It's been a long time I've had a wish to write this article but couldn't make a start because of scarce of time.However, today I gonna make a start.Here I adopt TOM and JERRY as my characters. In this article, I intend to give you some aerodynamics knowledge in a funny way.
One day, the day which is not raining :) (saisai's song :))
TOM: Hey JERRY ! JERRY ....!
JERRY: what's up man !
TOM: come on ,let's go get tea while the weather is fine.
JERRY: Ah..! Great ! Let's go .
While they were having their teas, a helicopter flied over their heads. And TOM mouse whispered:
TOM: What a noisy object !
JERRY: What ?
TOM: You see,it's so noisy that I can't hear Layphyu's song.
JERRY: HAHAHA...! It's not such a noisy one because it's already optimized it's noise factor.
TOM: Please give me quite a clear cut.
JERRY: Alright...! To get a certification(permit to fly), noise problem is one of the factors a designer must consider. If your aircraft doesn't meet this requirement, just stop and get back from the start to optimize this problem so we sometimes call it 'show stopper'.
TOM: Ah. I see. You, engineers, are stupid enough to make a start again.
JERRY: Hey ! Don't say like that. Why we are carrying out this is for the passengers' safety.
Think with a big brain not just with yours.
TOM: OK.OK ! Get back to the noise problem. Is that all you wanna say about noise?
JERRY: Not at all ! If you want to hear all about noise, go and get your blanket.
TOM: Hugh ! Your words are always flying in the sky.
JERRY: Shut up..! Listen carefully. There are so many noise sources such as vibration,BVI (blade vortex interaction) and so on.
TOM: WOW ! Noise and vibration are different. You mean like this,don't you?
JERRY: That's right ! People think noise and vibration are the same. Actually, it's not the same. Do you know acoustics?
TOM: Why not? I like IC acoustics live show so much.
JERRY: Ah.! what I mean acoustics here is the science which deals with sounds. It's a branch of scientific study and we call a subject Aeroacoustics if it deals with the sounds which have been generated by aerodynamic forces.
TOM: Ah..! I see.
JERRY: And you are very lucky that you didn't hear all noise the helicopter made.
TOM: Hey,man ! my ears are still working well. Watch your mouth.
JERRY: I know. Actually noises have their own specific directions. For example, some noise propagates into the direction of blade rotation and some goes into ups and downs of the blade. So you can't hear all of the noises at a time. It depends on where you and the noise sources are. It's one aspect of relativity theory.
TOM: Stop ! Stop ! It's enough. I'd better go home !