distortion?

 

[Cyrus]

I see.
So I can just use the formula.

This sentence makes me cringe. "Ok, so its fine if I plug and chug away"...

From looking at your formula (and never having seen it before in my life) I can say that it looks like its a metric to see the quality of the flow. If the flow is good (i.e. highly uniform), then the distortion pressure is zero. That would mean the pressure is the same average value anywhere and everywhere. Pressure is related to velocity along streamlines. If they all have the same pressure, then its uniform inflow at the same speed.

This equation appears as a pseudo 'variance' of the flow.

http://upload.wikimedia.org/wikipedia/en/7/7e/Standard_deviation_illustration.gif

I think you have more than enough knowledge to infer and deduce what's going on yourself. Part of your process in becoming an engineer is to learn how to think and solve things for yourself.

 

[PhysMaster]

I've calculated the distortions and submitted the assignment. I got numbers like 0.00196 (fan face). But I have no idea if its correct because I have no reference. I'll figure out when I get it back.

Thanks for help Cyrus and FredGarvin.

Neo