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Old   February 13, 2007, 11:43
Default Similarity on helicopter blade model
  #1
al-ayyubi
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Hi everyone! I would like to ask on how to simulate an helicopter blade by having scaled down model by 10:1 ratio. This means that the heli model is 10 times smaller that the actual size. I've done some sumulations and refered with some lecturers, it seems that my results are unlogic. This is due to a drastic scaled-down ratio yields hypersonic Mach no. at the tip of the blades. So,would it be possible if I simulate hover flight condition by maintaining the same ratio(10:1) in a different fluid properties, such as glycerine or something...can anyone guide me? This is due to limitation of computer capabilities and storage and also time consuming. If this could be done,I can take a shorter time to complete 12 simulations

For your info, i'm studying the blade tip effect on the heli performance...Hope to hear from all of you soon...Thanks

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Old   February 13, 2007, 11:50
Default Re: Similarity on helicopter blade model
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Lionel S.
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Did you use Reynolds similarity ?

Because as far as I know, I think that it's very difficult to get transonic phenomenas similars while performing a Reynolds similarity. You can either use Reynolds similarity, or Mach number similarity, but both may be impossible to achieve.

Still, maybe I'm wrong...
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Old   February 17, 2007, 11:42
Default Re: Similarity on helicopter blade model
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al-ayyubi
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Yes! I do consider the same Re no. But when I refer fluid dynamics again, in order to get an accurate result (dynamic similarity), both Re no and Mach no have to be consider the same...or in the same region. I found it too confusing. Oh my God....please anyone in this forum, please guide me. Can I simulate using different fluid properties other than air?
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Old   February 18, 2007, 08:20
Default Re: Similarity on helicopter blade model
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Lionel S.
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"both Re no and Mach no have to be consider the same" If you are working on transsonic motions, yes, that's right.

"Can I simulate using different fluid properties other than air?"

NO ! I think it's too difficult to find a situation where you have both the same (or nearly same) Re and Mach numbers. Maybe these situations exists somewhere, but it's not sure (depending on the situation). And if you are not used with fluid dynamics, it will be very difficult.

So I would say that you cannot use similarity in this case.

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