Subsonic and Transonic Flow

zacko · March 3, 2018, 10:20

Hello there,

I am simulating a 4-stage axial compressor with subsonic flow.
When I evaluated the mach-number at the inlet of the first rotor row, the Mach-number near the Shroud reached 0.85.
For me this is a little but curious since I defined the flow with subsonic.
Is it normal, that the Flow exceeds 0.8 for transonic flow conditions?

Thank you very much!

Far · March 3, 2018, 11:49

yes very much normal

zacko · March 3, 2018, 13:58

Thanks for the answer

But is there any explanation for this ?

Far · March 3, 2018, 14:01

isnt is the velocity triangle. at tip the blade speed is higher, so the mach number

Far · March 3, 2018, 14:02

you have to check it is relative mach number or mach number.

zacko · March 3, 2018, 14:04

I only can choose Mach Number and Mach Number in Stn Frame.
And for the Rotor I've chosen the regular Mach Number.

Far · March 3, 2018, 14:55

it is relative mach number

March 3, 2018, 10:20	Subsonic and Transonic Flow	#1
zacko Senior Member Daniel Join Date: Feb 2017 Location: Germany Posts: 172 Rep Power: 9	Hello there, I am simulating a 4-stage axial compressor with subsonic flow. When I evaluated the mach-number at the inlet of the first rotor row, the Mach-number near the Shroud reached 0.85. For me this is a little but curious since I defined the flow with subsonic. Is it normal, that the Flow exceeds 0.8 for transonic flow conditions? Thank you very much!

March 3, 2018, 11:49		#2
Far Senior Member Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,558 Blog Entries: 6 Rep Power: 54	yes very much normal zacko likes this.

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March 3, 2018, 13:58		#3
zacko Senior Member Daniel Join Date: Feb 2017 Location: Germany Posts: 172 Rep Power: 9	Thanks for the answer But is there any explanation for this ?

March 3, 2018, 14:01		#4
Far Senior Member Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,558 Blog Entries: 6 Rep Power: 54	isnt is the velocity triangle. at tip the blade speed is higher, so the mach number

March 3, 2018, 14:02		#5
Far Senior Member Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,558 Blog Entries: 6 Rep Power: 54	you have to check it is relative mach number or mach number.

March 3, 2018, 14:04		#6
zacko Senior Member Daniel Join Date: Feb 2017 Location: Germany Posts: 172 Rep Power: 9	I only can choose Mach Number and Mach Number in Stn Frame. And for the Rotor I've chosen the regular Mach Number.

March 3, 2018, 14:55		#7
Far Senior Member Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,558 Blog Entries: 6 Rep Power: 54	it is relative mach number