Pipe flow Mach number typical aerospace values

[jlchard1]

Hi,

Are pipe flows in pneumatic aerospace systems limited to certain Mach numbers? If so, what are the reasons for this? Are there any issues associated with high pipe Mach numbers? - damage from shocks in the pipe?

Any info is much appreciated.

Kind Regards

James

 

[LittleInch]

Mach 1 in a pipe is choked flow. Past that the velocity cannot increase, though the mass flow can if the upstream density increases.

Is that what you mean?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[jlchard1]

Hi,

No I meant do they size the pipes to limit the maximum pipe flow Mach number in the pipe? E.g. the pipe diameter is changed to ensure the maximum pipe Mach number is 0.6. However, in the case you just mentioned, would the flow rate not equal zero if the pipe is long enough for unity to be reached (according to Fanno flow)?

Cheers

James

 

[LittleInch]

Can you please define a little more what you mane by "pneumatic aerospace systems" do you mean pneumatic control lines or something else? It's probably clear to you, but I think I'm missing something. An example or typical size or air flow rate or pressure would help....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[jlchard1]

I was thinking that there may be some standard somewhere the defines a maximum flow speed for high pressure pneumatic aerospace systems; are there any standards that exist for high pressure pneumatic systems that cover internal pipe flow Mach number? Specifically I'm thinking about fluidic actuation systems such as circulation control, however I'm aware this technology hasn't yet been widely adopted. What are the implications of having a high Mach number flow in a pneumatic pipe network? Pressure could be anywhere between 1.1 bar and 10 bar

Cheers

James

 

[racookpe1978]

No. I think somehow your mixing up high pressure fluids (hydraulics perhaps, that have very, very low flows by definition - since they are pressurized by pumps to that high pressure!) with the high air flows and speeds through turbines and around wings.

A pipe moves fluids at low mach numbers because that the only efficient way to move them. Mach number flows only happen during very rapid blow down of high pressure fluids from safety or relief valves (for example) into open air.

 

[LittleInch]

I still don't understand what systems you are talking about, but for a control system you wouldn't be designing based on mach numbers - far too high a pressure drop. Define it better or provide more details / examples of what you mean

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[tbuelna]

The only pure pneumatic flight control systems that I can think of on a production aircraft are the wing tip roll ducts used on the Harrier and F-35B. The pressures and velocities in these duct systems are fairly high, but I doubt they are anywhere close to sonic conditions.