CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Main CFD Forum

Flow past orifice

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   January 27, 2009, 07:46
Default Flow past orifice
  #1
aurel
Guest
 
Posts: n/a
Hi all,

I wonder if anyone could confirm highly supersonic flow of methane (Mach(M) up to 4) downstream to orifice in pipe with pressure expansion ratio approx. 1:90. The result is from CFD simulation.

Model summary:

Geometry

pipe diameter (upstream orifice) = 0.15 m

pipe diameter (downstream orifice) = 0.3 m (abrupt diam. change)

orifice diameter = 0.037 m

orifice thickness = 0.025 m

BCs:

Pressure Inlet: (absolute pressures)

total pressure = 9 Mpa

initial static pressure = 9 MPa

Total temperature = 300 K

Pressure outlet:

static pressure = 101.325 kPa

Walls: adiabatic

Turbulence: RNG k-e, wall function

Fluid: methane, ideal gas

Result from CFD simulation reveals that the orifice work like overexpanded supersonic nozzle:

- supresonic expansion past orifice M up to 4

- creation of oblique shock wave after the overexpanded region (stat. pressure approx 20 kPa) when expanding fluid particles hit the wall

- normal shock wave as result of interaction of the oblique shock waves near the pipe centerline

- supersonic flow (M cca 2) further downstream the orifice

- low temperatures in supersonic region up to 140 K

- but interestingly creation of temperature boundary layer with nonzero gradient at the wall

- wall temperature cca. 290 K (neighter model with nonadiabatic wall causes (substantial) decrease in wall temperature

Could be all the CFD results considered as correct?

Collegues around me (non CFD spetialists) claim that the the expansion processin orifice should more resamble to throttling porcess.

Perforated plate, instead of orifice with equivalent flow area, shows almost the same results (supersonic expansion, low temperature, weaker oblique shock waves). Is ti correct?

Why is the process in throttling valve more liken to throttling process (isentalpic process, for ideal gas isthermal process)?

Many thanks.

  Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
flow over a cylinder urgent! kevin FLUENT 8 August 11, 2015 13:00
Unsteady simulation of flow past wheel Tom FLUENT 8 January 18, 2006 11:54
meshing for flow past a cylinder karthik FLUENT 1 July 15, 2005 06:17
Orifice Flow John Eichler Main CFD Forum 1 November 6, 2002 13:26
simulating separated flow past the airfoil Yusoff CFX 7 January 16, 2001 20:19


All times are GMT -4. The time now is 16:46.