Combustion Design

[CH3NO2]

Congratulations Chris! Take your time. You are going to be a bit more than pre-occupied with the greatest experience in life ever.

[smithy1]

Congrats Chris....hope mum and bub are both well when it eventually happens..

Smithy.

[madpatty]

Hi Chris,

Congratulations... Best wishes to the family.

Cheers.

[stoffe64]

Congratulations Chris,that is The greatest to get children!!

[finiteparts]

Thanks everyone for the well-wishes. We had a 6 lb 9 oz, happy and healthy baby girl. She is doing great and I need to start getting to work on spurring her interest in all things turbine related! Ha!

[madpatty]

Lots of best wishes Chris.

Congrats to the family.

[racket]

Hi Chris

Congratulations on the new arrival ............she'll keep you "spinning" ;-)

Cheers
John

[CH3NO2]

Congratulations Chris!

Now the best experience of life begins. Take lots of pictures along the way. The time goes by fast.

[Chuks]

Congratulations sir, make sure to get her a suitable ear muffs

[CH3NO2]

Hi Chris,

I was wondering... Why is Pressure Loss Factor (PLF) referenced to the outer case diameter as opposed to the annular flow area?
Is PLF to calculate the dynamic loss going to the flame can holes? It doesn't seem to account for the flame can diameter.

Thanks,
Tony

PS - How's life as a new Dad?

[finiteparts]

Hi Tony,

That is a weird thing about Lefebvre's method...it does not refer to flame can diameter. He specifically calls out that when defining the reference parameters, it refers to the largest cross-sectional area of the combustor case, "...in the absence of a liner,..." I'll have to look into this and see why it is like this. I was asked this same question when I presented the combustor design at school and I meant to find out back then.

As for the PLF, it also uses the reference dynamic pressure.

I thought that using the reference parameters was odd, neglecting the liner, etc...but when I tried to modify this approach, I found that my pressure drops at the design point were off quite a bit. When I have used the equations as presented, things fell in line quite nicely. As an example, my Senior Design project combustor, I designed for a pressure drop at the design point of 5% based on the design. CFD calculated 4.6% which I attributed to Cd differences on the larger holes (reading off Cd values from an old chart can definitely introduce errors). The cold flow checks, when corrected for compressible flow effects showed closer to 4%...not too bad for simple equations and once I found some errors in the actual amount of flow area. The modified calcs result in increased reference dynamic pressure and thus under predicts the required target effective area...this translates to a higher pressure drop than expected.

I should also mention that I have gotten bit in the past on leakages. The slip fits look small, but they can be a good percentage of the target effective flow area and when we added in the leakage flow areas to our Senior Design project combustor, it took us down closer to the 4% pressure drop that the cold flows showed. The problem is, discharge coefficients are hard to estimate for some of the leakage paths, small annular gaps, etc..

I really need to get back to this post. I feel like I mentioned a few first steps, but I haven't started talking about sizing holes, estimating zonal lengths, and other stuff that I have forgotten. Maybe soon I can get back into this.

Mom and baby are doing great. Ava is to the point where she looks at you and smiles, makes cute baby noises and then the face changes to a not so happy face and then my face turns not so happy when I have to change that diaper. Ha! I have heard that it gets worse when they start eating solid food, so I guess I have something to look forward too! ha! She is awesome though! It will be nice when she can sleep a bit longer. Melissa and I are trading off on the weekends so we can each get some good sleep. This means that I can't do anything for 6 or 8 hours on weekend mornings because everytime I get Ava to sleep, I crack open a book or log on, she wakes up...like she has a radar that is tuned to make sure that I can't do anything else but hold her. Ha! She is cute and totally worth it though!

Chris

[CH3NO2]

HaHa! That's awesome. Boy I remember it all like it was yesterday. Looking into her eyes. The smiles. The crying. The lullabys. The colic. Changing diapers. The sleep shifts. The anti-private time radar detector. And falling in love all over again.

Take TONS of pictures from now on! You will be glad you did.

Tony

[CH3NO2]

Hi Chris and all,

For a given Primary Zone hole area and air flow rate, when using a curved vane swirler at the dome of a flame can what is typically the percent of Primary Zone Air flowed through the swirler Vs how much is injected radially from the holes around the Primary zone?

Thanks,
Tony

[racket]

Hi Tony

Around a third of primary air through the swirler should do the job , so ~10% of overall FT hole area

Cheers
John

[finiteparts]

Hi Tony,

That is a very open ended question. Some combustors are designed to bring in all the primary air through the swirler, while some use both the swirler air and a portion of the primary jets, and lastly, some do not use a swirler at all, relying only on the primary jets to set up the dome recirculation needed in the primary zone. Assuming that you are using a swirler, properly placed primary holes will see the low pressure zone created by the swirler and the low pressure zone at the combustor exit, thus they will split the primary jet flow in some proportion between the two.

Lefebvre suggests that you assume 50% of the primary jet gets pulled forward into the swirler recirculation bubble, while the other half travels backward into the SZ flow. This is key, since without a swirler, you would assume all the air from the PZ jets goes to the PZ airflow, but now that you have a swirler, you have changed the combustor internal pressure field and only half of the primary jet flow contributes to the PZ airflow.

If you look at the work of Melconian and Modak in Sawyer's Gas Turbine Handbook, they do share that their experience shows satisfactory performance with 1/3 of the primary air going through the swirler. I took that to be their suggestion of the lowest PZ swirler flow, which is supported by them later suggest that because of the swirler airflow uncertainty, they suggest sizing the swirler to flow 50% of the PZ flow and using blanking plates to modify the PZ flow during development if necessary.

I would highly recommend using Lefebvre's book to size the swirler, as it gives some better rules of thumb to determine sizing and guessing a discharge coefficient for it might be challenging. Like John suggested, I also think that flowing a third of the PZ air through the swirler is a good start.

Good luck!

Chris